Effect of induced leucocyte migration on mammary cell morphology and milk component biosynthesis

Effects of increasing milk somatic cell count on milk composition, milk component biosynthesis, and quantitative mammary histology were studied following intramammary infusion of sterile oyster glycogen in lactating ewes. Oyster glycogen had no direct effect on mammary tissue utilization of radiolabeled acetate. Intramammary infusion of oyster glycogen following each of six consecutive milkings in six lactating ewes increased mean milk somatic cell count (6-fold) and increased percent fat and protein but decreased milk lactose concentration. Quantity of damaged or nonsecretory epithelial cells was increased. Infused glands had increased concentrations of neutrophils (3-fold) and plasma cells (1.3-fold) in the subepithelial stroma and of neutrophils (2.7-fold) within the epithelial lining of alveoli. Infusion of oyster glycogen every 3 d for 30 d in four ewes elicited similar changes in milk somatic cell count and mammary histology. Loss of functional mammary cells associated with leucocytosis may explain lost milk production associated with increased milk somatic cell count.