Utilization of Urea by Lactating Cows — an Industry Viewpoint

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Abstract
The major non-protein nitrogen (NPN) source in ruminant rations is urea. In palatability (preference) trials, non-lactating cows ate less of higher moisture urea-containing rations than lower moisture urea-containing rations. Atmospheric humidity, grain moisture and feeding conditions affect the level of urea which cows will discriminate against in consuming urea-containing rations. Generally, 1% urea in the milking ration is acceptable, but cows in late lactation consumed a 2.5% urea-containing ration under optimal conditions and produced the same quantity of milk as did cows consuming non-urea rations. Cows in early lactation also consumed their ration and produced the same quantity milk when 1.8% urea or no urea was present in the ration. In a large scale commercial dairy operation, cows fed a complete ration (22% of a 1.8% urea-containing milking ration and 78% silage) and a milking parlor ration with 1.8% urea consumed the same amount of ration and produced the same amount of milk as did cows on a non-urea ration. Feed consumption and milk production records over the last 2 years using urea-containing rations in that dairy operation have continued to provide evidence of the feasibility of that feeding program. NPN levels of forages should be considered in determining urea or NPN levels in milking rations. The daily feed intake of milking cows, the protein level used in the milking ration and handling characteristics of high levels of urea-containing concentrates are also considerations in the determination of urea levels to be used in milking rations and concentrates. Urea utilization in dairy rations is limited by its hygroscopic and soluble nature, by its unpalatability at higher dietary levels due to flavor and/or odor, and by decreasing utilization at increasing dietary levels. Urea will probably continue to be an economic protein replacement in the future. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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