Effect of substituting brown rice for corn on lactation and digestion in dairy cows fed diets with a high proportion of grain

The effects of the substitution of brown rice (Oryza sativa L.; BR) for corn (Zea mays L.) in ensiled total mixed ration (TMR) that had a high proportion of grain on feed intake, lactation performance, ruminal fermentation, digestion, and N utilization were evaluated. Nine multiparous Holstein cows (51 +/- 9 d in milk) were used in a replicated 3 x 3 Latin square design with 3 dietary treatments: a diet containing 0, 20, or 40% steam-flaked BR and 40, 20, or 0% steam-flaked corn (dry matter basis). Cows were fed ad libitum an ensiled TMR consisting of 40.7% alfalfa silage, 11.8% grass silage, 7.1% soybean meal, and 40.0% steam-flaked grain (dry matter basis). The ensiled TMR was prepared by baling fresh TMR, and then sealed by a bale wrapper and stored outdoors at 5 to 30 C for over 6 mo. Dry matter intake and milk yield were lower for cows fed 40% BR than for cows fed 40% corn. The ruminal pH and total volatile fatty acid concentrations were not affected by dietary treatment. The ruminal ammonia-N concentration decreased as the percentage of BR in the diets was elevated. The proportion of acetate decreased, and that of propionate and butyrate increased with the increasing levels of BR. Plasma urea-N concentrations was lower and glucose and insulin concentrations were higher for cows fed 40% BR than for cows fed 40% corn. The whole-tract apparent digestibility of dry matter, organic matter, and starch increased, and the digestibility of neutral detergent fiber and acid detergent fiber decreased with the increasing BR level in the diet, with no dietary effect on crude protein digestion. As a proportion of N intake, the urinary N excretion was lower and the retention of N was higher for cows fed 40% BR than for cows fed 40% corn, with no dietary effect observed on N secretion in milk and fecal N excretion. These results show that substituting BR for corn decreases urinary N losses and improves N utilization, but causes adverse effects on milk production when cows are fed high-grain diets at 40% of dietary dry matter.