A comparison between slow and fast-growing strains of broiler chickens on carcass traits and incidence of wooden breast and white striping
Wooden breast (WB) and white striping (WS) are myopathies observed in conventional broiler chickens. Selection for slower growth has been suggested to reduce these disorders. This study compared carcass traits and the incidence of WB and WS among 2 conventional (CO) and 9 slow-growing (SL) broiler strains. Using a randomized incomplete block design, 2,552 mixed-sex birds were allocated to 58 pens (44 birds/pen; 30 kg/m2) over 3 production cycles with 4-6 pens/strain. The strains differed in ADG from 44-69g/d, with ADG≥65g/d for strains C (ADG0-48=65 g/d) and B (ADG0-48=69 g/d), ADG 50-60g/d for strains H (ADG0-62=51 g/d), E (ADG0-62=53 g/d), F(ADG0-62=56 g/d), G (ADG0-62=56 g/d), M (ADG0-62=56 g/d), and I (ADG0-62=57 g/d), and ADG<50g/d for strains N (ADG0-62=44 g/d), D (ADG0-62=45 g/d), and J (ADG0-62=48 g/d). Birds had ad libitum access to the same three-phase diet. From each pen, 8 birds (4 males, 4 females) of CO (B,C) and SL (D-N) strains were processed at 48 and 62 days, respectively, based on the final target weight (BWCO=3.24±0.14 kg; BWSL=3.18±0.30 kg). The carcass, breast, drumstick, thigh, and wing weight were measured,and breasts were assessed visually and by palpation for the presence of WB and WS. Data were analyzed using Proc Glimmix in SAS 9.4, with strain and sex as fixed effects,and block and production cycle as random effects. Pearson correlation analysis was conducted to study relationships among WB, WS, and carcass traits. Strain D had a similar carcass weight to strains J and N, yet was lighter than other strains (P<0.01). Higher thigh and drumstick yields were observed in strain D compared to strains B, C, and F (P<0.01). Strain F had similar carcass and breast yield to strains B and C, yet greater than all other strains (P<0.01). Strains C and F showed a higher incidence of WB (P<0.01) and WS (P<0.01) than the other SL strains. Strain B tended to have a higher incidence of WB than strains G (P=0.07) and H (P=0.06) and had a higher incidence of this disorder than the other SL strains (P<0.05). There was no strain by sex interaction on any trait evaluated (P>0.05); males had a higher incidence of WB (P=0.034) and WS (P<0.01) than females. When carcass weight was included as a covariate, sex differences disappeared while strain differences remained, with strains C and F having a similar incidence of WB and WS to strain B, but higher than other SL strains (P<0.01). Both WB and WS were positively correlated with carcass and breast yields but negatively correlated with thigh, drumstick, and wing yields. The incidences of WB and WS observed in both SL and CO strains indicate these myopathies are more related to breast yield rather than growth rate.