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Effects of Various Hormone Treatments on Induction of Lactation in the Ewe¹

University of Florida^,2, Gainesville 32611 , Institut National de la Recherche Agronomique^,3, 78350 Jouy-en-Josas, France and , and Department de Physiologie Animale^,4, 37380 Nouzilly, France

Abstract

In Exp. I and II, 52 of 68 ewes were induced into lactation with twice-daily injections of estradiol-17β (E₂-β) and progesterone (P₄; .5 and 1.25 mg/kg body weight/day) for 7 days. Additional treatments were twice-daily injections (days 18 to 20) of hydrocortisone, growth hormone, thyroxine and thyrotropin releasing hormone alone or in various combinations. In Exp. III, 12 ewes were induced into lactation. In this experiment, all ewes were injected with E₂ -β and hydrocortisone, as previously, but four ewes (III-2) had P₄ injections extended to day 20, and four ewes (III-3) were not injected with P₄. Across experiments, lowest milk yields during lactation and the lowest percentage of ewes induced into lactation (58%) occurred when only E₂-β and P₄ were injected. Inclusion of hydrocortisone injections (50 mg/ day) induced the highest percentage of ewes into lactation (86%, 38 of 44), the highest peak daily yields of milk and the highest total yields during lactation. Including injections of growth hormone, thyroxine or thyrotropin releasing hormone alone or in combinations did not produce better results than injections of E₂-β and P₄ alone. Injections of E₂-β and hydrocortisone without concurrent injections of P₄ were less effective. Intramuscular injections of P₄ (10 mg/day) from days 8 to 20 did not inhibit lactogenesis or subsequent lactation. Across all experiments, 76% of multiparous (52/68) and 50% of nulliparous (6/12) ewes produced >100 ml milk/day during their lactation (34 to 95 days). However, yields of milk for ewes that lactated were only 25 to 50% of those from postpartum ewes. The importance of including injections of hydrocortisone in the induction procedure was established, but determination of optimum time to inject and potential importance of other hormones requires additional research.

¹ Florida Agr. Exp. Sta. Journal Series No. 1770.

² Dairy Sci. Dept.

³ Laboratoire de Physiologie de la Lactation.

⁴ Station de Physiologie de la Reproduction.

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