Effects of heat stress and insulin sensitizers on pig adipose tissue

Authors: SEIBERT, J.T. - Iowa State University; ABUAJAMIEH, M. - Iowa State University; SANZ FERNANDEZ, M.V. - Iowa State University; Johnson, Jay; KVIDERA, S.K. - Iowa State University; HORST, E.A. - Iowa State University; MAYORGA, E.J. - Iowa State University; LEI, S. - Iowa State University; PATIENCE, J.F. - Iowa State University; ROSS, J.W. - Iowa State University; RHOADS, R.P. - Virginia Tech; JOHNSON, R.C. - Smithfield Foods, Inc; LONERGAN, S.M. - Iowa State University; BAUMGARD, L.H. - Iowa State University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2017
Publication Date: 1/29/2018
Citation: Seibert, J., Abuajamieh, M., Sanz Fernandez, M., Johnson, J.S., Kvidera, S., Horst, E., Mayorga, E., Lei, S., Patience, J., Ross, J., Rhoads, R., Johnson, R., Lonergan, S., Baumgard, L. 2018. Effects of heat stress and insulin sensitizers on pig adipose tissue. Journal of Animal Science. 96(2):510-520.

Interpretive Summary: Heat stress impedes efficient pork production by reducing feed intake, altering metabolism, and ultimately compromising the animal’s genetic potential for maximum growth. Paradoxically, animals, including pigs, reared during heat stress accumulate more carcass fat than their feed intake predicts, likely stemming from heat stress-induced hyperinsulinemia. However, less is known about how heat stress influences adipose fatty acid characteristics, which can affect meat processing, product quality, and shelf life. The study objectives were to investigate insulin’s potential role in carcass fat characteristics following heat stress exposure. Therefore, insulin sensitizing compounds (chromium and sterculic oil) were fed to pigs exposed to heat stress and the effect on thermoregulation, productivity, and carcass fat characteristics were evaluated during a 21 day heat stress challenge. As a result of this experiment, it was determined that heat stress exposure increased all body temperature measures overall compared to thermoneutral controls, and that pigs fed sterculic oil in heat stress conditions had greater body temperature compared to those fed the control diet or chromium. In addition to thermoregulatory changes, heat stress reduced feed intake and body weight gain overall compared to thermoneutral conditions, but productivity was not affected by dietary treatments. Although the moisture content of adipose tissue was greater in heat stress exposed pigs, the insulin sensitizers had no impact on adipose tissue characteristics. In summary, the negative impact of heat stress on fat quality in pigs appears to be related to moisture content rather than fatty acid composition.

Technical Abstract: Heat stress (HS) negatively impacts several swine production variables, including carcass fat quality. Pigs reared in HS have more adipose tissue than energetically predicted, explainable 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 1 of 5 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 3 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. In 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.