Authors: A. Y. ABDULLAH, M. M. MUWALLA, M. Y. HARB
Abstract: Sixty four newly weaned Awassi lambs (initial BW = 21.0 ± 0.75 kg) from both sexes were randomly allocated to one of the four treatments (8 males & 8 females/treatment) and grouped into 8 pens with 8 lambs from each sex per pen. They were then used to evaluate the different sources of protein on a finishing performance trial. The lambs were fed for a period of 114 days using four different rations. These rations were so formulated as to contain the same percentage of crude protein 14 %, but from different sources namely sunflower seed meal (SSM), bitter vetch seed (BVS) and urea. Comparisons were made with the control diet having soybean meal (SBM) as a major source of protein. Four animals from each group were slaughtered and the right leg from each carcass was dissected for examination of differences in muscularity and for carcass and leg composition. Average feed intake over the first 8 weeks of the trial increased linearly (P<0.001) for both sexes within each treatment. Total feed intake for all lambs did not differ significantly between treatments, but there was a significant difference (P<0.001) between sexes, being higher for males. No differences (P>0.05) in final live weight, average live weight gain or average daily gain were detected between lambs given different protein sources. Male lambs, however, had significantly (P>0.001) higher final live weight (47.2 Vs 37.9 kg), average live weight gain (26719 Vs 16409g) and average daily gain (234 Vs 144 g/day) than female lambs. The SBM ration had significantly a higher feed efficiency value compared to the other experimental rations (3.22, 4.20, 3.99, and 3.77 kg/kg for SBM, SSM, BVS, and urea, respectively). The production responses to the rations were observed only in the first 14 days of the experiment. Thereafter, no significant differences in intake on body weight were obtained through day-56 or day-114. Thus, the BVS and urea rations both gave a high feed efficiency which was comparable to that of the SBM ration (6.21, 6.20 Vs 6.10 kg/kg for BVS, urea and SBM, respectively). The male lambs showed higher feed efficiency (P<0.05) than the female lambs over the three periods. Supplemental protein sources had no efect (P>0.05) on hot and cold carcass weight, dressing-out pencentage, tail fat weight, all non-carcass component weights, all carcass linear dimensions or on the dissected leg tissue weight. The male lambs, however, had higher (P<0.001) hot and cold carcass weight, kidney weight, liver weight and heart weight, but had lower (P<0.001) mesenteric fat weight, kidney fat weight, total leg fat weight (P<0.05) and muscle-to-bone ratio (P<0.05) than the female lambs.
Keywords: Awassi lambs; protein; performance; feedlot; carcass characteristics.
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