Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2007
Publication Date: 1/15/2007
Citation: Varel, V.H., Wells, J., Miller, D.N. 2007. Combination of a urease inhibitor and a plant essential oil to control coliform bacteria, odour production, and ammonia loss from cattle waste. Journal of Applied Microbiology 102:472-477. doi:10.1111/j.1365-2672.2006.03120.x Interpretive Summary: Concentrated animal feeding operations (CAFO) have the potential to emit unacceptable levels of ammonia nitrogen, odor, and pathogens. Two additives used in this study, a urease inhibitor, which keeps manure nitrogen in a non-volatile form (urea) as opposed to ammonia, and thymol, which kills pathogens and reduces odor, indicate thymol enhances the efficiency of the urease inhibitor. This effect is dependent upon diet of the cattle. Waste from cattle fed a 70% corn silage diet and amended with both additives retained 57% of the urea in the waste, in contrast to the waste amended only with the urease inhibitor, which retained 8% of the urea. The combination of these two additives in cattle waste offer the potential to retain nitrogen in manure, thus increasing its fertilizer value. These two additives also reduce malodor and pathogens in the waste.
Technical Abstract: Aim: To evaluate urea hydrolysis, VFA production (odour), and coliforms in cattle waste slurries after a urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and a plant oil (thymol) were added. Methods and Results: Faeces (diet was 70% corn silage and 30% alfalfa haylage), urine, and distilled water in the ratio 50:35:15 were blended at high speed for 1 min. Triplicate aliquots of 750 ml were amended with chemical additives and reblended for 1 min, and were poured into 1.6 L wide-mouth jars covered 90% with a lid. After 56 days, thymol (2000 mg kg**-1 waste) in combination with NBPT (80 mg kg**-1 waste) retained 5.2 g of an initial 9.2 g of urea in cattle waste slurries, compared to less than 1 g of urea retained when NBPT was the only additive (P < 0.05). Another experiment using excreta from cattle fed 76.25% high moisture corn, 19.25% corn silage and a 4.5% supplement with a low speed blending gave a similar response with urea hydrolysis; and thymol alone, and thymol in combination with NBPT reduced VFA production (P < 0.01), and eliminated all coliform bacteria by d 1. A third experiment indicated coliforms disappeared in the no addition treatment after 8 days; however, they were viable at 6.6 × 10**4 CFU g**-1 waste beyond 35 days in the NBPT treatment. Conclusions: Thymol supplements the effect of NBPT by increasing the inhibitory period for hydrolysis of urea in cattle waste slurries and nitrogen retention in the waste. Significance and Impact of the Study: Thymol and NBPT offer the potential to reduce odour and pathogens in cattle manure, and increase the fertilizer value.