Recent research results from the University of Kentucky indicate that NH3 emissions from swine manure can be reduced by lowering the dietary crude protein level or by adding certain additives to the diet.
Kentucky researcher Gary Cromwell conducted experiments to evaluate the link between protein and volatile gases emitted from hog manure. Exhaust gas concentrations from each of 12 simulated anaerobic manure pits were monitored every 2.4 hours for 2-3 weeks. The experiment looked at ammonia (NH3), hydrogen sulfide (H2S), methane (CH4) and carbon dioxide (CO2) using a multi-gas monitoring system. Manure pH and volatile fatty acid (VFA) concentrations were also determined.
In one experiment, 84 pigs (three replications of four groups of seven pigs, which weighed on average 50 lb.) were fed an 18% crude protein (CP) diet with or without Yucca schidigera extract (Ultimate Gold, 0.2%), a microbial product (Microsource S, 0.05%) or a fructooligosaccharide (inulin, 3%) for 6 days.
Cromwell says Yucca, inulin and the microbial product reduced NH3 emissions by 15, 29 and 38% (P<0.10).
In another experiment, 36 pigs (three repetitions of three groups of four pigs, average weight 72 lb.) were fed the 18% CP diet with or without a zeolite (clinoptilolite, 2%) or a 14% CP diet with lysine, threonine and tryptophan added to equal the level of these amino acids in the 18% CP diet. The trial lasted 15 days.
Feeding the low CP diet reduced NH3 emissions by 29%; the formulation with zeolite reduced emissions by 9%.
Although detectable, H2S emissions were too low for accurate quantification.
In a third experiment, fortified corn-soybean meal diets containing 16.5, 14.5, 12.5 or 10.5% CP were each fed to three pigs (average weight 114 lb.) in metabolism crates for 14 days. The 12.5% CP diet was supplemented with lysine and the 10.5% diet with lysine, threonine and tryptophan to equal the levels of these amino acids in the 14.5% CP diet.
The results were quite pronounced and clear on the relationships between the decrease in dietary protein and ammonia levels, notes Cromwell. NH3 and pH decreased linearly (P<0.01) as dietary CP decreased. (21.4, 13.8, 13.4, 10.1 ppm; 8.04, 7.75, 7.35, 6.75, respectively).
CH4 and CO2 were not affected and H2S was undetectable. VFA levels were not affected by diet, except for trends (P<0.15) in butyric acid and valeric acid.
Ration Formulation The research correlates with somewhat similar work done at Purdue University. Purdue animal scientist, Al Sutton, thinks the best approach to control odor through nutrition so far, still is to provide the pig, as closely as possible, with the essential available nutrients based upon its genetic potential and stage of growth.
"We want to keep that nutrient excretion as minimal as possible, giving that pig a lower potential for creating the compounds responsible for odor production," according to Sutton. Avoiding over-formulation, using phase and split-sex feeding regimens, the use of synthetic amino acids, and incorporating new products such as phytase and low phytate corn into the diet are the common means of applying this concept.
Another concept Sutton points to is the microbial route. "We can manipulate the microflora transversing the gastrointestinal tract of the pig. When we selectively inhibit certain microbial groups or alter the fermentation pattern of existing microflora, we've shown we can control potential odorous end products."
Finally, notes Sutton, changing the composition of the diet may change the physical characteristics (pH, dry matter content, buffering capacity, dietary electrolyte balance) of urine and feces that control odor production.
Phosphoric Acid Along those lines, North Carolina State University researcher Theo van Kempen has launched a project testing the use of phosphoric acid instead of dicalcium phosphorus in swine diets. Van Kempen theorizes that by supplying an undegradeable asset, the excreted pH will go down and by lowering excreted pH, ammonia emission can be lowered. Since phosphoric acid is cheaper than dicalcuim phosphorus, the idea makes sense from the ration cost side.
In Europe, Dutch research has shown positive results in a similar experiment using benzoic acid, but benzoic acid is not approved for use in the U.S., notes van Kempen.
Van Kempen is also upbeat about attacking odor nutritionally. "Where there's a will, there's a way," he says. "We can make diets such that they produce less ammonia and they don't have to have an increase in cost that is enormous."
The challenges for his experiment will be from an engineering side. "The question will be, 'Can we use phosphoric acid in the feed mill?' We use liquid methionine, we use liquid choline, why can't we use liquid phosphorus?"
Van Kempen says most pet food companies change cat food diets to drop the pH of the urine as an aid in preventing urinary tract infections, so the concept is not entirely new.
Another engineering problem arises with very acidic urine. "You can get to a point where you're dissolving the concrete," says van Kempen, noting that as we focus on solving one problem, others may arise.