Digestion by sheep of monosaccharide constituents of direct cut alfalfa silage made with SO 2-treated wheat straw

Abstract

Alfalfa was ensiled either by conventional wilting (WA) or as a mixture of fresh alfalfa plus SO 2-treated wheat straw (A+SWS) at a dry matter (DM) ratio of 67:33 and the digestibility of carbohydrate constituents and some aspects of N-metabolism were examined in sheep. By adding SWS to alfalfa, the content of neutral detergent fiber (NDF) was increased from 34.8 to 42.6% and that of total N was decreased from 2.84 to 2.61%. Silage pH was 4.51 and 5.91 in A+SWS and WA silages, respectively. The major part of uronic acids (74–78%), rhamnose (65–68%) and arabinose (65–67%) was found in the neutral detergent soluble (NDS) fraction of the silages, implying pectin survival following silage fermentation. The digestibility values of the major sugars, glucose and xylose in whole silage were higher in A+SWS than in the WA. Consequently, whole tract carbohydrate digestibility was 71% in WA and 75% in A+SWS. The difference between treatments in carbohydrate digestibility originated from the digestibility pattern of NDF-monosaccharide components. The major difference was found with NDF-xylose, 31.0% versus 58.3% in WA and A+SWS silages, respectively. Total NDF-monosaccharide digestibility values were 61.4 and 69.9% in the WA and A+SWS silages, respectively. Rumen ammonia-N was 23.1 and 16.5 mg/100 ml in sheep fed the WA and A+TWS silages, respectively. Although, N-intake by the WA sheep was higher, the amount of non ammonia-N present at the duodenum was almost equal in both treatments.