An investigation on the possibility of using eCG for presynchronization prior to ovsynch in dairy cow

Background: Presynchronization could enhance fertility in timed breeding programs. The best presynchronization method has to justify biological requirements and to provide practical and economic advantages. OBJECTIVES: Present study investigated the effectiveness of presynchronization with equine chorionic gonadotropin (eCG) before ovsynch (eCG-ovsynch) compared to conventional presynch-ovsynch program (2PG-ovsynch) in lactating cows. METHODS: Healthy lactating cyclic Holstein cows (n=110) without any particular pre, peri and post parturient problems were selected for this study. The first insemination following timed breeding program was conducted at 57 days after calving. Ovsynch (timed breeding program) consisted of two GnRH analogue injections, at 7 days before and 56 hours after PG, followed by insemination, 16 hours after the second GnRH. Cows in 2PG-Ovsynch group (n=55) received two PGs, 14 days apart, followed by ovsynch program 12 days later. Cows in eCG-Ovsynch group (n=55) received eCG (500 IU, IM), 84 hours before ovsynch program. Pregnancy was confirmed 40 d after insemination by rectal palpation. Progesterone concentrations were evaluated at presynchronization, at the first GnRH and at PG of ovsynch program. RESULTS: The respective first service conception rates, days open and service per conception were similar between 2PG-ovsynch (45.45%; 94.0±6.30 days; 1.95) and eCG-ovsynch (40%; 90.1±4.58 days; 1.81) groups (p>0.05). The percentage of cows with high progesterone concentrations increased significantly from the first GnRH (38.2%) until PG (85.4%) in eCG-ovsynch group (p<0.05). The percentage of cows with high progesterone concentrations at the time of PG injection of ovsynch program was greater in eCG-ovsynch (85.4%) compared to 2PG-ovsynch (69%). CONCLUSIONS: Administration of eCG (500 IU), 84 hours prior to ovsynch could optimize timed breeding program biologically, practically and economically in lactating dairy cows.