Heat abatement during the pre-weaning period: Effects on growth, feed efficiency, and metabolites of male Holstein calves

Heat stress abatement strategies for pre-weaned dairy calves are seldom evaluated. We conducted an experiment to evaluate the effects of heat stress abatement during the pre-weaning phase on calf hood performance. The hypotheses of the current experiment were that provision of solid shade and solid shade + fans would reduce air temperature and increase air speed to the extent that it would improve growth and feed efficiency of pre-weaned male Holstein calves compared with calves housed outside. In addition, we hypothesized that provision of fans would improve air quality, measured by reduce air ammonia (NH3) concentration and bacterial counts, to the extent that it would improve health of calves. The objectives of the current experiment were to evaluate the effects of provision of solid shade and solid shade + fans on growth and feed efficiency. Furthermore, we aimed to determine the effect of provision of fans on NH3 concentration and bacteria counts in the air and health scores during the pre-weaning phase. The environmental conditions during our experiment were representative of heat stress. The provision of heat stress abatement through shade + fans increased air velocity by nearly 3-fold, but it only reduced the air temperature by 1.3 to 3.2 °C. Thus, throughout the experiment and within 24-h periods, calves from all treatments were exposed to heat stress. This may be the reason why we did not detect an effect of treatment on feed intake, ADG, feed efficiency, and BW at weaning. The heat abatement strategies used in this experiment, however, improved welfare and health of calves measured by rectal temperature, respiratory frequency, and URTS. An important finding of our experiment that warrants further investigation was the difference in wither height at weaning between the HS and SHF treatments. We speculate that this could be a consequence of heat stress induced changes in post-absorptive nutrient partitioning and/or bone metabolism, but these theories remain to be proved