Studies in the Reproduction, Growth and Development of the Chinchilla
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STUDIES IN THE REPRODUCTION~ GROWTH AllD DEVELOP;MEN'r OF THE CHI)lCHILLA FORREST DONALD TIBBITTS A 'J."'dESIS tru;bmi tted to OREGON STATE COLLEGE in partial. fulfillment of the requirements for the degree of MASTER OF ARTS June 1955 &FSIBr Redacted for Privacy frtrfitr tFdwm ef lo*hgr , & Shr'gr- l(',ISt. Redacted for Privacy erima * n( ffioHr T-** Redacted for Privacy er(mrn o( eb#fiX $uahr,tl 0adttfi Redacted for Privacy D.B €f 0m&rtc {lohtr, &tr thd. l.a frrrnfint IE g. IfS tfa{ ry Elrfi ru&il,ttt An axpt'esSion ot sincere gratitud.e and thanka is due to Dr. Howard n. Uillemann o£ the ~artment of Zoology, <megcn State C-ollege for suggest:Utg this research inVestigation, allold.ng .full use a! his laboratory facilities and giVing freely of his time .and el'lergies toward .its successful comple tion. For the actual t,yping involved immeasurable apprecia tion is extended to my w.:tte, n!ileen. • '!'ABLE OF CONTEl-lTS I. Introduction • • • • . • . 1 II. Materials and Uethods . .. 1 III. General Remarks on Chinchilla Reproduction . • • 3 Su.~ •••• • • • •• • • • • • • • • • • • • 7 rv. The Ovarian Cycle • • • • • • • • • • • • • 8 ~ .... ' .• . • • • • • • • • • . • • 13 V. Reproductive Potential of the Chinchilla . 14 s'll:nl.!'nacy • • • • • • • • • • • • • • .. • .. • • 20 VI . Early Ege Loss in the Chinchilla 21 s~ ........... ' . 24 VII. Development of the Ova!:"'J • . .. - - 25 s Ul:illllary • • • • • • • • • • il .. 29 VIII. Postnatal Gr{)wth in the Chinchilla . .30 Gr-aph 1 • • • • • • • • • • • • . .31 Gr nph 2 .. .. .. 32 Summtllj" . .. ~ . .. 33 Platel . .. ~ . 35 Bibliography • • <If • M e • • 4 • • • • • • e • e STUDIES IN THE REPRODUCTION, GROtf:PH AND DEVELOPMENT OF THE ClU:NCHILLA I . Introduction Because of the chinchilla•s gain as an important £'Ill' bearer, COllllllercial breeders have become increasingly interested in obtain· :illg more and better qu.al.ity animals . This of course implies a thorough i:tJVestigation of the reproductive habits o£ this animal. A survey of the literature indicates that1. with the axception of the guinea pig, there is a. dearth of information e.oncerning the reproduction of' eystricomorph rodents in general and the chinchilla in particular. .Asdell (l) summarizes what work bad been done on the ohincllilla and other Hy'strieomorpha up to 1946 and in l948-49 Pearson (6), (7) contributed bis studies on reproduction of the lUOuntain visca.cha, I.asf:di~ peruanum !!eyen. 'thus, the present - $ . series of studies '7ere begun to .form a basis upon which could be developed later more comprehensive in~estigations on chinchilla reproduction. II. Materials and Methods The ebine-hillas used in these studies were donated p:rilnarily by west coast commercial breeders. Upon receipt of the animals thei.r weieht and crown- rump measurements were taken, the ova.ties and uteri rem~ed at sacri!iee, weighed and fiXed in Bollin ' s fiuid. In addition, if the !em.Ues were pregnant, the er.1bryos vrerE!t 2 removed, weighed and measured and prepared by the Spalteholtz technique for future skeletal studies. Amniotic fluid volumes were taken 'When practical and the placentae inject-ed and preserved in Bouin •s fluid. OVaries ere embedded in paraffin, sectioned at 10-12 microns and stained with hematoxylin and eosin. The slides were examined by projecting them onto a screen using a 35 mm. projector With a glass plate holder adapted for 2 x 3 inch slides. By using the 35 mm. slide projector the entire slide could be examined at once, thus reducing the possibility of counting the same corpus luteum. or follicle more than once. Uore specific accounts of the methods used in the analysis of the ovaries for the various studies Will be given under the appro priate discussions! In. General Remarks on Chinchilla Reproduction Among the Hystricoidea the estrous cycle and gestation are quite long in comparison i'fith other rodents. .Also a smaller litter size and fewer young per year seem to be the general rules although mucn variation is noted even w1thin genera. In the chinchilla the length of the estrous cycle is thirty six ~s (30-42) while gestation varies from 109 to 115 days de pending upon the breed of animal. In captivity the females are polyestrous and are capable of breeding at any time of the year1 but apparently breed most often during the winter months (Dec . . ar. ) • Usually females will undergo tr1o successive cycles during the winter and then lapse into a non-cycling or anestrous condition for the remainder of the year. However, litter records from breed ers indicate that some good breeding females may eycle during the entire year or1 on the other hand, poorer breeding ani.Jnals may cycle onl.y once per year or not at all. In the female chinchilla the external vaginal orifice is nor- mally closed by a thin, non-vascular epithelial plate except for a period of a fn days during estru.s. During the course of this study it became evident that the time of vaginal plate rupture and the time of ovulation were not precisely s.ynchronized; however, vaginal opening may be used as a relative indication that ovula tion he.s occurred within several fu\vs prior to rupture of the vaginal plate. Records kept of vaginal opening and closing indicate 4 that the vagina remains open for an average of one to five c:laya normally, but rn.ay remain open through the twentieth · ~ of the cycle. In two animals the vagina was observed to be open during pree.nancy, in one of which it remained open for three dqs. No explanation is offered for this abnormal behavior. ting is nocturnal (early evening) when the animals are most active, and a copulatory plug is formed of male accessory gland elements. This plug remains in the vaeina of the female for sev eral hours after mating and i ·s covered with a layer of cornified V'aginal epithelium when extruded (Asdell, 1). The uterine horns are filled with a 1lhiti.sh, mucilaginous fluid during estrus. This is uterine nrl.lk which presumably serves as an embryotrophic substance for the nourisbntent of the embryo before .implantation in the uterine mucosa occurs. A similar dis tension of the uterine horns with fluid at estrus is described by Pearson {6) in the mountain viscacha, Lagidium peruanum Meyen, a South American rodent closely related to the chinchilla. However, Pearson does not give measurements of the amount of fluid present, merely stating that it is quite voluminous and can easily flow fl"om one uterine horn to the other. In the chinchilla the volume of fluid was about two or three cc. for both uterine horns, al though in one case eleven cc. were found. This particul.ar animal as,. horrever,. injected with an estrogenic hormone four days pre vious to sacrifice. 5 The testes were removed from a total of thirty-seven males (ranging in age frCJn 131 days to five years) over a period of six months J weighed, measured and examined microscopically for the presence or absence of active epididymal sperm. Active sperm were found in all epididsmides and, judging from the relative constancy of the wights and measurements, the testes are uniform in size throughout the entire year. This confirms the state ments of ccmnercial breeders to the effect that males can and do successfully mate t he year around. The testes reach mature size at about nine months of age although it is said by breeders that males become sexually mature at four months. The average weieht of an adult testis is 2.5 gm. (0.9-3.6)., the average width 15 mm. (lo-18), and the average length 22 mm. (14•26). The copulatory plug which is characteristic of mating in lil8ey' rodents is thought to be conducive to fertilization since it par mits a gradual release of the spermatozoa. as it disintegrates.. The chemistry of its formation is rather involved and has not been thoroughly worked out but it is thought that the coagulation of the semen is due to an enz}'me, vesic'IU&se, produced by the pros tate gland (Asdell, 1). In the chinclUlla coagulation was ex perimentallY induced by bringing together semjnal vesicle fluid and prostatic fiuid. The bulbourethral glands were found to play no part in copulatory plug formation, at least as far as semen 6 eoagtilation was eoncernecl, since a combina.ti,on o£ oither setllinal vesiele fluid or prostatic fluid alone With btllbouretbral gland nuid failed to produce coagulation. 7 1 . In captivity female chinchillas are polyestrous, usually under going one o:r two estrous cycles during the winter months and remaining in an anestrous state for the remainder of ·t:.he year. 2. The vaginal orifice is closed by a thin epithelial plate ex cept for a short period (l-5 days) during estrus. Rupture of the vaginal plate i.s not precisely synchronized 1d.th ovula.. tion but mq be used as a relative indication that ovulation has taken place within several days prior to vaginal opening. 3• Active epididymal sperm were found in thirty-seven males of varying ages during a six month surve;y.. Also there was found to be no seasonal fluctuation in the size of the testes. 4. ·ating is nocW:rnal and a copulatory plug is formed of male accessory gland elements. Coagulation of the semen into a copulatQry plug was experimentally induced by bringing to gether seminal vesicle fluid and prostatic fluid. Fluid from the bulbourethral glands ·as found to play no part in semen coagulation in the chinchilla. 8 IV. The Ovarian Cycle For this phase of the investiga.tion twenty-six p.a.irs of seri ally seetioned ovaries from :f'et1ales in var.i.