Decreased concentration of plasma leptin in periparturient dairy cows is caused by negative energy balance

Dairy cows suffer from an intense energy deficit at parturition due to the onset of copious milk synthesis and depressed appetite. Despite this defici t, maternal metabolism is almost completely devoted to the support of mamma ry metabolism. Evidence from rodents suggests that, during periods of nutri tional insufficiency, a reduction in plasma leptin serves to co-ordinate en ergy metabolism. As an initial step to determine if leptin plays this role in periparturient dairy cows, changes in the plasma concentration of leptin were measured during the period from 35 days before to 56 days after partu rition. The plasma concentration of leptin was reduced by similar to 50% af ter parturition and remained depressed during lactation despite a gradual i mprovement in energy balance; corresponding changes occurred in the abundan ce of leptin mRNA in white adipose tissue. To determine whether negative en ergy balance caused this reduction in circulating leptin, cows were either milked or not milked after parturition. Absence of milk removal eliminated the energy deficit of early lactation, and doubled the plasma concentration of leptin. The plasma concentration of leptin was positively correlated wi th plasma concentrations of insulin and glucose, and negatively correlated with plasma concentrations of growth hormone and non-esterified fatty acids . In conclusion, the energy deficit of periparturient cows causes a sustain ed reduction in plasma leptin. This reduction could benefit early lactating dairy cows by promoting a faster increase in feed intake and by diverting energy from non-vital functions such as reproduction.