Ghrelin, leptin, and IGF-1 in goat milk and plasma

Seventeen Saanen goats at mid-lactation were fed a diet based on mixed hay, maize, beet pulp, barley and soyabean meal (40:60 forage to concentrate ratio) at 9.00 h and 17.00 h, and milked at 8.00 h and at 18.00 h. At 133, 148 and 163 DIM, milk samples were tested for milk leptin , IGF-1 and ghrelin content. At the same dates, five ml of jugular vein blood were taken before the first feeding of the day, 1 h and 4 h after the feeding. Mean milk production was 1.3 and 1.02 kg/milking (P<0.01). Milk leptin level and milk ghrelin level did not show significant difference between morning and evening milkings. Milk IGF-1 level was thrice higher in morning than in evening milking. Both in plasma than in milk, leptin was significantly positively correlated to ghrelin and negatively to IGF-1. The correlation between ghrelin and IGF-1 was significant only in plasma. Milk and plasma leptin were not correlated, but milk ghrelin and milk IGF-1 were significantly correlated to plasma ghrelin and IGF-1, respectively. During periprandial period (immediately pre-feeding, 1-h and 4-h post feeding) plasma leptin level and IGF-1 level did not significantly differ; meanwhile plasma ghrelin level was significantly lower 1 h post feeding than before feeding. In literature the results regarding periprandial variation of leptin in ruminants are conflicting; in fact post-prandial increments, decrements or no variation are reported. In this study no variation is observed in plasma leptin. In sheep, plasma ghrelin is reported to increase just before feeding, and to be involved in inducing GH surge during feeding. Analogously, in goat we observed the same periprandial variation, although lower. However, to explain the periprandial varisation of ghrelin, further investigation should be required. The milk levels of leptin and ghrelin were twice/thrice higher than their plasma levels, suggesting mammary synthesis or concentration. Although one site of action of milk-borne growth factors may be at intestinal level, the transfer of leptin from milk to the neonate has been shown for leptin in rat and for IGF-1 from indirect evidence in calf. Further research is needed to determine whether interspecific transfer can occur and whether these components from goat milk can maintain their biological activity in the systemic circulation of the young feeder.