Agricultural Research Division of IANR


Date of this Version



Published in Journal of Animal Science, Vol. 42, No. 5, 1976. Used by permission.


Two winter trials were conducted with 304 lactating range cows on dry grass to evaluate non-protein-nitrogen (NPN) in 30% protein supplements containing biuret (pure and feed grade), urea and extruded grain-urea. The NPN sources contributed one-half of the supplemental nitrogen with natural 15 and 30% protein supplements serving as negative and positive controls.
Winter weight loss of cows was greater (P~.02) on the negative than on the positive control in both trials. The apparent utilization of all NPN sources was low and the utilization of urea and extruded grain-urea was less than pure or feed grade biuret. Rumen biuretolytic activity was apparent within 6 days and reached and maintained a high level of activity 20 days after the initiation of feeding biuret, even with intermittent supplementation. Apparent value of NPN supplements was slightly improved with 40% dehydrated alfalfa but not with methionine- hydroxy-analogue (MHA). Palatability of supplements was lowered by urea and especially by MHA and extruded grain-urea.
In a third trial with yearling heifers fed prairie hay, gains were similar on natural protein and supplements containing urea or extruded grain-urea to provide one-half of the nitrogen. When the heifers were fed the same supplements but low quality winter harvested range grass, NPN utilization appeared to be low.

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