Effect of stress on blood leucocyte and milk somatic cell counts in dairy cows.

Blood and milk samples from Holstein cows were examined for total blood leucocyte count, differential blood leucocyte count, milk quality test, and somatic cell count in milk while the cows were stressed by corticotropin injection, confinement 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 conditions resulted in a moderate blood leucocytosis. Modest increases in somatic cell counts of milk were associated with corticotropin injection and environmental-heat stress. Positive 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.