Effect of dietary protein concentration and cimaterol on growth and body composition of entire male lambs

Abstract

Twenty-four Suffolk × Blackface ram lambs aged 14 weeks and weighing 24 kg were used. They were allocated 42 days prior to slaughter in a 2 × 2 factorial design to receive barley-based, isoenergetic diets formulated to contain 120 g (Diet L) or 180 g (Diet H) crude protein kg −1 dry matter (DM), either unsupplemented (U) or supplemented (C) with cimaterol at an inclusion level of 2 mg kg −1 DM. Liveweight gain, DM intake and food conversion ratio were not significantly altered by treatments. Cimaterol treatment on average: (1) increased cold carcass weight (CCW), gigot depth and circumference, chest width, Musculus longissimus dorsi depth and area, crude protein content of the carcass and the proportion of muscle in selected joints; (2) reduced backfat thickness, internal fat, carcass lipid concentration and liver weight. Increasing the dietary protein level resulted in an increase in CCW, chest width, carcass protein content, M. longissimus dorsi depth and fatness class and weight of liver and kidney. The effects of cimaterol and increasing the dietary crude protein level were additive for CCW, chest width and carcass crude protein content. The lack of a significant statistical interaction for these measurements suggested that different modes of action were involved. However, significant interactions for M. longissimus dorsi depth and plasma urea concentrations indicate that the effect of cimaterol was greatest in animals offered the low protein diets.