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Hormone Induced Lactation in the Bovine. II. Response of Nulligravida Heifers to Modified Estrogen-Progesterone Treatment¹

Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster 44691

ABSTRACT

Subcutaneous injection of 17 ß-estradiol (60 mg/600 kg body weight per day) and progesterone (150 mg/600 kg body weight per day) for 7 days initiated lactation in nulligravida heifers. Lactation was initiated with 17 ß-estradiol-proges-terone ratios of 1:2.5, 1:2, and 1:1 when constant 17 ß-estradiol (60 mg/600 kg body weight per day) was maintained. Varying the dose of 17 ß-estradiol (20, 40, or 60 mg/600 kg body weight per day) while maintaining a constant 17 ß-estradiol:progesterone ratio of 1:2.5 also initiated lactation at all rates of 17 ß-estradiol.

Number of days of injection (7 or 10) and, thus, the total amount of hormone injected had little effect on the abilitv of the treatment to initiate lactation. Lactation was not successfully induced following intramuscular injection of the hormones or when a suspension of estrone rather than dissolved 17 ß-estradiol was injected subcutaneously

Regardless of treatment the mammary gland did not change during hormone injection. Major glandular growth occurred between the last (7th) day of hormone injection and 14 days after the last hormone injection. Mammary glands of heifers that lactated continued to grow until approximately peak lactation.

Neither amount nor ratio of 17 ß-estradiol and progesterone is critical in initiation of lactation. Failure to initiate lactation following intramuscular injection or injection of a suspension of estrone may reflect an altered absorption pattern from the injection site and suggests that the dynamics of hormone absorption are important in success or failure of the treatment to initiate lactation

¹ Approved as Journal Article no. 100-73, Ohio Agricultural Research and Development Center, Wooster 44691.

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