The nutritive value of canola, heat-treated canola and fish meals as protein supplements for lambs fed grass silage

Twenty-eight lambs (23.4 ± 4.7 kg BW, 59 days old) were used to compare fish meal to canola and heat-treated canola meals as protein supplements to grass silage and their effects on the performance and apparent digestibility of diets. Silage was fed ad libitum, assuring 20% orts. In addition to silage, lambs received daily a fixed quantity of one of four supplements: C, a control supplement supplying 6.78 g kg−1 BW of a commercial diet (73.5% barley, 14.7% dry molasses and 11.8% minerals, vitamins and Bovatec); CM, control supplement + 8.05 g kg−1 BW of canola meal; HCM, control supplement + 7.52 g kg−1 BW of heated-canola meal (105 min at 150°C) and FM, control supplement + 4.0 g kg−1 BW of fish meal. Heating decreased the effective degradability of canola meal protein from 78.5% to 19.8%. Silage dry matter (DM) intake was not affected by protein supplementation. Supplementation with CM and FM improved the average daily gains (ADG) by 60.2% and 49.7%, respectively, when compared to lambs that were fed with C diet (P < 0.01). Heated CM had little effect on ADG (233 and 191 g for HCM and C, respectively; P > 0.10). Feed efficiency was 32.4% higher in lambs fed with CM and FM than in those receiving the C and HCM treatments (P < 0.05). Carcass yield and classification were not affected by the treatments. Fish meal supplementation did not affect the apparent digestibility of the diets, but CM and HCM decreased the digestibility of DM, neutral detergent fiber (NDF) and acid detergent fiber (ADF) (P < 0.05). The heating of canola meal resulted in decreased apparent digestibility of DM, energy, protein and NDF (P < 0.05) when compared to lambs fed with CM. Nutritive value (intake × digestibility) of the diets was lower for lambs fed with HCM than for those fed with CM and FM. Protein supplementation improved the efficiency of ME utilization for growth when compared to lambs fed with C diet. Canola meal was as good as fish meal as a protein supplement for lambs fed with high-silage diets. The heat-treatment applied to canola meal resulted in a decrease in protein availability, thus decreasing its nutritive value.