The Effect of Protein Source and Formaldehyde Treatment on Growth and Carcass Composition of Awassi Lambs

A trial with twenty-four newly weaned Awassi lambs (initial body weight=21.5$\pm$0.8 kg) was conducted using a 3$\times$2 factorial design to study the effect of feeding three sources of protein supplements (soybean meal (SBM), sunflower seed meal (SSM), and cottonseed meal (CSM)), either untreated or formaldehyde-treated on the growth performance and carcass traits of Awassi lambs. Lambs were randomly assigned to one of the six diets (4 lambs/treatment diet) and were individually fed for a period of 107 days. Experimental diets were isonitrogenous and isocaloric. Final live weight and average daily gain (ADG) were affected by both source of protein and formaldehyde treatment (undegradable protein). Lambs fed untreated diets had better (p<0.01) daily gain compared to those fed formaldehyde-treated diets. Similarly total feed intake per animal was significantly (p<0.05) affected by protein source and formaldehyde treatment. Formaldehyde treatment caused a significant decrease (p<0.01) in feed intake compared to lambs fed untreated diets. Feed requirement per unit of gain was not affected by formaldehyde treatment during all periods of the experiment except for the second period (the second 28 day period), whereby untreated SBM, SSM and CSM had better feed conversion ratio (FCR) than the treated groups. Source of protein had a moderate effect (p<0.10) on FCR but had a significant effect (p<0.05) on hot and cold carcass weight, digestive tract empty weight and liver weight, with lambs fed SBM having higher values than lambs fed SSM and CSM diets. Supplementation with undegradable protein had a significant effect (p<0.05) on dressing-out percentage (p<0.05), final live weight, and hot and cold carcass weight (p<0.01). The lower values pertain to lambs fed treated diets compared to lambs fed untreated diets. In general, there were no significant differences among all carcass linear dimensions, carcass cut weights and dissected loin tissue weights for both treatments (protein source and formaldehyde treatment). Supplementation with undegradable protein but not the source of protein resulted in significantly higher dissected leg total bone weight (p<0.05), tibia and femur weight (p<0.05), and femur length (p<0.01) at the same carcass weight. Results suggest that the treatment of SBM, SSM and CSM with formaldehyde did not improve efficiency of feed utilization, lamb performance or carcass traits and that the SBM diet resulted in an increase in lamb performance compared to other experimental diets.