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

Table 4 shows the contribution of animal variables (mother and calf age, mother weight and calf sex) together with physical environment variables (T, Hr, SR, W) to calf growth. The final model included all animal variables and physical environment variables except SR and the interactions SR x calf sex and W x calf sex on AIC model selection basis (Table 4). High temperature and strong wind hampered calf growth, as indicated by the negative estimates of these two coefficients in the model (T estimate = - 0.006, se = 0.003; p = 0.054; W estimate = - 0.02, se = 0.001, p = 0.069), while air humidity had a positive effect on calf growth rate (Hr esti- mate = 0.003, se = 0.001, p = 0.009, Fig 3). Air temperature had the stronger effect on calf growth rate of all physical environment variables, as shown in Fig 3. Calf growth rate responded to animal variables in a similar way to that described for THI and THIWS stress indices models (Table 4). S3 Fig shows actual data of males and females growth against calf age, highlighting the large variability across records. Calf growth increased asymptotically with calf age and this effect was hampered as air temperature increased, but less in males than in females as indicated by the interaction T × calf sex selected on AIC basis, though not supported by p-value significance (male calf effect estimate = 0.002; se = 0.004; p = 0.609; Table 4, Fig 3). Air Humidity had the inverse effect, the more humid the environment the faster calf growth

Table 3. Coefficients and statistics of an exponential asymptotic mixed linear model on calf weight (Kg) controlling for animal and a thermal stress index (THIWS) variables. THIWS: stress index based on air temperature, humidity, wind speed and solar radiation; Female is the sex level of reference. Acronyms as in Table 2. Random effects model 0 model 1 model 2 model 3 model 4 final model Groups (sd) Asym intercept calf cohort 5.68 5.73 6.17 6.26 4.98 4.98 Asym intercept mother 8.06 6.69 6.73 6.68 5.40 5.43 Asym intercept calf 9.76 9.31 9.35 9.23 7.42 7.41 Residual 1.44 1.43 1.42 1.42 1.41 1.41 Fixed effects Estimate se df t-value P Asym intercept Y ��� Y ��� Y ��� Y ��� Y ��� 51.127 7.990 8659 6.398 <0.001 Asym mother wt Y ��� Y ��� Y ��� Y ��� Y ��� 0.254 0.025 8659 10.091 <0.001 Asym sex (male) — Y ��� Y ��� Y ��� Y ��� 2.090 2.834 8659 0.737 0.461 Asym mother age (yr) — — Y ��� Y ��� Y ��� -0.564 0.131 8659 -4.279 <0.001 Asym calf age (d) — — — Y Y �� -0.148 0.049 8659 -3.006 0.003 Asym THIWS — — — — Y ��� 0.076 0.018 8659 4.038 0.001 Asym THIWS x sex (male) — — — — — 0.072 0.024 8659 2.984 0.003 R0 intercept Y ��� Y ��� Y ��� Y ��� Y ��� 5.979 0.626 8659 9.539 <0.001 R0 mother wt Y ��� Y ��� Y ��� Y ��� Y ��� 0.025 0.003 8659 8.570 <0.001 R0 sex (male) — Y ��� Y ��� Y ��� Y ��� 0.690 0.076 8659 9.031 <0.001 R0 mother age (yr) — — Y ��� Y ��� Y ��� 0.058 0.010 8659 5.609 <0.001

R0 calf age (d) — — — Y ��� Y -0.003 0.003 8659 -1.061 0.288 lrc intercept Y ��� Y ��� Y ��� Y ��� Y ��� -4.041 0.145 8659 -27.697 <0.001 lrc mother wt Y �� Y �� Y �� Y ��� Y + -0.001 0.000 8659 -1.914 0.056 lrc sex (male) — Y � Y � Y � Y 0.122 0.097 8659 1.256 0.209 lrc mother age (yr) — — Y ��� Y ��� Y ��� 0.006 0.002 8659 3.420 0.001 lrc calf age (d) — — — Y � Y � -0.002 0.001 8659 -2.631 0.009 lrc THIWS — — — — Y ��� -0.004 0.001 8659 -8.058 <0.001 lrc THIWS x sex (male) — — — — — -0.001 0.001 8659 -2.047 0.041 AIC 35966.43 35733.66 35583.53 35514.35 35421.7 35417.32 ΔAIC 549.11 316.34 166.21 97.03 4.38 0 weights AIC 5.18E-120 1.83E-69 7.26E-37 7.63E-22 0.10 0.90 Kullback–Leibler 1 1 1 1 0.90 — https://doi.org/10.1371/journal.pone.0233809.t003 PLOS ONE Heat stress and calf growth in red deer PLOS ONE | https://doi.org/10.1371/journal.pone.0233809 June 1, 2020 9 / 26