Norgestomet and gonadotropin-releasing hormone enhance corpus luteum function and fertility of postpartum suckled beef cows

Abstract

In Exp. 1,101 suckled beef cows were administered two injections of prostaglandin F2 alpha (PGF2 alpha) 11 d apart. Cows in Group 1 received no additional treatment. Cows in Groups 2 and 3 received 250 micrograms of GnRH plus 47-h calf removal. Cows in Group 3 also received a norgestomet ear implant that was inserted 4 d after the first PGF2 alpha injection and left in situ for 8 d. The second PGF2 alpha injection was administered approximately 28 h before the time of norgestomet implant removal. The GnRH was administered approximately 30 h after the time of norgestomet implant removal (or 58 h after the second PGF2 alpha injection). Calf removal was the period from the time of implant removal to AI. All cows were artificially inseminated once 75 h after the second PGF2 alpha injection (47 h after implant removal). Reproductive status before the time of GnRH treatment (presynchronization) was determined by multiple sampling (2, 13, and 23 d before GnRH treatment) for blood progesterone concentrations (62% anestrous and 38% cyclic). The GnRH treatment increased (P < .01) the ovulation response and norgestomet reduced (P < .01) the incidence of short luteal phases in the presynchronization anestrous cows. Norgestomet treatment increased (P < .05) the timed breeding pregnancy rates for both presynchronization anestrous and cyclic cows. In Exp. 2, 174 suckled beef cows were administered Syncro-Mate B (which includes norgestomet). Cows in Group 1 received no additional treatment, whereas cows in Group 2 received 250 micrograms of GnRH (30 h after norgestomet implant removal).(ABSTRACT TRUNCATED AT 250 WORDS)