Heat stress jeopardises pig health, reduces performance variables and results in a fatter carcass, according to S.C. Pearce of Iowa State University and co-authors there and Virginia Polytechnic Institute and State University. Whether heat stress directly or indirectly (via reduced feed intake) is responsible for the sub-optimal production is not known, they report in their latest paper in Journal of Animal Science.

Crossbred gilts (n=48; 35±±4kg bodyweight) were housed in constant 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. heat stress (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.

Pigs in the TN and HS conditions were sacrificed at one, three or seven days of environmental exposure while the PFTN pigs were sacrificed after seven days of experimental conditions. Individual rectal temperature (Tr), skin temperature (Ts), respiration rates (RR) and FI were determined daily.

Pigs exposed to HS had an increase (P<0.01) in rectal temperature (39.3 versus 40.8°C) and a doubling in respiration rates (54 versus 107bpm).

HS pigs had an immediate (day 1) decrease (47 per cent; P<0.05) in feed intake 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 1.65kg bodyweight, respectively, while the PFTN pigs lost 2.47kg bodyweight.

Plasma insulin was increased (49 per cent; P<0.05) in HS pigs compared to PFTN controls on day 7.

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

Also on day 7, compared to TN and PFTN controls, circulating N_T-methylhistidine levels were increased (31 per cent; P<0.05) in HS pigs.

In summary, despite similar nutrient intake, Pearce and co-authors remarked that the HS pigs gained more bodyweight and had distinctly different post-absorptive bioenergetic variables from the pair-fed (PFTN) controls. Consequently, 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. March 5, 2013 jas.2012-5738. doi: 10.2527/jas.2012-5738

Further Reading You can view the full report by clicking here.

April 2013