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 thedelay to first post-partum ovulation depends on the time taken to recover fromthis situation. Lactating cows rely heavily on body fat to meet theirrequirements, leading to the suggestion that leptin, a hormone secreted mainlyby adipocytes, is acting as a metabolic signal to sites that control thereproductive axis. The relationship between plasma leptin concentrations andthe timing of the first ovulation post partum in 20 high-producing Holsteindairy cows, using a radioimmunoassay based on recombinant bovine leptin wasstudied. Plasma leptin concentrations declined after parturition, reached anadir of 0.74 &plusmn; 0.17 ng mL<emph type="7">-1 on 10.1&plusmn; 2.2 days after parturition (all values are mean&plusmn; SEM). They then increased and became stable near the time ofovulation. Leptin concentrations averaged 1.81 &plusmn; 0.31 ng mL<emph type="7">-1 in the 14 days prepartum, 1.32 &plusmn;0.21 ng mL <emph type="7">-1 in the post-partum preovulatoryperiod, and 1.61 &plusmn; 0.24 ng mL <emph type="7">-1 inthe post-ovulatory period. The differences between periods were significant(P&lt;0.01). The interval from parturition to firstovulation averaged 25.9 &plusmn; 2.0 days and was not correlated withthe prepartum, preovulatory or post-ovulatory leptin values. However, theinterval to first ovulation correlated significantly (r= 0.83;P&lt;0.0001) with the intervalfrom parturition to the leptin nadir. These results show that plasmaconcentrations of leptin decrease in dairy cows in the early post-partumperiod and suggest that a delay in the recovery of leptin secretion increasesthe delay to the first ovulation.