Digestion properties of ammoniated rice straw in the rumen and lower tract of sheep

The effect of ammoniation of rice straw (2 g NH₃ per 100 g dry matter (DM)) on digestibilities and fermentation in the rumen and lower tract of sheep was investigated. Four sheep fitted with cannulae in the rumen and the duodenum were used in a 4 × 4 Latin square experiment. Diets were formulated to contain 80% rice straw and 20% supplement. These were an ammoniated rice straw diet (80% ammoniated rice straw +20% formula feed), a urea-supplemented diet (80% untreated rice straw +18.9% formula feed +1.1% urea), a soya-bean meal diet (80% untreated rice straw +11.1% formula feed +8.9% soya-bean meal) and a control diet (80% untreated rice straw +20% formula feed). There was a significant increase (P < 0.05) in apparent rumen organic matter (OM) digestibility in sheep on the ammoniated rice straw diet. Apparent total tract DM and OM digestibilities were increased (P < 0.05) in ammoniated rice straw-fed animals. The digestibility was 11% greater than that of the control. Apparent ruminal neutral detergent fibre (NDF) digestibilities were enhanced (P < 0.05) in animals on the ammoniated rice straw diet and the diet supplemented with soyabean meal. However, digestibility of the ammoniated rice straw diet was 13% greater than that of the diet supplemented with soya-bean meal. Total tract NDF digestibility in the ammoniated diet was 17% greater than that of the control. At all sampling periods, the total volatile fatty acid (VFA) was highest and pH lowest in animals on the ammoniated diet. Ruminal n-butyrate proportion was increased (P < 0.05) in sheep fed the ammoniated diet at 0 h. Total VFA and acetate proportion in rectal samples of animals fed the ammoniated rice straw diet were significantly lower (P < 0.05). However, n-butyrate and n-valerate proportions were increased (P < 0.05). Gram-negative cocci and gram-negative rods appeared to be the predominant bacteria in sheep on rice straw diets. There was a significantly higher (P < 0.05) rectal total bacterial count in sheep on the ammoniated diet. Ruminal cellulolytic bacterial count tended to increase in animals fed the ammoniated diet. Neither bacterial flow at the duodenum nor nitrogen retention differed significantly among treatments.