Three experiments were carried out in environmentally controlled rooms. In the Exp. 1, a total of 54 crossbred weanling pigs with an average initial age of 19.7 d and BW of 5.95 ± 0.84 kg were used and were allotted to a 2 × 3 factorial arrangement using 2 ambient temperatures (23.7 or 40.5°C during d 14 to 28) and 3 supplemental concentrations of dietary Cr (0, 1000 o 2000 µg/kg) as Cr(III) picolinate. Piglets were grouped into 3 blocks by sex and initial BW and randomly allotted to 6 treatment groups with 3 pigs/pen. In Exp. 2, a total of 54 pigs (BW of 5.94 ± 1.29 kg) were allotted in the same treatment arrangement but with different ambient temperatures (26.5 or 16.0°C during d 14 to 26 post-weaning). In Exp. 3, a total of 36 pigs (BW of 6.40 ± 0.72 kg) were allotted in the same treatment arrangement with ambient temperatures of 25.9 or 13.8°C during d 14 to 28 post-weaning. The treatment structure and other procedures of Exp. 2 and 3 were the same as Exp. 1. During d 0 to 14 of all experiments, a neutral ambient temperature (NT) was maintained. Animal BW and feed intake were measured weekly. Blood samples were collected in the d1, d4, and d13 (d11 in Exp. 2) after the change of ambient temperature for analysis of glucose and cortisol concentration in the plasma. Respiratory rate was visually measured by counting flank movements over a period of 1 min in resting pigs (between 19:30 and 22:00 h).
In Exp. 1, pigs in high ambient temperature (HT) gained less BW (575 vs. 663 g/d; P < 0.001) and consumed less feed (926 vs. 1,074 g/d; P = 0.001) than pigs in NT during d 14 to 28. However, G:F was not affected by ambient temperature (0.623 vs. 0.618 g/g; P = 0.702). Dietary Cr had no effect on growth performance. Pigs in HT had less plasma cortisol (42.0 vs. 53.7 ng/mL; P = 0.012) and glucose (6.68 vs. 6.96 ng/mL; P = 0.018). Respiratory rate of pigs in HT was greater compared with the pigs in NT (114.6 vs. 65.0 breaths/min; P < 0.001) on d 27. In Exp. 2 and 3 (pooled), pigs in low ambient temperature (LT) had decreased G:F (0.636 vs. 0.663 g/g; P < 0.01) associated with a tendency toward a greater ADFI (1,026 vs. 942 g; P = 0.079) during d 14 to 26 (28). Ambient temperature or dietary Cr supplementation had no effect on blood measurements. In Exp. 3, the respiratory rate measured on d 22 and 27 was less (43.2 vs. 54.2 breaths/min and 42.2 vs. 57.0 breaths/min, respectively; P < 0.001) in the pigs in LT than the pigs in NT with no effects of dietary Cr supplementation.
In conclusion, the growth performance is affected by thermal stress and plasma cortisol decreased by heat stress, but these effects were not modulated by dietary Cr.
BG Kim, MD Lindemann and GL Cromwell. 2009. Journal of Animal Science. 87:1695-1704.