Effects of crude protein content, protein degradability and energy concentration of the diet on growth and carcass characteristics of market lambs fed high concentrate diets

Abstract

Weaned lambs (186 females and 141 castrated males) of various genotypes averaging 16.2 kg were used in an experiment to determine the effects on growth of altering protein and energy content of the diet, and supplementing concentrate diets with undegradable protein. Dietary effects on carcass leanness were assessed using male lambs slaughtered at a live weight of 41 kg. Lambs were fed one of five barley and canola meal based diets: (1) high energy, 15% CP, no fishmeal, (2) high energy, 15% CP, added fishmeal, (3) high energy, 18% CP, no fishmeal, (4) high energy, 18% CP, added fishmeal, and (5) moderate energy, 18% CP, added fishmeal. Canola meal contained 42.3% CP with a rumen degradability of 48.1%, while fishmeal contained 76.2% CP with a degradability of 15.2%. Diet 5 reduced growth rate, increased days on test, decreased feed efficiency, decreased dressing percentage, reduced internal fat and marginally decreased subcutaneous fat deposition, compared with a higher energy diet. Level of CP and protein degradability had little effect on growth and carcass characteristics. Dietary regime has limited potential to alter carcass leanness of feedlot lambs except by feeding for reduced growth rate which may increase production costs. Genetic selection and use of low input production systems may be more promising methods of improving carcass leanness. Key words: Lamb, crude protein, undegradable intake protein, canola meal, fishmeal, carcass composition