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Muscle Protein Turnover and Tenderness in Broiler Chickens Fed Cimaterol^1,2,3,

University of Nebraska⁴, Lincoln 68583-0908

Abstract

To investigate the impact of cimaterol (CIM) on muscle protein turnover, carcass and muscle composition, muscle cathepsin B+L activity and meat tenderness, 21-d-old broiler chickens (n = 88) were assigned to dietary treatments of either 0 or 1 ppm CIM. Fractional synthesis rates (FSR), fractional accretion rates (FAR), proximate composition and collagen content were determined in the breast muscle (BM; pectoralis major) and a group of leg muscles (LM; gastrocnemius and peroneous longus) from groups of six birds per treatment within each of two time periods (age = 38 or 56 d). Whole body composition, serum hydroxyproline content and BM cathepsin B+L activity also were measured. Fractional degradation rates (FDR) were calculated as the difference between FSR and FAR. Feeding CIM increased (P < .01) whole body protein content. Weights of LM and percentage of body weight as BM and LM were increased (P < .05) when CIM was included in the diet. Although FSR was not significantly reduced by CIM feeding, it decreased (P < .05) with increasing age. Due to decreases in FAR, FDR thereby was reduced by CIM 31.5% and 11.9% in BM and 38.2% and 37.4% in LM at 38 d and 56 d of age, respectively. Cathepsin B+L activities also were reduced 33.6% (P < .01) and shear forces were increased by 41% (P < .05) by CIM feeding. For chickens fed CIM, the correlation between cathepsin B+L activity and shear force was -.63 (P < .01). Feeding CIM improved carcass leanness and muscling due to reductions in FDR and proteolytic enzyme activity. Feeding CIM also reduced meat tenderness.

¹ Paper number 8771, Journal Series, Nebraska Agric. Res. Div., Inst, of Agric. and Nat. Resources.

² Cimaterol provided as a gift from American Cyanamid, Princeton, NJ.

³ This research was supported by the Univ. of Nebraska-Lincoln Res. Council and NIH Biomed. Res. Support Grant RR-07055.

⁴ Dept. of Anim. Sci.