Superovulation of beef heifers with Pergonal (HMG): A dose response trial.

A study was designed to establish a dose-response curve for Pergonal (Human Menopausal Gonadotrophin) and to compare its efficacy in inducing superovulation with commercial FSH-P. A recognized treatment schedule for HMG of two ampoules at 0, 12, 24 and 36 hours and one ampoule at 48, 60, 72, 84, 96 and 108 hours was considered to be our 100% effective dose level. Fifty mature cycling cross-bred beef heifers were superovulated on day 10 +/- 1 of their cycle. Treatment groups were HMG I (200% dose), HMG II (100% dose), HMG III )50% dose), HMG IV (25% dose) and FSH-P (total dose 32 mg). All groups received 500 ug of cloprostenol 72 hours after initiation of treatments. The heifers were observed for onset of estrus and inseminated at 12, 24 and 36 hours. All heifers were slaughtered on day 7 post-estrus and their reproductive tracts removed for processing. All heifers were bled once daily for progesterone estimation and four times daily for two days beginning 24 hours after cloprostenol injection, for luteinizing hormone and estradiol-17beta estimations. A dose response to HMG was demonstrated for number of corpora lutea and all classes of ova/embryos. HMG II (100% dose) closely approximated the optimum dose for superovulation. There was no significant difference between the HMG II group and the FSH-P group for mean number of transferable embryos. The 200% HMG dose did not increase the numbers of ovulations or ova recovered but did decrease the numbers of fertilized and transferable ova.