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The Action of Stilbestrol on the Growth Response in Ruminants

University of California^,2

Abstract

The effects of stilbestrol implants on rate of gain, economy of feed utilization, endocrine weights, growth hormone and ACTH content of the pituitary, endocrine gland histology, nitrogen retention and differential blood counts were studied. Approximately 340 treated animals and a corresponding number of controls were used in these experiments. In different trials the dietary regime was varied such that in some the animals were maintained on irrigated pasture with and without supplements; and in others the animals received hay and concentrates. Treated steers in the feed lot or on pasture with supplemental concentrates made greater gains than controls, or than treated steers on pasture alone. The growth response of treated heifers in the feed lot was in no case as marked as treated steers. On pasture, treated heifers showed no increase in gain over controls. Feed consumption and economy of feed utilization was increased in all treated animals. The growth response in wether and ewe lambs on pasture was greater with a dose of 12 mg. than with 24 mg. of stilbestrol. Nitrogen retention was almost doubled in steers following stilbestrol administration. The weights of the pituitary and adrenal glands were significantly larger in the treated animals. Thyroids of treated steers were larger but not significantly. In treated heifers the thyroid weight was significantly depressed. Ovarian weight was not altered after treatment, but corpora lutea formation was depressed. Growth hormone and ACTH content of treated steer pituitaries was not significantly different from controls. The hypophysis of treated heifers contained twice as much growth hormone as the untreated. Wether and ewe lambs showed a marked eosinopenic response following stilbestrol treatment. The percent of treated animals in the higher carcass grades was less than the percent of untreated. The predominant signs of treatment were masculinization and mammary gland development. Several cases of vaginal prolapse occurred in heifers as a result of stilbestrol implantation. The role of the pituitary in mediating the growth response to stilbestrol is discussed.

¹ The authors wish to thank Reuben Albaugh and H. T. Strong, Extension Animal Husbandmen, University of California, for their cooperation and assistance in conducting these experiments; Norman Freed and Norman Fohrman, graduate assistants, for their help in the analytical work; the farm advisors in whose counties the trials were conducted: K. G. Baghott, D. M. Smith, Carl Rimbey, Albert Kolb, Walter Johnson, N. B. Coryell, R. A. Brendler, R. C. Geiberger, Roy Parker, Robert Anderson; the farmers on whose ranches the animals were tested: Maston Ramsey, Al Clark, Roy Carmichael, W. G. Waggoner, Al Zaniboni, Al Kuhn, Ben Overland.

² Department of Animal Husbandry, Davis.

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