Effect of ammonia treatment on physical strength of rice straw, distribution of straw particles and particle-associated bacteria in sheep rumen

We measured the physical strength (resistance to shearing) of untreated rice straw (UTS) and ammoniated rice straw (ATS) fragments with reference to bacterial attachment and colonization in the rumen of sheep. The animals were fed iso-nitrogenous diets, each consisting of either UTS or ATS, and concentrate with or without urea. Physical strength was determined from the resistance to shearing by a razor blade attached to a rheometer. The strength was significantly lower for ATS fragments, compared to UTS fragments in both the in situ and in vivo studies. The shear test also indicated that physical strength is higher for thicker straw fragments. Reduction in the strength with incubation time was apparent for in situ samples, but not for in vivo samples. ss of bacteria tightly associated with straw, calculated on the basis of diaminopimelic acid concentration, significantly increased (P<0.05) in ATS diets at 2 h after feeding. Ammonia treatment tended to reduce (P<0.20) the dry matter proportion of large particles (>5600 μm) and medium particles (1180–5600 μm) and to increase (P<0.10) that of small particles (300–1180 μm). Bacterial concentration tended to increase as the particle size decreased in both UTS and ATS diets, but the differences were not significant (P>0.20). Meanwhile, bacterial concentration on small particles tended to be greater in ATS than in UTS (P<0.15). results suggest that reduced mechanical resistance through ammoniation gives a higher fragility of rice straw to promote particle size reduction and exposure of particle sites available for bacterial attachment and growth.