RUMEN FERMENTATION CHARACTERISTICS AND DUODENAL NUTRIENT FLOW IN LACTATING COWS RECEIVING 2 TYPES OF GRASS-SILAGE WITH 2 LEVELS OF CONCENTRATES

Four lactating dairy cows were used, each equipped with simple cannula e in the rumen and duodenum. Each cow was given, in a 4 X 4 Latin squa re arrangement, four diets consisting of an early cut (EC) or late cut (LC) grass silage ad libitum each with either 3 (low) or 9 (high) kg dry matter (DM) of concentrates daily. Total and silage DM intake were significantly (P<0.01) higher on LC silage. Total DM intake was highe r but silage DM intake was lower with the higher level of concentrates . Acid detergent fibre and neutral detergent fibre digestion in the ru men were significantly (P<0.05) higher on EC silage diets compared wit h LC silages. Mean rumen pH was significantly affected by silage type and concentrate level, being lower on EC silages and on 9 kg concentra tes. Mean ammonia nitrogen and total volatile fatty acid (VFA) concent rations were similar on all diets although the concentrations of indiv idual VFA (except propionic) were significantly affected by silage typ e. Molar proportions of acetic acid were significantly (P<0.01) lower on high concentrate diets compared with low concentrate diets and thos e of propionic acid were significantly (P<0.01) higher. Proportions of butyric acid were significantly (P<0.01) lower on EC diets. Non-ammon ia nitrogen and microbial nitrogen flows at the duodenum were signific antly higher (P<0.05) on EC compared with LC silages and with diets co ntaining high compared with low levels of concentrates (P<0.01). Effic iencies of microbial protein synthesis were significantly higher (P<0. 05) on EC compared with LC based diets but there were no effects due t o concentrate level. Milk yields were significantly (P<0.05) higher on EC diets and with higher levels of concentrates with both silages (P< 0.01). Milk fat concentrations were significantly (P<0.05) lower on EC compared with LC diets and on 9 kg concentrate compared with 3 kg con centrate containing diets (P<0.01). Constituent yields were significan tly increased with the higher concentrate level on both silages but on ly lactose yield was influenced by silage type.