Evaluating sugarcane diets for dairy cows using a digestion model

To eliminate unnecessary feeding trials, a mechanistic model of sugarcane d igestion was used in the search for suitable supplements to improve milk pr oduction. Milk production simulated by the model was compared with data obs erved in four feeding trials published in the tropical literature where cro ssbred dairy cows were fed sugarcane/urea diets with different types of sup plements. The predicted effects of the supplements on the ruminal microbial population, concentrations of ammonia and volatile fatty acids were also c ompared with the published results in one experiment. The model indicated t he nutrient most limiting milk production for the different feeding situati ons. The addtion of Leucaena to the basal sugarcane/urea improved the avail ability of amino acids and long-chain fatty acids, with energy becoming the limiting factor. Supplementation with rice bran increased the availability of energy and long-chain fatty acids, but amino acids then became the limi ting factor. Supplementation with both Leucaena and rice bran further impro ved the milk yield, but availability of energy now limited milk production. Supplementation with Leucaena increased milk production more than suppleme ntation with king grass. The main reason for this increase was increased am ino acid absorption due to increased microbial outflow. In all feeding situ ations, the average difference between the predicted milk production and th at observed experimentally was 0.57 kg/d (ranging from 0.08 to 1 kg/d).