Effects of Cimaterol and Fishmeal on Performance, Carcass Characteristics and Skeletal Muscle Growth in Lambs 1

Two experiments were conducted in which cimateroI [CL263,780; (anthranilo-nitrile, 5-[1hydroxy-2-(isopropylamino) ethyl]-)] was fed at 0 or 10 ppm in a complete, mixed, high-concentrate diet to assess effects on growth performance and repartitioning of tissue growth in young, rapidly growing lambs. Average daily gain and feed efficiency (F/G) were not altered in Dorset wether lambs fed cimaterol for 6 or 11 wk in Exp. 1. Average daily gain and F/G were improved 16% (P<.05) in Suffolk X Dorset ram lambs fed cimaterol for 5 wk, but not 10 wk in Exp. 2. Cimaterol increased dressing percent by at least 3 percentage units (P<.05), increased longissimus area 26 and 32% (P<.001), reduced 12th-rib fat thickness 66 and 32% (P<.001) and reduced kidney and pelvic fat 34 and 44% (P<.001) at 6 wk and 12 wk, respectively (Exp. 1). Proximal hindleg muscles were 26% heavier (P<.001) in cimaterol-fed lambs in Exp. 1. Fishmeal (FM) replaced an equal amount of soy protein (3% of diet) to create a 2 • 2 • 2 factorial arrangement in Exp. 2. Cimaterol effects on carcass traits and muscle growth were similar to those observed in Exp. 1. However, hindleg and foreleg muscle weights and longissmus area were 16% greater (P<.001) in FM-fed lambs at 10 wk, and the cimaterol-induced muscle hypertrophy was slightly reduced in these lambs. Fat measures were unaffected by FM. These data demonstrate that cimaterol effectively repartitions skeletal muscle and adipose tissue accretion, and fishmeal fed for 10 wk significantly enhances skeletal muscle growth in lambs. (