Can a coated urea product be used as a method to neutralize the fermentation acids produced in the rumen of cows?
When ruminal pH drops below 5.4, it causes subclinical acidosis (characteristic of lactating cows) and feed intake to be irregular or reduced. When it drops below 5.0, it causes acute acidosis more typical with feedlot diets. Any pH below 6.0 also depresses Neutral Detergent Fiber digestion by cellulolytic bacteria, so holding ruminal pH up not only avoids acidosis, but increases fiber digestibility.
At the pH of the rumen, ammonia released from any free urea acts as a base, neutralizing fermentation acids and preventing ruminal pH from dropping. Dr. Mike Allen (J. Dairy Sci. 1447-1462) summarized the amounts of acids typically produced in the rumen and the degree of neutralization provided by salivary bicarbonate and feed buffers. Allen reported that adding more than 1% of the diet as a slow-release urea should never be necessary with dairy diets, but with high concentrate feedlot diets higher amounts may be needed. A 1% urea level would be far below the amount that is presumed to cause toxicity when urea (unbound) is added to the diet according to common rules of thumb for safe use (3% of diet dry matter or 1/3 of dietary protein, either of which would cause ruminal ammonia to exceed 100 mg/ml).
With slow-release qualities, microencapsulated urea should not cause ammonia toxicity and represents a source of supplemental nitrogen for rumen bacteria.