Effects of season on plasma progesterone profiles in repeat breeding cows

Forty six Holstein Friesian repeat breeding cows (the average AI/ conception was 5.2 +/- 0.2) were investigated using the progesterone assay after AI to determine possible differences in plasma progesterone profiles between summer and winter seasons. Twenty eight (60.9%) and 18 (39.1%) cows were followed in summer (June-August) and winter (December-February), respectively. In the summer season, the total progesterone concentrations were higher (P < 0.05) in pregnant cows with normal luteal function compared to those in non-pregnant animals with abnormal luteal function. In contrast, in the winter season, there was no difference (P = 0.12) in total progesterone concentrations between pregnant and non-pregnant cows with normal or abnormal luteal functions. When the progesterone concentrations were compared, the pregnant and non-pregnant cows with normal luteal functions exhibited no difference (P = 0.92) in summer and winter seasons. Thus, the present study indicates that there is no effect of season on plasma progesterone profiles in repeat breeding cows; however in the summer season, the total progesterone concentrations were considerably higher in pregnant cows with normal luteal function compared to non-pregnant cows with abnormal luteal function.