Association between udder inflammation and glycosidase activities and free sugar levels in bovine milk

Abstract Two milk glycosidases [N-acetyl-β-glucosaminidase (NAGase) and β-glucuronidase] have previously been associated with elevated somatic cell count (SCC). However, several other glycosidases are present in milk, potentially having effects on milk glycans. The activities of eight glycosidases (NAGase, α-fucosidase, α-galactosidase, β-galactosidase, α-glucosidase, β-glucosidase, α-neuraminidase, β-glucuronidase) were measured in milk samples from six cows with different SCC at quarter level. Glycosidase activities were related to levels of free sugars as assessed by NMR spectroscopy. NAGase, β-glucuronidase, β-glucosidase, α-galactosidase and β-galactosidase were the enzymes to increase most with SCC. Furthermore, free fucose level was positively correlated with SCC (r = 0.72, P ˂ 0.0001). The same tendency was observed for sialic acid, whereas galactose and N-acetyl-hexosamine were found to increase consistently in quarters of mastitic cows regardless of SCC. This indicates different potential origins of responsible enzymes and further illustrates the potential effects of milk glycosidases on the inherent glycans present in milk.