[The effect of monensin on rumen fermentation and weight gain in bulls fed a diet containing nontraditional feed]

Two groups of bullocks, each consisting of 125 animals, were subjected to a trial to study the effect of monensin (Rumensin premix) administered at doses from 125 to 175 mg per head/day on rumen fermentation and weight gains. For 135 days the animals were given a diet based on green juicy forage with a supplement of chopped straw and concentrate mixture; this mixture contained 20-30% of dried poultry droppings. In the experimental group with monensin, the concentration of total and protein nitrogen and the molar percentage of propionic acid significantly increased (23.7 and 28.5%, respectively, P less than 0.01) and the acetate: propionate ratio decreased four hours after feeding. Further, the energy yield of the production by volatile fatty acids (VFA) significantly increased in the rumen contents (76.89%, 78.64%, respectively, P less than 0.05). The levels of ammonia and non-protein nitrogen were not affected by the addition of monensin. The average daily live weight gains were 713 g in the control group and 800 g in the experimental group; this means that the gains of the experimental animals rose by 12.2%. Monensin had a positive influence on the proportions of the rumen-produced VFA in favour of propionic acid which, in turn, favourably influenced the energy balance of nutrient conversion and efficiency.