Effect of antioxidant and osmolyte enriched or energy-dense diet on heat−stressed fattening pigs

Heat stress negatively affects pig welfare, health and production. Osmolytes and antioxidants are considered potential mitigators of heat stress-induced damage. Modification of feed composition, specifically lower CP, also aims to reduce internal metabolic heat production. This study investigated the effect of an enriched or energy-dense (E-dense) diet on heat-stressed fattening pigs (n = 192 in total). Dietary treatments were administered (ad libitum) when pigs reached ± 80 kg. The control diet comprised 15% CP, 3.6% crude fat, 9.1 MJ/kg net energy, 0.4 mg/kg inorganic selenium (Se), and 100 ppm vitamin E; the enriched diet contained the same chemical composition but was supplemented with 0.2 mg/kg inorganic Se, 0.2 mg/kg selenomethionine, 200 ppm vitamin E, 200 ppm vitamin C and 0.1% betaine; the E-dense diet featured 13.6% CP, 6.6% crude fat, and increased energy (9.7 MJ/kg) and lysine content. The lysine:energy ratio of all three diets was the same. A 1-week heat wave (± 30 °C and Temperature-Humidity Index of ± 78.4) was induced 2 times when pigs were 20 and 22 weeks old. Physiological parameters and performance parameters were assessed weekly. At the end of the trial, carcass and meat quality were evaluated. Additive enrichment of the diet resulted in a numerically increased daily gain over the 6-week trial compared to the control group (925 vs 891 g/day), P = 0.090). The E-dense group had a higher increase in rectal temperature during heat load compared to the control group (0.38 vs 0.28 °C, P = 0.018). Over the entire trial, the E-dense group had a higher feed conversion ratio than the control group (2.95 vs 2.67, P = 0.006). Carcass traits revealed increased fat thickness of 0.9 mm in the E-dense group (P = 0.035), along with lower lean meat content (-1.1%, P = 0.002). The meat of the enriched group displayed elevated vitamin E and Se levels (P < 0.001), which may be beneficial for the consumer. Overall, the nutritional strategies did not significantly prevent physiological heat stress or enhance performance, but the supplementation of antioxidants and osmolytes tended to ameliorate daily gain over the entire trial.