In pursuit of a better broiler: carcass traits and muscle myopathies in conventional and slower-growing strains of broiler chickens

Abstract

Selection for accelerated growth rate and high breast yield in broiler chickens have been associated with an increase in myopathies, including wooden breast (WB) and white striping (WS). To investigate effects of growth rate on carcass traits and incidence of myopathies, 14 strains were evaluated, encompassing 2 conventional (CONV; strains B and C: ADG_0-48 > 60 g/d) and 12 slower-growing (SL) strains. The latter were categorized based on growth rate: FAST (strains F, G, I and M; ADG_0-62=53-55 g/d), MOD (strains E, H, O and S; ADG_0-62=50-51 g/d), and SLOW (strains D, J, K and N; ADG_0-62<50 g/d). In a randomized incomplete block design, 7,216 mixed-sex birds were equally allocated into 164 pens (44 birds/pen; 30 kg/m²), with each strain represented in 8 to 12 pens over 2 to 3 production cycles. From each pen, 4 males and 4 females were processed at 2 Target Weights (TWs) based on their expected time to reach 2.1 kg BW (TW 1: 34 d for CONV; 48 d for SL strains) and 3.2 kg BW (TW 2: 48 d for CONV; 62 d for SL strains). Weights and yields for the carcass, breast, drumsticks, thighs, and wings were obtained; breast fillets were assessed to determine the presence and severity of WB and WS. At both TWs, breast yield was higher as growth rate increased (P < 0.001), with CONV having greater breast yield than other categories. Strain F had the greatest breast yield at both TWs (P < 0.001) within the FAST category. At TW 2, CONV had the greatest incidence of WB and WS (P < 0.001). However, within FAST, strain F had the greatest incidence of myopathies (P < 0.001) at both TWs, exhibiting values as high or as greater than CONV birds. The incidence of WB and WS in strains with differing growth rates but high breast meat yield suggests that the latter may play a major role in the occurrence of these myopathies.

Keywords: chicken meat; meat yield; myopathies; processing traits; slow-growth.

Figure 1

Effects of category on the total incidence of breast fillets presenting wooden breast^1,2 and white striping ^3,4 at Target Weights 1 and 2 (LS-means ± SEM). At Target Weight 1, CONV and other categories were 34 and 48 d of age, respectively. At Target Weight 2, CONV and other categories were 48 and 62 d, respectively. ^a-cDifferent superscripts represent differences among categories (P < 0.05). ¹Number of birds per category at target weight 1: CONV: n = 104; FAST: n = 156; MOD: n = 175; SLOW: n = 173. ²Number of birds per category at target weight 2: CONV: n = 80; FAST: n = 176; MOD: n = 196; SLOW: n = 198. ³Number of birds per category at target weight 1: CONV: n = 91; FAST: n = 124; MOD: n = 159; SLOW n: = 125. ⁴Number of birds per category at target weight 2: CONV: n = 64 FAST: n = 132; MOD: n = 171; SLOW: n = 162.

Figure 2

Effects of strains (within category) on the total incidence of breast fillets presenting wooden breast^1,2 and white striping ^3,4 at Target Weights 1 and 2 (LS-means ± SEM). At Target Weight 1, CONV and other categories were 34 and 48 d of age, respectively. At Target Weight 2, CONV and other categories were 48 and 62 d, respectively. ^a-bDifferent superscripts within the same category represent differences among strains (P < 0.05). ¹Number of birds per strain at target weight 1: B: n = 52, C: n = 52, F: n = 30, G: n = 47, I: n = 47, M: n = 32, E: n = 48, H: n = 32, O: n = 47, S: n = 48; D: n = 32; J: n = 47, K: n = 47, N: n = 47. ²Number of birds per strain at target weight 2: B: n = 48, C: n = 32, F: n = 52, G: n = 48, I: n = 47, M: n = 29, E: n = 48, H: n = 52, O: n = 48, S: n = 48, D: n = 55, J: n = 48, K: n = 47, N: n = 48. ³Number of birds per strain at target weight 1: B: n = 45, C: n = 46, F: n = 25, G: n = 39, I: n = 39, M: n = 21, E: n = 47, H: n = 24, O: n = 44, S: n = 44, D: n = 26, J: n = 28, K: n = 39, N: n = 32. ⁴Number of birds per strain at target weight 2: B: n = 36, C: n = 28, F: n = 42, G: n = 41, I: n = 31, M: n = 18, E: n = 40, H: n = 48, O: n = 44, S: n = 39, D: n = 45, J: n = 37, K: n = 44, N: n = 36.

Figure 3

Effects of category on the total incidence of breast fillets presenting moderately severe (scores 2 or 3) wooden breast^1,2 and white striping ^3,4 at Target Weights 1 and 2 (LS-means ± SEM). At Target Weight 1, CONV and other categories were 34 and 48 d of age, respectively. At Target Weight 2, CONV and other categories were 48 and 62 d, respectively. ^a-cDifferent superscripts represent differences among categories (P < 0.05). ¹Number of birds per category at target weight 1: CONV: n = 104; FAST: n = 156; MOD: n = 175; SLOW: n = 173. ²Number of birds per category at target weight 2 CONV: n = 80; FAST: n = 176; MOD: n = 196; SLOW: n = 198. ³Number of birds per category at target weight 1: CONV: n = 91; FAST: n = 124; MOD: n = 159; SLOW: n = 125. ⁴Number of birds per category at target weight 2: CONV: n = 64 FAST: n = 132; MOD: n = 171; SLOW: n = 162.

Figure 4

Effects of strains (within category) on the total incidence of breast fillets presenting moderately severe (scores 2 or 3) wooden breast^1,2 and white striping ^3,4 at Target Weights 1 and 2 (LS-means ± SEM). At Target Weight 1, CONV and other categories were 34 and 48 d of age, respectively. At Target Weight 2, CONV and other categories were 48 and 62 d, respectively. ^a-bDifferent superscripts within the same category represent differences among strains (P < 0.05). ¹Number of birds per strain at target weight 1: B: n = 52, C: n = 52, F: n = 30, G: n = 47, I: n = 47, M: n = 32, E: n = 48, H: n = 32, O: n = 47, S: n = 48, D: n = 32, J: n = 47, K: n = 47, N: n = 47. ²Number of birds per strain at target weight 2: B: n = 48, C: n = 32, F: n = 52, G: n = 48, I: n = 47, M: n = 29, E: n = 48, H: n = 52, O: n = 48, S: n = 48, D: n = 55, J: n = 48, K: n = 47, N: n = 48. ³Number of birds per strain at target weight 1: B: n = 45, C: n = 46, F: n = 25, G: n = 39, I: n = 39, M: n = 21, E: n = 47, H: n = 24, O: n = 44, S: n = 44, D: n = 26, J: n = 28, K: n = 39, N: n = 32. ⁴Number of birds per strain at target weight 2: B: n = 36, C: n = 28, F: n = 42, G: n = 41, I: n = 31, M: n = 18, E: n = 40, H: n = 48, O: n = 44, S: n = 39, D: n = 45, J: n = 37, K: n = 44, N: n = 36.

Figure 5

Effects of category on average of wooden breast^1,2 and white striping ^3,4 scores at Target Weights 1 and 2 (LS-means ± SEM). At Target Weight 1, CONV and other categories were 34 and 48 d of age, respectively. At Target Weight 2, CONV and other categories were 48 and 62 d, respectively. ^a-dDifferent superscripts represent differences among categories (P < 0.05). ¹Number of birds per category at target weight 1: CONV: n = 104; FAST: n = 156; MOD: n = 175; SLOW: n = 173. ²Number of birds per category at target weight 2 CONV: n = 80; FAST: n = 176; MOD: n = 196; SLOW: n = 198. ³Number of birds per category at target weight 1: CONV: n = 91; FAST: n = 124; MOD: n = 159; SLOW: n = 125. ⁴Number of birds per category at target weight 2: CONV: n = 64 FAST: n = 132; MOD: n = 171; SLOW: n = 162.

Figure 6

Effects of strains (within category) on average wooden breast^1,2 and white striping ^3,4 scores at Target Weights 1 and 2 (LS-means ± SEM). At Target Weight 1, CONV and other categories were 34 and 48 d of age, respectively. At Target Weight 2, CONV and other categories were 48 and 62 d, respectively. ^a-b Different superscripts within the same category represent differences among strains (P < 0.05). ¹Number of birds per strain at target weight 1: B: n = 52, C: n = 52, F: n = 30, G: n = 47, I: n = 47, M: n = 32, E: n = 48, H: n = 32, O: n = 47, S: n = 48, D: n = 32, J: n = 47, K: n = 47, N: n = 47. ²Number of birds per strain at target weight 2: B: n = 48, C: n = 32, F: n = 52, G: n = 48, I: n = 47, M: n = 29, E: n = 48, H: n = 52, O: n = 48, S: n = 48, D: n = 55, J: n = 48, K: n = 47, N: n = 48. ³Number of birds per strain at target weight 1: B: n = 45, C: n = 46, F: n = 25, G: n = 39, I: n = 39, M: n = 21, E: n = 47, H: n = 24, O: n = 44, S: n = 44, D: n = 26, J: n = 28, K: n = 39, N: n = 32. ⁴Number of birds per strain at target weight 2: B: n = 36, C: n = 28, F: n = 42, G: n = 41, I: n = 31, M: n = 18, E: n = 40, H: n = 48, O: n = 44, S: n = 39, D: n = 45, J: n = 37, K: n = 44, N: n = 36.

Figure 7

Wooden breast^1,2 and white striping^3,4 profile in different categories of broiler chickens at Target Weights 1 and 2. Only descriptive statistics are provided for this variable. At Target Weight 1, CONV and other categories were 34 and 48 d of age, respectively. At Target Weight 2, CONV and other categories were 48 and 62 d, respectively. ¹Number of birds per category at target weight 1: CONV n = 104; FAST n = 156; MOD n = 175; SLOW n = 173. ²Number of birds per category at target weight 2: CONV n = 80; FAST n = 176; MOD n = 196; SLOW n = 198. ³Number of birds per category at target weight 1: CONV n = 91; FAST n = 124; MOD n = 159; SLOW n = 125. ⁴Number of birds per category at target weight 2: CONV n = 64; FAST n = 132; MOD n = 171; SLOW n = 162.