VOLUNTARY INTAKE AND DIGESTIBILITY BY MATURE BEEF-CATTLE AND HOLSTEINSTEER CALVES CONSUMING ALFALFA OR ORCHARDGRASS HAY SUPPLEMENTED WITH SOYBEAN OIL AND(OR) CORN

Effects and interactions of corn and soybean oil supplementation and f orage source on feed intake and digestibility by mature and growing ca ttle were determined. Eight mature beef cattle (571 +/- 17 kg initial body weight) were used in two simultaneous 4 x 4 Latin squares. Cattle in each square consumed long-stemmed alfalfa (AL; 16% crude protein, 54% neutral detergent fibre and 6.1% acid detergent lignin) or orchard grass (OR; 11% crude protein, 71% neutral detergent fibre and 9.4% aci d detergent lignin) hay ad libitum for 15 d followed by 6 d of restric ted consumption (85% of ad libitum). Supplement treatments were Contro l, ground corn (C; 0.5% body weight), soybean oil (O; 0.125% body weig ht), or C+O. Total ad libitum dry matter (DM) intake was greater for A L than for OR (P < 0.05) and with than without C (P < 0.05), and a cor n x soybean oil interaction occurred (P = 0.07; 11.8, 14.0. 13.6, 14.2 , 8.4, 10.7, 9.3 and 10.3 kg/d); total tract neutral detergent fibre ( NDF) digestibility was 66.0, 67.7, 65.8, 68.8, 52.5, 50.6, 55.1 and 59 .4% for AL, AL-C, AL-O, AL-C+O, OR, OR-C, OR-O, and OR-C+O, respective ly (SE 2.46). Eight Holstein steer calves (83 +/- 5 and 131 +/- 11 kg initial and final body weight, respectively) were subjected to the sam e dietary treatments, except for higher levels of C (1.0% body weight) and O (0.25% body weight) and periods with 21 d of ad libitum forage intake. Total DM intake was greater (P = 0.06) for AL than for OR, inc reased (P < 0.05) by C, and decreased (P < 0.05) by O (3.92, 4.17, 3.5 1, 4.00, 2.53, 2.90, 2.09 and 2.51 kg/d), and total tract NDF digestib ility was affected by forage source (P < 0.05) and a corn x soybean oi l interaction (P = 0.08; 58.8, 56.9, 60.1, 56.0, 41.9, 44.5, 45.8 and 40.1% for AL, AL-C, AL-O, AL-C+O, OR, OR-C, OR-O and OR-C+O, respectiv ely). In conclusion, effects of supplementation with corn and (or) soy bean oil on feed intake and digestibility were similar for AL and OR, which differed in voluntary intake and digestibility, and animal chara cteristics such as stage of maturity may have influenced effects of so ybean oil on feed intake.