Effect of Feeding Systems, Slaughter Weight and Sex on Histological Properties of Lamb Carcasses

Abstract

Two experiments were conducted. In Exp. 1, 72 Crossbred lambs (36 wethers and 36 ewes) were weaned at 18 kg and grown on bluegrass pasture with a 13% protein creep until the mean weight was 32 kilograms. Four of each sex were slaughtered and the remaining 64 lambs were randomly allotted within each sex group to four management systems: (1) PNC = bluegrass-clover pasture with no supplement systems: (2) PI3 = bluegrass-clover pasture with 13% crude protein (CP) supplemental concentrate offered ad libitum; (3) DL 13 = 13% CP diet offered ad libitum in drylot; and (4) DL 16 = 16% CP diet offered ad libitum in drylot. In Exp. 2, 41 rams and 41 wethers were raised in a like manner to 36 kg, then five of each sex were slaughtered. The remaining 72 lambs were randomly allotted within each sex group to either the PNC, PI 3 or DL 13 systems. Lambs in both experiments were slaughtered at a predetermined slaughter weight of either 41 or 50 kilograms. Carcass studies, including histological examinations of muscle and fat cells, were made. Muscle fibers in the longissimus were classified as βR, αR and αW fibers. Management systems affected only β Red fibers in Exp. 1. The available source of energy in the diets appeared to cause a physiological shift from αR to αW fiber types. Perhaps an even more important finding was the shift from beta to alpha fibers in Exp. 1 since it shows that ATPase activity may not be fixed at birth. β Red fibers in Exp. 1 and all three types in Exp. 2 increased in size with increased weights. Wethers had larger β Red fibers than ewes in Exp. 1, while rams had larger β Red fibers than wethers in Exp. 2. Muscle bundle size had no significant relationship to the histological parameters of diameter and percentage fiber types in the muscle. Fat cell size increased with an increase of energy in the diet and with an increase in carcass size. Fat cell size and β Red muscle cell size were generally significantly correlated with carcass fat measurements, carcass ether extract, and carcass juiciness and tenderness scores. Copyright © 1980. American Society of Animal Science . Copyright 1980 by American Society of Animal Science.