Dose-response evaluation of feed additive tert-butylhydroquinone on performance, hepatic antioxidant, gut health, and functional microbiome in heat-stressed broiler chickens.

Chronic heat exposure impairs broiler performance through intestinal oxidative damage and microbiota dysbiosis. Dietary tert‑butylhydroquinone (tBHQ), a synthetic phenolic antioxidant suggested using in feed preservation, may regulate some physiological responses, although mechanistic evidence and appropriate dosages in broiler is limited. To investigate the dose-response of dietary tBHQ on performance, antioxidant defence, gut health, and functional microbiome in heat-stressed broilers, two hundred male Ross-308 broilers (one-day-old) were randomly distributed across four dietary treatments (n = 50 birds/group; n = 10 birds/replicate); 0 (CT), 50 mg (tBHQ1), 100 mg (tBHQ2), or 200 mg (tBHQ3) of tBHQ/kg diet for 5 weeks. Additionally, chicks were reared under a temperature-humidity index (THI) value of 29 from 22 to 35 d of experimental period. Results showed that the appropriate dosages was 50 mg tBHQ/kg (tBHQ1), which led to a 4.8% increase in final body weight (P < 0.05), a 39.1% decrease in hepatic malondialdehyde levels (P < 0.05), and a 37.8% elevation in catalase activity (P < 0.05) when compared with the CT group. Consequently, gene expression analysis revealed 1.98-fold upregulation of glutathione peroxidase 4 (GPx4) and 1.78-fold upregulation of growth hormone (P < 0.05). Beta-diversity analysis demonstrated distinct clustering of cecal microbiota (ANOSIM R = 0.42, P < 0.05), which was distinguished by an enrichment of beneficial genera, including Ligilactobacillus, Bifidobacterium, and Lactococcus (LDA score > 3.0), and a reduction of potentially pro-inflammatory taxa, such as Streptococcus and Enterococcus, within the tBHQs groups. A non-linear dose-response relationship was observed, with reduced efficacy at a concentration of 100 mg/kg. Dietary 50 mg tBHQ /kg yielded enhancements in productive performance, liver antioxidant capacity, and the prevalence of beneficial gut bacteria in broilers subjected to elevated temperatures. Nevertheless, the absence of a thermoneutral control group complicates the attribution of these observed effects to either a reduction in heat stress or general performance enhancements. These results offer preliminary support for further investigation to elucidate the underlying mechanisms.