Fibre area and capillary supply in broiler breast muscle in relation to productivity and ascites

The objective in this study was to examine the capillary supply in the broiler breast muscle in relation to productivity and the incidence of ascites. Muscle samples (pectoralis superficialis) were collected from 24 pairs of broilers of a commercial paternal strain. The pairs consisted of full sib broilers (brothers and sisters). Of each pair one broiler had a high arterial pressure index, as an indication of ascites, and the other was a healthy chick of the same sex. Data collected were, among others, body weight, arterial pressure index, haematocrit and weight of breast muscle and lungs. Pectoral muscle samples were histologically analysed with respect to capillary density, fibre area and number of capillaries per fibre. Ascitic chickens (measured as high values for heart hypertrophy) had a lower number of capillaries per fibre and tended to have reduced fibre area, although they had a similar capillary density in the pectoral muscle in comparison with healthy chickens. The expected increase in capillary density was not observed. Normally capillary densities decrease in proportion to the increase in fibre size. So ascites has unfavourable relations with capillary traits. Fast growth was not significantly associated with capillary density. However, chickens with a higher percentage breast muscle had a lower capillary density. This implies that high muscularity might be a risk for a diminished oxygen supply to the breast muscle.