Abstract
BACKGROUND: Broiler diets are commonly supplemented by liquid methionine hydroxy analogue‐free acid (MHA‐FA) containing as product with 88% of active substance to meet sulphur amino acid (SAA) requirements. OBJECTIVES: Two experiments were conducted to assess the effects of different dietary MHA‐FA levels on growth performance, blood metabolites and immune responses in broilers. METHODS: In experiments 1 and 2, 432 and 360 male broilers were fed either a basal corn–soya bean meal diet that met the energy and nutrient requirements with the exception of SAAs or the basal diet supplemented with 5 graded levels of MHA‐FA (+0.9 and +0.8 g/kg), for 1–11 and 11–24‐day ages, respectively. Chicks were vaccinated with inactivated H9N2/Newcastle disease (ND) and live‐ND on days 5 and 11, respectively. RESULTS: Responses in both experiments had similar tendency at corresponding dietary MHA‐FA levels. By increasing dietary MHA‐FA level, weight gain (WG), feed efficiency (FE), relative breast weight (RBW) and immunity against ND and avian influenza virus inoculation improved with quadratic trend. Blood serum triglyceride, low‐density lipoprotein, alanine aminotransferase and alkaline phosphatase concentration were affected in response to dietary MHA‐FA levels with quadratic trends. By using broken‐line regression analysis, the optimum dietary MHA‐FA levels for optimized WG, FE and RBW during 1–10‐day age were obtained at 2.20, 3.31 and 3.33 g/kg, respectively; based on MHA‐FA content of Met equivalent, the digestible SAA requirements were estimated 0.81%, 0.91% and 0.92%, respectively. Similarly, for the 11–24‐day age period, the optimum dietary MHA‐FA supplementation levels were obtained 1.79, 2.21, 2.41 and 2.53 g/kg, with the digestible SAA requirements estimated 0.75%, 0.79%, 0.80% and 0.81% for optimized WG, FE, RBW and immune responses, respectively. CONCLUSIONS: Supplemental levels of MHA‐FA that optimize performance, breast meat and immunity in broilers fed corn–soya bean meal diet, varied from 0.18% to 0.33%, correspond to age and what traits are considered for optimization.