Variation among goats in the ability of their polymorphonuclear neutrophil leukocytes and mammary secretions to support phagocytosis: inhibitory effects of milk fat globules

The objectives of this study were to determine if fat globules and casein in goat milk were inhibitory to phagocytosis by polymorphonuclear neutrophils (PMN) isolated from blood, and to determine if variation existed among goats in the ability of PMN to phagocytose and in the ability of milk whey to support phagocytosis. Milk and blood were obtained from six goats. Serum, skimmed milk and milk whey was prepared by centrifugation. In the presence of either serum, whole milk, skimmed milk or milk whey, PMN were incubated with fluorescein isothiocyanate-labeled Staphylococcus aureus in a 1:20 ratio. Phagocytosis of S. aureus was determined by flow cytometry. Both pooled serum and pooled whey had a concentration-dependent effect on PMN phagocytosis (P < 0.01). In the presence of pooled serum, whole milk but not skimmed milk reduced (P < 0.01) phagocytosis when compared to serum and whey. Differences existed (P < 0.01) among goats in the ability of PMN to phagocytose and in the ability of milk whey to support phagocytosis. The inhibition of PMN phagocytosis by fat globules could contribute to susceptibility to intramammary infection by mastitis pathogens. Variation among goats in PMN phagocytosis and in mammary secretions to support phagocytosis may contribute to differences among goats in resistance to mastitis. © 2003 Elsevier B.V. All rights reserved.