Trans-Lactation Changes in the Activities of Selected Enzymes in Biopsy Samples of the Bovine Mammary Gland

Abstract

A surgical biopsy technique suitable for repeated sampling of bovine mammary secretory tissue is described. Samples from four cows obtained at 28-day intervals from calving were analysed for DNA content and for the activities of five enzymes selected as representing general metabolism and the synthesis of fat and carbohydrate. DNA concentrations fell during the first quarter oflactation in three cows, possibly indicating hypertrophy of the secretory cells in early lactation. Changes in enzyme activities were erratic, but statistically significant variation between cows was demonstrated in the activities of UDPglucose epimerase (E.C.5.1.3.2), glycerol-3-phosphate dehydrogenase (E.C.1.1.1.8), glucose-6-phosphate dehydrogenase (E.C.1.1.1.49). No significant changes in the activity of acetyl CoA synthetase (E.C.6.2.1.1) were detected.