Metabolic changes induced by high temperatures may in part explain the altered carcass phenotype observed in heat-stressed pigs.

That is the conclusion of a group of researchers from Iowa State University and Virginia Polytechnic Institute and State University - with S.C. Pearce as the first-named author - following a study looking at the effects of heat stress and plane of nutrition on metabolism in growing pigs and published in Journal of Animal Science.

Heat stress (HS) jeopardises pig health, reduces performance variables and results in a fatter carcass, they explained. Whether HS directly or indirectly (via reduced feed intake) is responsible for the suboptimal production is not known.

Crossbred gilts (n=48; 35 ± 4kg bodyweight) were housed in constantly climate-controlled rooms in individual pens and exposed to:

1. thermal-neutral (TN) conditions (20°C; 35 to 50 per cent humidity) with ad libitum intake (n=18)
2. HS conditions (35°C; 20 to 35 per cent humidity) with ad libitum intake (n=24), or
3. pair-fed [PF in TN conditions (PFTN), n=6, to eliminate confounding effects of dissimilar feed intake (FI)].

Pigs in the TN and HS conditions were sacrificed at one, three or seven days of environmental exposure, whereas the PFTN pigs were sacrificed after seven days of experimental conditions.

Individual rectal temperature (Tr), skin temperature (Ts), respiration rates (RR) and feed intake (FI) were determined daily.

Pigs exposed to HS had an increase (P<0.01) in Tr (39.3°C versus 40.8°C) and a doubling in RR (54 vs. 107 breaths per minute).

Heat-stressed pigs had an immediate (day 1) decrease (47 per cent; P<0.05) in FI, and this magnitude of reduction continued to day 7; by design, the nutrient intake pattern for the PFTN controls mirrored the HS group.

By day 7, the TN and HS pigs gained 7.76 and 1.65 kg bodyweight, respectively, whereas the PFTN pigs lost 2.47 kg bodyweight.

Plasma insulin was higher (49 per cent; P<0.05) in day 7 HS pigs than the PFTN controls.

Compared with TN and HS pigs, on day 7, PFTN pigs had increased plasma NEFA concentrations (110 per cent; P<0.05).

Compared with TN and PFTN controls, on day 7, circulating N^τ-methylhistidine concentrations were increased (31 per cent; P < 0.05) in HS pigs.

Pearce and colleagues concluded that, despite similar nutrient intake, HS pigs gained more bodyweight and had distinctly different post-absorptive bioenergetic variables compared with PFTN controls.

Consequently, they added, these heat-induced metabolic changes may in part explain the altered carcass phenotype observed in heat-stressed pigs.

Reference

^{Pearce S.C., N.K. Gabler, J.W. Ross, J. Escobar, J.F. Patience, R.P. Rhoads and L.H. Baumgard. 2013. The effects of heat stress and plane of nutrition on metabolism in growing pigs. J. Anim. Sci. 91 (5):2108-2118. doi: 10.2527/jas.2012-5738}

Further Reading

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