Department of Animal Science, Iowa State University, Ames, IA.
J Anim Sci. 2018 Apr 3;96(3):941-949. doi: 10.1093/jas/skx036.
Identifying traits associated with susceptibility or tolerance to heat stress (HS) is a prerequisite for developing strategies to improve efficient pork production during the summer months. Study objectives were to determine the relationship between the thermoregulatory and production responses to acute HS in pigs. Prepubertal gilts (n = 235; 77.9 ± 1.2 kg BW) were exposed to a thermoneutral (TN) period (P1, 24 h; 21.9 ± 0.5 °C, 62 ± 13% RH; fed ad libitum) followed immediately by a subsequent acute HS period (P2, 24 h; 29.7 ± 1.3 °C, 49 ± 8% RH; fed ad libitum). Rectal temperature (TR), skin temperature (TS), and respiration rate (RR) were monitored and BW and feed intake (FI) were determined. All pigs had increased TR, TS, and RR (0.80 °C, 5.65 °C, and 61.2 bpm, respectively; P < 0.01) and decreased FI and BW (29% and 1.10 kg, respectively; P < 0.01) during P2 compared to P1. Interestingly, body temperature indices did not explain variation in FI during P2 (R2 ≤ 0.02). Further, the percent change in BW during P2 was only marginally explained by each body temperature index (R2 ≤ 0.06) or percent change in FI (R2 = 0.14). During HS, TR was strongly correlated with P1 TR (r = 0.72, P < 0.01), indicating a pig's body temperature during TN conditions predicts the severity of hyperthermia during HS. Additionally, the change in TR (ΔTR, HS TR - TN TR) was larger in pigs retrospectively classified as susceptible (SUS) as compared to tolerant (TOL) pigs (1.05 vs. 0.51 °C, respectively; P < 0.01). In summary, thermoregulatory responses and production variables during acute HS are only marginally related. Further, changes in BW and FI were unexpectedly poorly correlated during acute HS (r = 0.34; P < 0.01). Collectively, suboptimal growth is largely independent on the thermoregulatory response and hypophagia during acute HS. Consequently, incorporating solely body temperature indices into a genetic index is likely insufficient for substantial progress in selecting HS tolerant pigs.
鉴定与耐热应激（HS）易感性或耐受性相关的特征是开发夏季提高猪肉生产效率策略的前提。本研究的目的是确定猪在急性 HS 下的体温调节和生产反应之间的关系。青春期前的母猪（n = 235；77.9 ± 1.2 kg BW）先经历一个热中性（TN）期（P1，24 h；21.9 ± 0.5°C，62 ± 13% RH；自由采食），随后立即进入随后的急性 HS 期（P2，24 h；29.7 ± 1.3°C，49 ± 8% RH；自由采食）。监测直肠温度（TR）、皮肤温度（TS）和呼吸率（RR），并测定 BW 和采食量（FI）。与 P1 相比，所有猪在 P2 时 TR、TS 和 RR 均增加（0.80°C、5.65°C 和 61.2 bpm，分别；P < 0.01），FI 和 BW 减少（29%和 1.10 kg，分别；P < 0.01）。有趣的是，体温指数不能解释 P2 期间 FI 的变化（R2 ≤ 0.02）。此外，P2 期间 BW 的变化仅被每个体温指数（R2 ≤ 0.06）或 FI 的变化（R2 = 0.14）略有解释。在 HS 期间，TR 与 P1 TR 呈强相关（r = 0.72，P < 0.01），表明猪在 TN 条件下的体温可预测其在 HS 期间的高热程度。此外，回溯分类为易感（SUS）的猪与耐受力（TOL）猪相比，TR 的变化（ΔTR，HS TR - TN TR）更大（1.05 与 0.51°C，分别；P < 0.01）。总之，急性 HS 期间的体温调节反应和生产变量仅略有相关。此外，急性 HS 期间 BW 和 FI 的变化出乎意料地相关性较差（r = 0.34；P < 0.01）。总的来说，亚最佳生长在很大程度上与急性 HS 期间的体温调节反应和食欲减退无关。因此，仅将体温指数纳入遗传指数中不太可能在选择耐热应激猪方面取得重大进展。
