Activities of gamma-glutamyltransferase, alkaline phosphatase and aspartate-aminotransferase in colostrum, milk and blood plasma of calves fed first colostrum at 0-2, 6-7, 12-13 and 24-25 h after birth.

Enzyme activities of gamma-glutamyltransferase (gamma-GT), alkaline phosphatase (AP) and aspartate-aminotransferase (AST) were measured from birth to the age of 28 days in calves which were fed colostrum at 0-2, 6-7, 12-13, or 24-25 h after birth. Enzyme activities were also measured in colostrum (first to fifth milking) and in mature milk. Activities were highest in the first colostrum milking and decreased to the lowest activities in mature milk. Plasma gamma-GT activity transiently increased after first colostrum intake and was greater in calves fed first colostrum within less than 6-7 h than in those fed first colostrum later than 12 h after birth. Activity of gamma-GT reflected the absorption of colostral gamma-GT, which decreased with time after birth. The AP activity transiently increased after colostrum intake and was higher in calves fed colostrum within the first 12 h of life than in those fed later after birth. The transient rise of plasma AP activity also indicated absorption of colostral AP, although endogenous sources of AP could not be excluded. The activity of AST also transiently increased after colostrum intake but there was no association with time of first colostrum feeding, indicating that the rise of plasma AST activity was the consequence of enhanced endogenous production and was independent of colostrum intake. In conclusion, there are different causes leading to postnatal changes in enzyme activities.