Evaluation of canola meal derived from Brassica juncea and Brassica napus on rumen fermentation and nutrient digestibility by feedlot heifers fed finishing diets

Abstract

Five yearling heifers (387 ± 6.5 kg) were utilized in a 5 × 5 Latin square to evaluate the substitution of canola meal (CM) derived from Brassica (B.) napus and B.juncea seed for barley grain on feed intake and nutrient utilization. The control diet (CONTROL) consisted of 88.3% barley grain, 4.4% barley silage, and 7.3% supplement [dry matter (DM) basis]. The four CM treatments included 10% and 20% B.napus or B.juncea meal, with CM replacing barley grain. Dry matter intake was not affected (P > 0.05) by treatment. Total duration and area under rumen pH 5.8, 5.5, and 5.2 increased (P < 0.05) with greater inclusion of CM, regardless of type. Cattle fed 20% CM had elevated rumen ammonia-N concentration and urinary N excretion. Cattle fed B. juncea meal exhibited greater (P < 0.05) apparent nutrient digestibility compared with those fed B. napus meal. In conclusion, meal derived from B. napus or B. juncea can be used to replace barley grain at levels up to 20% (DM) in finishing diets without compromising rumen fermentation or total tract nutrient digestibility. However, animal performance and possible economic benefits need to be balanced against the increasing N excretion resulting from over-feeding protein to cattle.