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Effect of Breed, Slaughter Weight and Sex on Histological Properties of Ovine Muscle^{1 ,2,}

University of Kentucky, Lexington 40546

Abstract

Thirty-three wether and ewe lambs of two breed groups-Suffolk ram x Suffolk-Rambouillet ewe (Su x R) and Suffolk ram x Finnish Landrace-Southdown ewe (Su x F x So)—and two slaughter weight groups (32 and 41 kg) were studied. Carcass studies, including histological examinations of muscle fiber types, sarcomere lengths and fat cell, were made. The longissimus (LD) muscle at the 13th rib and a sample of the semimembranosus (SM) from the upper proximal location were used. Fibers in both muscles were classified as βR, R or W. Su x F x So lambs had more W fibers and fewer R fibers in both muscles. Breed type appeared to cause a physiological shift from R to W fiber types. Furthermore, βR fibers were larger in the SM of the Su x F x So lambs than in that of the Su x R lambs. βRed fibers in the LD, and all three type fibers in the SM, increased in size with increased weight. Wethers had fewer R fibers in the SM, while ewe lambs had larger R and W fibers in the SM. The more phasic LD muscle had fewer βR fibers, more W fibers and smaller R and W fibers than the more tonic SM. Su x F x So lambs were fatter, as indicated by larger fat cells in both muscles. In addition, as slaughter weight increased, there was a concurrent increase in fat cell diameters in both muscles. Fat cells were larger in the LD than in the SM. Sarcomere lengths were not affected by breed, slaughter weight or sex. However, sarcomeres were longer in the SM than in the LD. Fat cell size and βRed cell size for the LD were positively correlated with carcass fat indices, while shear values were negatively correlated with fat cell diameters. There was also a positive relationship between sarcomere length and fat cell size in the SM.

¹ This manuscript (80-5-68) is published with the approval of the Director of the Kentucky Agr. Exp. Sta.

² The assistance of Ms. Sue Baugh in the histological investigations and Dr. W. M. Muir in statistical analysis is greatly appreciated.

³ Present address: Dept. of Anim. Sci., Univ. of Florida, Gainesville.

⁴ Dept. of Anim. Sci.