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Nutritional Value of Urea Versus Preformed Protein for Ruminants. I. Lactation of Dairy Cows Fed Corn Based Diets Containing Supplemental Nitrogen from Urea and/or Soybean Meal¹

Department of Dairy Science, University of Illinois, Urbana 61801

ABSTRACT

Fifty Holstein cows were in a 310-day lactation study to determine the nutritional value of urea versus soybean meal as sources of supplemental nitrogen in corn-based diets that contained 9 to 14.5% crude protein. Throughout lactation cows were fed 1 kg of concentrate per 2.75 kg of milk produced, 2.25 kg of hay per day, and corn silage ad libitum. Production of milk, 4% fat-corrected milk, milk protein, and milk fat was greatest when the percentage of crude protein in the diet was highest (14.5%). Cows fed diets that contained 11 to 12% crude protein, with supplemental nitrogen supplied either as urea or soybean meal, produced similar quantities of milk, milk protein, and milk fat. However, cows fed a diet that contained 13.5 to 14.5% crude protein with supplemental nitrogen supplied as soybean meal produced more milk and milk protein than cows fed a similar diet that contained urea. The greater production of milk and milk protein by cows fed the diet that contained soybean meal was probably because more dietary protein escaped degradation in the rumen, resulting in a greater quantity of amino acids being absorbed from the small intestine. At least 13.5 to 14.5% crude protein is required in the diet of high producing dairy cows during early lactation, and all supplemental nitrogen should be preformed protein during this time.

¹ Supported in part by the Illinois Agricultural Experiment Station, the National Soybean Producers Association, and HEW PHS FD 00849.

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