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Skeletal Muscle Protein Turnover in Broiler and Layer Chicks¹

Purdue University, West Lafayette, IN 47907

Abstract

Dietary infusion of L-[U-¹⁴C] tyrosine was used to estimate the fractional protein synthesis rates (FSR) in broiler and layer chickens. Six 2-wk-old birds of each strain were placed in individual metabolism cages and given a purified diet in agar-gel containing 2 µCi L-[U-¹⁴C] tyrosine for 6 h. The birds were sacrified and the pectoralis major (PM) and two combined leg (LM) muscles (gastrocnemius and peroneous longus) were removed for analysis. Subgroups of chickens were sacrificed 3 d before and 3 d after infusion to observe changes in muscle composition to calculate fractional protein accretion rates (FAR). Fractional protein breakdown rates (FBR) were calculated by difference (FBR = FSR - FAR). Protein, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) concentrations were determined to observe relationships between these cellular constituents and FSR. Fractional whole body growth rate and FSR in PM was greater (P<.05) in broiler than layer birds. The FSR in LM of the layer was not different (P>.05) from that of broilers, and from the FSR of the PM in each bird-type. The calculated FBR in the layer PM was at least 17% higher than that of the other muscles. Ratios of FSR to FBR indicated that 16% of the protein synthesized in the layer PM was retained, compared with 45% in the broiler PM. The RNA activity of the layer PM was less (P<.05) than that of the other muscles investigated. Deoxyribonucleic acid activity was lower (P<.05) in the PM than LM of either bird-type. These results indicate that differences in FAR between the two strains of birds were caused by higher FSR in the broiler PM and lower FDR in both muscles of broiler as compared with layer chicks.

¹ Journal paper No. 10408, Purdue Univ. Agr. Exp. Sta., Dept. of Anim. Sci.

² Present address: Dept. of Anim. Sci., Univ. of Nebraska, Lincoln 68583-0821.

³ Fairview Farms, Remington, IN.

⁴ Commercial Chicks Inc., Thorntown, IN.