ENDOGENOUS PROTEOLYTIC-ENZYMES IN CHICKEN MUSCLES - DIFFERENCES AMONGSTRAINS WITH DIFFERENT GROWTH-RATES AND PROTEIN EFFICIENCIES

The theory that net muscle growth is, at least partly, regulated by ca tabolic factors has been tested in order to set up an animal model to study meat aging and post-mortem tenderization. Male and female chicke ns of a layer strain (White Leghorn), a commercial broiler strain (Ros s), and two experimental broiler lines (designated GL and FC) were use d to estimate differences in proteolytic enzyme activities in the brea st muscles. The GL and the FC lines were selected for high body weight gain and high feed efficiency, respectively. At 6 wk of age the birds were slaughtered and the activities of endogenous proteinases and the ir specific inhibitors in breast muscles measured. The Leghorns showed significant differences in all traits compared with the three broiler genotypes. Within the broiler types, FC birds tended in the direction of the Leghorns and GL birds in the opposite direction. Ross birds we re intermediate between FC and GL birds. All types and sexes differed significantly in slaughtering weight. Feed conversion ratio and protei n conversion ratio were highest for Leghorns. The FC birds showed the lowest feed conversion. Ross and GL birds showed intermediate values. The Leghorns showed higher calpain activities and lower calpastatin ac tivity than the three broiler genotypes. The FC broilers showed interm ediate calpain and calpastatin activities but higher cathepsin H and t otal cystatin values. The GL broilers showed lower cathepsin B, D, and H activities. In all cases the Ross broilers showed intermediate valu es. From these figures it is concluded that the strains of birds used in this study can be used as a natural source of variability to study the mechanisms involved in post-mortem proteolytic degradation and thu s in the study of muscle tenderization and meat aging. It is also conc luded that it could be very interesting to study the behavior of the d ifferent proteolytic systems more carefully in relation to muscular gr owth characteristics and compare them to anabolic factors involved in muscle growth.