Urea for Lactating Dairy Cattle. I. Effect of Concentrate Fiber and Urea Levels on Nutritive Value of the Ration

Sixteen individual digestion balances were carried out, using four Holstein cows in the second through fifth months of their first lactation, to study the effect of concentrate fiber and urea on ration utilization and production. Body weights of the four animals at the beginnnig of the experiment ranged from 400 to 500 kg and daily milk production was between 20 and 23 kg. Concentrate mixtures containing corn meal, oat mill feed, crimped oats, wheat bran, corn gluten feed, brewer's grains, molasses, soybean oil meal, and minerals were fed according to milk production. Levels of urea (42% N) in the concentrate mixtures were 0 and 2%, and the levels of fiber were 5 and 8%. Fairquality timothy hay was fed as the only forage at the rate of 2% of body weight. Generally speaking, only minor changes occurred in ration intake, protein digestibility, milk production, blood and rumen metabolite concentrations. Urea significantly improved digestibility of fiber in the ration when included in the lowfiber concentrate mixture and had the opposite effect in the high-fiber concentrate. Otherwise, the higher levels of concentrate fiber and urea significantly depressed ration digestibility and nutritive value, the fiber causing a much more pronounced effect.