The aim of this study was to evaluate the effect of calving to first service interval and Flunixin Meglumine (FM) injection on reproductive performance in Holstein dairy cows. The experiment was conducted as a completely randomized design with 2×2 factorial method. For this purpose 80 multiparous cows at about 30 d after calving and before first service were selected. There was no Timed Artificial Insemination program for synchronization. The treatmrnts were: 1) Interval of calving to first service 51-70 d, without FM injection, 2) Interval of calving to first service 51-70 d, with FM injection, 3) Interval of calving to first service 71-90 d, with FM injection, without FM injection, 4) Interval of calving to first service 71-90 d, with FM injection. Each cow received 1.1 mg/kg FM by I.M. injection on day 14 after first and second insemination. Conception rate, number of service per conception, days open, serum progesterone concentration at 3, 9, 15, 21 and 27 d after insemination, non-return rate and abortion rate was determined. Results showed that cows inseminated 71-90 d postpartum need lower (P 0.05) service per conception compared to cows inseminated 51-70 d postpartum. This cows had higher conception rate after second service than other cows. FM injection decresed (P = 0.09) the number of service per pregnancy. The cows inseminated at 71-90 days postpartum had higher (P 0.05) progesterone at 15, 21 and 27 d after insemination. On the other hand, the cows tended to have higher (P = 0.07) serum progesterone entire the study. The cows inseminated 71-90 d postpartum and also the cows which received FM had higher (P 0.05) non-return rate. Also the cows inseminated 71-90 d postpartum had lower (P = 0.09) abortion rate compared. It was concluded that delay in first service after parturition and FM injection may have some beneficial effect on reproduction performance of high producing dairy cows.
