Influence of protein level on growth performance, dietary energetics and carcass characteristics of Pelibuey × Katahdin lambs finished with isocaloric diets

Forty Pelibuey × Katahdin intact male lambs (23.0 ± 1.8 kg initial shrunk weight) were used in an 84-day feeding trial (5 pens per treatment, randomized complete block design) to evaluate crude protein level (110, 140, 170, and 200 g/kg diet DM) in isocaloric diets (2.03 Mcal NEm/kg) on finishing-phase growth performance, dietary energetics and carcass traits. Increases in protein levels were accomplished by increasing levels of canola and meat meal. Tallow was used to equilibrate energy levels among diets. Increasing dietary protein level increased (linear effect, P = 0.01) 84-d average daily gain, dry matter intake (linear effect, P = 0.03), and gain efficiency (linear effect, P < 0.01). The ratio of observed:expected dietary net energy increased (linear effect, P ≤ 0.02) with increasing protein level during initial 56 days. However, overall the 84-d effect was not appreciable (P = 0.17). Hot carcass weight, kidney-pelvic-heart fat, and fat thickness increased (linear effect, P ≤ 0.03) with dietary protein level. However, treatments effects on longissimus thoracis area, wall thickness, estimated yield grade, and carcass composition were not appreciable. It is concluded that during the initial growing phase (first 56 days) increasing dietary CP level up to 170 g CP/diet DM will enhance growth performance and efficiency of energy utilization. Thereafter (final 28 days), the effect of dietary CP levels greater than 110 g CP/kg diet DM on growth-performance and dietary energy utilization are not appreciable.