NITROGEN UTILIZATION BY LACTATING COWS FED UREA-TREATED CORN SILAGE OR GRASS SILAGE
Nitrogen utilization was studied when eight lactating cows were offered ad libitum urea-treated corn silage (15.3% crude protein) or grass silage (14.5% crude protein), plus a grain ration at 1 kg grain to 3.5 kg of 4% fat-corrected milk, in a digestion and nitrogen (N) balance trial. Analyses of the forages indicated greater acid detergent fiber content for the grass than for the corn silage: 46.8 and 35.1% on a dry matter basis, respectively. Digestibility of dry matter, energy, crude protein, true protein, acid detergent fiber, neutral detergent fiber, and N balance were significantly greater (P < 0.05) for cows fed urea–corn silage than for those fed grass silage. The nitrogen of urea–corn silage was used more efficiently for milk and tissue protein synthesis. Decreased nitrogen utilization for cows fed grass silage was associated with lower energy and higher acid detergent fiber content for grass silage than for urea–corn silage.