Response of High Producing Dairy Cows Fed Alfalfa Hay and Corn Silage to Supplemental Protein and Urea

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Abstract
High producing Holstein cows (32) were randomly assigned to 3 rations of varying percents and sources of protein: 14.4% crude protein from natural sources, 17.5% crude protein from natural sources and 17.7% crude protein from natural and nonprotein N (urea) sources. Urea N constituted 11.1% of the total N in ration 3. Dietary treatments were examined in 2 trials during the first 84-140 days of lactation. Mean daily intakes of dry matter and total digestible nutrients were higher for cows fed elevated protein: 20.1, 14.0; 21.7, 15.2; and 22.1, 15.2 kg for rations 1, 2 and 3. Means of 3.5% of fat-corrected milk were 32.5, 34.8 and 34.3 kg/day. The principal effect of elevated protein was an increase in intakes of dry matter and energy which may have been contributory to the small increase in milk production. The trend for higher milk production was established during the first 28 days of lactation when energy intakes were equal. No adverse effects of urea supplementation on feed intake or milk production were apparent.