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Thermal Stress and Circulating Erythrocytes, Leucocytes, and Milk Somatic Cells

Animal Physiology and Genetics Institute, Agricultural Research Center, USDA, Beltsville, Maryland 20705

ABSTRACT

From five to six Holstein cows were selected for each of eight trials. When compared to 21 C control periods, neither 2 nor 4 consecutive weeks of either constant 32 C or fluctuating (32 C day and 21 C night) environmental temperatures caused any detectable increase in the concentration of somatic cells in milk. for all trials, body temperatures increased and milk production usually decreased during high temperature exposure. There were no significant changes in either circulating erythrocytes or leucocytes for cows exposed to constant 32 C. However, in those trials where cows were held under fluctuating temperature conditions, significant depressions did occur for both erythrocytes and leucocytes. There was no evidence to support the claim that high ambient temperature will cause the concentration of somatic cells in milk to increase.