Effects of the nature of roughage and concentrate and their proportion on ruminal characteristics of non lactating goats, consequences on digestive interactions

The effects on ruminal characteristics of 14 diets differing in nature and level of roughage and concentrate have been studied. The roughages were alfalfa hay (AH) or maize stover silage (MS) distributed alone or in a mixed diet containing 30 or 60% concentrate on a dry matter basis. Three types of concentrate were formulated to be either rich in rapidly degradable starch (RS), slowly degradable starch (SS) or digestible fibre (DF). The post feeding evolutions of pH, volatile fatty acids (VFA) and ammonia (NH3) concentrations in ruminal fluid were measured. Microbial protein synthesis has been estimated. Ruminal pH was consistently high (pH > 6.3) and VFA concentrations in the rumen were 88.4 mmol L−1. VFA concentrations were higher after AH compared with MS, whereas differences between concentrates were not significant. The proportion of acetate decreased with the concentrate level while that of propionate increased. The NH3 concentration was always over 50 mg L−1 and varied significantly with the tested diets. The efficiency of microbial nitrogen synthesis (EMS) was 32.7 g per kg of organic matter apparently digested in the rumen without significant differences between roughages or concentrates. No difference (P < 0.05) was observed between the depressive effect of concentrates on the cellulolysis in the rumen.