Heat stress reduces growth rate of red deer calf: Climate warming implications

during the study (end of May–mid-September) was very low (45–55%) when compared with average values of tropical areas (80%), where air humidity is a major contributor to thermal stress in livestock [43, 55, 63] and probably in wild species. It is plausible that increasing humidity up to a 55% threshold might have contributed to decrease thermal stress, for exam- ple, by being a surrogate index of rainfall and so promoting sward growth in our experimental arena, a more dense sward reduces reflective solar radiation from the ground as so mitigates heat [5]. Solar radiation did not have any significant contribution in calf growth after air tem- perature, humidity and wind speed were controlled for. Yamamoto et al [64] found that nei- ther the rate of heat production nor heart rate of Holstein heifers responded to solar radiation in summer, though rectal temperature increased under no shade conditions. In moose (Alces alces), a species which is sensitive to suffer heat stress over 14˚C, changes in activity rates were associated to air temperature but not to solar radiation in boreal forest, activity increased at night during hot periods [53]. Fig 7. Predicted mother weight (kg) against daily mean wind speed (m�s-1) and solar radiation (MJ�m-2) and the additive effect of bearing a male or a female through lactation from model in Table 6. Dashed line: ± standard error. Response variable has been centred by subtraction of the mean value. https://doi.org/10.1371/journal.pone.0233809.g007 PLOS ONE Heat stress and calf growth in red deer

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