Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 19, 1999
Publication Date: N/A
Interpretive Summary: Feedlot cattle normally retain less than 20% of dietary nitrogen (N) intake. The nonretained N is primarily excreted in the urine as urea. Sixty to 80% of the nitrogen excreted by livestock is normally lost through volatilization of ammonia. Urease is an enzyme produced by microorganisms which results in the breakdown of urea to ammonia. Urease inhibitor compounds were used on the surface of cattle feedlot pens with the objective to reduce the breakdown of urea in the manure. The compounds significantly reduced urea breakdown and ammonia emissions when applied once per week for 5 weeks. It is concluded that urease inhibitors could play a major role in controlling ammonia emissions from livestock and poultry waste because urea and uric acid, respectively, are the predominant nitrogen excretory products which would be retained in these wastes.
Technical Abstract: Feedlot cattle normally retain less than 20% of their dietary nitrogen (N) intake. Sixty to 80% of the N excreted is normally lost through volatilization of ammonia which is primarily generated from urea. This loss of ammonia N pollutes the environment and creates an unfavorable ratio of nitrogen to phosphorous (N:P) in the waste for crop growth. Two urease inhibitors, cyclohexylphosphoric triamide (CHPT) and N-(n-butyl) thiophosphoric triamide (NBPT) were evaluated for their ability to reduce the rate of urea hydrolysis in beef cattle feedlot pens. Initially, a total of six pens were used, two pens per treatment, with approximately 70 cattle per pen and a topical application of CHPT or NBPT at 20 mg/kg of manure. Essentially no urea was found in untreated pens. However, with CHPT treatment, 2 g urea per kg dry manure accumulated by d 4, which all gradually disappeared by d 11; whereas, NBPT produced 3- and 3.5 g urea per rkg by d 4 and 9, respectively, which disappeared by d 14 (trt x d, P = .003). A second study which involved application of NBPT every wk for 6 wk, caused urea to accumulate to a peak concentration of 17 g per kg manure by d 30 (trt x d*2, P = .001). Once the treatment was stopped the urea concentration began to decrease. When the NBPT was applied weekly, the concentration of ammonia was less for the treated pens (trt x d, P = .01), the total N was greater (trt x d, P = .04), pH tended to be less (trt x d, P = .10) and the total volatile acids were not different (trt x d, P = .51). It is concluded that urease inhibitors could be used to control ammonia emissions from animal wastes, prevent environmental damage, and produce a more balanced (N:P) fertilizer from manure.