Nutritive Value of the Dairy Cattle Ration as Affected by Different Levels of Urea and Quality of Ingredients1,2

Abstract

Summary Two types of concentrate mixtures for dairy cattle, a low-fiber and a high-fiber, which contained four levels of urea, were fed together with two types of field-cured hay to three sets of unbred twin dairy heifers. The levels of urea were 0, 10, 20, and 40lb per ton of concentrate mixture and the hays were harvested in the post-bloom stage the first year, and pre-bloom stage for the second and third years. The nutritive evaluations of the 16 rations were made on the basis of digestible protein, total digestible nutrients, digestibile energy, metabolizable energy, and net energy, all directly determined. Results of the experiment showed that without urea the low-fiber rations were generally superior to the high-fiber rations in digestible energy and total digestible nutrients, but when the level of urea in the concentrate mixtures was increased to 40lb per ton, the high-fiber ration fed with early-cut hay was comparable to the low-fiber, more expensive concentrate mixture. The increase was due to a decrease in the heat increment as the urea in the ration was increased. The substitution of urea for protein did not affect the digestible crude protein content of the rations and had no significantly adverse effect on their nutritive values. A 15% fiber concentrate mixture containing 40lb of urea per ton fed as the sole ration also had a somewhat lower heat increment than a comparable ration containing no urea.