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Factors Influencing Intake of High Urea-Containing Rations by Lactating Dairy Cows

Ralston Purina Company, St. Louis, MO 63188

ABSTRACT

In a series of experiments we investigated effects of several factors on intake of urea by lactating dairy cows. Cows given an unfamiliar ingredient or altered moisture in the ration reduced their intake, and this effect was attributed to a newness factor. Addition of urea to a ration may have a similar effect. An experimental design providing both no-choice and two-choice data was devised to minimize the effect of newness. When urea was isolated physically by pellets coated with ground corn, cows selected against urea-containing pellets on a two-choice basis and reduced intake on a no-choice basis. When the choice was between two urea-containing rations, cows preferred the pellets in which urea flavor and odor should have been most evident. Urea odor in the feedbox or urea in the drinking water did not reduce feed intake. Eating rate of a 2.5% urea-containing ration over two daily 30-min feeding periods was about one-half that of a non-urea ration. This effect was evident during the first 5-min eating interval. Administration of urea solution into the rumen prior to feeding a nonurea ration markedly reduced subsequent intake. Reticulum pH and ammonia indicated possible sublethal ammonia toxicity. Intake and eating rate were depressed and reticulum pH was elevated when cows were fed a ration with 2.5% urea versus 1% urea or nonurea rations. Elevated reticulum ammonia occurred on both 1 and 2.5% urea-containing rations. Cows

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