Nutritional regulation of leptin in dairy cattle

Leptin, a hormone secreted primarily from white adipose tissue, plays a role in the regulation of energy balance and reproduction. Studies were conducted to determine the tissue distribution of leptin and leptin receptor and to examine the role of nutrition in the regulation of leptin secretion in Holstein cattle.;In male calves, leptin mRNA was detectable in adipose tissue with similar transcript abundance among adipose depots. The mRNA for the long-form of the leptin receptor, Ob-Rb, was detectable in a wide array of central and peripheral tissues whereas the short-form, Ob-Ra, was expressed in only a few tissues.;Plasma leptin concentrations were acutely responsive to short-term fasting and refeeding but the response differed among cattle of varying physiological states. The fasting-induced hypoleptinemia was delayed in non-lactating cows and postpubertal heifers compared to the rapid response observed in early lactation cows.;Rumen and duodenally cannulated cows were used to determine the effects of canola oil supplementation on leptin and cholecystokinin (CCK) gene expression and release. Both feeding and abomasal infusion of canola oil resulted in a similar increase in gene expression and plasma concentrations of CCK but only infusion caused a reduction in feed intake, which is suggestive of a paracrine/neurocrine role for CCK in mediating satiety. Neither body condition score (BCS) nor plasma leptin concentrations were altered with fat supplementation, indicating that leptin does not mediate fat-induced satiety and/or that the leptin response to fat is dependent on BCS.;The leptin response to lipid or glucose supplementation was determined in early and late-lactation cows. Late lactation cows, with high BCS, exhibited a robust leptin response to parenteral glucose or lipid infusions, whereas early lactation cows, with low BCS, were unresponsive. In comparison to the direct rapid effects of lipid infusion on leptin secretion, the glucose-induced hyperleptmemia was delayed and was preceded by a strong insulin response in late-lactation cows.;Long-term changes in body composition and plasma leptin concentrations were determined in heifer calves fed diets varying in energy and protein density. Puberty occurred at a constant body composition and body weight independent of growth rate. Plasma leptin concentrations increased with approaching puberty suggesting that leptin might relay information on body reserves to the brain to initiate puberty in heifers.;In summary, leptin is secreted from adipose tissue and may have multiple physiological functions in cattle. In the short-term, the response of leptin to feed deprivation or nutrient infusions is dependent on physiological state and body fat reserves. In the long-term, leptin secretion reflects changes in body weight and adipose tissue reserves.