Digestibility by dairy cows of monosaccharide components in diets containing wheat or ryegrass silages.

Digestibility by dairy cows of monosaccharide constituents in rations based on wheat or ryegrass silage as the sole roughage component was examined in this study. Six cows in early lactation were divided into two groups with similar performance data at the onset of the experiment and fed for ad libitum intake for two 28-d periods in a change-over design. Cows were fed a TMR of concentrate plus either wheat or ryegrass silage, contributing 19% of silage NDF in the TMR. Digestibilities of ration DM and total carbohydrate were 3.3 and 3.1 percentage units higher, respectively, for ryegrass than for the wheat silage. The digestibility of ration NDF was 64.1% in ryegrass silage and 49.6% in wheat silage. The trend was similar for digestibilities of NDF monosaccharide components. Ration NDF carbohydrate digestibility was 74.8% for ryegrass silage versus 59.7% for wheat silage. For both TMR, the digestibility of NDF xylose was lower than that for NDF glucose and arabinose. Based on carbohydrate digestibility, ryegrass silage can be considered to be a successful roughage alternative for wheat silage in TMR for lactating cows.