Serum progesterone concentrations at the insemination time and pregnancy rate in dairy cows

In this study the concentration of serum progesterone at the time of insemination and its effect on fertility in dairy cows were determined. In addition, it was assessed the impact of parity, number of services, puerperal condition, inseminating bull breed, AI technician and herd. Blood samples were obtained from 560 cows (25 herds) at the time of insemination and progesterone concentrations were determined. Pregnancy was diagnosed 40 to 45 days later by transrectal palpation. Using a logistic regression analysis the effect of progesterone (<= 0.5 vs. > 0.5 ng/mL), parity (primiparous vs. multiparous), number of services (< 4 vs. >= 4 services), bull breed (Holstein vs. other breeds), puerperal condition (normal vs. abnormal), AI technician (1 vs. 2) and herd on pregnancy rate were determined. The proportion of cows inseminated with values > 0.5 ng/mL was 5.9%. Cows with progesterone levels > 0.5 ng/mL had a lower conception rate (18.2) than cows with levels <= 0.50 ng/mL (32.8) (Odds ratio = 2.46; P < 0.05). There was no significant effect (P>0.05) of parity, number of services, breed of bull, AI technician, puerperal condition or herd. It is concluded that 5.9% of the cows had suprabasal progesterone concentrations at the time of insemination, which negatively affected the pregnancy rate.