Net and metabolizable protein requirements for body weight gain in hair and wool lambs

Protein is one of the limiting factors in animal production, and the knowledge of protein requirements by livestock is crucial for the success of a commercial animal raising enterprise. Thirty-four castrated lambs, 17 of them F1 Ideal × Ile de France wool lambs and the remaining ones were Santa Inˆes hair lambs, with homogeneous initial BW, were used in the experiment. Five animals from each genotype were slaughtered in the beginning of the experimental period and used as reference. Diets (D) were composed of concentrate mix (C) and Cynodon sp. c.v. Tifton 85 hay (R), combined in three different ratios: D1 = 60C:40R; D2 = 40C:60R and D3 = 20C:80R. Animals of each group of three lambs, that showed simultaneously an initial BW of 20±0.14 kg at the beginning of the dietary regimen, were slaughtered when one of them reached 35 kg, what always happened to be the one fed with D1. Net requirements for BW gain in wool lamb, fleece-free, ranged from 101 to 110 g of protein/kg BW, and for hair lamb ranged from 110 to 118 g of protein/kg BW. Net protein requirements for wool production ranged from 634 to 642 g/kg of produced wool. Hair lambs presented a 7.8–9.5% higher estimated net protein requirements than wool lambs, according to BW and daily weight gain (DG). Total net protein requirements for Santa Inˆes and wool lambs, with 30 kg of initial BW and an approximate 200 g mean DG, were 48.5 and 45.4 g/day, respectively. Metabolizable protein requirements for Santa Inˆes and wool lambs, with 20 kg of initial BW and an approximate 200 g mean DG were 59.4 g and 76.5 g/day, respectively. Net protein requirements for wool production was 64 g/100 g of produced wool. Thus, under the conditions of this experiment, it is concluded that hair lambs showed a higher concentration of protein in the body, more efficient use of the ingested protein and a consequent additional BW gain when fed isoproteic diets as compared to F1 Ideal×Ile de France wool lambs. © 2006 Elsevier B.V. All rights reserved.