Leptin, insulin and ghrelin levels in goat milk and in plasma of suckling kids

Milk is not just the basic source of nourishment for the neonate, but it is also a vector of bioactive peptides that can play a possible role in neonatal development. For the increasing utilization of goat milk in infant formulas for human nutrition, it could be of interest to quantify the levels of leptin, insulin and ghrelin in goat milk and in plasma of the suckling kids and to evaluate the relationships between ingested and circulating levels of hormones in growing animals. For this purpose, 10 suckling kids (fed goat milk containing 0.53 nmol/l of leptin, 0.30 nmol/l of insulin and 1.01 nmol/l of ghrelin) were analysed from the 3rd to the 5th week of age (before the beginning of the weaning period). During the experimental period, body weight and milk consumption were recorded. Blood samples were taken before the first meal of the day on week 3, 4 and 5. Plasma was analysed for leptin, insulin and ghrelin. As expected, body weight and milk intake increased during the experimental period. Although daily intake of hormones and growth factors with milk increased, it was observed a decrease of leptin levels (P<0.02) in plasma of suckling kids. On the contrary, plasma levels of insulin increased more than 4 times (P<0.01), with a high correlation with the quantity of hormone ingested daily (P<0.01). This latter result is probably due to the increasing amount of milk consumption during the entire period, but it is possible to hypothesize the presence of receptors that can help milk-born insulin to transpass the gastrointestinal mucosa of the suckling kids. Insulin, in fact, can play a fundamental role in the functional development of pancreas. It has been reported in rats that plasma insulin levels arise just before weaning and this can be a stimulator of pancreatic amylase gene expression.