Performance and carcass composition of pigs from two sire lines are affected differently by ambient temperature

Context. Differences among breeds or lines of pigs in terms of growth and carcass characteristics may be affected by rearing environment (genetic x environment interaction). Aims. The present study compared the growth performance and carcass composition of pigs from two sire lines reared under constant thermoneutral (22 degrees C; TN) or high ambient temperature (33 degrees C; HT) conditions. Methods. Hampshire (HAM) and synthetic-cross (SYN) castrated male pigs (n = 12 per group; 32.0 +/- 2.0 kg) were kept in individual pens at either 22 degrees C (TN) or 33 degrees C (HT) for 55 days (two experimental phases: 0-27 and 28-55 days) following an adaptation period of 7 days. Throughout the experimental period, growth performance and body composition (by dual-energy X-ray absorptiometry on Days 27 and 55) were assessed, and a range of other measurements (serum parameters and physiological responses), which were divided into four measurement groups, was taken on 9 days. Key results. Irrespective of genetic line (G), the pigs in the HT treatment had lower average daily feed intake values (P < 0.001, by 29% and 41%) than did the pigs in the TN treatment during both experimental phases (0-27 and 28-55 days). During the second growth phase, the average daily gain of the SYN pigs in the HT treatment was reduced by 50%, whereas that of the HAM pigs was reduced by 24% (P < 0.05 for G x ambient temperature (AT)). On Days 27 and 55, pig bodyweight was lower (P < 0.05) in the HT treatment than in the TN treatment. On Day 27, a G x AT interaction was detected for backfat thickness (P < 0.05); among the SYN pigs, the value of this trait was lower (16%; P < 0.05) in the HT treatment than in the TN treatment, while for the HAM pigs, it was not influenced by treatment type. Conclusion. Despite progeny from both genetic lines being affected negatively by high AT, the purebred HAM pigs were less affected by the high AT conditions than were the pigs from the synthetic line. Implication. The present findings suggest that individual farm conditions and AT are among the most important factors to consider before implementing a G. (AU)