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 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 suckling goat kids and to evaluate the relationship between ingested and circulating levels of hormones in growing animals. For this purpose, 10 suckling kids were observed from the 3rd to the 5th week of age (before the beginning of theweaning period). During the experimental period, bodyweight and milk intake were recorded. Milk and blood samples were taken before the first meal of the day on week 3, 4 and 5. Plasma and milk were 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, plasma leptin level of suckling kids decreased (P = 0.02). On the contrary, plasma level of insulin increased more than four times (P < 0.01) and was highly correlated (P < 0.01) to the daily quantity of hormone ingested. This trend was probably associated to the increased milk intake, but it is even possible to hypothesize the presence of receptors that facilitate the migration of milk-borne insulin through the gastrointestinal mucosa of the suckling kids. This hypothesis is supported by the fundamental role played by insulin in the functional development of pancreas; in fact in rats plasma insulin level arises just beforeweaning and this is supposed to stimulate pancreatic -amylase gene expression