Effects of high ambient temperature on meat quality, serum hormone concentrations, and gene expression in the longissimus dorsi muscle of finishing pigs

Abstract

This study examined the effect of high ambient temperature on the growth performance, meat quality, activity of the hypothalamo-pituitary-adrenal axis, and related gene expression in finishing pigs. All pigs received the same corn-soybean meal-based diet. Twenty-four Landrace pigs (initial bodyweight of 77.64 ± 0.67 kg) were assigned into three groups: Group 1 (22°C, ad libitum, 81% humidity); Group 2 (22°C, pair-fed to Group 3, 78% humidity); Group 3 (35°C, ad libitum, 78% humidity). The experiment lasted for 30 days. The average daily feed intake and average daily gain were markedly reduced in Group 3 compared with Group 1 (P < 0.05). The intramuscular fat content of longissimus dorsi muscle was decreased in Groups 2 and 3 (P < 0.05) when compared with Group 1. Muscle pH at 24 h post-mortem was higher in Group 3 (P < 0.05) compared with Groups 1 and 2, and the pH at 48 h post-mortem was higher in Group 3 (P < 0.05) than in Group 1. The MyHC IIb transcript abundance was lower in Group 3 (P < 0.05) than in the other two groups and that of MyHC IIx was higher in Group 3 than in Group 2 (P < 0.05). The relative abundance of calpastatin transcripts was lower in Group 3 (P < 0.05) than in the other two groups. Cortisol concentrations were lower in Group 3 (P < 0.05) than in Groups 1 and 2 on Day 3. Corticotropin releasing hormone concentrations in Group 3 were lower at Day 3 (P < 0.05) when compared with Group 2 and at Day 30 when compared with Groups 1 and 2. Glucagon concentrations were lower in Group 3 (P < 0.05) when compared with Groups 1 and 2 on Day 30. These results indicate that the decreased intramuscular fat content of pigs at high ambient temperature results from the reduction in feed intake. Independently of its effect on feed intake, high ambient temperature affected the meat quality of finishing pigs by increasing pH value probably due to the lower serum concentrations of corticotropin releasing hormone, and inducing a transition of muscle fibre types from IIb to IIx.