Ammonia versus urea-treated silages with varying urea in concentrate

In four factorial experiments, 96 lactating Holstein cows averaging 100 days postpartum were fed corn silage (21 to 31% dry matter) ad libitum treated with aqueous ammonia (.3 to .4%) or urea (.5 to .7%). Concentrates fed at 1 kg/3 kg milk contained 0, .7, or 1.4% urea in Experiment 1 and 0 or 1.4% in Experiments 2, 3, and 4. Following 14-day pretreatment, experimental rations were fed for 65 days in Experiment 1 and 84 days in Experiments 2, 3, and 4. Urea in grain and urea in silage depressed intakes of silage and total dry matter. Milk persistences were lowered only by the diet containing urea in both grain and silage. Bodyweight changes, percent milk fat, and feed efficiencies were not altered significantly by treatments.