Effect of hot temperatures on the hematological parameters, health and performance of calves.

The objective of this paper was to evaluate the effects of high temperatures on calves. The hypothesis that the red and white blood cells, health, and performance of calves would be influenced by the temperature period at birth and gender was tested. Sixty-three Holstein calves were used. They were reared in individual hutches from the second day of life to weaning at the age of 8 weeks. All calves were allotted to treatment groups according to the temperature period at birth: moderate temperature period 1 (MT1), high temperature period (HT), moderate temperature period 2 (MT2). The same conditions of nutrition were ensured. We recorded 62 summer days and 14 tropical days during HT. Sixty-six days with a value above 72.0 of the temperature-humidity index (THI) and 26 with values greater than 78.0 were found. No significant differences were found in red blood cells with the exception of hemoglobin between MT1 and MT2 (p = 0.031) during the 8th week. Significant differences were observed among treatment groups in the percentage of eosinophiles during the 6th week (p = 0.044). The HT calves had the least body weight from the first week to weaning (p = 0.053) and the highest water consumption (p = 0.042). The results emphasize the ability of dairy calves to maintain homeostasis during prolonged periods of heat stress. The exposure to high temperatures resulted only in a significant decrease of starter concentrate consumption and reduced growth.