331. INFLUENCE OF THE ON GROWTH AND DEVELOPMENT R. J. GERRITS A. R. S., U. S. D. A.

Introduction

The field of cannot be defined in a manner entirely acceptable to all biologists or animal scientists. This is understandable as there are many points of view and many voids in our knowledge in this area. It is very hard to give a precise definition for an because all cells possess some secretory capacity and therefore contribute to the internal environment of the organism. For the most part the term "" is probably applied too loosely and to a great variety of unrelated substances. can be identified as chemical agents which are synthesized by circumscribed parts of the body, generally specialized ductless glands, and are carried by the circulatory system to another part of the body where they evoke systemic adjustments by acting on rather specific target tissues or organs (Turner, 1966). In general, hormones regulate many processes such as growth, regeneration, reproduction, blood chemistry, metabolic rate, etc. Hormones act on the organs and tissues of the body by regulating the rate of specific metabolic reactions without contributing much at all to the constituent . It can be said that ad- justments to hormone levels require duration rather than speed, as opposed to the rapid coordinations of the body that are controlled by the nervous system. These biochemical adjustments are accomplished at the cellular level by virtue of their power to augwnt or restrain special enzyme sys- tems. It is important that hormones be released at the right time and in the proper amounts of the normal organism if they are to accomplish their specific mission. Hormones are ineffective unless the target cells and tissues are capable of responding to them.

While it is neaxly impossible to separate the neural and the hormonal components of regulatory processes, the complex system of endocrine glands in the vertebrates is quite clear. This system includes the pitui- tary, , parathyroid, adrends, gonads, , and the hormone-producing part of the gastrointestinal tract. The material pre- sented in this paper will be limited to a very small segrnent of the endo- crine system and the effects on growth. More specifically, I will attempt to discuss in this paper some of the important influences that are exerted by the hormone somatotrophin (STH ). Also I will present some selected material on the effect of (as an endogenous hormone) and of melengestrol acetate (a synthetic hormone) on growth.

Hormones of the adenohypophysis

Seven hormones are known to have been released from the adeno- hypophysis, namely: somatotrophin ( STH or growth hormone) ; corticotrophin (ACTH) ; thyrotrophin (TSH) ; (lactogenic hormone or luteotrophin) ; follicle-stimulating hormone (FSH) ; (LH or interstitial cell-stimulating hormone) ; and melanophore-stimulating hormone (MSH) . All 332.

of these hormones are proteins or , and three of them (FSH, LH, and TSH) contain carbohydrate in addition to amino acids.

Somatotrophin (STH) It has been well established that STH is secreted by the acidophil cells of the -pars distalis and that the principal action of growth hormone is on growth of and muscle. Growth hormones isolated from different species exhibit different physiochemical properties. The molecular weight of STH hormone ranges from 21,500 to 48,000 in man, pig, beef, and sheep. The growth hormones with lower molecular weights are more acidic thhn those with higher weights. Also, it is important to know that body growth response of STH hormone is different among the various vertebrates and that the rat responds to somatotrophin from numerous mammalian species. The most common test employed is the tibia test. After administration of the hor- mone, the increase in width of the proximal epiphyseal of the tibia of the hypophysectomized female rat or mouse is determined. STH pro- duces continuous growth and widens the in proportion to the amounts given.

Mechanisms of hormone action

There is a considerable amount of knowledge about the chemistry of hormones and their --in vivo and --in vitro effects. However, sufficient re- search, especially in vertebrates, has not been conducted to disclose fully how any hormone actually performs at the molecular level. Levine and Gold- stein (1955) and Smith --et al. (1961) have demonstrated that promotes the transfer of into the cells of certain tissues, such as muscle and fat. Three general points, each with varying modifications, have been proposed to explain the mechanisms of hormone action, namely:

1. Hormones exert a direct effect on intracellular enzyme systems.

2. Hormones act to control permeability relationships at the cell surface or elsewhere and hence indirectly control condition enzymic react ion.

3. Hormones may produce their effects directly by activating or suppressing particular genes.

In our attempt to understand the mechanisms of hormone action we must refer to work that has been conducted with insects. Microscopic ex- amination of the giant chromosomes of chironomous larvae has shown that the administration of ecdysone causes a puffing of certain genes. The inference is that the activated genes (DNA) begin to synthesize specific RNA which is transferred to the cytoplasm where it acts as template for the synthesis of a particular protein, e.g., enzymes (Karlson, 1962). The work of Liao and Williams-Ashman (1962) suggests that certain vertebrate hormones may act in a similar manner. It will be most interesting to see how far this concept can be substantiated in processes other than development in mannals. 333.

Biological action

At one time it was assumed that STH had only an effect on general body growth, particularly the skeleton, and when extracts rich in STH pro- duced other action they were attributed to contaminating factors. There is now sufficient evidence to show that STH plays an important role in the metabolism of proteins, fats, and carbohydrates and also serves as a synergist to enhance the effects of other hormones.

The effect of STH on protein metabolism

Amino acids not utilized by animals are normally converted to urea and eliminated through the . It has been ably demonstrated that STH encourages the animal to retain amino acids which are the essential building blocks for protein and that the body weight increase normally observed after treatment with STH is an actual increase in tissue protein.

Knobil (1961) states that one important aspect of STH action is to promote the transfer of extracellular amino acids across cell membranes, particularly into muscle cells.

Milman and Russell (1950), Li --et al. (1949), and Luck --et al. (1954) have demonstrated that the administration of growth hormones lowers blood nitrogen. Swislocki and Szego (1965) also demonstrated this effect in hypophysectomized ad lib fed rats. In the later study blood-amino nitrogen (BAN) levels in the growth hormone treated rats were significantly lower than the controls at one and five hours after treatment with STH.

In a recent study Beach and Kostyo (1968) showed that when rats were injected daily intraperitoneally with bovine growth hormone for seven days the amount of DNA in the muscles rectus femoris, gastrocnemius, pectoralis -'major and diaphragm was increased significantly. When STH was administered for one day it had no effect on the DNA of these muscles. However, following seven days of treatnmt, with the hormone, the amount of DNA in each of the muscles was markedly elevated. Since there was a con- comitant increase in muscle weight, the concentration of DNA in terms of micrograms per mg. of wet muscle was altered significantly. These data show that growth hormone can increase the amount of DNA in skeletal muscles of hypophysectomized rats. Thus, it seems reasonable to assume that the increase in muscle DNA which occurs during the normal course of growth in rats is dependent in some measure on pituitary growth hormone.

Effect of STH on liDids metabolism

The experiments of Welt and Wilhelmi (1950) suggested that growth hormone administration leads to a reduction of lipid synthesis. Their initial studies have subsequently been supported by several workers.

Hypophysectomy retards the mobilization of depot fat and tends to ameliorate ketosis in the diabetic subject. STH encourages the movement of unesterified fatty acids from fat reserves, consequently decreasing body fat and increasing the lipid content of the blood plasma and live. In support of this, Swislocki and Szego (1965)showed that elevated levels of plasma nonesterified fatty acids occurred after the administration of growth hor- mones to hypophysectomized rats. 334.

Effect of STH on carbohydrate metabolism The following general statements may be male regarding the action of STH on carbohydrate metabolism when administered to mammals (Turner, 1966) :

1. The hormone tends to produce , thils aggravating .

2. It inhibits the action of insulin and insulin effect.

3. It increases muscle glycogen when given to hypophysec- tomized subjects.

4. It produces a permanent diabetes mellitis in certain species when given over prolonged periods.

The latter effect probably results from the eventual destruction of the 8-cells of the pancreatic islets which secrete insulin. It has been shown that rats receiving excessive carbohydrates by tube feeding develop tem- porary diabetes when given STH. Studies on STH in animals

Baird --et d. (1952) assayed the hypophysis of two strains of pigs selected for eight generations on the basis of rapid and slow rate of gain. The two strains reached ultimate size at significantly different ages. When the growth hormone content of the pituitary glands of the two strains was determined, it was found that at dl ages at which cornpaxisons were made the glands of the faster growing strain contained significantly more somatotro- phin per unit of gland tissue than did the glands of the slower growing strain. This study showed that the amount of somatotrophin per unit of pituitary tissue was the same in the youngest and the oldest animal and that it did not vwy significantly throughout the growth period.

Armstrong and Hansel (1956) also demonstrated that the role of STH for control of growth was true in Holstein heifers. They showed that the concentration of somatotrophin per unit of pituitary tissue was the same in young growing calves as it is in animals which have reached the growth plateau. These studies, along with the study of Simpson --et al. (1950), show that rapid growth occurs as long as the ratio of the circulating somatotro- phin per unit of body tissue remains sufficiently high to stimulate protein synthesis and to cause bone and muscle growth. The three latter studies cited all support the "dilution theory," that is, when the size of the animal increases, the amount of hormone available per unit of weight is "diluted." Thus, older, heavier animals retain their ability to repair tissue but lose their capacity to grow at a rapid rate.

Related studies on Duroc swine selected for high and low back.fat

Hetzer and Peters (1965) and Hetzer and Harvey (1967) reported on the effect of selection on Duroc swine for both high and low backfat thick- ness. A non-selected control line derived from the same source as the selected line was maintained. After 10 generations of selection, the high- 335. and low-fat Duroc lines differed in backfat by 2.6 cm. or 68% of the initial mean. Selection basis on backfat depth was effective in both the upward and downward direction. Pigs from the Duroc low backfat line produced higher yields of lean meat and less fat than the line selected for maximum depth of backfat.

Davey and Kincaid (1964) conducted in ividud feeding trials with pigs from high- and low-fat Duroc lines. Carcasses were separated into lean, fat, bone, and skin at ages varying from 90 to 400 days. The abso- lute weight of fat and lean up to 220 days of age showed linear trends with age. Differences in carcass composition for pigs fed normal diets as estimated from regressions on age were: high Duroc, 23.2, 0; low Duroc, 17.3, 4.1; kg. of fat and lean, respectively. The data show that the high- fat line began to lay down more fat than lean at 18 weeks of age. However, the low-fat line did not begin to lay down more fat than lean until 10 weeks later.

Gerrits --et al. (1964) found that the weight of animals from the lines of Duroc swine selected for high and low backfat differed significantly from those of the control. This study also revealed that the , , and length of small intestines from the selected lines differed significantly from the control. Thyroid weights between the lines were not significant. Johnson and Gerrits (1965) reported that cholesterol levels in the Duroc selected for high backfat were significantly correlated with depth of backfat.

Growth hormone study in Duroc swine selected for hi& and low backfat

In considering the findings in the previously cited experiments and because of the specific effects known to be mediated by the action of growth hormone and the responses manifested in other species, a study was designed to determine if selection for high and low backfat had altered the concentration of growth hormone per -se. The growth hormone content of anterior pituitaries from 30 Duroc swine balanced by line and sex and selected on the basis of backfat depth was assayed using hypophysectomized female rats. The animals were dl slaughtered at a constant weight, and there was no significant difference in the average age of the animals at the time of slaughter. There was a significant difference between all lines with respect to depth of backfat and percent of lean cuts. One ham fron each animal was separated into lean, fat, and bone. The values from the three parts of the ham between lines were significantly different except for the percent of lean between control and low-line Duroc. The anterior pituitaries from five animals of each sex in each line were pooled for the assay. The assay procedure used was that of Greenspan --et al. (1950). The anterior pituitaries from the control line were significantly heavier than those from both of the selected lines. Based on two assay criteria, each line contained the same amount of growth hormone per unit of tissue. The amount of growth hormone contained per unit of tissue tested in each animal was not different as measured by the increase in the growth of hypophysectomized female rats or in size of epiphyseal cartilage width. When the anterior pituitaries were adjusted For weight, .the total STH potency ranged from highest to lowest in the control, low, and high lines, respectively. Growth hormone concentration ner unit of tissue 336. between the three lines was not significantly different. This suggests that genetic selection for high and low backfat has probably altered the ability of the tissues to respond to STH.

Effect ~f endogenous and exogenous hormones on growth It has been ably demonstrated that the implantation or addition of diethylstilbesterol (a synthetic ) to the rations of cattle, mainly steers and heifers, is a common and beneficial practice. Since many articles have been published on DES and it has been reviewed by previous speakers at the Reciprocal Meat Conference, I will not discuss any speci€ic effects of DES at this time.

Recent studies have shown that the feeding of melengestrol acetate (MGA), an active progestin originally tested to synchronize the estro-ds cycle, improves rate of gain and promotes growth in heifers. Bloss --et al. (1966) reported increases in rate of gain and feed efficiency when KA-fed heifers were compared to controls. In a recent study reported by O'Brien --et al. (1968), crossbred heifers fed .3 mg. of EAin the feed per head per day for 140 days gained significantly faster (21%) and made 11% more efficient use of their feed than heifers receiving the same feed without MGA. In the latter study, carcass grades, marbling score, and dressing percentage of %A-fed heifers and controls conformed substantially with the results of Bloss et aL. (1966). In the study of O'Brien -cet al. (1968) dressing was unaffected-- by EAin the feed; however, no specific measurements taken with regaxd to the amount of fat or lean in the carcass were reported.

No changes in general body conformation or vaginal prolapses, as reported to occur in estrogen-treated heifers, were observed among any of the EA-treated heifers (Bloss --et al., 1966). Zimbelman and Smith (1966) showed that EAdos-.s of approximately .2 mg/heifer/day will prevent estrus in some heifers, and doses of .5 mg/day will prevent estrus in almost all heifers. They also reported ovulation occurred regularly in untreated animals but rarely in MGA-treated animals. Heifers which were found to be sexually mature and then spayed grew more slowly and had poorer feed ef - ficiency than mature intact heifers. The feeding of EAto spayed heifers did not improve growth rate or feed efficiency significantly. These re- sults, along with results on follicular size, substantiate the hypothesis proposed by Bloss L-et al. (1966) that EAcaused increased weight gain by allowing continual endogenous estrogen secretion. The failure of steers to respond to MGA seems to be consistent with this hypothesis.

Effect of testosterone on growth It is well known that testosterone promotes protein and decreases the urinary loss of nitrogen without increasing the non-protein nitrogen of the blood and that it produces at least a temporary increase in body weight. This suggests that the hormone causes a true storage of nitrogen in the form of tissue protein. It should be noted that increase the body weight of young hypophysectomized rats; but most of this gain is accounted for by the increased mass of the genital. coml;lex, ap- parently consequent upon protein retention (Turner, 1966). The changes in body weight produced by testosterone vary with the species and also depend on the nutritional status of the animal.. Karlson (1963) and Liao and 337.

Williams-Ashman (1962) have demonstrated that the microsomes from the prostate gland of the testosterone-treated rat have a greater ability to incorporate saline C-14 into protein than microsomes from castrated sub- jects. Since nucleic acids are intimately associated with the synthesis of proteins, the growth processes initiated by androgens and various target tissues could be mediated at the level of the gene.

Bratzler --et al. (1954) reported that barrows castrated at 180 lbs. and boars had a higher percentage of lean in the loin, a lower dressing per- centage, and less backfat than pigs castrated at 70 days and 100 lbs. Zobrisky --et al. (1959) and Teague --et al. (1962) also reported a significantly higher yield of lean meat from the carcasses of boars. Charette (1961) also showed that the carcasses of boars and gilts were longer and had less fat covering over the shoulder and back area of loin and a higher iodine number than those castrated late. In this study, acceptability tests showed that the age of castration did not affect flavor, odor, or tenderness of meat.

The study of Frescott and Lamming (1964) showed that castration consistently depressed growth rate in cattle and sheep. They further point out in their study that the carcasses of castrates contain much more fat and less lean and bone than those of the intact animals. Boars also yielded a much leaner carcass containing 19 lbs. less fat and 7 lbs. more lean than the carcasses of hogs at 260 lbs. of liveweight.

Collectively, these studies point out that the use of the intact male holds considerable potential with present demands for more efficient production and the production of more lean meat.

Concludim remarks

On the foregoing pages, I have considered only a handful of the issues on problems germane to the effect of the endocrine system on growth and development. Without doubt, many other considerations could or should have been included. Those familiar with the vast amount of literature per- taining to the field of endocrinology will understand the difficulties in trying to present a comprehensive discussion of the topic in a limited time. On the other hand, it is hoped that the central theme has been presented. Surprisingly little work has been conducted on the specific effects and benefits that might be realized in meat animals through studies in endo- crinology. Also, we as animal scientists have been particularly slow in applying basic discoveries in biology to all aspects of meat animal prcduc- tion. Resolution of the problems and realization of the benefits will re- quire maximum effort as well as effective utilization of talents from many scientific disciplines working together. Thus, in meeting our responsi- bilities to society as animal scientists, we are faced with a demanding but exciting challenge for the future. 338.

REFERENCES

1. Armstrong, D. T. and W. Hansel. 1956. "Effect of age and plane of nutrition on growth hormone and thyrotropic hormone content of pituitary glands of Holstein heifers." J. An. Sei. 15:640.

2. Baird, D. M., A. V. Nalbandov, and H. W. Norton. 1952. "Some physiological causes of genetically different rates of growth in swine." J. An. Sei. 11:292.

3. Beach, R. K. and J. L. Kostyo. 1968. "Effect of growth hormone on the DNA content of muscles of young hypophysectomized rats .I' Endocrin. 82: 882.

4. Bloss, R. E., J. I. Northam, L. W. Smith, and R. G. Zimbelman. 1966. "Effects of oral melengestrol acetate on the performance of feedlot cattle." J. An. Sei. 25:1048.

5. Bratzler, L. J., R. P. Soule, Jr., E. P. Reineke, and P. Paul. 1954. "The effect of testosterone and castration on the growth and carcass characteristics of swine. J. An. Sci. 13: 171.

6. Charette, L. A. 1961. "The effects of sex and age of male at castra- tion on growth and carcass quality of Yorkshire swine." Canad. J. An. Sci. 41:30. 7. Davey, R. J. and C. M. Kincaid. 1964. "Response of swine selected for backfat thickness to different energy intakes." J. An. Sei. 23: 1197. ( Abst .)

8. Gerrits, R. J., L. A. Johnson, H. 0. Hetzer, and C. M. Kincaid. 1964. "Some anatomical and physiological measurements on swine selected for high and low backfat." J. An. Sci. 23:905. (Abst.)

9. Greenspan, F. S., Choh Hao Li, M. E. Simpson, and H. M. Evans. 1949. "Bioassay of hypophyseal growth hormone: the tibia test. Endocrin, 45: 455.

10. Hetzer, H. 0. and W. H. Peters. 1965. "Selection for high and low fatness in Duroc and Yorkshire swine." J. An. Sei. 24:849. (abst.)

11. Hetzer, H. 0. and W. R. Harvey. 1967. "Selection for high and low fatness in swine." J. An. Sei. 26:1244.

12. Johnson, L. A. and R. J. Gerrits. 1965. "Biochemical and hematological measurements on swine selected for high and low backfat. J. An. Sci. 24:1217. (Abst.) 339.

13. Karlson, P. 1962. "On the chemistry and mode of action of insect hormones." Gen. & Comp. Endocrin., Suppl. 1:l. 14. Karlson, P. 1963. "New concepts on the mode of action of hormones." Perspect . Biol. & Med. 6: 203. 15. Knobil, E. 1961. "The pituitary growth hormone: some physiological considerations." In M. X. Zarrow (ed.), Growth in Living Systems. Basic Books, Inc., New York. 16. Levine, R. and M. S. Goldstein. 1955. "On the mechanism of action of insulin." Recent Progr. Horm. Res. 11:343.

17. Li, C. H., I. Geschwind, and H. M. Evans. 1949. J. Biol. Chem. 177:91. (Cited in Endocrin. 76: 671, 1965).

18. Liao, S. and H. G. Williams-Ashman. 1962. "An effect of testosterone on amino acid incorporation by prostatic ribonucleoprotein particles." Roc. Nat. Acad. Sci., U.S.A., 48: 1956.

19. Luck, J. M., A. C. Griffin, G. Boer, and M. Wilson. 1954. "On the endocrine regulation of blood amino acid content." J. Biol. Chem. 206: 767.

20. Milman, A. E. and J. A. Russell. 1950. "Some effects of purified pituitary growth hormone on carbohydrate metabolism in the rat .'I Endocrin. 47: 114.

21. O'Brien, C. A., R. E. Bloss, and E. F. Nicks. 1968. "Effect of melengestrol acetate on the growth and reproductive physiology of fattening heifers." J. An. Sci. 27:664.

22. Prescott, J. H. D. and G. E. Lamming. 1964. "The effects of castra- tion on meat production in cattle, sheep and pigs." 9. Agric. Sci. 63:341. 23. Simpson, M. E., C. W. Asling, and H. M. Evans. 1950. "Some endocrine influences on skeletal. growth and differentiation." Yale J. Biol. Med. 23:l.

24. Smith, G. H., P. J. Randle, and F. C. Battaglia. 1961. "The mechanism of action of insulin in muscle." Memoirs SOC. Endocrin. 11:124.

25. Swislocki, N. I. and C. M. Szego. 1965. "Acute reduction of plasma nonesterified by growth hormone in hypophysectomized and houssay rats. I' Endocrin. 76: 665.

26. Teague, H. S., V. R. Cahill, R. F. Plimpton, A. P. Grifo, and L. E. Kunkle. 1962. Ohio Agric. Sci. Sta. Anim. Sci. Mimeo. 127.

27. Turner, C. D. 1966. General. Endocrinology. W. B. Saunders Co., Philadelphia and London. 340.

28. Welt, I. D. and A. E. Wilhelmi. 1950. "The effect of adrenalectomy and of the adrenocorticotropic (ACTH) and growth hormones on the synthesis of fatty acids." Yale J. Biol. Med. 23:99.

29. Zimbelman, R. G. and L. W. Smith. 1966. "Control of ovulation in cattle with melengestrol acetate. 11. Effects on follicular size and activity." J. Reprod. Fertil. 11:193. 30. Zobrisky,S.E.,D.E. Brady, J. F. Lasley, and L. A. Weaver. 1959. "Significant relationships in pork carcass evaluation. I. Lean cuts as criteria for live hog value." J. An. Sci. 18:420.

D. A. CRAMER: Thank you very much, Dr. Gerrits, and I will thank all of you gentlemen for a series of very fine papers. I think you wodd all make top-notch men. Fortunately, the group upstairs is also running a few minutes behind, so we do have time for a few questions. I think we can run until about two o'clock for questions. I won't take time out from our discussion to introduce Dave Topel, because most of you know him, anyway. 1'11 just let him get started with the questions.

D. G. TOPEL: Thank you, Dave. I'm sure you will all agree that a2.1 of the people on this program are very interested in composition, and maybe not directly with meats, but certainly in the end product to 8 certain degree. At this time I would like. to ask for questions regarding the papers. Are there any questions?

PAUL LEWIS, Arkansas: I would like to direct this to the second speaker--how are you analyzing for sodium and potassium?

DR. EWAN: Our meat analyzing is by photometric methods. LEWIS: Do you worry about any interferences?

EWAN: We haven't investigated this point as yet. I believe there are differences in response depending on the levels of sodium and potassium that aze present, and this in particular. In other words, when you go to look between tissues, with a system that is geared to work with plasma or serum, you would have to alter your system to be sure that you are getting accurate measurements, because of the relative enhancements.

DR. HENDRICKSON, Oklahoma: I would like to address a question to Gene Allen. Fat is deposited in connective tissue and I am wondering as the fat builds up, is there an increase in the connective tissue? 341.

DR. ALBN: In thinking back, in dressed beef animals, I don't think we have shown a large difference in fatty tissue in some of the mus- cles we have looked at. These changes have been more in the composition, but as far as I am aware of, I would say no.

HENDRICKSON: You don't feel that there is a generation of con- nective tissue as life proceeds?

ALLEN: Not much.

DR. TOPEL: If there are no further questions, I will turn it back to Dr. Cramer.

DR. CRMR: Thank you, Dr. Topel. This has been an excellent session. We are running a bit behind schedule and are due back in the Main Auditorium for a paper which you all will want to hear on Changes in Standards for Pork Carcasses and Slaughter Hogs by John Pierce and Peter Williams of the U.S.D.A. So let's adjourn this session and proceed to the Main Auditorium.

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STATISTICAL COMMITTEE WNAUDITORIUM GEORGIA CENTER

H. W. OCKERMAN: I'll call the meeting to order and since we're a bit behind schedule I'll not name the other Embers of the Statistical Committee. They are listed in the back of the program. We are fortunate to have two interesting papers this afternoon and two highly qualified speakers: George Brissey of Swift on "Sampling" and C. F. Parker of Ohio on "Biological Variation". George will be OUT first speaker.