Synchronization of Estrus in Beef Cows and Beef and Dairy Heifers with Intravaginal Progesterone Inserts and Prostaglandin F2α with or Without Gonadotropin-Releasing Hormone

Abstract

Intravaginal progesterone (CIDR) inserts consist of a layer of silicone containing 10% progesterone (P4) by weight (1.38 g) molded over a T-shaped nylon spine. In the absence of a corpus luteum, the CIDR insert releases sufficient P4 to maintain concentration >2 ng/ mL in blood. A synchronization of estrus program utilizing a 7-d administration of CIDR inserts with the administration of 25mg of prostaglandin F2α(PGF2α) on d 6 (CIDR + PGF2α) was compared with a single injection of PGF2αor no treatment (control) in beef cows (six locations), beef heifers (five locations), and dairy heifers (four locations). These studies indicated that estrus was synchronized more precisely over a 3- to 4-d interval with the CIDR + PGF2αtreatment regimen than with a single injection of PGF2α. Furthermore, administration of the CIDR insert induced estrous cyclicity in some of the anestrous cows and prepubertal heifers. Cows and heifers inseminated over the 3-d period following removal of inserts had conception rates (CR) comparable with the CR of cows and heifers administered PGF2αalone and comparable with those of untreated controls. Pregnancy rates (PR) were significantly greater in the CIDR + PGF2αtreatment group than in the PGF2αonly group after the first 3 d or after 7 d of AI in beef cows and beef heifers, but not in dairy heifers. Estrus after CIDR insert removal was distributed over a 3- to 4-d interval; therefore, this treatment regimen may not be acceptable for use with fixed-time artificial insemination (TAI). The COSynch synchronization of ovulation program [100 μg of gonadotrophinreleasing hormone (GnRH), PGF2α7 d later, and a second injection of 100 μg of GnRH and AI at 48h after PGF2α] has been developed to allow TAI of beef cows. Two studies compared PR to TAI in suckled beef cows following the COSynch program with PR of beef cows on the CO-Synch program with administration of a CIDR insert for the 7 d between the first injection of GnRH and the injection of PGF2α(CO-Synch + CIDR). Mean PR were greater in beef cows receiving the CO-Synch + CIDR treatment than in cows receiving the CO-Synch treatment in one but not both studies. Among cows that were anestrous prior to treatment administration, a greater PR was observed in cows in the CO-Synch + CIDR group than in cows in the COSynch group.