Complete feed versus concentrate and straw fed separately: Effect of feeding method on eating and sorting behavior, rumen acidosis, and digestibility in crossbred Angus bulls fed high-concentrate diets

Abstract

The aim of this study was to evaluate the effect of feeding method on eating and sorting behavior, rumen acidosis, and apparent total tract digestibility of crossbred Angus bulls fed a high-concentrate diet. Twenty-one Angus beef bulls (497 ± 7.7 kg of initial BW, and 324 ± 3.0 d of age) were housed individually and fed ad libitum. Three experimental treatments were tested: complete feed of pellet and chopped straw in a single feeder (TMR), pellet and chopped straw fed separately in two feeders (SS); pellet and long unprocessed straw fed separately in two feeders (LS). Feed consumption, fecal and bloat scoring were recorded daily. Every 2 wk TMR sorting, eating behavior, general activity, social and oral behaviors, and BW were recorded. At days 14 and 35 apparent total tract digestibility during one week was measured. At days 28 and 42 rumen samples were collected via rumenocentesis to measure rumen pH and determine ruminal volatile fatty acids (VFA) concentrations. At the study end (day 57) animals at slaughterhouse liver and rumen wall color and lesions were recorded by a macroscopic inspection. No differences among treatments in total DMI, and fecal and bloat scoring were observed. The straw to concentrate ratio was smaller in the SS and LS treatments (8–92) than in the TMR (15–85), and sorting analyses indicated that TMR bulls refused large particles (> 4 mm) and small particles (< 1.5 mm). TMR bulls spent less time eating (P < 0.01) and tended to perform more self-grooming (P = 0.06), oral non-nutritive behaviors (P < 0.01) and stereotypes (P < 0.01) than bulls fed straw separately. Animals fed TMR had a greater (P < 0.01) pH than SS and LS, however rumen pH was above 5.6 in all treatments and rumen wall lesions did not differ among treatments. Feeding TMR increased (P < 0.05) the rumen acetate to propionate ratio. Bulls fed LS had greater total apparent DM (P < 0.05) and CP digestibility (P < 0.01), but no differences among treatments were observed in starch digestibility. In conclusion, even if straw to concentrate ratio and NDF intake was smaller in the SS and LS treatments than in the TMR, feeding pellet and straw separately, independently of straw length, did not predispose animals to suffer rumen acidosis as indicated by rumen pH, feed consumption, animal behavior, fecal and bloat scoring and rumen wall macroscopic evaluation.