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

kg for females and males, respectively. At weaning time the predicted calf body masses for THI = 67 (0.5 quantile) were 42.1 kg for females and 48.0 kg for males. Calves of both sexes were 0.6 kg heavier than average calf weight when they experienced low heat stress (THI = 60, 0.1 quantile) but were 0.4 kg lighter than average calf weight under high heat stress (THI = 72, 0.9 quantile) (Table 2, Fig 2). In relation to the animal variables fitted in the same model, the growth rate of males was higher than that in females (estimate [male] = 0.008, se = 0.002, p = 0.001), and calf growth rate increased with mother age following AIC information crite- rion but not corroborated by p-values (estimate = 0.117, se = 0.135, p = 0.391). After control- ling for the effect of mother age, mother weight had a negative effect of the rate of calf growth (estimate = - 0.001, se = 0.0001, p = 0.023), and as calf grew older its rate of growth decreased, only confirmed by AIC criterion (estimate = - 0.001, se = 0.0001, p = 0.137). Table 2. Coefficients and statistics of an exponential asymptotic mixed linear model on calf weight (Kg) controlling for animal and a thermal stress index (THI) variables. 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 5.41 5.40 Asym intercept mother 8.06 6.69 6.73 6.68 5.88 5.93 Asym intercept calf 9.76 9.31 9.35 9.23 8.07 8.04 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 ��� 50.433 9.716 8659 5.19 <0.001 Asym mother wt Y ��� Y ��� Y ��� Y ��� Y ��� 0.299 0.030 8659 9.97 <0.001 Asym sex (male) — Y ��� Y ��� Y ��� Y ��� -0.443 5.146 8659 -0.08 0.931 Asym mother age (yr) — — Y ��� Y ��� Y ��� -0.724 0.150 8659 -4.80 <0.001 Asym calf age (d) — — — Y Y �� -0.169 0.056 8659 -2.96 0.003 Asym THI — — — — Y ��� 0.186 0.059 8659 3.16 0.002 Asym THI x sex (male) — — — — — 0.179 0.076 8659 2.35 0.019 R0 intercept Y ��� Y ��� Y ��� Y ��� Y ��� 6.129 0.621 8659 9.85 <0.001 R0 mother wt Y ��� Y ��� Y ��� Y ��� Y ��� 0.025 0.002 8659 8.43 <0.001 R0 sex (male) — Y ��� Y ��� Y ��� Y ��� 0.683 0.078 8659 8.68 <0.001 R0 mother age (yr) — — Y ��� Y ��� Y ��� 0.059 0.010 8659 5.67 <0.001 R0 calf age (d) — — — Y ��� Y -0.004 0.003 8659 -1.30 0.192 lrc intercept Y ��� Y ��� Y ��� Y ��� Y ��� -4.100 0.175 8659 -23.36 <0.001 lrc mother wt Y �� Y �� Y �� Y ��� Y � -0.001 0.0001 8659 -2.26 0.023 lrc sex (male) — Y � Y � Y � Y 0.117 0.136 8659 0.85 0.391 lrc mother age (yr) — — Y ��� Y ��� Y ��� 0.008 0.002 8659 3.90 0.001 lrc calf age (d) — — — Y � Y -0.001 0.0001 8659 -1.48 0.137 lrc THI — — — — Y ��� -0.009 0.001 8659 -6.29 <0.001 lrc THI x sex (male) — — — — — -0.002 0.001 8659 -1.36 0.173 AIC 35966.4 35733.7 35583.5 35514.4 35408.4 35405.1 ΔAIC 561.3 328.5 178.4 109.2 3.32 0

weights AIC 1.08E-122 3.82E-72 1.52E-39 1.59E-24 0.16 0.84 Kullback–Leibler 1 1 1 1 0.84 — Asym: horizontal asymptote; R0: response at calf age = 0; lrc: natural logarithm of the rate constant. THI: thermal stress index based on air temperature and air humidity; Y: term included in the model, Model 0–4 and final: six competing models in the model selection process; calf age: in days; mother age: in years; calf cohort: calf year of birth; df: degrees of freedom; AIC: Akaike information criterion; wAIC: AIC weights of the model; ΔAIC: delta AIC; Kullback–Leibler discrepancy ratio: normalised probability that reference model in column i is to be preferred over model in column i + 1; significance of the terms p-value: ��� = 0–0.001, �� = 0.001–0.01, � = 0.01–0.05, + = 0.05–0.1. Female is the sex level of reference. https://doi.org/10.1371/journal.pone.0233809.t002 PLOS ONE Heat stress and calf growth in red deer PLOS ONE | https://doi.org/10.1371/journal.pone.0233809 June 1, 2020 7 / 26