Orally administrated L-serine modulates physiological and oxidative responses in broiler chickens exposed to feed restriction and heat stress

Broiler production in tropical environments is often constrained by heat stress, which compromises growth and induces oxidative and inflammatory imbalances. Nutritional strategies such as feed restriction and amino acid supplementation have been proposed to mitigate these challenges; however, limited information exists on their combined effects under hot climatic conditions. This study investigated the effects of early feed restriction and L-serine supplementation on growth performance, oxidative stress indicators, antioxidant enzyme activity, and inflammatory responses in broiler chickens reared under natural heat-stress conditions. The experiment was conducted during the hot-dry season (March-April), with ambient temperature averaging 32.84 ± 0.49 °C and a temperature-humidity index (THI) of 31.25 ± 1.30 in the poultry house. A total of 120 Arbor Acre chicks were assigned to four groups: feed-restricted (FR), ad libitum-fed (AL), feed-restricted with L-serine supplementation (FR + L-serine), and ad libitum-fed with L-serine supplementation (AL + L-serine). Feed restriction (20%) was applied from day 7 to 14, and L-serine was administered orally at 200 mg/kg body weight from day 1 to 14. Feed restriction was associated with reduced early body weight gain but lower malondialdehyde (MDA) concentrations (FR: 5.46 ± 0.12 vs. AL: 8.21 ± 1.22 nmol/L on day 21). L-serine supplementation appeared to enhance superoxide dismutase (SOD) activity (FR + L-serine: 8.79 ± 0.44 vs. FR: 4.53 ± 0.55 U/L) and was associated with lower IL-2 (FR + L-serine: 40.37 ± 1.96 vs. FR: 94.58 ± 11.47 pg/mL) and TNF-α concentrations (FR + L-serine: 80.54 ± 2.37 vs. FR: 100.50 ± 3.22 pg/mL). The combination of feed restriction and L-serine supplementation corresponded with reduced HSP70 expression (0.34 ± 0.03 ng/mL vs. AL: 1.88 ± 0.04 ng/mL). By day 35, feed-restricted birds exhibited compensatory growth, achieving comparable final body weights to ad libitum-fed groups. Overall, the findings suggest that combining early feed restriction with L-serine supplementation may help strengthen antioxidant defense, reduce oxidative and inflammatory stress, and support growth recovery in broiler chickens under tropical heat conditions. These results provide preliminary evidence for a practical nutritional strategy to enhance resilience in poultry production systems exposed to high ambient temperatures.