Effect of processing high moisture ear corn on ruminal fermentation and milk yield.

Thirty-six multiparous dairy cows (8 fitted with ruminal cannulas) and 16 primiparous dairy cows were blocked by days in milk and parity and assigned to one of four diets containing 53% alfalfa silage [dry matter (DM) basis] plus 1) high moisture ear corn, 2) high moisture ear corn plus expeller soybean meal, 3) ground high moisture ear corn, or 4) ground high moisture ear corn plus expeller soybean meal. The high moisture ear corn was rolled before ensiling at 68% DM. Ground high moisture ear corn was prepared by further grinding through a 9.5-mm screen; grinding reduced the geometric mean particle size from 4.33 to 1.66 mm. Diets contained 1.69 Mcal of net energy for lactation/kg of DM. Relative to cows fed diet 1, milk yield was 4 kg/d greater for cows fed diet 2; numerically, milk yield was about 2 kg/d greater for cows fed diets 3 and 4 than for cows fed diet 1. Yield of milk components also was greater for cows fed diets 2 and 3 but not for cows fed diet 4. Intake of DM and yield of 4% FCM were greatest for cows fed diet 3 and lowest for cows fed diet 1. Digestibilities of DM, organic matter, starch, neutral detergent fiber, and acid detergent fiber were increased, and ruminal NH3 concentration was depressed, by the grinding of high moisture corn; expeller soybean meal increased ruminal NH3. Total volatile fatty acid concentration was not different among in vivo treatments, but the molar proportion of acetate decreased, and propionate increased, for cows fed diet 3. The grinding of high moisture corn significantly decreased pH, increased total volatile fatty acid concentration, and increased the rate of decline of NH3 concentration in ruminal in vitro incubations. Grinding improved the utilization of high moisture corn by lactating cows by stimulating ruminal fermentation.