This dissertation has been 65—9367 microfilmed exactly as received
PALMER, W illiam Martyn, 1930- MACROSCOPIC AND MICROSCOPIC CHANGES IN THE REPRODUCTIVE TRACT OF THE LAC— T A TING SOW.
The Ohio State University, Ph.D., 1965 Agriculture, animal culture
University Microfilms, Inc., Ann Arbor, Michigan MACROSCOPIC AND MICROSCOPIC CHANGES IN THE REPRODUCTIVE
TRACT OF THE LACTATING SOW
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University
By
William Martyn Palmer, B.S.A., M.Sc.
The Ohio State University . 196$
Approved by
Adviser Department of Animal Science ACKNOWLEDGMENTS
Sincere appreciation is expressed to Dr. Howard S. Teague and
Dr. Walter G. Venzke for the advice, interest, and guidance which they afforded the writer during the course of this investigation.
The assistance given by Dr. Martin Y. Andres,
Dr. Vance L. Sanger, and Dr. Allen L. Trapp in histological techniques and interpretation of histological slides is gratefully acknowledged.
The willing assistance given by Mr. Glenn Berkey and
Mr. Clarke L„ Robey in photographing the graphs and histological sections is deeply appreciated.
Acknowledgment is given to Dr. C. R. Weaver for conducting the statistical analyses.
Thanks is given to Mr. Glenn W. Todd, Mr. James H. Foster, and
Mr. David L. Stickel for caring for the animals and transporting them to the slaughtering establishments.
The cooperation of The Ohio State University Meat Laboratory;
Sheller Meats Incorporated, Smithville, Ohio; Bob Evans Farms, Xenia,
Ohio; and The Superior Provision Company, Massillon, Ohio, in the slaughter of the animals materially aided in carrying out the study.
Appreciation is expressed to The Ohio State University and the
Ohio Agricultural Experiment Station for the facilities and financial assistance provided.
ii Hy most heartfelt thanks to ny wife, Han, for the sacrifices which she made during the period of bqt graduate study and for typing this dissertation.
iii VITA
July 26, 1930 Born - Vita, Manitoba, Canada
1953 .... B.S.A., The University of Manitoba, Winnipeg, Manitoba, Canada
19^3-1960 . . Extension Livestock Fieldman, Manitoba Department of Agriculture and Conservation, Winnipeg, Manitoba, Canada
1962 .... M.Sc., The University of Manitoba, Winnipeg, Manitoba, Canada
1962-1965 . . Research Assistant, Ohio Agricultural Experiment Station, Wooster, Ohio
PUBLICATIONS
"Postpartum Changes in the Reproductive Tract of the Lactating Sow.1* Jour. Animal Sci. 23:1227 Abstr., November, 196li
FIELDS OF STUDY
Major Field: Animal Science
Research in Reproductive Physiology. Professors Howard S. Teague and Walter 0. Venake
Studies in Histology. Professor Martin Y. Andres
iv CONTENTS
Page
ACKNOWLEDGMENTS...... Ii
VITA ...... iv
ILLUSTRATIONS...... vii
TABLES ...... *
INTRODUCTION...... 1
LITERATURE R E V I E W ...... 3
The estrcras cycle during lactation ...... 3 Changes In the reproductive organs during lactation ...... 7 Physiological and histological changes during the estrual cycle and early pregnancy ...... 11
O v a r y ...... 11 U t e r u s ...... 15 Oviduct...... 17 Cervix and vagina...... 18
EXPERIMENTAL PROCEDURE...... 20
RESULTS ...... 2U
Macroscopic observations...... 2U
Gross morphology of the ova ry...... 21* Weight and length of uterus...... 33
Histological observations ...... 36
O v a r y ...... 36 U t e r u s ...... UP Oviduct...... 53 Cervix and vagina ...... 56 CONTENTS— Continued
Page
DISCUSSION...... 62
SUMMARY ...... 70
APPENDIX I ...... 7h
LITERATURE C I T E D ...... 81
vl ILLUSTRATIONS
Figure Page
1 Ovaries fro* a sow 1 day after parturition . . . . . 29
2 Ovaries fro* a sow 7 days after parturition. 29
3 Ovaries fro* a sow 12* days after parturition .... 29
1* Ovaries fro* a sow 1*5 days after parturition .... 29
5 Average dianeter of the corpora lutea of pregnancy at predetermined intervals after farrowing and w e a n i n g ...... 31
6 Average dianeter of all follicles equal to or larger than 2.0 *m. in dianeter at predetermined Intervals after parturition and w e a n i n g ...... 32
7 Average number of follicles equal to or larger than 5-0 *m. in dianeter at certain periods during lactation and post-weaning .... 31*
8 Weight of the uterus at predetermined intervals after parturition and w e a n i n g ...... 3$
9 Total length of the uterine horns at certain tine intervals after parturition and w e a n i n g ...... 37
10 Corpus luteu* of pregnancy of a sow at 110th day of gestation...... 39
11 Corpus luteu* of pregnancy section of a sow at 1 day after parturition...... 39
12 Corpus luteu* of pregnancy of a sow 7 days after f a r r o w i n g ...... 2*0
13 Corpus luteu* of pregnancy of a sow 11* days after f a r r o w i n g ...... 1*0
vii ILLUSTRATIONS— Continued
Figure Page
lli Corpus luteum of pregnancy of a sow at 1 day after parturition...... Ii3
15 Ovarian follicle of a sow showing intense alkaline phosphatase reaction in theca i n t e r n a ...... U3
16 Newly forming corpus luteum from a sow 3 days post-weaning showing distribution of alkaline phosphatase...... Uk
17 Uterus and placenta of a sow at 110th day of gestation...... hh
18 Uterine epithelium of a sow at 1 day postpartum . . . U6
19 Epithelium of sow's uterus at 7 days after parturition...... U6
20 Uterine epithelium from a sow lit days postpartum...... hi
21 Uterine epithelium of a sow 28 days after f a r r o w i n g ...... h9
22 Epithelium of sow's uterus at 3 days post-weaning ...... U9
23 Uterus of a sow at 7 days postpartum showing slight alkaline phosphatase activity in epithelium and g l a n d s ...... 52
2h Uterine section of a sow at 3 days post-weaning illustrating strong alkaline phosphatase reaction in epithelial cells ...... 52
25 Transverse section from ampullar region of oviduct of sow at 1 day after f a r r o w i n g ...... 5h
26 Higher magnification of Figure 25 showing epithelium of oviduct of sow at 1 day after farrowing...... 5h
viii ILLUSTRATIONS— Continued
Figure Page
27 Oviduct epithelium of sow lli days postpartum .... 55
28 Oviduct epithelium of sow 3 days post-weaning .... 55
29 Cervical epithelium of a sow at 110th day of gestation...... 57
30 Cervical epithelium of a sow at 3 days after farrowing showing aldehyde-fuchsin reaction in the cytoplasm of the epithelial c e l l s ...... 57
31 Cervical epithelium of a sow at 21 days after farrowing...... 59
32 Vaginal epithelium of a sow at 1 day after parturition ...... 59
33 Vaginal epithelium of a sow XI4. days postpartum . . . 61
3U Vaginal epithelium of a sow 3 days post-weaning ...... 61
Plate
I Ovaries of sows at certain time intervals after parturition...... 29
ix TABLES
Table Page
1 Day of slaughter and number of sows ...... 20
2 Means of macroscopic Measurements adjusted for breeding, size of nursing litter, and unequal subclass mufeers...... 2£
3 Analyses of variance of macroscopic d a t a ...... 27
U Slaughter day, breeding, and number of pigs farrowed and nursed by sows used in s t u d y ...... 7h
$ Macroscopic observations of the reproductive organs...... 77
x INTRODUCTION
Cyclical ovarian activity and eatrus are markedly inhibited or abaent during lactation in nearly all mammalian species. The sow frequently exhibits a non-fertile estrus a few days after parturition but ovulation is generally inhibited throughout the usual 8-week lactation period. However, ovulation and regular periodicity of the estrous cycle are resumed if the young are removed from the sow at any time following parturition. The successful induction of estrus a^d ovulation with subsequent fertilisation and pregnancy in the lactating sow would be of great economic value to the swine producer, since it could increase the reproductive capacity of the breeding herd.
However, experimental attempts to modify this period of lactational anestrus in swine have not achieved any consistently satisfactory results to date.
Several accounts exist in the literature which outline in detail the gross anatomical and histological changes that occur in the
reproductive organs of sows throughout the regular estrous cycle and
early pregnancy. There are, however, only fragmentary reports of
similar observations made on sows following parturition and throughout
the lactation period. Consequently, relatively little is known about
the condition of the sex organs or the endocrine balance which exists
during this portion of the sowfs reproductive life. 2
The objective of the present study was to observe the macroscopic and microscopic changes that occur in the reproductive tract of the sow following parturition and during lactation, thereby gaining information which could aid in determining what experimental approach might be employed to bring the lactating sow into fertile estrus. LITERATURE REVIEW
A search of the literature revealed few references relative to the gross appearance and histology of the reproductive organs of the postpartum sow. Hence, this review Is limited mainly to the obser vations which have been made during the normal estrous cycle and early pregnancy, which for the most part were used as a guide in the obser vations recorded in the present study. Results of studies made on
other species are included in cases where it is felt that the
information Is pertinent to this study. The review is prefaced with a
summary of reproductive phenomena which have been recorded for some mammalian species during the lactation period.
The estrous cycle during lactation
Inhibitory effects of lactation on the normal estrual cycle
pattern have been noted in nearly all species of mammals. An
exception to the general rule is found in the greater majority of
mares, which will exhibit estrus and resume regular cyclic behavior
within 18 days after foaling (Trum, 19E>0).
Lactation In the sow usually causes coaplete suppression of
ovarian activity but some animals may exhibit an anovulatory estrus 2
to 3 days after farrowing (Warnick et al., 1950; Burger, 1952; Heitman
and Cole, 1956). Removal of the suckling stimulus for a sufficiently
long period re-initiates the cycle. Baker et al. (1953) removed the k litters from sows either at parturition or within 2 days after farrow ing. About 76 percent came into heat and ovulated within 8 to 16 days after farrowing. Some limited success has been achieved in inducing estrus and ovulation in lactating sows by injection of gonadotrophic hormone preparations (Cole and Hughes, 19h6; Heltman and Cole, 1956;
Allen et al., 1957; Kirkpatrick et al., 1963).
Robison (1918) was able to produce estrus and ovulation in sows by separating them from their litters overnight for four or five consecutive nights when using sows that were in the later stages of lactation. The earliest that estrus was observed was U3 days after farrowing. Smith (1961) in a similar experiment noted that second-
litter sows exhibited estrus 5 to 7 days after overnight separation
commenced, while first-litter sows required 13 to 16 days of separa
tion. Burger (1952), on the other hand, reported very poor success
in inducing estrus in sows using this overnight litter separation
technique. The majority of the animals in his limited study never
exhibited estrus, even though partial separation of the litter was
continued for up to 90 days postpartum in some cases. Most workers
agree that the majority of the sows will exhibit estrus and begin
cycling within a week after the litter is weaned subsequent to an
8-week lactation period (Burger, 1952; Lasley, 1955).
Both Burger (1952) and Lasley (1955) indicated that spontaneous
estrus and ovulation does occur (although rather infrequently) in
swine during the lactation period, but in the majority of cases it
occurs later than 1*0 days postpartum when lactation is waning. Their 5 reports also suggested both individual and breed differences. Thus,
it is apparent that, subject to certain genetic and environmental
variation, lactation and/or the suckling stimulus does markedly alter
the usual estrous cycle in swine.
Reports on the interval from parturition to uterine involution,
estrus and ovulation in dairy and beef cattle exengjlify wide ranges in
these reproductive characteristics (Hansel, 1959). Significant
differences in these traits in the bovine have been found to be due to
breed, parity, season, and various hormone treatments (Buch, 1957;
Norwood, 1963).
Norwood (1963) found that injection of beta-estradiol signifi
cantly increased the interval from parturition to uterine involution
in plur5parous dairy cows. Foote and Hunter (1961j) and Foote and
Saiduddin (196U) reported, however, that the interval from calving to
uterine involution, estrus and ovulation was significantly reduced in
pluriparous Hereford cows by injections of estrogen and progesterone,
either singly or in coatoination. Cameron and Fosgate (1961*) injected
multiparous Holstein and Jersey cows with oxytocin and reported no
effect on uterine involution, estrus or ovulation.
Clapp (1937) found that the interval between calving and first
estrus was considerably longer in cows milked four times a day and in
nurse cows than in cows milked only twice a day (69 and 72 days vs. U6
days) which would suggest that the frequency of udder stimulation
affects the interval to first postpartum estrus in the bovine. The
data of Wiltbank and Cook (1958) lend further support to this 6 hypothesis. They found that the interval from parturition to first estrus was 30 days longer in suckled cows than in cows milked twice a day. Also, the interval from calving to first ovulation was 53 days in the cows nursed by their calves, while it was 36 days in the milked
cows.
It is generally agreed that lactation inhibits ovarian activity
in sheep. However, Hiller and Wiggins (196U) found that lactating
fall-lambing Rambouillet ewes did ovulate, although many did not
exhibit overt signs of estrus. Lactating ewes have been brought into
fertile estrus with moderate degrees of success by injecting varying
amounts and combinations of pregnant mare serum, estrogen, and
progesterone (Gordon, 1963j Morrow et al., 1963).
Estrus and ovulation usually occur in the imediate postpartum
period (generally within 2U hours after parturition) in certain
species of rodents such as the rat and mouse (Perry and Rowlands,
1962). However, a luteal phase may then persist throughout lactation
and cyclical activity is not resumed until after the litter is weaned.
If the female Is bred at this postpartum estrus, the fertilized eggs
of the new pregnancy develop Into blastocysts, but, according to
Nalbandov (1958)> they fail to implant In the uterus until after the
suckling stimulus of the nursing litter is removed. Whitten (1958)
has shown that the injection of either estradiol benzoate or serum
gonadotrophin on the fifth postpartum day results in implantation at
the normal time in mice and he believed that the delay in Implantation
therefore resulted from decreased production of gonadotrophin which In 7 turn caused lowered estrogen levels. The estrous cycle suppression and the inplantation delay In the mouse and rat are In part Influenced by the size of the litter, being less pronounced when there is a small number of suckling young (Parkes, 1926; Bruce and East, 1956; Bruce, 1961).
Changes in the reproductive
Rumjancev (195k) made chemical, macroscopic, and histological
observations on 50 sows from 2 to 3 weeks before to 30 days after
farrowing. He concluded that involution of the genital tract was
couplets 18 days after parturition and ovulation took place at 21 days
postpartum. Burger (1952) studied the morphology of the ovaries of
two Large Black and six Large White first-litter sows slaughtered
between k and 7 days after parturition. He reported that the corpora
lutea were dark yellow in color, 6.5 mm. in diameter., atrophic, and
therefore, were the degenerating corpora lutea of pregnancy. The
follicles averaged 3.76 aim. in diameter, thus resenfcling in sise those
normally found during the diestrous period in swine. Corner (1919),
based upon observations on only two postpartum sows, stated that the
corpus luteum, which was a flesh-colored body 10 or 11 mm. in diameter
prior to parturition, was only half this sise and had acquired a
yellow-brown color by the seventh day after parturition. Lauderdale
et al. (1963) observed the reproductive organs of groups of primi-
parous sows killed either 2 days prior to expected parturition, the day
of parturition or on the 6th, 11th, or 16th day after parturition. 8
They reported a rapid decline In corpora lutea weight, progesterone content of the corpora lutea, follicular dlaneter, and uterine weight following parturition. Kirkpatrick et al. (1963) studied the effect of follicle stimulating hormone (FSH) injections on lactating primlparous sows. The sows were killed either 6, 11, or 16 days post partum following FSH injections which were given daily for the $ days immediately prior to slaughter. Dissectable luteal tissue (indicating postpartum ovulation) was present in the ovaries in four of five FSH- treated sows killed on the sixth day and in three of five sows killed on the 11th day, but was not present in any of the five studied 16 days postpartum. This suggests that either the endogenous level of
FSH has decreased after 16 days of lactation or that the ovary has become refractory to FSH stimulation. Meites et al. (1963) cited evidence suggesting that there is a reciprocal relationship between the release of follicle stimulating hormone-luteinizing hormone
(F3H-LH) and prolactin, and suckling may promote prolactin release by inhibition of FSH-LH secretion.
Labhsetwar et al. (196U) studied some pituitary-ovarian relation ships in periparturient multiparous Holstein cows. Observations were made just prior to parturition, 18 hours following calving, and 21 days postpartum (with or without daily progesterone injections from the tine of calving). There was no detectable progesterone in the corpora lutea of pregnancy on the day of calving and the corpora lutea were also significantly smaller than just prior to parturition.
Follicular size was much smaller in the prepartum and day-of-calving 9 groups as compared to both groups at 21 days postpartum. The level of follicle stimulating hormone (FSH) in the pituitary increased, while luteinizing hormone (LH) decreased from the prepartnm to the immediate postpartum observations. The limited observations of Saiduddin and
Foote (1961*) also would suggest low levels of pituitary LH in the bovine at the time of parturition, which appear to gradually increase as postpartum anestrus progresses toward resumption of estrual cycles.
Histological studies of the reproductive tract of the lactating mouse have been made by Atkinson and Leathern (191*6) and Oreenwald
(1958). The so-called corpora lutea of lactation, which are formed as
a consequence of the immediate postpartum ovulation in this species,
grow more slowly than those of any other physiological state,
hypertrophy of the luteal cells, leading to an increase in the sise of
the corpora lutea does not occur until the 11th day of lactation
(Oreenwald, 1958)* Up to this time the corpora lutea of lactation are
smaller than the corpora lutea of pregnancy even though the latter
begin a gradual regression following parturition. Oreenwald (1958)
also found little ovarian follicular growth during the first 11 days
of lactation.
Accordingly, Oreenwald (1958) suggested that the morphological
changes in the reproductive tract of the lactating mouse can be
accounted for by the following hypothesis. Due to the neurohormonal
stimulus of suckling, the pituitary secretes sufficient prolactin to
maintain functional corpora lutea of lactation. Progesterone from
these corpora in turn, prevents the release of gonadotrophic hormones 10 from the pituitary. The follicles are therefore small and the secre tion of estrogen is negligible during the first part of the lactation period. Between 10 and l£ days postpartum the level of prolactin drops for some unknown reason. Although the corpus luteum is still functioning, progesterone declines sufficiently to permit the release of additional gonadotrophins. This leads to some increase in follicular size which results in higher secretion of estrogens. As the young become independent and suckling lessens, the secretion of prolactin drops even lower and the corpora lutea of lactation become non-functional. The final pre-ovulatory growth of the follicles can then occur.
Contrary to the above mentioned hypothesis, the maintenance of lactational anestrus is not mediated through the corpora lutea of lactation, at least in the rat, according to McKeown and Zuckerman
(1938).
Although all studies reviewed to this point indicate that the
corpora lutea of pregnancy regress rapidly following parturition,
Dawson (19U6a) suggests that such is not the case in the cat. The
corpora lutea of lactating animals became bright pink due to an
increase in vascularity by the end of the first week after parturition
and retained this color until at least the end of the fourth week.
Histologically the luteal cells remained active with little evidence
of degeneration.
Dawson (I9l*6b) also studied the effects of lactation on the post
partum involution of the catfs uterus. He recognized two degrees of 11 involution: the normal involution of non-lactating animals which takes place by 2 to 3 weeks after parturition and the hyperinvolution induced by prolonged lactation. Ifyperinvolution of the uterus was correlated with low estrogen levels as a result of inactivity of the ovarian follicles during lactation.
Physiological and histological changes during the estrual cycle and early pregnancy
Detailed histological and histochemical investigations of the
changes in the reproductive organs during the nornal estrous cycle and
early pregnancy have been reported by Corner (1915, 1919, 1921),
McKensie (1926), and Tamashita (1959, 1960a, 1960b, 1961, 1962) for
the sow; Weeth and Herman (1952), Foley and Reece (1953), Moss et al.
(1956), and Foley and Qreenstein (1958) for the cow; and Casida and
McKensie (1932), and Hadek (1958a, 1958b) for the sheep. The observa
tions that have been made on the various organs and glands during
these periods may be summarised as follows:
Ovary.— The histological changes of the follicle and corpus
luteum of the sow during the estrous cycle and pregnancy have been
described in the papers by Corner (1915, 1919, 1921). Two to three
days before the onset of estrus the follicles which range up to 5 ■»*
in diameter during the interestrual period begin to enlarge rapidly
bringing them to a diameter of 7— 10 mm. just prior to ovulation.
Ifypertrophy of the theca interna occurs and at ovulation the ova have
matured to the formation of the second polar body spindle. With the
collapse of the follicle at ovulation, the granulosa remains intact, 12 except for the loss of the cumulus oophorus with the ovum. The granulosa cells undergo hypertrophy and develop into the so-called
"lutein" cells of the mature corpus luteum. Blood vessels from the theca Interna ramify throughout the developing corpus, carrying with them the lipid containing cells of the theca interna, which become
interspersed with the cells of granulosa origin. The granulosa lutein
cells of the corpus luteum, which is fully formed by the seventh day,
range from 30 to 1*0 mLcra in diameter while the cells of thecal origin
are smaller (10 to 2£ mLcra) and are packed with small vacuoles and
fat droplets. Regression of the corpus luteum begins on about the
l£th day of the estrous cycle. The granulosa lutein cells undergo
rapid degeneration, becoming vacuolated with pyknotic nuclei. The
blood capillaries collapse, and as regression proceeds, the connective
tissue becomes thicker and more dense. The cells of thecal origin do
not degenerate as abruptly and are the last of the luteal elements to
disappear.
If pregnancy occurs, the corpus luteum retains its mature sise of
8 to 10 nan. in diameter and does not regress until after parturition.
Corner (191f>) gave a very detailed account of the histological
structure of the corpus luteum as it appeared throughout pregnancy in
swine. Based on this cytological study he suggested that the corpus
luteum of pregnancy was an actively secreting organ, which only showed
some lessening activity in the later stages of pregnancy. In his
entire series of ovaries from pregnant sows no follicles were found 13 having an outside diameter of more than 6 mm. This same obserration was made by Burger (1952).
The presence of lipids in the corpus luteum is an established fact and, although there are no specific histocheidcal tests, may be associated with progesterone and other steroid secretions. Barker
(1951) y ejqjloying a number of cytochemical tests for fat, found that all the lutein cells contained large lipid droplets during the first 3 days after ovulation. They were, however, the most numerous in the cells derived from the theca interna. During regression of the corpus luteum the lipid droplets became Insoluble In acetone suggesting that they may have been steroid condensation products. Hadek (1958a) demonstrated lipid globules in the membrana granulosa and theca
interna cells of follicles which measured more than 500 miera in the
ovaries of cycling sheep. The granulosa lutein cells were almost com pletely occupied by lipid and the theca Interna cells also contained a
large amount during the period of highest luteal development.
Cholesterol and phospholipids could not be detected in either the
follicle or the corpus luteum. However, the earlier chemical studies
on the corpus luteum by Bloor et al. (1930) and Boyd and Elden (1935)
Indicated that the phospholipid content varies with the physiological
activity of the corpora, while total cholesterol increases with
retrogression of the gland.
According to Moss et al. (1956) glycogen was absent from the
corpus luteum of early pregnancy in the bovine, as it was during the
estrous cycle. Periodic acid Schiff (PAS) positive spherules were 1U seen In some granulosa lutein cells during the estrous cycle but not during early pregnancy. Hadek (1958a) found that the PAS staining method for polysaccharides was strongest in atrophying follicles and the cells of the corpora alblcantia in sheep. Although the liquor folllculi and the meifcrana granulosa cells In small follicles showed only weak affinity toward PAS, the reactions became stronger with
Increasing follicular size.
The distribution of the enzyme alkaline phosphatase in the ovary of the various species has been studied. Corner (19U1|) found that in mature follicles of the pig the theca interna cells are heavily laden with alkaline phosphatase, whereas the cytoplasm of the granulosa cells is entirely free of the enzyme. The same pattern was observed in the sheep*s ovary by Hadek (1958a). At the 18th day of pregnancy, the corpus luteum of the sow is made up of phosphatase-free granulosa lutein cells interspersed with phosphatase-laden theca interna cells
(Corner, 19Uh). Later in pregnancy the granulosa cells also acquire
cytoplasmic phosphatase and the picture becomes less clear. Moss
et al. (1956) reported that alkaline phosphatase was present in both
the granulosa and theca interna lutein cells of the bovine corpus
luteum of the estrous cycle, but high enzyme activity was present only
in the arteriolar endothelium of corpora between 30 and 66 days of
pregnancy.
The functional significance of alkaline phosphatase in the ovary
or any other tissue is not known. The enzyme appears to be present in
highest concentrations in physiologically active cells and, therefore, 15 its presence or absence in a particular cell or tissue can perhaps be used a8 an index of metabolic activity.
Uterus.— The histological changes of the uterus of the sow during the estrous cycle and early pregnancy were described in great detail by Corner (1921) and Snyder and Corner (1922) and later reaffirmed by
McKenzie (1926).
During the estrous cycle the morphology of the sow's uterus undergoes regular alternations of structure which are correlated with
the ovarian cycle. The uterine epithelium has a height of 25 to 30 micra at the time of estrus, appears pseudostratified and numerous
dividing cells can be seen. The stroma is edematous and the sub-
epithelial connective tissue is invaded by many polymorphonuclear
neutrophilic leucocytes. During the first week after ovulation, at
which time the corpus luteum is becoming fully formed, the epithelial
cells hypertrophy and the pseudostratified condition is replaced by a
high columnar type of epithelium which attains a height of 35 to 50
micra toward the end of this period. The gland cells begin to
hypertrophy and multiply and the leucocytes in the stroma increase in
number. During late diestrus (12th to 15th day of the cycle) the
surface epithelial cells become vacuolated and are low columnar or
cuboidal (15 to 20 micra high) in appearance, cytoplasmic processes
extrude from the cells, the gland epithelium returns to its original
size and the leucocytes in the sub-epithelial stroma decrease in
number. The same histological changes are found during the first 15
days of pregnancy. Shortly after this, however, the surface 16 epithelial cells lose their vacuolation, become medium or high columnar, and so persist throughout pregnancy.
Corner (1921) was unable to demonstrate glycogen in any part of the uterine mucosa in the non-pregnant sow. Wislocki and Dempsey
(191*6), likewise, were unable to observe glycogen in either the gravid or non-gravid uterus of the pig. Hadek (1958b) obtained a positive
PAS reaction in the uterine glandular epithelium of sheep at the time of estrus, but found that it was not glycogen, hyaluronic acid or acid mucopolysaccharide and regarded it as mucoprotein. Weeth and Herman
(1952) and Moss et al. (1956) reported that glycogen was present in the uterine epithelium of the bovine at estrus and during pregnancy.
Cecil et al. (1961*), using a chemical determination, demonstrated that
estrogen injections markedly increased the amount of glycogen in the
uterus of the rat.
Corner (1921) was unable to demonstrate unsaturated neutral fats by means of osmium tetroxide in the uterus of cycling sows. Wislocki
and Denpsey (191*6), however, demonstrated lipid material in both the
surface and glandular epithelium by several histochemical techniques.
Hadek (1958b) found that lipid showed periodical alteration in the
cycling sheep. It was absent in proestrus and estrus and reappeared
after metestrus, reaching its maximum in diestrus. He suggested that
estrogen suppresses the presence of lipid in the uterine epithelium,
while progesterone causes its reappearance. No reliable histochemical
tests are yet available to characterise the lipids which have been
demonstrated. 17
Although the physiological significance of alkaline phosphatase can only be conjectured, there is, nevertheless, a cyclical variation in the strength of the enzyme's histochemical reaction in the uterus which can be correlated with the ovarian hormones. Wislocki and
Dea^jsey (191*6) observed the enzyme in the surface and glandular epithelium of the uterus of a non-pregnant sow but not in pregnant animals. Hadek (1958b) noted alkaline phosphatase in the distal parts of the uterine surface and glandular epithelium of the sheep. The strength of the reaction was lowest during late diestrus and pro- estrus, highest from estrus to early diestrus and no reacting material was observed during anestrus. Weeth and Herman (1952) reported similar findings in the cycling bovine and noted some decrease in alkaline phosphatase activity in late pregnancy. Estrogen injections caused a marked increase in alkaline phosphatase in the uterine glands, surface epithelium and circular muscle of the mouse, while progesterone depressed the activity (Atkinson and Elftman, 191+6).
Similar observations were made by Pritchard (191+9) and Velardo (195U) in the rat.
Oviduct.— The morphological changes in the oviduct during the estrous cycle and early pregnancy have been outlined by Sqyder (1923) for the pig; Weeth and Herman (1952) for the bovine; and Casida and
McKenzie (1932), and Hadek (1955) for the sheep.
The oviduct is lined by a single-layered epithelium, composed of ciliated and non-ciliated cells which are about equally distributed.
The cyclic changes seen by Sr+yder (1923) in the sow may be summarized 18 as follows: During proestrus the cells increase in height, and reach a maximum of about 25 micra 2 to 3 days after estrus. During the second week after ovulation the surface becomes studded with knob-like or finger-shaped cytoplasmic projections from the non-ciliated secretory cells. These processes, which often contain nuclei, eventually become detached from the cell and are extruded into the lumen of the duct. The epithelium decreases to a height of 10 micra and the secretory cells become thin rod-like structures by the end of the second week after ovulation. Pregnancy interrupts the cyclic alterations and the epithelium tends to remain in the condition that is found during the second week after ovulation when the corpus luteum is fully formed. Similar observations were reported by Casida and
McKenzie (1932) and Hadek (1955) for cycling sheep. Hadek (1955) characterized the secretory material in the sheep*s oviduct as an acid mucopolysaccharide. He also reported that alkaline phosphatase was detected in the secretory cells and it showed cyclical alteration similar to that of the mucopolysaccharide. * Cervix and vagina.— McKenzie (1926) described the histological changes of the vagina of the sow during the estrous cycle. The strat ified squamous epithelium varied in height from three to six cell layers during diestrus to 20— 25 layers at the time of estrus.
Following estrus there was a marked sloughing of the epithelial cells, but with no true corniflcation of the cells as seen in rodents.
Leucocytes in the vaginal stroma were most numerous during the first
U days after estrus and were fewest from the middle of diestrus to the 19 onset of estrus. Casida and McKenzie (1932) observed such the sane changes in the vaginal epitheliua of the cycling ewe. Wilson (1926) noted that the vaginal snicosa of the sow in early pregnancy presented a histological picture which was practically identical with that of diestrus.
Herrick (19^1) studied the cytological changes that occur in the cervix of the cow throughout the estrous cycle, but similar observa tions have not been recorded for the sow. EXPERIMENTAL PROCEDURE
The reproductive organs Here obtained from i*0 sons which Here slaughtered throughout the lactation period at either 1, 3, 7, 1U, 21,
28, 3£, h5, 52, or 62 days after farrowing and from 27 sohs which were slaughtered at daily intervals up to Ij days post-weaning subsequent to an 8-week lactation period. The number of sows slaughtered at each interval after farrowing or weaning is outlined in Table 1.
TABLE 1
DAT OF SLAUGHTER AND NUMBER OF SOWS
No. of sows Day of slaughter Duroc Crossbred
• ■ After farrowing
1, 3, 7, lh, 21, 28, A J . . . 2 35, U5, 52, and 62 J
After weaning
1 2 h
2 - 6
3 2 6
k - 7
20 21
The experimental group consisted of 21* Duroc sous from the Ohio
Agricultural Experiment Station, Wooster, Ohio, and 1*3 crossbred sows
from the swine herd of the Western Substation of the Ohio Agricultural
Experiment Station located at South Charleston, Ohio. The crossbred
animals were of either Hampshire-Torkshire-Duroc, Duroc-Haspshire-
Yorkshire, or Hasp shire-Yorkshire-Poland China breeding. All sows
were sacrificed either during or subsequent to their second lactation period and were nursing or had nursed litters ranging in muriber from
3 to 11*, with the average litter size being 9.7. Animals from four
different farrowing seasons during the period from August, 1963, to
August, 1961*, were included in the study. The breeding, farrowing
season, size of litter farrowed, size of litter nursed, and interval
from farrowing or weaning to slaughter for each sow used in the
investigation are listed in Table 1* in Appendix I.
Tissue sections were taken from the ampulla region of the
oviduct; the mid-region of the right uterine horn; the central region
of the cervix; and the vagina at a point midway between the posterior
end of the cervix and the external urethral orifice. These sections
and one of the ovaries were placed in buffered 10 percent formalin
solution for tissue fixation. The other ovary and sections from the
same regions of the genital tract were also placed in cold acetone.
In most instances the ovaries were photographed immediately before
being placed in the fixing solutions. The tissues were usually in the
fixatives within 30 to 60 minutes from the time of slaughter.
Gross morphological observations on the reproductive tract 22
Included the weight of the uterus (minus the sections taken for histology) and the length of the uterine horns. The following macro scopic observations of the ovary were recorded: the diameter of the corpora lutea of pregnancy; the diameter of all follicles 2.0 mm. or larger; and the number of follicles that were 5.0 mm. or larger in diameter. The measurements on the ovary were taken after fixation of the organ. The diameter of each corpus luteum was determined by selecting its largest section and averaging the long and short diameters. The follicle diameters were determined by measuring the longest diameter, with the glassy membrane which separates the merabrana granulosa from the theca interna considered as the outside boundary. Analyses of variance were performed on the data concerning the macroscopic observations using the least squares method of Harvey
(I960) for unequal subclass numbers.
The tissues that were fixed in buffered formalin were embedded in paraffin and sectioned at 6 or 7 micra. Staining procedures employed on the paraffin-embedded sections included: Harris' hematoxylin and eosin (Armed Forces Institute of Pathology, I960); Crossman's modifi cation of Mallory's triple stain using Wiegert's iron hematoxylin, acid-fuchsin-orange-G solution and light green counterstain (Conn et al., I960); and aldehyde-fuchsin (Halml, 1952).
The acetone-fixed tissues were embedded in paraffin and stained for alkaline phosphatase by the method of Gomori (Lillie, 195k). The tissue sections were Incubated routinely for 1 hour in the sodium 23 beta-glycerophoaphate substrate solution and counterstained in 1 per cent alcoholic eosin solution for $ minutes. RESULTS
Macroscopic observations
Mean values of the gross measurements Bade on the reproductive
organs were adjusted for breeding, size of nursing litter, and unequal
subclass numbers by using constants obtained through least squares
analysis and are summarized in Table 2. The actual measurements recorded for each animal examined in the study are outlined in Table 5
of Appendix I. Two sows observed at 3 days post-weaning and two at h
days post-weaning showed evidence of recent ovulation. The gross
observations on these four sows were omitted from the summary data
since these animals represented a stage of the reproductive cycle that
was not truly coiqparable with that of the other animals studied at the
same post-weaning intervals. The mean squares from the analyses of
variance conducted on the data are listed in Table 3.
Gross morphology of the ovary.— The gross morphological appear
ance of the ovary of the sow at certain time intervals after partu
rition is illustrated in Figures 1— 1*.
The corpora lutea of pregnancy, which are believed to be formed
following the ovulation which occurred at the time of conception and
are thought to persist and function throughout the duration of
pregnancy, were still readily apparent 1 day after parturition. At
that time they were creamy-yellow in color and averaged 8.1 mm. in
2U TABLE 2
MEANS OF MACROSCOPIC MEASUREMENTS ADJUSTED FOR BREEDING, SIZE OF NURSING LITTER, AND UNEQUAL SUBCLASS NUMBERS
Ave. diam. Ave. diam. No. Weight of Length of No. of corpora of Item follicles uterus uterus sows lutea follicles > £.0 mm. (gn>.) (cm.) (mm.) (mm.)
Days after farrowing 1 h 8.1 + 0.3a a.6 + 0.5 3.2 + 2 .a 272a.fi + 139.3 237.2 ± 17.7 3 h 6.5 ± o.a 3.5 i 0.8 1.3 ± 1.5 1680.3 ± 155.0 213.6 + 12.0 7 k a.7 i 0.1 2.7 ± 0.2 0.0 ± 0.0 969.7 ± 87.2 231.8 + 23.3 lii h 3.6 + 0.1 3.1 i 0.2 0.0 + 0.0 aau-9 + 53.3 178.6 + ia.6 21 h 2.7 ± 0.2 1*.3 i 0.2 a .9 + 1.0 3aa.9 ± 38.8 iaa.i + 19.5 28 h 2.1* t 0.3 3 .a + 0.6 2 .a + 1.6 2aa.o + 9.0 120.8 ± 10.1 35 h 2.1 ± 0.1 a.7 + 0.2 7.3 + 1.8 21*3.7 ± 28.6 119.6 ± 3.1 U5 h 2.0 + 0.2 5.1 ± o.a 7.8 + 0 .$ 299.6 + 2a.i 129.1 ± 7.9 52 k 1.6 + 0.2 a .9 + o.a 7.7 + 0.6 230.2 + 7.2 111.9 ± 3.3 62 h 1.7 ± 0.2 5.8 + 0.5 13.0 + 2.9 288.7 + ao.2 12a.9 ± 17.6
Days after weaning 1 6 1.5 t 0.1 . 6,0 + o.a 13.a + 1.1 310.0 + 51.2 109.9 ± 7.6 2 6 1.3 + 0.1 6.2 + 0.2 11.5 ± 2.0 393.0 + 78.8 136.6 + 11.9 3 6 l.h ± 0.1 7.5 ± 0.2 13.6 ± 2.7 397.6 + 29.3 iai.i + 9.a h 5 1.3 + 0.1 7.6 ± 0.8 12.0 + 1.9 502.a ± 59.7 155.9 + ia.5 TABLE 2— Continued
Ave. diam. Ave. diam. ^ Wei?ht of 0f Item °* 0 °fP° a ® follicles uterus uterus sows lutea follicles f \ , \ (a.) (a.) ^5.0 a. (gm.) (c.)
Breeding* D 2h 2.7 + 0.5 li *6 + 0.3 6.a i 1.2 6U 1.3 + 156.6 165.0 + 12.6 H-Y-Dc IS 3.0 + 0.U 5.6 + 0 .I4 5.2 + 1.0 683.0 + 156.3 VSh.S ± 9.8 D-H-Y*3 is 2.8 ± 0.6 1.1 + 0.5 9.3 + 2.3 738.7 ± 200.h 166.1* t 11.li H-Y-Pe 9 3.2 + O.li 5.? ♦ 0.1* 6.8 + 1.1 567.9 i 120.2 129.8 + 8.9
aStandard error of the mean.
bDuroc.
cHanpshire-Yorkshire-Duroc.
^Duroc-Hasp shire-Yorkshire.
eHan|)8hire-Yorkshlre-Poland China.
r\a O s TABLE 3
ANALYSES OF VARIANCE OF MACROSCOPIC DATA
Mean squares
Source of variation d.f. No. Diam. of Diam. of follicles Weight of Length of corpora follicles > 5.0 mm. uterus uterus lutea in diameter
lime 13 18.31 9.29** 116.12** 19761*81*. 50** 7366.96**
Breeding 3 0.50* 1*.83** 28.68 3921*0.01 2298.61**
Regression (No. pigs nursed) 1 0.001 0.18 2.67 171*8.1*7 2013.29
Error U5 0.15 0.72 Ih.Sl 21037.20 61*9.11*
*P<0.05.
ro -0 PLATE I
OVARIES OE 9CWS AT CERTAIN TIME INTERVALS AFTER PARTURITION
Figure 1.— Ovaries (cut longitudinally in mid-line) from a sou 1 day after parturition. Several large corpora lutea can be seen in cross section at the periphery of each ovary.
Figure 2.— Ovaries from a sow 7 days after parturition. Corpora lutea are much smaller than those in the 1 day postpartum sow.
Figure 3.— Ovaries from a sow lU days after parturition. Corpora lutea further regressed from appearance on day 7. No large follicles present.
Figure ii.— Ovaries from a sow U5 days after parturition. Several large vesicular follicles can be noted at the periphery of the right ovary.
28 PLATE I
OVARIES OF SOWS AT CERTAIN TIME INTERVALS AFTER PARTURITION 30 diameter, which Is nearly the size regarded as normal for fully formed functional corpora lutea. However, as can be noted from the data which are shown in Table 2 and illustrated graphically in Figure these structures then rapidly diminished in size during the postpartum period. They had decreased to an average diameter of J+.7 mm. by 7 days after parturition and continued to diminish in diameter through out the remainder of the period under study. As they regressed in size they became dark brown in appearance and were seen only as dark brown spots or streaks in the ovarian stroma by the end of the observational period. Corpora lutea diameter differed significantly
(P<0.0$) among the breeds observed. Durocs and Duroc-Hai^>shire-
Yorkshire crossbreds had smaller corpora lutea than the other two
classes of crossbreds used in the study (Table 2).
Data on the average diameter of all follicles that were 2.0 mm.
or larger in size are given in Table 2 and shown graphically in Figure
6. The analysis of variance (Table 3) indicated highly significant
(P<0.01) differences in follicle diameter due to the time interval
after parturition or weaning. Ovarian follicular development, as
indicated by follicle size, was suppressed during the early postpartum period. The h.6 mm. average follicle diameter 1 day after parturition
decreased significantly (P<0.01) during the first week to an average
of 2.7 mm. at 7 days after parturition. Thereafter, follicle size
gradually increased at the postpartum intervals observed throughout
the remainder of the lactation period. However, it was only after the
litters were weaned from the sows that a marked Increase in follicular 31
E E < Ll) z> _ l < cr o CL a: o o u. o a: Oi h-
AFTER FARROWING AFTER WEANING
0 3 7 14 21 26 35 45 52 62 0 2 3 4 DAYS
Figure $.— Average diameter of the corpora lutea of pregnancy at predetermined intervals after farrowing and weaning. 32
to U i -I
tli
AFTER FARROWING AFTER WEANING
DAYS
Figure 6.— Average diameter of all follicles equal to or larger than 2.0 mm. in diameter at predetermined intervals after parturition and weaning. 33 size was noted, being most pronounced at 3 and 1* days post-weaning.
Follicles differed significantly (P<0.01) in size among the breeds involved in the investigation, being smaller in Duroc and Duroc-
Hamp shir e-York shire crossbred animals than in sows of the other two crossbred groups.
Ovarian follicular development was also assessed by recording the number of follicles that were equal to or greater than 5.0 mm. in diameter. The data therefrom are summarized in Table 2 and portrayed by the bar graph in Figure 7. A decrease in follicle size again was noted in the early postpartum period, as Indicated by a significant
(P<0.01) reduction in the mufeer of large follicles from 1 to lij days after parturition. There was an average of 3.2 follicles — 5.0 mm. in diameter at 1 day after farrowing, whereas, none were observed that measured this size 1U days postpartum. A gradual increase in the nui&er of larger follicles then occurred subsequent to day 1U post partum, and an average of 13.0 follicles were equal to or larger than
5.0 mm. in diameter at 62 days after farrowing.
Weight and length of uterus.— The data on the average total uterine weight of the sows observed at the various time periods after parturition and weaning from Table 2 are plotted graphically in Figure
8. The analysis of variance revealed a highly significant difference
(P<0.01) in uterine weight that was related to the various time
intervals observed. A rapid decline in uterine weight occurred from
day 1 to day 28 of lactation (from 272U.8 gm. at 1 day after partu
rition to 2HU.0 gm. on the 28th postpartum day). There was then 0 1 3 7 14 21 28 39 45 52 62 0 1 2 9 4 DAYS
Figure 7.— Average muriber of follicles equal to or larger than 5.0 am. in dianeter at certain periods during lactation and post- weaning. parturition and weaning. iue8—Weightofthe uterusatFigure 8.— predetermined Intervals after
WEIGHT OF UTERUS (kfl.) 2.4 2.0 2 2.2 0,8 0.4 0.6 0.2
6 a 6 8 0 4 2 0 I 3 r FE FARROWING AFTER 4 1 8 3 3 2 2 O 62 32 43 33 28 21 14 DAYS FE WEANING AFTER I 2 3 4 35
36 relatively little change in weight for the remainder of the lactation period up to 62 days postpartum, but a gradual increase in weight was noted during the U days after the litters were removed from the sows
(from 210.0 gm. to $02.k gm. from day 1 to day U post-weaning).
Total length of the uterine horns, shown graphically in Figure 9, indicated a pattern that was quite similar to the weight changes
noted. Total length of the uterine horns decreased markedly up to 28
days after parturition (from 237.2 cm. on day 1 to 120.8 cm. on day
28), then remained relatively unchanged for the remainder of
lactation. Some increase in length occurred during the post-weaning
period as the effect of lactation or suckling was removed. Uterine
length was significantly (P<0.0£) influenced by breeding, with the
Haiq?shire-Torkshire-Poland China crossbreds having shorter cornua than
the Durocs or the other two classes of crossbreds.
Histological observations
Ovary.— Considerations in the histological examination of the
ovary included: the structure of the corpus luteum of pregnancy; the
cytological appearance of the follicles; and the intensity and
cytological distribution of the alkaline phosphatase enzyme reaction.
The microscopic study of the corpus luteum of pregnancy revealed
that this ovarian structure rapidly degenerated after parturition and
soon became composed of connective tissue. Figure 10 illustrates the
structure of the corpus luteum found in a sow at the 110th day of
gestation, or approximately $ days prior to expected farrow date. intervalsafter parturition andweaning. TOTAL LENGTH OF UTERINE HORNS (CM.) 200 250 IOO 150 50 iue9—Totallength Figureof the9.— uterine horns atcertain time FE FARROWING AFTER DAYS FE WEANING AFTER
37 Although not from an animal in the experimental group under study,
this corpus luteum section was useful in making comparisons with those
observed after parturition. Prior to parturition the corpora were
composed mainly of large round or polyhedral lutein or so-called
"blossom" cells. These cells measured from 1*0 to 60 micra in diameter
and had large vesicular nuclei, varying from 6 to 10 micra in
diameter. The cytoplasm was finely granular and had an intense
affinity for the acid-fuchsin-orange-G dye staining solution used in
the Crossman trichrome staining technique. There was no indication of
any cell degeneration as was seen in the corpora section from a sow at
1 day after farrowing which is shown in Figure 11.
In this section the lutein cells were much smaller than just
prior to parturition, having a diameter of approximately 25 micra.
Mary of the nuclei were pyknotic and the cytoplasm was undergoing
fatty degeneration as shown by the vacuolation of most cells.
Collagenous connective tissue fibers were quite abundant and numerous
fibroblasts were evident throughout the section, suggesting that the
theca lutein cells had reverted back to connective tissue elements.
Figures 12 and 13, showing sections from sows at 7 and lJU days after
parturition, respectively, illustrate further regression of the corpus
luteum. Much of the tissue was now composed of connective tissue
elements and the few remaining scattered lutein cells were completely
vacuolated with pyknotic and fragmented nuclei. Mary lynphocytes and
histiocytes were evident, particularly near the collapsed blood
vessels which now were quite conspicuous due to the over-all shrinkage 39
Figure 10.— Corpus luteum of pregnancy of a sou at 110th day of gestation. Crossman's stain, x 160.
Figure 11.— Corpus luteum of pregnancy section of a sow at 1 day after parturition. Crossman's stain, x 160. - i
Figure 12.— Corpus luteum of pregnancy of a sow 7 days after farrowing. Crossnan's stain, x 160.
Figure 13.— Corpus lutexua of pregnancy of a sow ll| days after farrowing. Crossnan's stain, x 160. Ill of the corpora. The corpora lutea had diminished in site to approxi mately 3.5> in diameter by lli days after parturition and at 21 days after farrowing were almost indistinguishable from the connective tissue of the ovarian stroma.
Histological examination of the ovarian follicles suggested that many of the larger ones were in an atretic condition. This degener ative condition was indicated by chromatolysis of the membrana granulosa cells and pyknosis of their nuclei. The degenerated granulosa cells had become detached from the follicular wall in most instances and had floated freely to the center of the follicular cavity. Although seen in ovaries from sows at every time period
observed, it appeared that atretic follicles were more prevalent in
ovaries obtained from sows during the early postpartum period.
However, the ovaries were not serially sectioned and this suggestion
is based only on a limited number of observations on each organ. It
would seem, though, that follicular atresia would be a probable
occurrence in the early post-farrowing intervals since follicle size
decreased during this period.
Although follicles increased in size during the later stages of
lactation and several were noted which measured from 6 to 7 mm. in
diameter, ovulation as indicated by newly forming corpora did not
occur at apjr time during the lactation period. However, ovulation did
take place in sows soon after their litters were weaned and the
lactation or suckling effect was removed. Two of eight sows observed
at 3 days post-weaning and two of seven animals at U days after 1*2 weaning had visible rupture points on their ovaries and newly forming corpora lutea, signifying recent ovulation.
A weak alkaline phosphatase reaction was seen in cells of the corpora lutea of pregnancy of sows at 1 and 3 days after parturition as shown in Figure 11*, but could not be demonstrated in the lutein tissue at any subsequent observation period. The enzyme was observed in the ovarian follicles at all observation periods in the study, but always was restricted to the theca interna layer. Figure 15> illustrates the histochemical reaction in an ovarian follicle from a
sow 28 days postpartum, and Figure 16 shows the enzyme still limited to the theca interna cells that are being carried toward the center of a newly forming corpus luteum in a 3-day post-weaned sow that had recently ovulated.
Uterus.— Histological investigation of the uterus concerned primarily the condition of the epithelial lining, the cytology and
development of the uterine glands, and the intensity and distribution
of the non-specific alkaline phosphatase enzyme reaction. The
histological structure of the uterine epithelium of a sow at the 110th
day of gestation is shown in Figure 17. The uterine gland, seen in
cross section in the lower left corner of the photomicrograph was
coiiposed of columnar epithelial cells, approximately 35> micra in
height, with basally located large vesicular nuclei. The chorionic
epithelium of the placenta was seen in apposition to the uterine
epithelium. The uterine epithelium was greatly folded and the
epithelial cells were cuboldal in shape. The appearance of the sow's U3
Figure lU.— Corpus luteuai of pregnancy of a sow at 1 day after parturition. Bark deposits indicate site of alkaline phosphatase activity. GomoriTs procedure, x 75-
Figure 15.— Ovarian follicle of a sow showing intense alkaline phosphatase reaction in theca interna. Gomori's procedure, x 35. uu
Figure 16.— Newly forming corpus luteum from a sow 3 days post- weaning showing distribution of alkaline phosphatase. Gomori's procedure, x 3J>.
\
Figure 17.— Uterus and placenta of a sow at 110th day of gestation. H. & E. x 262. uterine epithelium 1 day after parturition, illustrated in Figure 18, was seen at this time to closely resemble the condition observed during late pregnancy. The folding of the uterine lining seen during pregnancy was still evident, although to a much less degree. The
epithelial cells remained low columnar to cuboidal in shape and measured 10 to 12 ndcra in height.
The histological structure of the uterine epithelium at 7 days
after farrowing is shown in Figure 19. The majority of epithelial
cells were very low and almost flattened in appearance. They were
only 5 to 6 micra high and their cytoplasm was deeply staining. In
certain small areas of the epithelial lining, however, numerous
mitotic figures were present, indicating cell multiplication. The
epithelium was slightly higher and presented a pseudostratified appear
ance. The folding of the endometrial epithelium had disappeared and
numerous leucocytes were present in the sub-epithelial stroma. The
edematous condition of the endometrium noted at 1 day postpartum had
lessened considerably by this time, as suggested by a greater density
in the number of nuclei In the connective tissue stroma.
Figure 20 shows a histological section from the uterus of a sow
11* days after parturition. By this time the epithelium was taller
than at 7 days after farrowing (measuring V~> to 20 ndcra) and had a
structure that may be described as pseudostratified. The epithelial
cells had increased in number and as a result the nuclei had become so
crowded that there appeared to be more than one layer of cells. Many
mitotic figures were noted in the epithelial layer, Indicating that 1*6
Figure 18.— Uterine epithelium of a sow at 1 day postpartum. H. & E. x 262.
Figure 19.— Epithelium of sow’s uterus at 7 days after partu rition. H. & E. x 262. h7
Figure 20.— Uterine epithelium from a sow ll* days postpartum. H. & E. x 262. U8 cell multiplication was still occurring. However, the contrary process was indicated also by the presence of numerous cells located
near the basement membrane, which were coiqpletely vacuolated with pyknotic nuclei. Numerous leucocytes were present in the imaediate
sub-epithelial stroma. Some had migrated through the epithelial layer
into the uterine lumen.
The epithelium of the sow's uterus at 28 days after farrowing is
illustrated in Figure 21. The pseudostratified appearance still
remained but the cells had increased slightly in height from that
observed 1U days postpartum and measured up to 25 micra. There was
then relatively little change in the structure of the uterine
epithelium during the remainder of the lactation period, except for
some increase in cell height near the end of the nursing period and
during the post-weaning period. Figure 22 shows the epithelium of a
sow 3 days post-weaning at which time the epithelial layer varied from
30 to 35 micra in height. The number of polymorphonuclear neutrophils
and eosinophils increased in the uteri of sows observed subsequent to
lactation. They were particularly numerous in the sub-epithelial
stroma of sows at 3 and li days post-weaning and had invaded the
epithelium in sows that had already ovulated.
There were no marked changes in the appearance of the uterine
glands during the lactation period. Reuser (1927) who described in
detail the extent and manner of branching of the sow's uterine glands
stated that they were greatly hypertrophied In pregnant uteri. The
gland, seen in cross section, from a sow at the 110th day of gestation Figure 21.— Uterine epithelium of a sou 28 days after farrowing. H. & E. x 262.
Figure 22.— Epithelium of sow's uterus at 3 days post-weaning. H. & E. x 262. 50 in Figure 17 would support this observation. The epithelial cells were 35 to UO Micra high with large vesicular nuclei and had a well defined finely granular cytoplasm. However, the cells of uterine glands in postpartum uteri were much shorter with poorly staining cytoplasm. At 1 day postpartum the gland cells were only 12 to 15 micra high. Most were almost entirely vacuolated and presented a lacy appearance. Many of the nuclei were shrunken and pyknotic. The uterine glands presented much this same appearance throughout the
entire lactation period, although some of the superficial tubules
located near the uterine lumen had increased cell height and better
defined cytoplasm subsequent to the 28th postpartum day. Increased
glandular activity, as indicated by numerous mitotic figures and more
deeply staining cellular cytoplasm, was noted in the uteri of post
weaned sows. Glands were much more numerous, particularly in the
basal zone of the endometrium near the inner muscle layer, in sows
examined at 3 and days post-weaning.
Alkaline phosphatase activity in the uterus varied from no
detectable amount at 1 day postpartum to an intense reaction at 3 and
h days post-weaning. At 1 and 3 days postpartum the enzyme was only
visualized in the endothelial cells of blood vessels located ;Just
under the epithelium. A slight reaction became apparent In the
epithelium and cells of the more superficial glands at 7 days after
farrowing as seen in the photomicrograph illustrated In Figure 23.
The Intensity and location of the histochemical reaction in the endo
metrium then remained much the same for the remainder of the lactation period and for the first 2 days a * waning. However, the reaction became much stronger in sows observ&u at 3 and li days post-weaning as shown by Figure 2h, which is a photomicrograph of a uterine section from a sow at 3 days post-weaning. The enzyme was now located in glands situated in the basal area of the endometrium as well as in the
endometrial regions previously noted. The enzyme was apparent also in
cells of the inner layer of the myometrium in sows slaughtered at 7,
lli, and 21 days after farrowing, but was not detected in muscle layers
of the uteri of animals observed at any subsequent time periods.
hypertrophy of the uterine musculature, which occurs during
pregnancy, was evident in uterine sections taken from sows during the
early postpartum period. The myometrium was very thick in sections
from uteri at 1 and 3 days after parturition due both to hypertrophy
of the individual muscle fibers and to the abundance of connective
tissue surrounding the muscle bundles and between the circular and
longitudinal muscle layers. The nyometrium decreased in thickness Tip
to 21 days after parturition due to a decrease in size of muscle
fibers and reduction in amount of interspersed connective tissue.
Relative thickness of the endometrium and myometrium then remained
unchanged from day 21 postpartum until the end of the 62-day lactation
period. The endometrium increased in thickness and was edematous in
3- and ii-day post-weaned sows. It had a fluid or gelatinous consist
ency and would exude from the transversally sectioned uterus. 52
Figure 23.--Uterus of a sow at 7 days postpartum showing slight alkaline phosphatase activity in epithelium and glands. Gomori*s procedure, x 59.
S i "
Figure 21*•— Uterine section of a sow at 3 days post-weaning illustrating strong alkaline phosphatase reaction in epithelial cells. Aomori*s procedure, x 59. 53
Oviduct.— The general structure of the s o n ' s oviduct is shoHn by the photomicrograph in Figure 25. The mucous lining of the oviduct projects into the lumen as finger-like folds and is covered Nith a single-layered epithelium composed of ciliated and non-cillated cells which are about equally distributed. Changes in the structure and height of the epithelium occurred throughout lactation and early post- weaning. The epithelium at 1 and 3 days after farrowing, as illustrated in the photomicrograph presented in Figure 26, appeared pseudostratified columnar and was 30 to 35 micra high.
A striking change in the appearance of the epithelium was noted at 7 days after parturition. The epithelium had decreased in height to 15— 20 micra and had lost its pseudostratified appearance to become simple columnar in shape. The most conspicuous feature of the epithelium was the very numerous cytoplasmic processes which projected out from the distal edge of the epithelial layer. These processes, many of which contained nuclei, were eventually extruded out of the epithelial layer into the lumen of the duct. The epithelial layer displayed this cellular arrangement for much of the remainder of the lactation period and is illustrated by the photomicrograph presented in Figure 27.
Some lessening of the cellular extrusion was noted during the later stages of lactation (52 and 62 days post-farrowing) and cell height increased slightly. At 3 and U days post-weaning the epithe lium, as seen in the photomicrograph presented in Figure 28, had increased markedly in height to 35— i|0 micra and had regained the Figure 25.— Transverse section from anpullar region of oviduct of sow at 1 day after farrowing. H. 4t E. x 59.
Figure 26.— Higher magnification of Figure 25 showing epithelium of oviduct of sow at 1 day after farrowing. H. & E. x 262. 55
Figure 27.— Oviduct epithelium of sow 11* days postpartum. H. & E. x 262.
Figure 28.— Oviduct epithelium of sow 3 days post-weaning. H. & E. x 262. 56 pseudostratifled condition seen at 1 and 3 days postpartum. A few aldehyde-fuchsin-negative droplets of secretory material could be seen protruding from the distal border of the epithelial cells.
Cervix and vagina*— The epithelial lining of the cervix of the
sow is comprised of a layer of columnar cells some of which are ciliated. Just prior to parturition the epithelial cells, as illus trated in Figure 29, were high columnar measuring 2$ to 30 micra. The basally located nuclei were large and vesicular. The cytoplasm was aldehyde-fuchsin-positive in the distal portion of the non-clliated
cells indicating that a mucoproteinaceous material was present. The
epithelium at 1 and 3 days postpartum closely resembled the prepartum
structure. The purple coloration caused by the aldehyde-fuchsin stain
is seen in the epithelial cells of the cervix of a 3-day postpartum
sow in Figure 30. Alkaline phosphatase was present also in the
epithelial layer of the cervix with the reaction being strongest in
the distal border of the cells.
A gradual diminution in cell height, alkaline phosphatase
activity, and the aldehyde-fuchsin staining reaction occurred after
the third postpartum day. At 21 days after farrowing the epithelium
had decreased to 15 micra in height and was low columnar or in some
instances pseudostratified in appearance as shown in Figure 31.
Little alkaline phosphatase activity was evident and the aldehyde-
fuchsin reaction had disappeared. Marjy vacuolated cells with pyknotic
nuclei were located near the basement meirt>rane. Polymorphonuclear
neutrophils and eosinophils which were very numerous until lU days 57
Figure 29.— Cervical epithelium of a sow at 110th day of gesta tion. H. & E. x 262.
Figure 30.— Cervical epithelium of a sow at 3 days after farrow ing showing aldehyde-fuchsin reaction in the cytoplasm of the epithelial cells. Ciliated cells are not distinguishable at this magnification. Halmi's aldehyde-fuchsin. x 160. 58 postpartum had decreased in number at 21 days after parturition.
The morphology of the cervical epithelium as seen on the 21st day
then remained relatively unchanged until 3 and U days post-weaning.
At that time the epithelium had increased in height, the cytoplasm of
the cells was aldehyde-fuchsin-positive, and a strong alkaline
phosphatase reaction was present in the epithelial cells. Thus, it
was nearly identical to the histological appearance noted at 1 and 3
days postpartum.
The vagina is lined with a stratified squamous type of epithelium
which underwent changes in number of cell layers and thickness during
the period under study. The vaginal epithelium at 1 day after
farrowing, as shown by the photomicrograph in Figure 32, was cosqposed
of five to eight layers of cells. The nuclei in the basal layers of
cells were large and vesicular, while those in the superficial layers
stained more deeply. Large numbers of polymorphonuclear neutrophils
were present in the sub-epithelial stroma and mai^r had invaded the
epithelial layer.
Considerable sloughing of the superficial cells was noted in
vaginal sections from sows at 3 and 7 days after parturition and the
epithelium decreased in thickness until only two or three layers of
cells were observed at lU days postpartum as shown by the section
illustrated in Figure 33. A heavy infiltration of neutrophils into
the epithelium occurred during this period. Many were observed lying
in clumps in lacunae in the epithelial layer and a considerable number Figure 31.— Cervical epithelium of a sow at 21 days after farrow ing. H. & E. x 262.
Figure 32.— Vaginal epithelium of a sow at 1 day after partu rition. H. & E. x 131. 60 were floating in the lumen of the vagina at 3 and 7 days after partu rition.
There were no marked changes in the condition of the epithelium from llj to days after parturition. The epithelium increased in thickness, however, at days postpartum at which time the number of cell layers increased to six or eight. Thereafter, little change occurred until 3 and li days post-weaning. The epithelium then had increased to 70— 80 micra in height and was 12 to 1? cell layers thick. Polymorphonuclear neutrophils had increased in number and had invaded the epithelial layer. The cellular structure of the vaginal epithelium at this time Is shown in Figure 3h. The cytoplasm of the superficial cell layers had less affinity for stain than that in the more basal layers of cells. The surface cells also had shrunken and pyknotic nuclei. 61
Figure 33-— Vaginal epithelium of a sow lli days postpartum. H. & E. x 262.
Figure 3U.— Vaginal epithelium of a sow 3 days post-weaning. H. & E. x 262. DISCUSSION
Based upon limited observations during the immediate postpartum period, Corner (1919) and Burger (1952) indicated that the corpora lutea of pregnancy rapidly atrophy following parturition in the sow.
Rumjancev (1951*) also reported that degeneration of these‘ovarian structures occurred very quickly in postpartum sows. Macroscopic and microscopic observations made in the present study on corpora lutea of pregnancy of the sow support the findings of these earlier investigators. The prospt retrogression of the corpora following parturition indicates that lactational anestrus in swine is not mediated through a corpus luteum which remains functional during the
suckling period, as Dawson (19l*6a) suggested was the case in the
lactatlng cat. Greenwald (1958) also conjectured that the corpora
lutea of lactation, which are formed by a postpartum ovulation in
certain species of rodents, account for the anestrous condition in the
lactatlng mouse. However, according to McKeown and Zuckerman (1938),
maintenance of lactational anestrus is not caused by the corpora lutea
of lactation in the rat.
The data on ovarian follicular size from the present study agree
closely with those reported by Lauderdale et al. (1963), although the
latter workers only Included data up to 16 days postpartum.
Lauderdale et al. (1963) also noted a significant reduction in
62 63 follicle size during the early postpartum period in the lactatlng eon.
Burger (1952) reported, too, that there Has little ovarian activity in eight sons observed at periods ranging from U to 7. days after farrowing. Rumjancev (195U) observed little ovarian activity in sows during the first week after parturition, but he indicated that rapid follicular growth then occurred subsequent to day 9 post-farrowing and ovulation took place within 21 days after farrowing, which is contrary to the findings of this study. Bo indication was found to suggest that ovulation had occurred in any of the 1*0 sows which were studied throughout the 62-day lactation period. However, follicle siae increased during the later stages of lactation and ovulation occurred as early as 3 days after the litters were weaned from the sows. This agrees with other investigators (Baker et al., 1953; Lasley, 1955) who have reported that estrus will usually occur within the first week after the lactation or suckling stimulus is removed.
Some workers (Parkes, 1926; Bruce and East, 1956; Bruce, 1961) have reported that lactational suppression of the estrous cycle in the mouse and rat is in part influenced by the strength of the suckling stimulus, that is, siae of nursing litter, and is less pronounced when there is a small number of suckling young. The analysis of the macro scopic data from this study indicated that such is probably not the case in swine. Regression analysis (Table 3) revealed no significant
(P <0.05) differences due to size of nursing litter on any of the macroscopic observations considered.
It would appear from the uterine weight and length data recorded 614 in this study that the uterus of the son had beeone involuted at between 21 to 28 days after parturition. The uterus remained relatively constant in weight and length from the 28th postpartum day until the termination of lactation at 62 days after farrowing. This indicates that the uterus does not become hyperinvoluted in the sow during lactation, which Dawson (l9U6b) reported as occurring in the lactatlng cat.
Rumjancev (195U)* based on histological examination, felt that postpartum involution of the uterus was conplete by the 15th day after parturition and that the endometrium was capable of receiving and implanting an embryo by the 18th postpartum day. The macroscopic and microscopic observations of this study suggest that the postpartum involution of the uterus and the endometrial lining continues until 21 days after farrowing. Wallace (I96I4) believes that conception rates
are not as good when sows are bred at first estrus after 2 weeks of
lactation as they are after 3 weeks of lactation, but he has no
detailed records to support this observation. Paredis (1962) found
that the interval from weaning to conception was longer with sows weaned after 6 days of lactation than with ones weaned after a l|2-day
lactation period. However, only a small number of animals were
involved in this study and there was considerable individual
variation.
The post-weaning increase in uterine weight and length and the
edematous condition of the endometrium noted at this time were most
likely a reflection of increased levels of circulating estrogens. 65
Estrogens are known to cause increased water retention and edema in
the uterus (Zuckerman et al., 1950), as well as an increase in dry weight (Astwood, 1938), and the weight Increase of the uterus of the
ovarlectomized rat or mouse has been used extensively in the bio-assay
of these hormones. The Increased ovarian follicular development noted
during the post-weaning period could conceivably result in this
apparent Increase in estrogen level. Lunaas (1962) and Raeside
(1963a) have reported that urinary estrogen levels are highest in the
sow Just prior to estrus when follicles are approaching their maximum
sise.
The structure and appearance of the uterine epithelium noted in
this study during the early postpartum period was similar to that
reported by Rumjancev (195i|). The flattened, deeply-staining, almost
cornified appearance of the cells at 3 and 7 days postpartum indicated
a degenerative state. Nalbandov (1958) suggests that there may be
sloughing off and regeneration of the uterine endometrium in non
primates as well as in primates. This process was indicated by the
histological structure of the epithelium during the period of rapid
involution of the sow's uterus in this investigation. Regeneration of
the epithelium indicated by cell multiplication in certain small areas
of the uterine lining at 7 days postpartum appeared to be complete by
the 21st day after parturition. The low columnar or pseudostratified
structure of the epithelial layer which was present from 21 days after
farrowing throughout much of the remainder of lactation resembled the
condition described by Corner (1921) and McKenzie (1926) as occurring 66
during late diestrus of the regular estrone cycle when estrogens were
at a low level. The Increased epithelial height and glandular
development noted in the uteri of sows at 3 and h days post-weaning was also outlined by Corner (1921) and McKenzie (1926) as the
condition of the uterus just prior to estrus.
Snyder (1923) in describing the morphological changes in the
oviduct of the sow during the estrous cycle reported that the epithe
lial cells were at their maximum height just prior to and during
estrus. The epithelium decreased in height and many cells were
extruded out into the lumen of the duct during dlestrus when endoge
nous estrogens were at low levels. The same pattern was noted in the
bovine by Weeth and Herman (1952), and in the sheep by Casida and
McKenzie (1932) and Hadek (1955). The histological structure of the
sow*s oviduct epithelium in the current study would therefore suggest
that estrogens were at moderately high levels immediately after
parturition, decreased to low proportions by 7 days after farrowing,
and remained as such until 3 or U days post-weaning.
No description was found in the literature concerning the
cytological changes in the cervical mucosa of the sow throughout the
estrous cycle, but Herrick (1951) has described the cyclical changes
in the cervix of the cow. He reported that the columnar epithelial
cells of the cervix were tallest at estrus and mucus was most abundant
at this time. The histological examination of the sow*s cervical
epithelium in this investigation revealed that the cells were tallest
at 1 and 3 days postpartum and again at 3 and u days post-weaning. 67
Mucoprotein also appeared to be more abundant during these two periods. Therefore, it appeared that estrogens, if they are primarily responsible for the observed cytologlcal changes In the cervical epithelium, were at their highest level immediately postpartum and at
3 and U days post-ueaning.
McKenzie (1926) described the stratified squamous epithelium of the sow as varying in height from three to six cell layers during diestrus to 20— 2$ layers in thickness at the time of estrus. In the current study the vaginal epithelium was five to eight cell layers thick 1 day after farrowing, had decreased to two or three layers at lli days after parturition and then increased in height from the U5th postpartum day to 12—IS cell layers at h days post-weaning. Thus, the cytologlcal changes noted in the vaginal epithelium throughout the period studied indicated the same changes in apparent endogenous estrogen amounts as those suggested by the histological examination of
the mucosa of the uterus, oviduct, and cervix.
The alkaline phosphatase reaction, which was of moderate
intensity during the first 3 days after parturition, weak or absent
for the remainder of lactation, and very strong at 3 and b days post-
weaning, also gave an Indication of levels of circulating estrogen.
Although the physiological significance of the enzyme still remains
largely a matter of conjecture, there is, nevertheless, a variation in
the strength of its histochemlcal reaction in the reproductive tract
which may be correlated with ovarian activity. Hadek (I9*>8b) noted
that the enzyme reaction was lowest during late diestrus, highest 68 during estrus and absent during anestrus in the eve's uterine epithe lium and glands. Estrogens have been shown to cause a marked Increase in alkaline phosphatase in the glands, surface epithelium, and circular muscle of the uterus of the mouse (Atkinson and Elftman,
19^6), and rat (Pritchard, 19149; Velardo, 19$h).
Thus the histological structure of the reproductive tract which is correlated with ovarian activity during the regular estrous cycle, according to Corner (1921) and McKenzie (1926), appears also to be associated with ovarian follicular development during lactation and early post-weaning in the sow. The apparent high level of estrogens at parturition and marked decline shortly thereafter indicated by the histological observations in this study is further supported by
Raeside (1963b). He reported that large amounts of urinary estrogens are excreted by the sow during late pregnancy, but a marked decrease occurs in excretion immediately after farrowing.
In conclusion, the data from this study indicate that lactation and/or the suckling stimulus, at least in the early postpartum period, apparently brings about a cessation in the production, release, or effectiveness of follicle stimulating hormone and luteinizing hormone, the pituitary gonadotrophic hormones believed to be responsible for ovarian follicular development. Two other pituitary hormones, prolactin and oxytocin, are known to be physiologically active during lactation and perhaps one or both of them counteract the action of the gonadotrophic hormones or prevent their release from the pituitary.
Heites et al. (1963) have cited evidence suggesting that there is a 69 reciprocal relationship between the release of follicle stimulating hormone-luteiniiing hormone (FSH-LH) and prolactin, and suckling may promote prolactin release by inhibition of FSH-LH secretion. SUMMARY
The nacroscopic and microscopic appearance of the reproductive tract of second-lltter lactating sous was studied at 1, 3 , 7, lh, 21,
28, 35, U$, 52, and 62 days after farrowing. Four sows (two Durocs and two crossbreds of either Hanpshire-Yorkshire-Duroc, Hanpshire-
Yorkshire-Poland China, or Duroc-Hampshire-Yorkshire breeding) were examined at each postpartum period. Observations were also made on the reproductive organs of sows either 1, 2, 3, or U days after their litters were weaned subsequent to an 8-week lactation period. A total of 67 sows were included in the investigation.
Macroscopic observations included diameter of corpora lutea of pregnancy, diameter of ovarian follicles, number of follicles
> 5.0 mm. in diameter, weight of uterus, and length of uterine horns.
The ovary, uterus, oviduct, cervix, and vagina were examined microscopically.
The corpora lutea of pregnancy, which averaged 8.1 mm. in diameter 1 day after parturition, rapidly decreased in sise and appeared only as dark brown spots or streaks in the ovarian stroma by the end of the lactation period. Histological examination revealed that they pronptiy degenerated after parturition and were composed mainly of connective tissue elements by 7 days postpartum.
The ovarian follicles, which averaged U.6 ram. in diameter 1 day
70 71 after parturition, decreased significantly (P<0.01) in size during the first week to an average of 2.7 »m. at 7 days after farrowing.
Follicles gradually increased in size, thereafter, to £.6 mm. at 62 days after farrowing, and rapidly enlarged to 7.6 mm. in diameter at
U days post-weaning. The same trend in follicular development was indicated by the number of follicles ^ £.0 mm. in diameter recorded at the various intervals after parturition and weaning. Atretic follicles, although noted at all observation periods, appeared to be more prevalent during the early postpartum period. Ovulation had occurred in two of eight sows observed at 3 days post-weaning and in two of seven animals at U days post-weaning.
The uterus decreased in weight and length until 28 days after parturition, changed little in this respect for the remainder of
lactation, and then increased in both measurements after the pigs were weaned from the sow. The uterine epithelium appeared degenerate
during the immediate postpartum period, then underwent regeneration, which began at 7 days postpartum and appeared to be complete by the
21st day after parturition. The low columnar or pseudostratified
structure of the epithelial layer, which was present from 21 days
after farrowing throughout the remainder of lactation, resembled that
described as existing during late diestrus of the regular estrous
cycle and was indicative of low endogenous estrogen levels. The
Increased epithelial height and glandular development noted at 3 and
U days post-weaning were similar to the condition normally present
Just prior to estrus. 72
The epithelium of the oviduct was tall and pseudostratified in appearance during the immediate postpartum period and again at 3 and 1* days post-weaning. It was low columnar and studded with knob-like or finger-shaped cytoplasmic protrusions from 7 days post-farrowing throughout the remainder of the lactation period, indicative of little estrogenic stimulation.
The cervical epithelial cells were tall columnar and contained aldehyde-fuchsin-positive material at 1 and 3 days postpartum and again at 3 and U days post-weaning. They were low columnar or pseudo stratified with no aldehyde-fuchsin reaction throughout the remainder of the study. The stratified squamous vaginal epithelium was five to eight cell layers thick 1 day after farrowing, had decreased to two o1' three layers at lh days after farrowing and then increased in height from the l*5th postpartum day to 12— 15 cell layers at U days post- weaning.
Alkaline phosphatase was demonstrated histochemically in the
epithelium and glands of the uterus and in the epithelial cells of the
cervix. The reaction was of moderate intensity during the first 3
days after parturition, was weak or absent for the remainder of
lactation and very strong at 3 and U days post-weaning.
The observations of the study indicated that the uterus of the
sow had become involuted by 21 to 28 days after farrowing. The
corpora lutea of pregnancy rapidly regressed after parturition.
Ovarian activity was depressed, particularly during the early stages
of lactation, and the mucosa of the reproductive tract exhibited 73 morphological changes corresponding to the extent of ovarian follicu lar development throughout the lactation and early post-weaning periods. APPENDIX I
TABLE h
SLAUGHTER DAT, BREEDING, AND NUMBER OF PIGS FARROWED AND NURSED BT SOWS USED IN STUDY
Season No. No. Day of Sow no. Breed pigs pigs slaughter of farrow farrowed nursed
After farrowing
111-6 2w 1 H-Y-Da 1963-summer 8 8 113-6 3w 1 D-H-Y I96I*- summer 13 11 338-62s 1 D 1963-fall 12 9 516-6 2 s 1 D 1963-fall 13 13 87-6 2w 3 H-Y-Pb 1963-summer 13 10 69-63w 3 D-H-Y 1961*- summer 13 11 1*10-62 s 3 D 1963-fall 13 12 ll*9-62s 1* D 1963-fall 10 8 1 * 0 6 - 6 2s 7 D 1963-fall 17 12 97-63v 7 D-H-Y 1961*-summer 12 1*62-623 8 D 1963-fall 8 8 1 * 2 - 6 2w 9 H-Y-D 1963-summer 11 11 11*-6 3* 11* D-H-Y 1961*- summer 15 12 73-^3w 11* D-H-Y 1961*- summer 11* 9 362-623 11* D 1963-fall 13 7 1 8 9 - 6 2s 11* D 1963-fall 10 10 37i*-62f 20 D 1961*- spring 12 11 12i*-6 2f 20 D 1961*-spring 17 12 97-62w 22 H-Y-P 1963-summer 10 10 113-62* 22 H-Y-P 1963-summer 9 8 10l*-6 2 f 27 D 1961*-spring 12 10 123-6 2 f 28 D 1961*- spring 9 8 10-62w 28 H-Y-P 1963-summer 1* 6 76-62* 30 H-Y-D 1963-summer 12 8 385-62f 3? D 1961*- spring 8 8 1*01-62 f 35 D 1961*- spring 7 7 88-62* 36 H-T-P 1963-summer 16 8 38-62* 37 H-Y-D 1963-summer 13 10 7h 75
TABLE h— Continued
D f Season No. No.
^ 0 0 ' slaturhtersiaugn^er Breed farrow of farrowed pigS nursed pigS
6l-62f UU D 196 h-spring 12 3 303-62f 1*5 D 196 U-spring 17 9 1*9-6 2w 1*5 H-Y-P 1963-summer 9 9 112-62w U5 H-Y-P 1963-summer 12 10 £0-62* 52 H-Y-D 1963-summer 9 9 89-62w 52 H-Y-D 1963-summer 13 10 U3U-62f 53 D 19614- spring 3 11 l*66-62f 53 D 196 U-spring 17 11 367-62f 60 D 1961*- spring 8 8 175-62f 62 D 1961*-spring 9 8 10i*-62w 62 H-T-P 1963-stammer 9 10 11-6 2w 62 H-T-P 1963- summer 11 10
Ifter weaning after 8-week lactation period
160-6 2 s 1 D 1963-fall 10 7 277-62s 1 D 1963-fall 111 11 3ii9-62s 1 H-Y-D 1963-fall 10 10 223-6 2 s 1 H-T-D 1963-fall 111 11 20li-6 2 s 1 H-T-D 1963-fall 12 11 306-62 s 1 H-T-D 1963-fall 11 10 3$6 -6 2 s 2 H-T-D 1963-fall 13 11 205-62 ar 2 H-T-D 1963-fall 12 10 35^-628 2 H-T-D 1963-fall 13 13 32l*-6 2 s 2 H-T-D 1963-fall 13 9 2U-63w 2 D-H-Y 196 U-summer 13 10 3J4-63W 2 D-H-Y 1961*-summer 11 12 288-6 2 a 3 D 1963-fall 12 7 112-6 2 s 3 D 1963-fall 12 9 16-6 3w 3 D-H-T 1961*-summer 11 11 5U-63w 3 D-H-Y 1961*- summer 3 11 93-63w 3 D-H-T 1961*- summer 9 9 99-63w 3 D-H-T 196 li-summer 13 11 287-62s c 3 H-T-D 1963-fall 111 11 317-62sc 3 H-T-D 1963-fall 10 11 30U-62s h H-T-D 1963-fall 15 11 33-63w h D-H-T 1961*- summer 9 13 70-63w h D-H-T 1961*- summer 12 1U 72-63w h D-H-T 1961*- summer 12 111 76
TABLE U— Continued
Season No. No. So’' ao- slighter Breed of pigs pigs farrow farrowed nursed
H5-63w h D-H-Y 196 U- summer 11* 11 207-62s h H-Y-D 1963-fall 10 12 301-62sc h H-Y-D 1963-fall 16 11
aH— Hampshire; Y— Yorkshire; D— Duroc.
kp— Poland China.
°Had ovulated. TABLE 5
MACROSCOPIC OBSERVATIONS OF THE REPRODUCTIVE ORGANS
_ Ave. diam. Are. diam. ,T . ,, . T ., . DaJ of corpora of So. follicles W«1*ht of ***** of “ >• lutes follicles £ 5.0 •». “}ertt? u?“ ™f slaughter j (g«.) (e».)
After farrowing
lll-62w 1 8.3 3.7 0 2787 213 113-63* 1 7.7 3.6 0 3090 265 338-62s 1 8.8 1*«6 2 21*29 221* 5l6-62s 1 7.3 5.8 10 2633 289 87-62w 3 6 .1* 5.7 6 11*21 187 69-63w 3 6.8 2.5 0 2110 21*1* l*10-62s 3 7.2 2.7 0 1620 211* ll*9-62s 1* 5.3 2 .1* 0 11*95 227 l*06-62s 7 1*.7 2.0 0 1175 305 97-63w 7 I*.6 2.5 0 101*5 213 1(62-628 8 i*.7 2.3 0 955 233 1*2-62* 9 l*.l* 2.9 0 760 201 ll*-63w 11* 3.8 2.8 0 555 180 73-63* 11* 3.5 2.0 0 510 228 362-62s 11* 3.1 2.5 0 615 192 189-628 11* 3.1* 2.7 0 365 158 37l*-62f 20 2.7 lt.1* 3 355 136 12i*-62f 20 2.6 5.3 6 371* 192 TABLE 5— Continued
Day . ' * ?lam* w , ... _ Weight of Length of >, of corpora of No. follicles .6 7s Sow no. of , .T , , s. r- a uterus uterus lutea follicles > 5.0 mm. , \ , v slaughter (nffl>) (-u) (gm.) (cm.)
97-62w 22 2.1* 1*.5 2 261* 111* 113-62w 22 3.5 1*.6 6 209 105 10l*-62f 27 1.6 i*.l 0 215 131* 123-62f 28 3.1 2.0 0 288 91* 10-62w 28 2.6 1*.8 7 188 89 76-62w 30 2.1* 3.9 1 197 105 385-62f 35 2.1 i*.2 2 160 113 i*01-62f 35 1.8 I*.6 6 220 122 88-62w 36 2.0 5.1 10 295 107 38-62w 37 2.5 5.2 9 195 11i* 6l-62f 1*1* 1.9 ' 1*.6 7 230 121 303-62f 1*5 1.6 1*.7 9 250 135 1*9-6 2w 1*5 2.5 6.2 8 310 107 112-62w 1*5 2.0 5.0 7 195 99 50-62w 52 1.9 6 .1* 8 21*5 112 89-62w 52 1.8 1*.7 5 225 116 l*3l*-62f 53 1.0 l*.l* 7 210 126 l*66-62f 53 1.3 1*.7 6 225 121* 367-62f 60 1.3 1*.6 11 350 168 175-62f 62 1.5 5.5 21 210 97 10l*-62w 62 2.0 5.8 12 175 106 ll-62w 62 2.0 7.0 7 190 92 TABLE 5— Continued
Ave. diam. Ave. diam. Day Weight of Length of of corpora of No. follicles Sow no. of lutea follicles > ^.0 mm. uterus uterus slaughter (cm.) (ram.) (mm.) (ga.)
After weaning after 8-week lactation period
l60-62s 1 1.5 5.2 16 250 127 277-62s 1 1.5 5.a 10 160 101 3l*9-62s 1 i.i* 5.8 12 325 96 223-62s 1 1.7 6.1 9 270 116 20l*-62s 1 1 .1* 7.3 11 525 11*5 306-62s 1 1.5 7.8 U 380 101* 356-62s 2 1.5 7.2 9 810 199 205-62s 2 l-l* 6.7 8 1*25 135 351i-62s 2 1.6 6.7 5 260 122 32l*-62s 2 1.5 6.0 10 l*l*o 132 21*-63* 2 0.8 5.9 18 380 157 3l*-63* 2 1.1 5.6 16 325 125 2 8 8 - 6 2s 3 1.0 7.0 11 1*90 152 112-62s 3 1.2 6.9 9 1*80 151 16-63w 3 1.1 6.9 20 1*95 188 51*-63* 3 2.0 6.0 8 310 120 93-63* 3 1.1 7.0 21* 1*15 11*0 99-63* 3 1.2 7.1* 18 1*75 166 2 8 7 - 6 2s « 3 ------—- 610 221 317-62sa 3 ------— --- 71*5 215 TABLE 5— Continued
_ Ave. diam. Ave. diam. „ . . . _ T - ^ of corpora of So. follicles We^ ht of of So* no- , ° i lutea follicles > 5.0 mm. u*ernf ^ eru» slaughter (mu) (gm.) (cm.)
30it-62s b 1.2 10.0 9 570 155 33-63w h 1.0 l*-7 9 360 129 70-63w k 1.3 6.6 13 605 202 72-63w, h 1.5 6.8 17 590 205 H5-63*ib h 1.3 7.a 18 730 182 207-62sa b — ... a6o 207 301-62sa b — -- — a6o 155
aHad ovulated.
bIn estrus. LITERATURE CITED
Allen, A* D., J. F. Lasley, and A. W. Uren. 1957. The effects of gonadotrophic hormone injections on induction of estrus in lactating sows. J. Animal Scl. 16:1097. Abstr.
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Astwood, E. B. 1938. A six-hour assay for the quantitative deter mination of estrogen. Endocrinology 23:25.
Atkinson, W. B., and H. Elftman. 191:6. Effect of steroid sex hormones on distribution of alkaline phosphatase in uterus of mouse. Proc. Soc. Exp. Biol. Med. 62:11:8.
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