Effect of Streess on Blood Leucocyte and Milk Somatic Cell Counts in Dairy Cows

Abstract

Blood and milk samples from Holstein cows were examined for total blood leucocyte count, differential blood leuco- cyte count, milk quality test, and somatic cell count in milk while the cows were stressed by corticotropin injection, con- finement in a heat-humidity chamber, or environmental-heat stress by exposure during the hot summer months of June through November in southern Arizona. All three stressing ¢onditions resulted in a moderate blood leucocytosis. Modest in- creases in somatic cell counts of milk were associated with corticotropin injec- tion and environmental-heat stress. Posi- tive correlations were recorded between blood leucocytes and somatic cell counts of milk in mastitis-free cows injected with corticotropin and between percent blood neutrophils and somatic cell counts of milk in environmental-heat stressed cows with no evidence of current mastitis.