Sixteen ruminally cannulated yearling beef cattle (British x British; average BW = 295 +/- 25 kg; three steers and one heifer per treatment) grazing dormant intermediate wheatgrass (Thinopyrum intermedium Host) were allotted to four treatments: 1) no supplement (CON); 2) alfalfa hay (ALF; .52% of BW); 3) cottonseed meal (CSM; .22% of BW); and 4) corn gluten meal-wheat bran feed (CGMWBF; .36% of BW). Supplements were formulated (DM basis) so that intakes were isonitrogenous and were provided once daily (0700). Sampling periods were in February (FEB; .96% N in masticate), March (MAR; 1.06% N in masticate), and April (APR; 1.12% N in masticate) following an initial 21-d adaptation period. Daily grazing time was 1.1 to 1.5 h longer (P < .05) for CON cattle than for supplemented cattle. Forage OM intake (OMI) was not altered (P > .15) by supplemental protein; however, total OMI was greater (P < .04) for supplemented than for unsupplemented cattle. Harvesting efficiency (grams of OM intake-kilogram of BW-1.minute spent grazing-1) was greater (P < .05) for cattle fed CSM than for those fed CGF or CON; cattle fed ALF were intermediate in harvesting efficiency. Ruminal fluid kinetics, in situ rate and extent of NDF digestion, and total VFA concentration were not influenced (P > .10) by type of supplemental protein. Ruminal NH3 N concentration exhibited a treatment x sampling time interaction (P < .05). Type of protein supplement did not seem to affect most digestion measures; however, harvesting efficiency was influenced by supplement type.

Crossbred wethers (n = 18, 7.5 month of age and 31 +/- 0.8 kg) were used in a 23-day experiment to determine effects of ad libitum consumption of diets differing in proportions of coarsely chopped bermudagrass and ryegrass-wheat hay (0, 33, 67 and 100%) on oxygen consumption by splanchnic tissues. Bermudagrass and ryegrass-wheat were 9 and 13% CP and 78 and 71% NDF, respectively. Intake of dry matter (1.03, 0.92, 0.92 and 0.76 kg/d) and digestible energy (13.5, 10.7, 10.6 and 8.2 MJ/d for 0, 33, 67 and 100% bermudagrass, respectively) changed linearly and cubically (P < 0.05) as bermudagrass level increased. Consumption of oxygen by the portal-drained viscera tended to decrease linearly (P = 0.14) with increasing bermudagrass (182, 154, 156 and 137 mM/h), and hepatic oxygen consumption decreased linearly (P < 0.05) and changed cubically (P = 0.07; 150, 113, 116 and 103 mM/h for 0, 33, 67 and 100% bermudagrass, respectively). Splanchnic tissue energy consumption expressed as a percentage of digestible energy intake increased linearly (P = 0.08) with increasing bermudagrass (24.0, 27.6, 28.6 and 33.2% for 0, 33, 67 and 100% bermudagrass, respectively). In conclusion, the level rather than presence alone of different grass sources consumed ad libitum affected energy use by the splanchnic bed, and as a percentage of digestible energy intake splanchnic bed energy consumption increased with increasing dietary bermudagrass level and decreasing digestible energy intake.

Effects and interactions of corn and soybean oil supplementation and forage source on feed intake and digestibility by mature and growing cattle 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 orchardgrass (OR; 11% crude protein, 71% neutral detergent fibre and 9.4% acid detergent lignin) hay ad libitum for 15 d followed by 6 d of restricted consumption (85% of ad libitum). Supplement treatments were Control, ground corn (C; 0.5% body weight), soybean oil (O; 0.125% body weight), or C + O. Total ad libitum dry matter (DM) intake was greater for AL than for OR (P < 0.05) and with than without C (P < 0.05), and a corn 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, respectively (SE 2.46). Eight Holstein steer calves (83 +/- 5 and 131 +/- 11 kg initial and final body weight, respectively) were subjected to the same 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, increased (P < 0.05) by C, and decreased (P < 0.05) by O (3.92, 4.17, 3.51, 4.00, 2.53, 2.90, 2.09 and 2.51 kg/d), and total tract NDF digestibility was affected by forage source (P < 0.05) and a corn x soybean oil 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, respectively). In conclusion, effects of supplementation with corn and (or) soybean oil on feed intake and digestibility were similar for AL and OR, which differed in voluntary intake and digestibility, and animal characteristics such as stage of maturity may have influenced effects of soybean oil on feed intake.