Abstract
Six ruminally cannulated steers (1012 lb) were fed prairie hay ad libitum supplemented with cooked molasses blocks that contained either 60% crude protein 83% of which came from urea (UREA block) or 60% crude protein with 42% from urea and 42% from biuret (UREA/BIURET block). Blocks were broken into small pieces to facilitate consumption and were fed once daily at .125% of body weight. Rumen samples were collected on days 3, 7, 14, and 21 at 0, 1, 2, 4, 6, 8, 12, and 16 hours after feeding blocks. Averaged over time, ruminal ammonia and total volatile fatty acid concentrations and plasma urea concentrations were lower (P<.05) for steers fed the UREA/- BIURET block than for those fed the UREA block. Acetate and propionate concentrations followed patterns similar to those of total volatile fatty acids, whereas butyrate increased rapidly after block consumption. Release of ammonia from biuret was not demonstrated clearly. Ruminal ammonia concentrations were no greater with the UREA/BIURET block at times distant from feeding than with the UREA block.
Highlights
Cattle consuming dormant range often are supplemented with crude protein as nonprotein nitrogen (NPN) or ruminal degradable protein
Six ruminally cannulated steers (1012 lb) were fed prairie hay ad libitum supplemented with cooked molasses blocks that contained either 60% crude protein 83% of which came from urea (UREA block) or 60% crude protein with 42% from urea and 42% from biuret (UREA/BIURET block)
Blocks were broken into small pieces to facilitate consumption and were fed once daily at .125% of body weight
Summary
Cattle consuming dormant range often are supplemented with crude protein as nonprotein nitrogen (NPN) or ruminal degradable protein. A common NPN source is urea, its release of nitrogen in the rumen is rather rapid and not well synchronized with the slower release of fermentable energy from forages. This rapid nitrogen release canresult in toxic levels of ammonia. A more slowly released NPN source, such as biuret (a compound formed by thermal treatment of urea), might reduce the risk of ammonia toxicity and improve synchronization of nitrogen release and carbohydrate fermentation. Our objective was to evaluate the effects of NPN source (urea or a urea/biuret combination) in cooked molasses blocks on ruminal parameters and plasma urea concentrations
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