Influence of Site of Administration of Urea on Voluntary Intake of Concentrate by Lactating Cows

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Abstract
Four rumen-fistulated cows were fed isonitrogenous diets in a Latin square de- sign with 14-day periods. Treatments were: Control (C), urea-oral (UO), urea-rumen (UR), and urea-abomasum (UA). Concentrates fed C, UR, and UA cows contained I% urea while that fed UO cows had 370. Sufficient urea in an aqueous solution (1:5) to equal 270 of the concentrate intake was placed twice daily directly into the rtmaen of UR cows or into the abomasum of UA cows. Con- centrate was offered ad libitum just be- fore urea administration, and hay (5.4 kg) was fed once-a-day. Daily intakes of concentrate were similar for C (13.3 kg), UR (12.6 kg), and UA (13.1 kg) treatments but depressed for UO (10.6 kg) (P < .05). Treatment did not af- fect average concentrations of blood urea nitrogen or blood ammonia. Intake de- pression on high-urea diets is due to the undesirable taste of urea and not to ruminal or post-ruminal effects. In a second experiment dissolution of urea in molasses masked the undersirable taste of a concentrate containing 3.570 urea and resulted in slightly higher intakes than a concentrate supplemented with soybean meal and molasses and higher (P < .05) than when urea was not dis- solved in molasses before mixing with other dry concentrate ingredients.