PSXII-9 Complete feed versus concentrate and straw fed separately: effect on feed intake, sorting, animal behavior, and rumen pH and digestibility in crossbred Angus bulls fed high-concentrate diets

Abstract Twenty-one crossbred Angus bulls (497 ± 7.7 kg of BW and 324 ± 3.0 d of age) were housed individually to evaluate the effect feeding method on feed intake, sorting, animal behavior, and digestibility. Dietary treatments, offered ad libitum, were: complete feed of pellet (concentrate) mixed with chopped straw (5 cm length; TMR); pellet and chopped straw (5 cm length; SS); pellet and long unprocessed straw (15–20 cm length; LS). In SS and LS straw and concentrate were fed separate feeders. Feed intake, fecal and bloat scoring were recorded daily. Behavior (scan sampling), BW, and TMR particle size sorting were recorded fortnightly. Total tract apparent digestibility (day 14 and 35) and rumen pH and VFA samples via rumenocentesis (day 28 and 42) were analyzed. Data were analyzed using a mixed-effect model. No differences in concentrate and straw intake, fecal and bloat scoring among treatments were observed. The straw to concentrate ratio did not differ between SS and LS (8 to 92), and was smaller than the ratio fixed in TMR (15 to 85). TMR bulls sorted (P < 0.05) particles with a size between 1.7 and 4 mm. Treatment did not affect rumination time. TMR showed (P < 0.05) more oral non-nutritive behaviors than SS. Rumen pH was greater (P < 0.01) in TMR than in SS and LS, although it was above 5.6 in all treatments. Rumen acetate to propionate ratio was greater (P < 0.05) in TMR than in SS and LS. LS bulls had greater DM (P < 0.05) and CP (P < 0.01) digestibility compared with SS or TMR bulls. Feeding concentrate and straw (short or long) separately does not increase the risk of rumen acidosis compared with TMR, and feeding long straw separately from the concentrate improves the total tract apparent DM and CP digestibility.