Relations between blood Zinc oncentrations and udder health in dairy cows

Abstract

The aim of this study was to determine the influence of zinc on the mammary gland health. Somatic cell number in milk, thickness of stratum corneum in ductus papillaris and leukocyte infiltration of udder parenchyma were used as indicators of udder health in 30 dairy cows and blood Zn concentrations were measured at the 1st and 6th months of lactation. Blood Zn concentrations slightly increased at the 6th month but not significantly. Negative and significant correlations were found between Zn concentrations in one hand and SCC in the 6th month and the degree of leukocyte infiltration in the other hand, whereas Zn concentrations were highly positively associated with the stratum corneum thickness. The optimal cut off value that separated cows with subclinical mastitis (over 400.000 cells/mL) from healthy cows was 9.64 μmol/L (sensitivity: 71.22%, specificity: 65.7%) and the area under the ROC curve was 0.657. Cows in which Zn concentration was above 9.64 μmol/L (in the 1st and 6th month) exhibited significant decreases in SCC in the 6th month, a significantly thicker keratin layer in ductus papillaris and significantly lower leukocyte infiltration whereas in cows with low zincaemia, a thin stratum corneum of ductus papillaris was commonly evidenced associated to acinus atrophy of the mammary gland with proliferation of connective tissue and intense leukocyte infiltration mainly involving macrophages. These results demonstrate that zincaemia is an important predictor of the occurrence of mastitis in cows, a low value (< 9.64 mmol/L) being coupled to thinning of the stratum corneum and to increase in leukocyte infiltration of udder parenchyma.