FSH and LH variations in beef cows during the postpartum period

To study the plasma gonadotrophin profiles of 9 cows after parturition, blood samples were obtained every 20 min for 12 hrs on three occasions between 5 and 50 days postpartum and analysed by RIA techniques. The time of the first ovulation, as judged by plasma progesterone levels, varied from 30 to more than 60 days postpartum. Variations in mean levels of FSH and LH were not significantly correlated with the postpartum interval. However, the mean levels of plasma FSH and number of LH pulses were lower in females which had not ovulated than in those which had. The cows could be classified into four groups: group 1 with less than 4 LH pulses in 12 hrs and a mean plasma FSH level less than 138 ng/ml; group 2 with more than 4 LH pulses in 12 hrs and varying plasma FSH levels; group 3 with less than 4 LH pulses in 12 hrs and a mean plasma FSH level greater than 138 ng/ml; group 4 which had ovulated. This classification indicated that the LH and FSH levels progressed significantly (2.46 to 3.56 ng/ml, P less than 0.05; 120 to 159 ng/ml, P less than 0.01, respectively) from groups 1 to 3, and that they decreased in the females which had ovulated (group 4). Since the time of the first ovulation after parturition varied, it was not possible to demonstrate any relationship between that interval and the mean plasma gonadotrophin profiles. However, when ovulation was considered as time zero there was a clear increase in plasma gonadotrophin before ovulation.