Effects of lipoic acid on performance, slaughter performance, intestinal digestive enzymes and apparent digestibility of nutrients in heat-stressed broilers.

This study aims to investigate the impact of supplementing α-lipoic acid (ALA) on the growth performance, intestinal digestive enzymes, and apparent digestibility of nutrients in broiler chickens under high ambient temperature. A total of 160 28-day-old Cobb broiler chickens were randomly divided into four groups with four replicates per group and ten chickens per replicate. The experiment employed a 2 × 2 factorial design, consisting of two diets (basal diet or diet supplemented with 250 mg/kg ALA) and two temperature conditions (24 ± 1 ℃ or 33 ± 1 ℃). Starting from day 28, chickens were raised either under thermos neutral conditions (24 ± 1 ℃ from 18:00 to 08:00) or subjected to cyclic heat stress (33 ± 1 ℃ from 08:00 to 18:00 and 24 ± 1 ℃ from 18:00 to 08:00). Feed intake, body weight, and fecal output were recorded from day 28 onwards; with average daily feed intake and average daily weight gain were calculated. Serum biochemical parameters, antioxidant levels, and intestinal enzyme activities were measured on days 35 and 42. In comparison to thermoneutral, heat stress on day 35 decreased feed intake, weight gain, and feed conversion (P < 0.01), increased full bore rate and breast muscle pH (P < 0.05/0.01), reduced digestibility (P < 0.01), and lowered lipase, trypsin levels (P < 0.01). On day 42, heat stress reduced weight gain, increased feed conversion, decreased thigh meat yield, pH, drip loss, with higher shear force (P < 0.05). ALA supplementation on day 35 increased weight gain, breast muscle P value, organic matter digestibility, lipase, and trypsin levels (P < 0.05/0.01). By day 42, ALA had no significant impact (P > 0.05), but showed interaction (P < 0.05), increasing weight gain in heat-stressed chickens (P < 0.05), reducing breast meat yield, increasing shear force, and altering thigh muscle quality (P < 0.05), with higher amylase, trypsin levels (P < 0.05/0.01).In summary, dietary supplementation of ALA improved the apparent digestibility of nutrients in heat-stressed broiler chickens by enhancing digestive enzyme activities, thereby enhancing growth performance.