Relationships between changes in plasma concentrations of leptin before and after parturition and the timing of first post-partum ovulation in high-producing Holstein dairy cows

Abstract

During early lactation, dairy cattle are in negative energy balance and the delay to first post-partum ovulation depends on the time taken to recover from this situation. Lactating cows rely heavily on body fat to meet their requirements, leading to the suggestion that leptin, a hormone secreted mainly by adipocytes, is acting as a metabolic signal to sites that control the reproductive axis. The relationship between plasma leptin concentrations and the timing of the first ovulation post partum in 20 high-producing Holstein dairy cows, using a radioimmunoassay based on recombinant bovine leptin was studied. Plasma leptin concentrations declined after parturition, reached a nadir of 0.74 ± 0.17 ng mL^–1 on 10.1 ± 2.2 days after parturition (all values are mean ± SEM). They then increased and became stable near the time of ovulation. Leptin concentrations averaged 1.81 ± 0.31 ng mL ^–1 in the 14 days prepartum, 1.32 ± 0.21 ng mL ^–1 in the post-partum preovulatory period, and 1.61 ± 0.24 ng mL ^–1 in the post-ovulatory period. The differences between periods were significant (P<0.01). The interval from parturition to first ovulation averaged 25.9 ± 2.0 days and was not correlated with the prepartum, preovulatory or post-ovulatory leptin values. However, the interval to first ovulation correlated significantly (r = 0.83;P<0.0001) with the interval from parturition to the leptin nadir. These results show that plasma concentrations of leptin decrease in dairy cows in the early post-partum period and suggest that a delay in the recovery of leptin secretion increases the delay to the first ovulation.