Effects of corn particle size and source on performance of lactating cows fed direct-cut grass-legume forage

We conducted two experiments to evaluate the effects of corn supplementatio n, source of corn, and corn particle size on performance and nutrient utili zation of lactating dairy cows. In experiment 1, treatments were 1) direct- cut grass-legume forage without supplement, 2) direct-cut forage plus 10 kg DM of ground dry shelled corn-based concentrate, and 3) direct-cut forage plus 10 kg DM of coarsely ground high moisture ear corn-based concentrate. In experiment 2, treatments were 1) direct-cut grass-legume forage plus 10 kg DM of ground dry shelled corn-based concentrate, 2) direct-cut forage pl us 10 kg DM of coarsely ground high moisture ear corn-based concentrate, an d 3) direct-cut forage plus 10 kg of DM finely ground high moisture ear cor n-based concentrate. Both experiments were designed as 3 x 3 Latin squares replicated three times. In experiment 1, yields of milk and milk protein in creased with concentrate supplementation, but were not affected by source o f corn. Solids-corrected milk yield tended to increase with grain supplemen tation. Dry matter intake increased with concentrate supplementation, but w as not affected by source of corn or corn particle size. Corn supplements d ecreased ruminal pH and acetate to propionate ratio and increased ruminal p ropionate concentration. Grain supplements reduced ruminal ammonia concentr ation, increased concentration of urine allantoin, and increased the urinar y allantoin to creatinine ratio. In the second study, fine grinding of high moisture corn reduced fecal starch plus free glucose levels and tended to increase its apparent digestibility. In both experiments, starch plus free glucose intake was higher on the diets with dry corn, but its utilization w as not affected by source of corn.