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

Physical environment and limitations of heat stress indices Studies on heat stress focus on three types of animal response [51], (i) behavioural: seeking thermal cover, sheltering from wind, or reducing activity [52, 53, 54]; (ii) physiological: among the most common rectal and skin temperature, heart and respiration rates, and metabolic markers based on stress related hormones [33, 55, 56, 57, 58]; and (iii) animal performance: changes in body condition and animal production, such as body weight and milk yield [59, 52, 53, 60]. Translating these animal responses into energy expenditure without relying on calo- rimetry measurements is not possible [30], as a compromise, proxies of thermal stress using physical environment variables have been developed; though the limitations on the use of indi- ces has been recognised [44], the main problem being that the particular contribution of the variables that constitute the index disappears within the index. Another problem is that a ther- mal stress index may have solid foundations in expressing a particular thermal environment, Fig 5. Predicted mother weight (kg) against mother age (years) and calf age (days) 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.g005 PLOS ONE Heat stress and calf growth in red deer PLOS ONE | https://doi.org/10.1371/journal.pone.0233809 June 1, 2020 16 / 26