Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/26/1999
Publication Date: N/A
Citation: Interpretive Summary: In the 1980's, a sheep producer in Oklahoma recognized that some progeny of an individual ram were very heavily muscled. Since then, it has been determined that this heavily muscled condition, called "callipyge," is caused by a single gene. The callipyge condition greatly improves carcass composition and, thus, might offer the sheep industry a method to improve retail cut leanness. However, we have shown that the callipyge condition decreases loin muscle tenderness. In the present experiment, we determined the mechanism responsible for the increased muscle growth rate of callipyge lambs. Both the increased muscle growth rate and the decreased meat tenderness of callipyge are caused by a single change in the level of activity of a key muscle metabolism system. Thus, it appears unlikely that one could select for callipyge lambs with improved meat tenderness without loss of the muscling effect.
Technical Abstract: Callipyge sheep (Clpg) are characterized by increased skeletal muscle mass. We studied Clpg and normal lambs at 5, 8, and 11 wk of age (n = 4-7/group) to determine how protein kinetics are altered by this trait. Total protein, DNA, and RNA, and calpastatin activity were measured in five skeletal muscles, the heart, kidneys, and liver, and protein accretion rates were calculated. At 8 wk, the fractional synthesis rates of proteins in these tissues were measured in vivo using a primed, continuous 8-hr infusion of [2H5]-phenylalanine. Fractional rates of protein degradation were estimated by differences. Muscle hypertrophy was present at 5 wk in Clpg lambs, and was associated with greater increases in protein:DNA, RNA:DNA, and calpastatin activity; fractional rates of protein synthesis and degradation at 8 wk of age were lower than in normal lambs. The organs of Clpg lambs exhibited reduced growth at 11 wk. Greater DNA and RNA accumulation and increased calpastatin activity in muscles of Clpg lambs likely sustained higher rates of protein snythesis and decreased degradation rates in the perinatal period which resulted in the enhanced muscle growth.