Steroid priming shortens prostaglandin-based estrus synchronization program from 14 to 7 days in cattle

Single injection of estrogen and progesterone before prostaglandin (steroid priming) was used to shorten the prostaglandin-based estrus synchronizatio n program. Sixty-five cyclic Sistani cattle, with parity ranging from 1 to 4 and postpartum period of >80 days were selected at unknown stages of the estrous cycle and assigned to 2 groups according to their age, weight and p arity. Females in the control group (n=33; 58.4 +/- 4.3 months; 277 +/- 8 k g LW) received two consecutive injections of prostaglandin F(2)alpha analog ue (500 mug; Cloprostenol, PG) 14 days apart (Day 0 = First PG injection). On Day 7, treated females (n=32; 60 +/- 4.8 months; 292 +/- 9 kg LW) were g iven an intramuscular injection of 100 mg progesterone and 2 mg estradiol b enzoate followed by prostaglandin 7 days later, concurrent with the second PG injection of the control group. Estrus detection was carried out every 6 hours for 7 days, commencing from 24 hours after the last PG injection. Fe males that allowed to be mounted were identified (standing estrus) and inse minated with frozen semen 12 hours later. Pregnancy was diagnosed on Day 50 after AI through palpation per rectum, Data were analyzed using Chi-square d and t-test. The tightness of estrus synchrony (%), the interval from the end of treatment to estrus (h) and conception rates (%) were similar (P > 0 .05) between control (69.6%, 77.7 +/- 5.96 h and 56.5%) and treatment (68.2 %, 82.6 +/- 7.64 h and 54.5%) groups. In conclusion, steroid priming is an efficient way to shorten the prostaglandin-based estrus synchronization pro gram from 14 to 7 days without compromising estrous response and fertility. (C) 2001 by Elsevier Science Inc.