Intake and digestion by wethers fed a tropical grass-based diet supplemented with increasing levels of canola meal

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Eight Polwarth×Texel wethers (31±3.8kg body weight (BW)), housed in metabolic cages and offered sudangrass (Sorghum sudanense) ad libitum, were used in a replicated 4×4 Latin Square experiment to evaluate the effects of increasing levels of canola meal supplementation on intake, digestibility, duodenal flow of N compounds and on N excretion. Four of the eight wethers were fitted with duodenal cannula. Treatments included no supplement (0) or daily supplementation with 5, 10 or 15g/kg BW of a canola meal mixture (nine parts canola meal one part cracked corn grain). Forage dry matter (DM) intake decreased linearly and total DM, organic matter (OM), digestible OM and N intake increased linearly with increasing levels of supplementation. Supplementation did not affect neutral (NDF) or acid detergent fiber (ADF) digestibility whereas it tended to improve DM and OM digestibility. Fecal and urinary N excretion, as well as duodenal flow of α-amino N and non-ammonia non-microbial N increased linearly with increasing levels of supplementation. Rumen microbial protein flowing to duodenum and the efficiency of rumen microbial protein synthesis were not affected by treatments. The proportion of rumen degradable protein which was used for microbial protein synthesis decreased linearly with increasing levels of supplementation, but at a higher rate than was the reduction of the proportion of N intake which reached the small intestine as α-amino N. In conclusion, despite increasing N excretion and exerting a depressive effect on forage intake, supplementation with a high-degradable true protein source improves α-amino N and energy supply in ruminants fed tropical grass based-diets.