Dose-Response Relationships in Synchronized Beef Heifers treated with Follicle Stimulating Hormone

Abstract

Seventy-seven beef heifers ranging in weight from 308 to 563 kg. were used to determine FSH treatments that would give a controlled increase in potentially fertile ova following synchronization of estrus. Estrous cycles were synchronized by feeding 180 mg. medroxyprogesterone acetate (MAP) for either 9 or 11 days (first day of MAP feeding equal day 1) and an injection of 5 mg. estradiol valerate given on day 2. FSH treatment levels were total dosages of 3.12, 6.25, 12.50, 25.00, 50.00 or 75.00 mg. All heifers were laparotomized and bilaterally ovariectomized 60 to 72 hr. following breeding. Oviducts were removed and ova recovered for microscopic examination. Feeding MAP for 11 days with estradiol valerate given on day 2 followed by FSH injected twice daily on days 8, 9, 10, 11 and 12 produced the most predictable ovarian response. Total FSH dosages of 12.50 mg. or higher gave excessive ovarian stimulation. Average number of ovulations and fertilization rates were 1.1 and 92.9%, 2.1 and 93.8%, 8.0 and 79.4% and 14.6 and 83.7% for total dosages of 3.12, 6.25, 12.50 and 25.00 mg. FSH, respectively. Statistical analyses indicated a linear dose-response relationship between dosage increase and the ovarian characteristics studied. No evidence was noted indicating a relationship between size of heifer and response to FSH treatment. Doseresponse effects indicated synchronization of estrus and total FSH dosages of 3.12, 12.50 and 25.00 mg. depressed numbers of sperm per ovum. However, a total dose of 6.25 mg. FSH did not result in this reduction, and this dosage overcame the depression in numbers of sperm per ovum caused by synchronization. Copyright © 1969. American Society of Animal Science . Copyright 1969 by American Society of Animal Science