Abstract
Rambouillet × Finn crossbred wether lambs were evaluated for differences in longissimus muscle cross-sectional area and overlaying subcutaneous adipose tissue thickness resulting from the use of the beta-agonist clenbuterol. Treatment groups received 0 and 2 ppm clenbuterol in the diet for approximately 40 d prior to slaughter. Longissimus muscle cross-sectional area and fat depth over the 12th–13th rib juncture were measured by real-time ultrasound before and during administration of the compound. At slaughter, muscle metabolism in vitro and carcass characteristics were measured. Based on comparisons with an initial-kill group of sheep, longissimus muscle cross-sectional area increased in control sheep by 12% (P>.05) over the 40-d experimental period, and increased in clenbuterol-fed sheep by 48% (P<.05). Conversely, subcutaneous fat thickness increased significantly in the control sheep (88%) during this period, but was unchanged in the clenbuterol-fed animals. Warner-Bratzler shear force values of cooked longissimus samples from clenbuterol-fed sheep were significantly greater than shear force values in cooked samples from control lambs; this was not correlated with the extractable neutral lipid content of the muscle. Simple linear regression between ultrasound and carcass measurements of longissimus muscle cross-sectional area and subcutaneous fat thickness yielded correlation coefficients of .80 and .64, respectively. A significantly greater amount of net glycogen synthesis from [U-14C] glucose was observed in longissimus muscle strips from clenbuterol-fed animals than in muscle strips from control sheep. As with longissimus muscle cross-sectional area, total glucose utilization in vitro was greatest in the clenbuterol-fed sheep and least in the initial-kill sheep. Palmitate esterification into neutral lipids decreased virtually to zero in muscle from five of the eight clenbuterol-fed sheep. Similarly, the neutral lipid content was 44% lower (P<.05) in longissimus muscle from clenbuterol-fed sheep than in muscle from control sheep. The results suggest that the increased muscle hypertrophy caused by clenbuterol was associated with an increase in the diameter of Type II muscle fiber types. Copyright © 1986. American Society of Animal Science . Copyright 1986 by American Society of Animal Science.