Pattern of γ-glutamyl transferase activity in cow milk throughout lactation and relationships with metabolic conditions and milk composition1

Abstract

The main objective of this experiment was to study the γ-glutamyl transferase (GGT) activity in milk during lactation and its relationship with metabolic status of dairy cows, milk yield, milk composition, and cheesemaking properties. The study was performed in a tied stall barn and involved 20 lactations from 12 healthy multiparous Italian Friesian dairy cows. During lactation starting at d 10, milk samples were collected weekly and analyzed for composition, somatic cells count, titratable acidity, and milk coagulation properties. The GGT activity was measured in defatted samples. Blood samples were collected weekly to assess biochemical indicators related to energy, protein, and mineral metabolism, markers of inflammation and some enzyme activities. The lactations of each cow were retrospectively categorized into 2 groups according to their milk GGT activity value through lactation. A median value of GGT activity in the milk of all lactations was calculated (3,045 U/L), and 10 lactations with lower GGT activity were classified as low while 10 lactations with greater GGT activity were classified as high. The average value of milk GGT activity during lactation was 3,863 and 3,024 U/L for high and low, respectively. The GGT activity decreased in early lactation and reached minimum values in the second month (3,289 and 2,355 U/L for high and low, respectively). Thereafter GGT activity increased progressively, reaching values in late lactation of 4,511 and 3,540 U/L in high and low, respectively. On average, milk yield was 40.81 and 42.76 kg/d in high and low, respectively, and a negative partial correlation with milk GGT activity was observed. A greater milk protein concentration was observed in high (3.39%) compared with low (3.18%), and a positive partial correlation with milk GGT activity was observed. Greater titratable acidity in high than that in low (3.75 vs. 3.45 degrees Soxhlet-Henkel/50 mL, respectively) was also observed. Plasma glucose was greater in cows of high than in low group, while plasma urea was lower in the high than in the low group. No relationship between plasma GGT and milk GGT activity was observed. Our results show an important effect of lactation stage on milk GGT activity. The individual effect observed from consecutive lactations and the relationship between milk GGT activity and milk protein concentration in healthy cows could open prospects for GGT as a future tool in improving milk protein content.

Plasma hormone levels in the green turtle Chelonia mydas reared under captivity as a tool to predict mating and oviposition

“…In mallards, egg laying activity significantly influences serum enzyme activity and GGT activity was reported to be elevated tenfold compared to other reproductive periods (Fairbrother et al, 1990). In cattle, GGT was identified as one of the enzymes found in milk and was found active during lactation but with no change in plasma GGT during this process (Calamari et al, 2015). Yet, the reason for GGT elevation in female green turtles before the nesting activity itself, is yet to be understood.…”

Biochemical Indicators of Energy Balance in Blood and Other Secretions of Dairy Cattle: A Review

“…In addition, a positive correlation of BHBA was observed with ALT, AST and LDH and negative correlations was observed between plasma BHBA and TC levels. Calamari et al (2015) studied the relationship of GGT activity in milk with EB and milk yield in healthy cows and found that GGT activity was in decreasing trend during early lactation period until second month. They found negative correlation between milk yield and BUN and positive correlation between glucose and GGT activity.…”

Changes in superoxide dismutase activity postpartum from Laoshan goat milk and factors influencing its stability during processing

“…Human milk exerts direct pharmacologic relaxation effects and provides better antioxidant protection compared with infant formulas because of the presence of specific enzymatic components, such as human SOD (Lugonja et al 2013). The previous study showed that an important effect of lactation stage on milk c-glutamyl transferase (GGT) activity, and a positive relationship between GGT activity and milk protein concentration was observed, which could influence protein synthesis, as well as protein composition, with possible implications for cheese-making properties related to the milk protein fractions (Calamari et al 2015). The time-dependent alterations of IgA, IgG, IgM, the C3, C4 protein and CuZn-SOD in human breast milk collected in the diurnal and nocturnal colostrum were observed by the studies of França and Nicomedes (2010).…”