Effect of weaning and milk replacer on aminotransferase activity in plasma and liver of Saanen goat kids

The aim of the present study was to investigate the effect of weaning on plasmatic and hepatic activity of aminotransferases in goats. Moreover, considering that in modern intensive farms weaning is often conducted with the use of a milk replacer, instead of whole milk, the effect of milk replacer feeding was also investigated in goat kids.Thirty-six three-day old Saanen goat kids were divided into four groups (GM, WGM, MR and WMR). GM kids received goat milk to age 48 days. WGM group was initially fed goat milk, but started weaning at 25 days and was completely weaned by 40 days. MR kids were fed a milk replacer to age 48 days. WMR kids were initially fed the milk replacer and then subjected to the same weaning protocol used for WGM kids. During the experimental period, total consumption per group was recorded daily. Weekly, body weights were recorded and plasma samples were taken and analyzed for alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity. On day 48, all the kids were slaughtered, liver weight was recorded and liver samples were taken and analyzed for DNA and RNA content, ALT and AST activity. Obtained data suggest that nor milk replacer feeding, neither weaning practiced under the conditions of the present study, result in any negative effect on the performance of the kids. Milk replacer feeding has no different effect than goat milk feeding on aminotransferase activity in both plasma and liver of goat kids. By contrast, weaning reduces liver weight and increases liver AST activity per gram and plasma ALT, without affecting the number of cells per liver nor hepatic ALT activity per gram. Results suggest that at weaning the liver is stimulated to fulfil a larger portion of the animal’s glucose requirement, by increasing hepatic activity of gluconeogenic enzymes and by increasing amino acid transamination, which is the first step in the catabolism of most amino acids for glucose production). Whereas the most of liver AST is localized into the mitochondria, hepatic ALT is limited to the cytosol of the hepatocyte, which is the principal site of ALT synthesis in the body. In light of this, it is possible to hypothesize that hepatic activity of ALT does not change at weaning, because of the secretion of the enzyme into the bloodstream, thereby raising its plasmatic activity.