Rearing factors affecting myopathy rate and meat quality in broiler chickens

The present work aimed at evaluating the effect of some rearing factors on performance and myopathy rates of broiler chickens slaughtered at 45 d of age. A total of 768 chicks were housed in 16 pens (48/pen) according to a factorial arrangement: 2 genders x 2 pens shapes (short, 2.4 x 2.5 m vs. long, 1.2 x 5 m) x 2 feeding treatments (standard diet vs. the same diet supplemented with 150 mg sodium butyrate/kg). In the long pens, feeders and drinkers were placed at the opposite sides to increase animal activity. Performance and meat quality data were analysed by a mixed model with gender, pen shape, dietary treatment, and interactions as the main effects, and pen as random effect. The same effects on myopathy rates were analysed by PROC CATMOD. Final live weight was higher in males than in females (3586 vs. 2965 g; P<0.001) and in broilers from short pens compared to those from long ones (3327 vs. 3234 g; P<0.001). The Nasupplementation had no effect on performance. At gross examination, 35.9%, 14.6%, and 14.1% of breasts showed white striping (WS), wooden breast (WB), or spaghetti meat (SM), respectively. Breasts with SM and WB also showed WS. Gender did not affect WS, whereas WB rates were lower (7.28% vs. 21.9%; P<0.01) and SM rates higher (25.2% vs. 3.13%; P<0.001) in females than males. Pen shape and dietary treatment did not affect myopathy rate. However, females fed Na-butyrate tended to show a lower SM rate (16.7% vs. 33.3%; P=0.06). Myopathies affected meat quality: WB had higher lightness index (50.7 vs. 48.2, on average), cooking losses (29.9% vs. 24.2%), and shear force (3.85 vs. 2.85 kg/g) than other meat types (P<0.01). In conclusion, WB occurred more in males than females, whereas SM showed an opposite trend. Differences in SM rate according to Na-supplementation deserve further investigations for confirmation and clarification of the action mechanisms.