Postweaning adaptation of liver activity to solid diet in goat kids

In ruminants, the transition from milk diet to solid diet requires the adaptation of liver metabolism and activity, that shift from glycolytic to gluconeogenic pathways. Moreover, the requirement of amino acid by the digestive apparatus is high and may affect amino acid availability for growth, so the first days after the removal of milk represent a critical phase during which kids can experience growth stasis or weight loss. The aim of the present study was to investigate changes in liver composition and activity in Saanen goat kids, during the first days after the completion of weaning. Two trials were conducted on male Saanen goat kids, reared by two different weaning programs. In the first trial, 3-days old kids were divided into two homogeneous groups: MILK, that received goat milk ad libitum for the entire study period, and WEAN2 that was subjected to weaning. In the second trial, 3-days old kids were assigned to one of two homogeneous groups: MILK, that was fed goat milk ad libitum, and WEAN8, that was weaned. All the kids studied in the trials were slaughtered 2 days (in the first trial) or 8 days (in the second trial) after the complete removal of milk from the diet of WEAN2 and WEAN8 groups, respectively. Body weight did not differ between weaned and milk-fed kids, nor 2 days, neither 8 days after weaning, but WEAN8 kids exhibited a lower carcass weight than milk-fed ones. Two days after weaning, liver weight was similar in the experimental groups, but 8 days after weaning, liver weight significantly decreased in WEAN8 kids, in comparison to the MILK ones. DNA and phospholipids contents did not differ between groups of the first trial, but DNA and phospholipids were higher in the weaned kids (WEAN8) of the second trial. In the first trial was noted a reduction of 25% in the glycogen content of the liver of WEAN2 kids. This reduction was greater in WEAN8 kids, compared to MILK ones. Two days after weaning, no difference was observed in aminotransferase activity between the experimental groups, but 8 days after weaning, both ALT and AST activity were higher in WEAN8 kids, compared to milk-fed ones. In conclusion weaning alters liver composition and activity, without affecting the number of cell within the tissue. Liver activity shifts from glycolytic to gluconeogenic pathways and the effects of this transition are significant 8 days after the complete removal of milk from the diet. The reduction in hepatic glycogen content is accompanied with the increase in amino acid transamination, which is the first step in the catabolism of amino acids.