COMPOSITION OF RUMINAL BACTERIA HARVESTED FROM STEERS AS INFLUENCED BY DIETARY FORAGE LEVEL AND FAT SUPPLEMENTATION

The objective of this study was to examine the effects of dietary fora ge level and fat supplementation on the chemical composition of mixed ruminal bacteria (MRB). Six ruminally cannulated beef steers (354 kg /- 18) were given ad libitum access to six diets (13.2% CP; DM basis) that were offered twice daily in a 6 x 6 Latin square design. Treatmen ts 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 fat supplementation including no canola seed or canola seed added at 10% of dietary DM as whole treated with alkaline hydrogen peroxide or untreated crushed. C anola seed contributed 5% added fat to the total diet. The remaining d ietary ingredients were corn, canola meal, molasses, and urea. No inte ractions (P >.05) between dietary forage level and canola seed supplem entation were observed. Concentrations of OM, N, and all amino acids w ere higher (P <.05) in MRB from steers fed low forage than in MRB from steers fed high forage. Concentrations of purines and GE and the N:pu rines ratio in MRB were not affected (P >.05) by dietary forage level or canola seed supplementation. Canola seed supplementation did not af fect (P >.05) concentrations of OM, N, or most of the amino acids in M RB. Concentrations of four essential amino acids (i.e., isoleucine, le ucine, lysine, and phenylalanine) in MRB were decreased (P <.05) due t o canola seed supplementation. Dietary forage level did not affect (P >.05) concentrations of long-chain fatty acids in MRB. However, canola seed supplementation decreased(P <.05) concentrations of C17:0 and in creased (P <.05) concentrations of C18:0, C20:0, and total long-chain fatty acids in MRB. Supplementation of diets with crushed untreated ca nola seed increased (P <.05) concentrations of C18:1 and C18:3 fatty a cids. Because canola seed is rich in C18 unsaturated fatty acids, espe cially C18:1, results indicate dietary incorporation into bacterial ce lls when the fatty acids were made available by crushing.