UREA IN CORN SILAGE AS A SUPPLEMENTAL NITROGEN SOURCE FOR LACTATING COWS
Thirty-two Holstein cows in second or later lactation were randomly allocated to four treatment groups within 7 to 10 wk postpartum. Treatment rations were fed ad libitum as a complete feed and consisted of a negative control group which was fed a corn-oats-barley concentrate-corn silage mixture (40:60) with 9.4% crude protein, a urea silage group fed the same grain concentrate mixed with corn silage that contained 0.6% urea (on a fresh weight basis) to give 12.5% total ration crude protein, a group fed a soybean meal concentrate mixed with corn silage (12.7% crude protein), and a group fed a 3% urea corn-oats-barley concentrate mixed with corn silage to give a 12.8% total ration crude protein. The three groups supplemented with protein or non-protein nitrogen had greater weight gains, feed consumption, milk yields, milk persistencies, rumen ammonia nitrogen concentrations and greater rumen microbial cell populations than the negative control group. The results indicate that urea supports milk production when fed as part of a complete feed. Previous work showed that the same daily intake of urea when fed twice daily as part of the concentrate was ineffective.