The use of urea in ensiled versus nonensiled complete feeds for lactating dairy cattle

Four experiments were conducted to investigate the use of urea in ensiled and nonensiled complete feeds for lactating dairy cows All feeds were mixed in a 60:40 concentrate to forage ratio on a dry matter basis A fermentation study, Experiment I, was conducted to compare the nitrogen distribution in ensiled complete feeds, with or without the addition of urea at ensiling, to that of corn silage with either 0 or 1.5 percent urea added at ensiling. Results indicated that in an ensiled complete feed with corn silage as the forage, given sufficient carbohydrates, a dynamic microbial population fixed a significantly greater amount (P \u3c 0.05) of ammonia nitrogen than in urea corn silage with no added carbohydrates. In neither system was there a significant loss (P \u3e 0.05) of nitrogen as volatilized ammonia. Thirty-seven cows were used in Experiment II to compare the feeding value of complete feeds containing a 3 percent urea concentrate, both ensiled and mixed at feeding, with a non-urea complete feed mixed at feeding. As in Experiment I, after ensiling in the presence of excess carbohydrate, there was a significant reduction in the urea content of the ensiled urea-containing complete feed. The dry matter intake of cows fed the ensiled urea complete feed was significantly lower than those fed a urea complete feed mixed at feeding or those fed a non-urea complete feed mixed at feeding. The cows fed the ensiled urea feed gained 9.4 pounds per week as compared to 11.4 pounds per week for those fed the urea ration mixed at feeding and 16.2 pounds per week for those fed the non-urea ration. No significant differences (P \u3e 0.05) were found in milk production, fat test, or 4 percent fat-corrected-milk (FCM) production between the three rations tested. The two urea rations had a predictable advantage in feed costs; however, this advantage was reduced in the ensiled urea feed by a non—significant reduction in salable milk production. Experiment III was a digestion trial conducted to study nutrient digestibility in animals fed urea versus non-urea complete feeds, both mixed at feeding and at ensiling. The urea complete feeds were pre-pared using a 3 percent urea concentrate. The ensiled complete feeds were both significantly lower (P \u3c 0.05) in intake than their counter-parts mixed at feeding. The digestibilities of dry matter, nitrogen, and acid detergent-fiber (ADF) were significantly lower (P \u3c 0.05) for the ensiled complete feed without urea than the ensiled urea complete feed or either of the complete feeds mixed at feeding. There were no other significant differences (P \u3e 0.05) in digestibilities between treatments. The higher nitrogen content of the ADF of the ensiled non—urea ration^ as well as its appearance, would indicate overheating or caramelization, which may have been responsible for the lower digestion coefficients. Forty—one cows were used in Experiment IV to study the intake and performance of lactating cows fed one of four complete feeds: I) corn silage and a 3 percent urea concentrate mixed at ensiling; II) the same feed as I, mixed at feeding; III) corn silage and non-urea concentrate mixed at ensiling; IV) the same feed as III, mixed at feeding. These feeds were from the same silos as those used in Experiment III. The ensiling of complete feeds significantly reduced (P \u3c 0.05) intake with both urea and non-urea feeds. The weight gains were 4.7, 4.3, 3.2, and 6.1 pounds per week for Treatments I - IV, respectively. There was no significant effect (P \u3e 0.05) of either ensiling or urea addition on actual milk produced. The en-siling of the complete feeds did, however, cause a significant re-duction (P \u3c 0.05) in fat test with a resultant significant decrease (P\u3c 0.05) in 4 percent FCM production. The addition of 3 percent urea to the concentrates used in mixing the feeds had no significant effect (P \u3e 0.05) on any of the production variables measured. The two urea rations had an advantage of lowering feed costs; however, this advan-tage was obscured with the ensiled urea feed because of the reduction in fat test. The complete feed with urea mixed at feeding resulted in a feed cost reduction while maintaining production at a level equal to that of the non-urea feeds