Effect of different levels of supplemental DL-Methionine on performance, carcass traits, immune system and blood proteins of broilers

In a completely randomized design، the effects of different levels of supplemental DL-methionine in starter diet of broilers on performance، humeral immunity، carcass efficiency and heamatological indices were investigated. Two hundred and eighty eight day-old Ross 308 hybrid chicks were divided into 16 groups (4 treatments، 4 replicates and 18 chicks per replicate). Dietary treatments were four levels of sulfur amino acids (SAA)، (0. 7، 0. 8(control diet based on NRC)، 0. 9 and 1. 0%). At day of 21 old، feed intake and weight gain of 0. 7% SAA group، were significantly lower than other three groups (36. 72 vs. 40. 07، 41. 52 and 39. 92 g/chick/ day، for feed intake; 21. 62 vs. 24. 41، 25. 59 and 25. 96 g/chick/ day، for weight gain، respectively) (p≥0. 05). Chicks consuming diet with highest level of SAA had lower feed conversion rate than first group (1. 54 vs. 1. 70 g/g، respectively) (p≥0. 05). Antibody titer (HI) against Newcastle Disease Virus (NDV) in chicks of third and fourth groups were higher (p≥0. 05) than second group and second group was higher (p≥0. 05) than first group (4. 5، 4. 0، 2. 5 and 1. 0، respectively). Chicks consuming diet with 0. 9% of SAA، in starter، had lower abdominal fat than first group at day of 42 old (1. 58% vs. 2. 5%، respectively) (p≥0. 05). The results of this investigation indicated that for developing of humeral immunity of broilers and lowering of abdominal fat، quantity of SAA in starter diet must increase than NRC (1994) recommendation.