COMPARISON OF WHOLE, RAW SOYBEANS, EXTRUDED SOYBEANS, OR SOYBEAN-MEAL AND BARLEY ON DIGESTIVE CHARACTERISTICS AND PERFORMANCE OF WEANED BEEF STEERS CONSUMING MATURE GRASS HAY

Two experiments were conducted to compare whole, raw soybeans (WSB), extruded soybeans (ESB), and soybean meal + barley (SBM+BAR) as supplemental protein sources for growing beef steers consuming low-quality, mature grass hay (6.5% CP). In Exp. 1, a 23-d digestion study, four ruminally cannulated steers were assigned to the following treatments in a 4 x 4 Latin square design: 1) control, no supplement; 2) 1.5 kg.animal-1.d-1 of WSB; 3) 1.36 kg.animal-1.d-1 of ESB; and 4) 1.48 kg.animal-1.d-1 of 62%:38% SBM+BAR. Apparent DM digestibility was increased by supplementation (P < .10), but NDF digestibility was not changed (P > .10). No differences in digestibility were observed among supplement treatments (P > .10). In situ rate and extent of supplement CP disappearance in Dacron bags did not differ among supplements (P > .10), but extent of DM disappearance was greater for WSB than for ESB (P < .10). In situ rate of forage NDF disappearance was decreased by protein supplementation (P = .10). In Exp. 2, 40 Polled Hereford and Red Angus x Simmental weanling steer calves were stratified by weight (average BW, 250 kg) and allotted randomly to one of two replications of the four treatments used in Exp. 1 (eight pens, five animals per pen). Forage DMI was not affected by treatment (P > .10). Average daily gain and feed efficiency were increased by supplementation (P < .05). Supplement source had no effect on intake or ADG (P > .10), but ESB tended to exhibit better feed efficiency than WSB (P = .10). In conclusion, WSB and ESB seem to be as effective as SBM+BAR protein supplements for growing beef cattle. In addition, WSB and ESB, at the levels used in these experiments, can be incorporated into diets for cattle consuming low-quality roughage without deleterious effects on fiber digestion or subsequent performance.