Abstract
The objective of this study was to investigate the effect of post-AI luteal function on first AI conception rate in dairy cows. A total of 119 Holstein Friesian cows from four dairy herds were used in this study. Milk samples were collected twice a week and progesterone concentrations in whole milk were measured by direct ELISA. The luteal function post-AI was shown by days to commencement of luteal activity after AI, progesterone concentrations during early luteal phase and these combinations. Cows with commencement of luteal activity during a period from 1 or 2 to 5d post-AI had the highest conception rate. Increasing progesterone concentrations during 5 to 9d post-AI were associated with higher conception rates. Animals with delayed luteal activity 9d post-AI or later, those with delayed and insufficient luteal activity and those with insufficient luteal activity had lower conception rates compared to cows with normal luteal activity (22.2%, 12.5%, 0.0%, vs 51.5%, respectively; P<0.10). Logistic regression analysis revealed that CL function (OR=0.6; p=0.001) significantly affects the first AI conception rate, whereas the other factors including parity, resumption of ovarian activity postpartum, season of AI and interval from calving to first insemination had no significant effect. In conclusion, both commencement of luteal activity post-AI and progesterone concentration during early luteal phase affect the conception rate.
