influence of parity on reproductive performance in postpartum dairy cows

the purpose of this research was the study of reproductive performance in postpartum dairy cows with different parities. twenty holstein dairy cows were assigned into two equal primiparous and multiparous groups. body weight and body condition score (based on 1-5 scoring) were measured every other week, starting from two weeks before calving till pregnancy confirmation. daily milk yield was also recorded. reproductive parameters including days from calving to the uterus returning time, to the initiation time of clinical oestrus signs, to the first time of insemination and number of insemination per pregnancy were recorded. meanwhile, blood serum concentrations of estrogen and progesterone were measured. results indicated that, the mean (±se) of body weight and milk production was significantly higher for multiparous cows. blood serum concentration of estrogen (mean ±se) was significantly lower for primiparous cows (61.86±17.91 vs. 71.39±17.02 pg/ml). the number of insemination per pregnancy and estrus frequency did not differ between both groups. however, the intervals (mean ±se) of calving to the uterus returning time (40.0±5.41 vs. 24.0±5.41 days), to the first insemination (119.62±14.17 vs. 67.5±14.17 days) and the initiation of clinical oestrus signs (28.5±4.5 vs. 19.67±8.5 days) was significantly higher for primiparous than multiparous cows. in general, this study demonstrated that the effect of parity on postpartum reproductive performance is modulated through its effect of blood serum estrogen level, uterus returning time and estrus initiation time.