EFFECTS OF FORAGE LEVEL AND CANOLA SEED SUPPLEMENTATION ON SITE AND EXTENT OF DIGESTION OF ORGANIC-MATTER, CARBOHYDRATES, AND ENERGY BY STEERS

The objective of this study was to determine the effects of fat supple mentation from canola seed (CS) on ruminal fermentation and postrumina l digestion of OM, carbohydrates, and energy of diets containing diffe rent levels of forage. Six ruminally and duodenally cannulated beef st eers (354 kg +/- 18) were given ad libitum access to six isonitrogenou s diets that were offered twice daily in a 6 x 6 Latin square design. Treatments were arranged as a 2 x 3 factorial with two forage levels ( 70 vs 30% of dietary DM as corn silage) and three forms of CS suppleme ntation including no CS or CS added at 10% of dietary DM as whole CS t reated with alkaline hydrogen peroxide or untreated crushed CS. Fat fr om CS provided 5% of dietary DM. The remaining dietary ingredients wer e corn, canola meal, molasses, and urea. No interactions (P >.05) betw een dietary forage level and CS supplementation were observed for rumi nal characteristics or digestion of OM, carbohydrates, and energy in t he numen, postruminally, or in the total tract. Fat supplementation fr om CS did not affect (P >.05) DMI. With few exceptions, fat supplement ation did not affect (P >.05) ruminal, postruminal, or total tract dig estibilities of OM, structural and nonstructural carbohydrates, and GE . Ruminal disappearance of GE was decreased (P <.05) when diets were s upplemented with fat fi om whole treated CS, and total tract digestibi lities of OM and GE were decreased (P <.05) when diets were supplement ed with fat from CS in either form. Ruminal pH, concentrations of NH3 N and total VFA, and molar proportions of acetate, propionate, and but yrate were not affected(P >.05) by fat supplementation. Results sugges t that fat supplementation from CS (at 5% of dietary DM) as whole trea ted or untreated crushed had no negative effects on ruminal fermentati on of OM, carbohydrates, or energy when steers were given ad libitum a ccess to diets containing high or low forage.