Grain supplementation for grazing lactating dairy cows

Three experiments were conducted to evaluate the effect of corn as supplemental concentrate for lactating cows under grazing conditions or fed direct cut forages. The first experiment studied the impact of increasing levels of a ground dry shelled corn based concentrate on nutrient utilization and performance in lactating dairy cows grazing grass-legume pasture. Increasing dietary concentrate was associated with increased yield of milk and solids corrected milk, and intake and digestibility of dry matter and organic matter. Concentrations of ruminal ammonia and milk urea were reduced by increasing levels of supplementation, presumably due to a greater use of ammonia for rumen microbial protein synthesis. The second experiment studied the effect of corn processing (steam rolling or dry grinding) with or without supplemental alfalfa hay on performance and nutrient utilization by lactating cows. Milk production and composition were not altered by corn processing, however, steam rolling tended to increase milk protein content. Supplemental hay reduced fecal starch concentration and decreased digestibility of organic matter. Feeding supplemental hay reduced the rate of liquid passage and tended to reduce the rate of particle passage. Corn processing did not improve starch utilization. The third experiment was a simulation of a grazing situation in which cows were fed direct cut grass-legume forage, with or without supplement containing ground dry shelled corn or high moisture ear corn. Milk and non fat milk solids yields increased with supplementation, but were not affected by corn moisture level. Starch utilization was not affected by moisture level of corn. Cows fed grain supplements had reduced ruminal ammonia concentrations and reduced milk urea. Grain supplementation also resulted in higher urinary allantoin to creatinine ratios which indicated that there was greater energy available for microbial growth. Performance and nutrient utilization by grazing lactating dairy cows was improved by supplementing up to 10 kg/d of concentrate based on dry shelled corn. Corn processing had little impact on production or nutrient utilization.