Effects of reduced digestible lysine density on myopathies of the Pectoralis major muscles in broiler chickens at 48 and 62 days of age.

Quantitative control of nutrient intake may decrease the incidence of wooden breast (WB) and white striping (WS) myopathies with some impairment of live performance. Two experiments (Exp) utilizing Yield Plus × Ross 708 male broilers were conducted to determine if a reduction in myopathies may be obtained through a qualitative approach by reducing digestible lysine (dLys) density. All birds received an identical starter diet until 11 d of age. In Exp 1 (63 pens; 22 birds/pen), each pen was then randomly assigned to 1 of the following 7 dietary treatments (TRT) for a 47 d production period. Seven dietary treatments were provided for the grower 1 (G1; 12 to 18 d of age) and grower 2 (G2; 19 to 26 d of age) phases: 1) 100% of primary breeder recommendations for dLys throughout Exp; 2) 85% of TRT 1 dLys for G1; 3) 85% of TRT 1 dLys for G2; 4) 85% of TRT 1 dLys for G1 and G2; 5) 75% of TRT 1 dLys for G1; 6) 75% of TRT 1 dLys for G2; 7) 75% of TRT 1 for G1 and G2. In Exp 2 (24 pens; 30 birds/pen), birds were randomly assigned to 1 of the following 4 dietary TRT (Table 2) during a 61 d production period. Four dietary treatments were provided for the grower (G; 12 to 28 d) and finisher 1 (F1; 29 to 40 d of age) phases: 1) 100% of primary breeder recommendations for dLys 2) 85% of TRT 1 dLys for G; 3) 85% of TRT 1 dLys for F1; 4) 85% of TRT 1 dLys for G and F1; thereafter, birds received common finisher 1 (Exp 1: 27 to 42 d of age), finisher 2 (Exp 2: 41 to 48 d of age) and withdrawal (Exp 1: 43 to 47 d of age; Exp 2: 49 to 61 d of age) diets. Ideal amino acid ratios were not maintained in reduced dLys diets in either Exp. At 48 (Exp 1; 18 birds/pen) and 62 (Exp 2; 30 birds/pen) d of age, selected birds were processed and fillets were visually scored for WB and WS. No differences (P > 0.05) in cumulative live performance responses between TRT 1 and the remaining TRT were observed in either Exp. In Exp 1, the incidence of severe WB (20.8%) and WS (42.3%) at 48 d of age among birds receiving TRT 7 was reduced (P < 0.01) compared with TRT 1 (WB: 36.6%; WS: 64.3%), at the expense of reduced (P = 0.003) breast weights and yield. In Exp 2, the incidence of severe WB (18.8%) and WS (17.8%) at 62 d of age for birds receiving TRT 4 was reduced (P < 0.05) compared with TRT 1 (WB: 39.3%; WS: 38.3%), without any detrimental effects on processing characteristics. These results indicate that altering dietary dLys during critical periods of the growth trajectory may be a viable strategy for reducing the incidence and severity of WB and WS.