Activities of AST, ALT and GGT in clinically healthy dairy cows during lactation and in the dry period

This study examined the activities of aspartate aminotransferase (AST; EC 2.6.1.1), alanine aminotrans-ferase (ALT; EC 2.6.1.2) and gamma-glutamyltransferase (GGT; EC 2.3.2.2) in the plasma of 120 dairy Hol-stein breed cows divided into four groups according to production period. The cows were held in an intensive farm breeding premises. Their meal consisted of ordinary alfalfa, silage, hay and concentrates with energy and protein supplements. The first group consisted of animals from the 10th until 45th day of lactation, the second from the 46th until 90th day of lactation, and the third group from the 91st day of lactation until the end of milk production. Cows in the dry period comprised the fourth group. The highest activity of AST was determined in the first production period, while enzyme activity in the second and third periods was higher than in the dry period. ALT activity showed a statistically significant increase from the 46th day of lactation until the dry period, and activity in the second and third periods was statistically higher than in the dry period. GGT activity in the first production period and in the dry period was statistically higher in comparison with the second and third periods. Research results showed a significant influence of milk production and the dry period on the activities of examined enzymes in the blood plasma, and we can conclude that there is a need for constant monitoring o