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

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 mai nly by adipocytes, is acting as a metabolic signal to sites that control th e reproductive axis. The relationship between plasma leptin concentrations and the timing of the first ovulation post partum in 20 high-producing Hols tein dairy cows, using a radioimmunoassay based on recombinant bovine lepti n was studied. Plasma leptin concentrations declined after parturition, rea ched a nadir of 0.74 +/- 0.17 ng mL(-1) on 10.1 +/- 2.2 days after parturit ion (all values are mean SEM). They then increased and became stable near t he 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 preo vulatory 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 f rom parturition to first ovulation averaged 25.9 <plus/minus> 2.0 days and was not correlated with the prepartum., preovulatory or post-ovulatory lept in values. However, the interval to first ovulation correlated significantl y (r = 0.83, P < 0.0001) with the interval from parturition to the leptin n adir. These results show that plasma concentrations of leptin decrease in d airy cows in the early post-partum period and suggest that a delay in the r ecovery of leptin secretion increases the delay to the first ovulation.