Nitrogen Metabolites and Enzymatic Activity During the Weaning Period in Goat Kids

At birth, 11 Saanen goat kids were assigned to one of the two experimental groups: MILK (6 animals) and WMIX (5 animals). All kids were fed colostrum for 3 days and then goat milk for the first 4 weeks of life. Starting from the 5th week, MILK group continued to receive goat milk, while WMIX group was fed milk in decreasing quantity plus a weaning feed mixture ad libitum; on day 47 of age, the WMIX group was completely weaned. On week 3, 4, 5, 6 and 7 of age, blood samples were taken before the first meal of the day. On day 50 of age, all kids were slaughtered and carcass and liver weight recorded. Liver and pancreas samples were analyzed for DNA and RNA. Phospholipid and soluble protein level and alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity were analyzed in liver. Zymogen content and α-amylase activity were determined in pancreas. On day 50 of age, liver weight, hepatic DNA, RNA and phospholipid content and ALT and AST activity were not different between the two experimental groups. However, liver weight expressed as percentage of body weight (P<0.05), as well as liver RNA expressed on kg of body weight and liver content of soluble protein on mg of RNA were lower in WMIX animals than in MILK group. On day 50 of age, pancreatic zymogen, DNA and RNA content was not different between groups. By contrast, pancreatic α-amylase activity expressed as unit on g of fresh tissue, as well as when expressed on zymogen, on DNA and on RNA was more than three times lower (P<0.05) in WMIX group than in MILK one. Pancreatic amylase activity was also correlated with plasma free aminoacid concentration (r=+0.80; P<0.01). The data here reported suggest that weaning can affect protein metabolism and pancreatic amylase activity. However, it is surprising that the MILK group had higher level of pancreatic α-amylase, even if there was no starch in milk diet. So, more extensive experiments are required in order to establish which could be the stimulator of pancreatic α-amylase synthesis and secretion, at the time of weaning.