Performance and indicators of thermal stress in Holstein x Guzerá female calves fed mild replacer and probiotic in a semi-arid region of Brazil

Abstract

An experiment was conducted to study the effects of feeding a milk replacer with or without addition of an acidifying probiotic until weaning at 6 weeks of age, and of climatic conditions in a semi-arid region during four dry summer months on the performance of female crossbred (Holstein x Guzera) calves from 7 to 60 days of age. In a factorial arrangement of two principal treatment factors in complete protection against solar radiation in individual hutches, versus supplemental tree shade for the hutches, and use or not of the probiotic (four treatments), the effects on liveweight gain, intake of water and of dry matter, heart rate, respiration rate, and rectal temperature were determined. The results showed that provision of supplementary shade was unnecessary since its small effect on the environmental temperature did not improve animal performance; neither did use of the probiotic during the dry season benefit health and performance of the calves, probably because of little animal exposure to infectious agents, unlike what commonly occurs in the rainy season. The climatic conditions recorded of high maximum daily ambient temperature in the morning (34°C) and afternoon (36.2°C) but low relative humidity (46 to 67%) did not produce signs of thermal discomfort as indicated by the physiological indicators recorded (In Portuguese).