Efficacy of Synthetic Gonadotropin Releasing Hormone Analogs for Control of Ovulation During Estrus Synchronization Protocols

Two experiments were conducted to determine efficacy of GnRH analogs, Cystorelin (CYS, gonadorelin diacetate tytrahydrate) and Factrel (FAC, gonadorelin hydrochloride), for use in beef timed AI synchronization. In Experiment one 342 beef cows from 7 herds were assigned CYS or FAC treatment as part of the Ovsynch protocol (GnRH d 0 and 9, Lutalyse d 7). Cattle treated with FAC had greater tendency (P=.09) to be pregnant at d 45. One individual herd demonstrated FAC-treated cows had more pregnancies at day 45. In Experiment two, 18 beef cows received either CYS or FAC as part of the Ovsynch protocol, intensive blood samples, from time -30 to 525 min post GnRH, were collected at each GnRH injection. Ultrasounds were conducted daily over the course of the protocol. A treatment by phase interaction (P=.03) was found for the time to maximum LH concentration, where CYS-treated follicular cows had a shorter interval than did FAC treated follicular or luteal cows. The duration of detectable LH response showed a treatment by phase interaction (P = .02) where follicular and luteal CYS-treated cows had shorter interval than follicular or luteal FAC-treated cows. The variables maximum LH concentration, and area under LH curve did not differ. Cows treated with CYS had more (P=.02) non-dominant follicles. In Experiment three, 16 ewes randomly received either CYS, FAT or Fertagyl (FER; gonadorelin diacetaate tytrahydrate), and FAT's induced LH maximum concentration occurred sooner (P=.02) than CYS. We conclude that either product may be used in beef cows without compromising fertility.