Effects of thymol and eugenol supplementation on reproductive performance, egg quality, and offspring health in broiler breeders

This study investigated the effects of a thymol and eugenol blend on broiler breeders and maternal effects on offspring health. A total of 60,000 55-wk-old Hubbard broiler breeders were allocated to 8 houses (n = 4 houses/group, 7,500 birds/house) and assigned to either a basal diet or a treatment supplemented with 12 mg/kg thymol and 4.5 mg/kg eugenol for 60 d. Breeder samples were collected at the end of the trial, and fertile eggs were incubated. A total of 144 one-day-old chicks (72 per group) were selected for a 7-day rearing trial. Results indicated that supplementation increased the percentage of settable eggs, eggshell strength, and Haugh units ( P < 0.05). In breeders, the essential oil blend improved breeder intestinal morphology, characterized by increased villus height ( P = 0.002) and the villus height-to-crypt depth ratio ( P = 0.012), while concurrently enhancing systemic antioxidant capacity and reducing pro-inflammatory cytokines in the ovary and uterus ( P < 0.05). In offspring, the average daily feed intake of 7-day-old chicks was significantly reduced ( P = 0.036); however, average daily gain remained unaffected ( P > 0.05), indicating improved feed utilization. Furthermore, serum and tissue analyses revealed sustained maternal benefits: progeny at 1 and 7 d of age showed reduced pro-inflammatory cytokines and increased antioxidant enzyme activities in the serum, liver, and heart ( P < 0.05). These benefits demonstrated a maternal transmission effect, enhancing the early-life antioxidant and anti-inflammatory status of offspring. These findings suggest that this essential oil blend is a viable nutritional strategy for optimizing productivity throughout the breeder-progeny cycle.