The Use of Varying Levels of Urea in Concentrates Fed to Dairy Cattle

Five experiments were conducted to investigate the use of concentrates that contained varying levels of urea for dairy cattle fed corn silage as the only forage.

Three experiments were conducted using 84 Holstein cows. Twenty-seven cows were used in Experiment I to compare a concentrate supplemented with soybean meal with a concentrate in which 2 percent urea (by weight) replaced a portion of the soybean meal on an equal nitrogen basis. Effects of frequency of feeding of concentrates containing urea were also studied. Results indicated that ration intake, body weight changes, milk production, milk protein, and milk SNF were not significantly different (P>0.05) for cows fed corn silage plus a concentrate containing either 0 or 2 percent urea. No significant differences were observed between treatments when a concentrate containing 2 percent urea was fed six times a day versus twice a day.

Thirty cows were used in Experiment II to compare a concentrate that contained soybean meal with a concentrate that contained 3 percent urea. Effect of the addition of sodium sulfate to a concentrate that contained 3 percent urea was also studied. Results indicated that silage intake, total dry matter intake, milk production, milk protein, and milk SNF were not significantly different (P>0.05) in cows fed corn silage plus a concentrate that contained either 0 or 3 percent urea. Milk fat percent was significantly higher (P<0.05) in cows that were fed the concentrate that contained 3 percent urea. The data indicated that a ration of corn silage (0.17 percent sulfur on a dry matter basis) plus a concentrate that contained 3 percent urea (concentrate contained 0.15 percent sulfur on a dry matter basis) did not appear to be deficient in sulfur.

Twenty-seven cows were used in experiment III to study the utilization of concentrates containing 3 percent urea with and without phosphate supplements. Results indicated that the addition of dicalcium phosphate and monosodium phosphate did not appear to improve the ration utilization of concentrates containing 3 percent urea. However, it should be pointed out that the phosphate source may be needed for purposes other than for the utilization of urea.

Two experiments using 32 Holstein heifers were conducted to study the effects of concentrates containing urea on nitrogen balances and palatability. In Experiment IV, nitrogen balances were conducted on 16 heifers fed concentrates which contained no protein supplement, soybean meal, 1.3 percent urea plus monosodium phosphate, or 1.3 percent urea without the monosodium phosphate supplement. Results indicated that nitrogen retention was directly related to nitrogen intake and digestibility. The addition of the monosodium phosphate to the concentrate containing urea did not significantly affect nitrogen balances. In Experiment V, 16 heifers were used in a palatability study of concentrates containing urea with and without phosphate supplements. A palatability study was also conducted comparing concentrates which contained either 0 or 3 percent urea. Results indicated that animals adapted to a concentrate which contained no phosphate supplements preferred concentrates which contained no dicalcium phosphate over concentrates which contained dicalcium phosphate, or dicalcium phosphate plus monosodium phosphate. If the animals were adapted to a concentrate that contained urea plus dicalcium phosphate and monosodium phosphate, the animals preferred the concentrate that contained both phosphate supplements over concentrates that contained only one of the phosphate supplements. Results indicated that the animals preferred the concentrates that contained no urea as compared to concentrates that contained 3 percent urea. However, it should be noted that animals offered concentrates that contained 3 percent urea did consume these concentrates, but at a reduced rate.