Single injection of estrogen and progesterone (steroid priming) prior to prostaglandin was utilized to shorten prostaglandin-based estrus synchronization program from 14 to 7 days. Sixty-five cyclic
Sistani cattle at unknown stages of estrous cycle were selected and assigned into two groups according to their age and weight. Females in Group one (Control; n=33; 58.4±4.3 months; 277±8 kg LW) received two consecutive injections of Prostaglandin F2a analogue (500mg; Cloprostenol) 14 days apart. Group two females (Treatment; n=32; 60±4.8 months; 292±9kg LW) were given an intramuscular injection of 100mg progesterone and 2mg estradiol benzoate, 7 days before prostaglandin injection. Estrus detection was carried out every 4 hours for 7 days, commencing from 24 hours after cessation of the last prostaglandin injection. Females allowed to be mounted were identified (standing estrus) and inseminated with frozen semen 12 hours later. Pregnancy was diagnosed on day 50 after Al through rectal examination. Data were Analyzed using Chi-squared 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 56.5%) groups. In conclusion, priming with steroids is an efficient way to shorten prostaglandin- based estrous synchronization program from 14 to 7 days.
)