ENDOCRINE CHANGES IN BEEF HEIFERS SUPEROVULATED WITH FOLLICLE-STIMULATING-HORMONE (FSH-P) OR HUMAN MENOPAUSAL GONADOTROPIN

The effects of superovulatory treatment (FSH-P vs human menopausal gonadotropin, HMG) and of route of administration (i.m. vs. i.v.) of prostaglandin F2-alpha (PGF2-alpha) on hormonal profiles were determined in 32 Angus x Hereford heifers. Heifers were superstimulated with either FSH-P (total of 26 mg) or HMG (total of 1,050 IU) beginning on d 9 to 12 of an estrous cycle and PGF2-alpha (40 mg) was administered at 60 and 72 h after the beginning of superovulatory treatments. Heifers were artifically inseminated three times at 12-h intervals beginning 48 h after PGF2-alpha treatment. Blood serum samples were collected immediately before treatments began, at 12-h intervals during the first 60 h, each 4 h during the next 96 h, and each 12 h until day of embryo collection. Concentrations of LH and FSH were not affected by hormone treatments, route of PGF2-alpha injection, or interactions between them. Estradiol-17-beta (E2-17-beta) levels were higher (P < .05) in HMG- than in FSH-P-treated heifers 60 h after gonadotropin treatment. Peak concentration of E2-17-beta occurred earlier (P < .05) in HMG- than in FSH-P-treated heifers and earlier in heifers injected with PGF2-alpha i.m. than in those injected i.v. Progesterone concentrations were not influenced by treatment or route of PGF2-alpha administration, but were affected (P < .01) by the interactions between treatment and route of PGF2-alpha administration. Progesterone declined to basal levels earlier in the FSH-P- than in the HMG-treated heifers. Progesterone began to increase 24 h after the LH peak in the FSH-P group but remained at basal levels at 24 h for the HMG-treated heifers. The progesterone:E2-17-beta ratio was also higher in FSH-P- than in HMG-treated heifers 24 h after LH peak. Premature regression of corpora lutea was observed after estrus in 19% of the heifers, as indicated by decreased progesterone concentrations at the time of embryo collection. Based on the endocrine changes presented here we suggest that more research is needed to determine clearly whether HMG can be used as successfully as FSH-P to obtain viable bovine embryos.