RESUMEN
Limited information exists on the use of zinc-l-selenomethionine (Zn-L-SeMet) in broiler diets and its effects on the growth performance, body temperature, mortality rates, blood profile, and gene expression, especially when animals are reared under cyclic heat stress conditions. This study aimed to investigate the impact of Zn-L-SeMet in broiler diets from 1 to 42 days of age reared under cyclic heat stress and its effects on growth performance, cloacal temperatures, mortality rate, blood parameters, and insulin-like growth factor 1 (IGF-1) and growth hormone receptor (GHR) gene expression in the breast muscle. A total of 1000 male Cobb 500® broiler chicks were randomly assigned to five treatments: 0, 0.15, 0.23, 0.47, and 1.30 mg/kg of Zn-L-SeMet. Each treatment consisted of 10 replicates with 20 birds each. No statistically significant differences in growth performance were observed from 1 to 21 days of age (P > 0.05). However, from 1 to 42 days, feed intake (FI) and feed conversion ratio (FCR) decreased linearly (P < 0.05). Cloacal temperatures showed no significant effects (P > 0.05), while overall mortality rate exhibited a quadratic response (P < 0.05), with the optimal inclusion level predicted to reduce broiler mortality at 0.71 mg/kg. Triglyceride (TRG) levels increased with 0.97 mg/kg (P < 0.05), and gama-glutamil transferase (GGT) levels decreased with the inclusion of 1.19 mg/kg (P < 0.05). No significant effects on IGF-1 and GHR gene expression were found (P > 0.05). In conclusion, the inclusion of 1.30 mg/kg of Zn-L-SeMet in diets of heat-stressed broilers improved growth performance from 1 to 42 days of age. An inclusion of 0.71 mg/kg reduced mortality rate, while 0.97 mg and 1.19 mg increased and reduced TRG and GGT levels, respectively.
