Effect of cereal processing (grinding to 3·5 mm or dry-rolling) in maize- or barley-based high-concentrate diets on rumen environment of beef cattle during the late fattening period.

The type and processing of cereals for beef cattle are key factors to maximize performance without increasing the risk of ruminal acidosis. The current work studied the effect of grinding (G) or dry-rolling (R) the cereals in a concentrate based on maize (M) or barley (B) on the rumen environment of eight 6-month-old Holstein calves, which received either M or B for 70 days, offered as G and R in two consecutive periods. Daily feed intake pattern, rumen fermentation traits, total rumen bacteria and relative proportions of Streptococcus bovis and Selenomonas ruminantium were characterized twice in each period at 0, 4 and 8 h after feeding. Dry-rolling promoted a 0·25 reduction of concentrate intake during the first 4 h after feeding. Neither cereal type nor its processing form promoted differences in ruminal fermentation at 0 and 4 h; however, 8 h after feeding R cereals resulted in higher rumen pH (6·17 v. 5·71) and lower concentration of lactic acid (88·1 v. 156 mg/l) and volatile fatty acids (only in diet B, 118 v. 164 mm/l) compared with G. Little effect of dietary factors in the target rumen microorganisms were observed. The more balanced fermentation observed with R cereals may be explained by the lower concentrate intake promoted during the first 4 h, coupled with a more difficult access of bacterial enzymes to their starch, thus reducing its fermentation rate. Therefore, feeding dry-rolled cereals may be useful to reduce the risk of acidosis by regulating the intake pattern of the concentrate and/or its fermentation rate. [ABSTRACT FROM PUBLISHER]