Effects of heat stress on adipose tissue fatty acid composition and moisture content in pigs

Abstract Text: Heat stress (HS) negatively impacts several production variables in swine, including carcass fat quality. Study objectives were to evaluate insulin’s role (via feeding insulin sensitizing compounds) in decreasing fat quality during HS. Forty crossbred barrows (113±9 kg BW) were randomly assigned to 1 of 5 treatments during 2 experimental periods: 1) thermoneutral (TN) ad libitum feed intake control (TNAL), 2) TN pair-fed control (TNPF), 3) HS ad libitum (HSAL), 4) HS ad libitum with dietary sterculic oil (HSSO; 13 g/d), and 5) HS ad libitum with dietary chromium propionate (HSCr; 0.5 mg/d; Kemin Industries, Des Moines, IA). During period 1 (7 d), all pigs were exposed to TN conditions (23±3°C, 68±10% RH) and fed ad libitum. During period 2 (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 (to eliminate the confounding effect of dissimilar nutrient intake), respectively. Rectal temperature (T_r), respiration rate, and skin temperature were increased (0.9°C, 37 bpm, and 2.5°C, respectively) in HS pigs. Interestingly, HSSO increased T_r relative to HSAL and HSCr (0.45 and 0.42°C, respectively) during the last week of period 2 (P < 0.05). HS decreased feed intake and ADG compared to TNAL (2.43 vs. 3.26 kg/d and 0.74 vs. 1.09 kg/d, respectively; P < 0.01) and neither variable was affected by SO or Cr supplementation. Moisture content was increased in pigs from all HS treatments compared to TNAL controls in abdominal (7.7 vs. 5.9%; P < 0.09) and inner subcutaneous adipose tissue (11.4 vs. 9.8%; P < 0.06) depots. Interestingly, TNPF pigs had increased adipose tissue moisture content in abdominal (7.3 vs. 5.9%; P < 0.01), inner subcutaneous (11.0 vs. 9.8%; P < 0.07), and outer subcutaneous (14.9 vs. 12.1%; P < 0.01) depots compared to TNAL pigs. HS had little or no effect on fatty acid (FA) composition of abdominal, inner, and outer subcutaneous adipose tissue depots. Feeding SO decreased the desaturase index in the abdominal (0.36 vs. 0.43; P < 0.01), inner subcutaneous (0.46 vs. 0.52; P < 0.01), and outer subcutaneous (0.51 vs. 0.55; P < 0.01) adipose tissue. In summary, HS did not alter FA composition in any adipose depot, but both TNPF and HS markedly increased adipose tissue moisture content.

Keywords: heat stress, swine, adipose tissue