Department of Animal Science, Iowa State University, Ames, IA.
Department of Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA.
J Anim Sci. 2018 Mar 6;96(2):510-520. doi: 10.1093/jas/skx067.
Heat stress (HS) negatively impacts several swine production variables, including carcass fat quality and quantity. Pigs reared in HS have more adipose tissue than energetically predicted, explainable, in part, by HS-induced hyperinsulinemia. Study objectives were to evaluate insulin's role in altering fat characteristics during HS via feeding insulin-sensitizing compounds. Forty crossbred barrows (113 ± 9 kg BW) were randomly assigned to one of five environment by diet treatments: 1) thermoneutral (TN) fed ad libitum (TNAL), 2) TN and pair-fed (TNPF), 3) HS fed ad libitum (HSAL), 4) HS fed ad libitum with sterculic oil (SO) supplementation (HSSO; 13 g/d), and 5) HS fed ad libitum with dietary chromium (Cr) supplementation (HSCr; 0.5 mg/d; Kemin Industries, Des Moines, IA). The study consisted of three experimental periods (P). During P0 (2 d), all pigs were exposed to TN conditions (23 ± 3 °C, 68 ± 10% RH) and fed ad libitum. During P1 (7 d), all pigs received their respective dietary supplements, were maintained in TN conditions, and fed ad libitum. During P2 (21 d), HSAL, HSSO, and HSCr pigs were fed ad libitum and exposed to cyclical HS conditions (28 to 33 °C, 58 ± 10% RH). The TNAL and TNPF pigs remained in TN conditions and were fed ad libitum or pair-fed to their HSAL counterparts. Rectal temperature (TR), respiration rate (RR), and skin temperature (TS) were obtained daily at 0600 and 1800 h. At 1800 h, HS exposed pigs had increased TR, RR, and TS relative to TNAL controls (1.13 °C, 48 bpm, and 3.51 °C, respectively; P < 0.01). During wk 2 and 3 of P2, HSSO pigs had increased 1800 h TR relative to HSAL and HSCr (~0.40 and ~0.42 °C, respectively; P ≤ 0.05). Heat stress decreased ADFI and ADG compared to TNAL pigs (2.24 vs. 3.28 and 0.63 vs. 1.09 kg/d, respectively; P < 0.01) and neither variable was affected by SO or Cr supplementation. Heat stress increased or tended to increase moisture content of abdominal (7.7 vs. 5.9%; P = 0.07) and inner s.c. (11.4 vs. 9.8%; P < 0.05) adipose depots compared to TNAL controls. Interestingly, TNPF pigs also had increased adipose tissue moisture content and this was most pronounced in the outer s.c. depot (15.0 vs. 12.2%; P < 0.01) compared to TNAL pigs. Heat stress had little or no effect on fatty acid composition of abdominal, inner, and outer s.c. adipose tissue depots. In summary, the negative effects of HS on fat quality do not appear to be fatty acid composition related, but may be explained by increased adipose tissue moisture content.
热应激（HS）对几个猪生产变量产生负面影响，包括胴体脂肪质量和数量。在 HS 中饲养的猪比能量预测的有更多的脂肪组织，部分原因是 HS 诱导的高胰岛素血症。研究目的是通过喂养胰岛素增敏化合物来评估胰岛素在 HS 期间改变脂肪特征的作用。40 头杂交阉公猪（113±9kgBW）随机分为五种环境-饮食处理之一：1）热中性（TN）自由采食（TNAL），2）TN 配对采食（TNPF），3）HS 自由采食（HSAL），4）HS 自由采食加蓖麻油（SO）补充剂（HSSO；13g/d），5）HS 自由采食加铬（Cr）补充剂（HSCr；0.5mg/d；KeminIndustries，DesMoines，IA）。研究分为三个实验期（P）。在 P0（2d）期间，所有猪都暴露于 TN 条件（23±3°C，68±10%RH）并自由采食。在 P1（7d）期间，所有猪都接受了各自的膳食补充剂，在 TN 条件下保持，并自由采食。在 P2（21d）期间，HSAL、HSSO 和 HSCr 猪自由采食，并暴露于周期性 HS 条件下（28 至 33°C，58±10%RH）。TNAL 和 TNPF 猪保持在 TN 条件下，并自由采食或配对采食以匹配 HSAL 猪。每天在 0600 和 1800h 测量直肠温度（TR）、呼吸率（RR）和皮肤温度（TS）。在 1800h，与 TNAL 对照相比，暴露于 HS 的猪的 TR、RR 和 TS 增加（分别为 1.13°C、48bpm 和 3.51°C；P<0.01）。在 P2 的第 2 和第 3 周，HSSO 猪的 1800hTR 与 HSAL 和 HSCr 相比增加（分别约为 0.40 和 0.42°C；P≤0.05）。与 TNAL 猪相比，HS 降低了 ADFI 和 ADG（分别为 2.24 与 3.28kg/d 和 0.63 与 1.09kg/d；P<0.01），SO 和 Cr 补充剂对其没有影响。HS 增加了腹部（7.7%与 5.9%；P=0.07）和内部皮下（11.4%与 9.8%；P<0.05）脂肪组织沉积的水分含量与 TNAL 对照组相比。有趣的是，TNPF 猪的脂肪组织水分含量也增加了，在外皮下（15.0%与 12.2%；P<0.01）与 TNAL 猪相比最为明显。HS 对腹部、内部和外部皮下脂肪组织沉积的脂肪酸组成几乎没有影响。总之，HS 对脂肪质量的负面影响似乎与脂肪酸组成无关，而可能与脂肪组织水分含量增加有关。
