Heat tolerance, biochemical, and hematological responses of Holstein cows under different feeding and environmental conditions in the semi-arid region of Brazil

Abstract This study evaluated heat tolerance and changes in biochemical and blood parameters in dairy cows under varying environmental and dietary conditions. Sixteen adult Holstein cows were used in four treatments: full sun with or without concentrate in the diet and shade with or without concentrate. Environmental parameters assessed included air temperature, relative humidity, and temperature-humidity index (THI). The cows' rectal temperature, respiratory rate, heat tolerance index, and blood parameters were also evaluated. Results showed that the cows experienced mild to severe heat stress, with the highest air temperature, humidity, and THI recorded in full sun during the afternoon (p < 0.05). Rectal temperature and heat tolerance index were also higher (p < 0.05) in full sun conditions, particularly in the afternoon. In shaded conditions with concentrate, respiratory rate did not differ between morning and afternoon (p > 0.05). Weight loss was greater (p < 0.05) in cows exposed to full sun. Cows in the sun with concentrate exhibited altered plasma glucose, triglyceride, and cholesterol levels (p < 0.05). Shaded cows had higher red blood cell counts but lower hemoglobin, hematocrit, mean corpuscular volume, and mean corpuscular hemoglobin levels (p < 0.05). Sun-exposed cows with concentrate had fewer monocytes, lymphocytes, and platelets but increased eosinophils (p < 0.05). Overall, cows kept in shade with concentrate demonstrated better heat tolerance and metabolic and hematological profiles.