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 matt er (DM) basis] plus 1) high moisture ear corn, 2) high moisture ear co rn plus expeller soybean meal, 3) ground high moisture ear corn, or 4) ground high moisture ear corn plus expeller soybean meal. The high mo isture ear corn was rolled before ensiling at 68% DM. Ground high mois ture 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. Re lative 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. In take of DM and yield of 4% FCM were greatest for cows fed diet 3 and l owest for cows fed diet 1. Digestibilities of DM, organic matter, star ch, neutral detergent fiber, and acid detergent fiber were increased, and ruminal NH3 concentration was depressed, by the grinding of high m oisture corn; expeller soybean meal increased ruminal NH3. Total volat ile fatty acid concentration was not different among in vivo treatment s, but the molar proportion of acetate decreased, and propionate incre ased, for cows fed diet 3. The grinding of high moisture corn signific antly 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.