Effects of substituting barley grain with corn on ruminal fermentation characteristics, milk yield, and milk composition of Holstein cows

The influence of corn or barley, or the equal mixture of both, on digestion characteristics and dairy cow performance was evaluated in metabolic and production experiments. Three rumen-cannulated early-lactation cows were used in a 3 x 3 Latin square design experiment to study the effect on ruminal fermentation characteristics and whole-tract digestion of substituting barley grain with corn.. Production responses were determined by the use of 27 early-lactation Holstein cows. Cows in the production study were fed the test diets for 12 wk after a 2-wk covariate period. Results from the metabolic study indicated the effects of grain source on ruminal and total-tract digestion to be minimal. Total ruminal volatile fatty acids and acetate concentrations decreased linearly, butyrate increased linearly, and pH and lactic acid concentration were not affected by increasing levels of corn. Apparent digestibility of DM and organic matter showed a quadratic response with increasing the corn level in the diet, with no dietary effect on neutral detergent fiber, acid detergent fiber, and cellulose digestion. Ruminal fermentation characteristics suggest that substitution of barley grain with corn may alter the site of digestion and the end products of digestion that are absorbed by the animal. Multiparous cows failed to respond to treatment, whereas primiparous animals showed the greater response in milk yield and milk-component yield to diets that contained an equal mixture of corn and barley. These results probably reflect a more optimal synchronization of dietary protein and energy for dairy cows fed the 50:50 barley/corn diet.