Broiler producers commonly grow five or six flocks on the same bedding over the course of a year. The aged litter is then applied as fertilizer. As uric acid builds in the litter over time, it decomposes and generates ammonia. When this gas enters the air in poultry houses it can cause problems. It decreases growth rate and feed efficiency, damages respiratory tracts, and increases airsacculitis, keratoconjunctivitis and susceptibility to Newcastle disease in broilers.

Ammonia concentrations within poultry houses can soar above 100 ppm during winter as growers decrease ventilation to hold heating costs in line. This level is well above the 25 ppm cited as safe³. Growers can control ammonia by creating conditions unfavorable to its formation, e.g., by lowering pH.

This Study Summary reviews two papers, one from Poultry Science¹ and the other from the Journal of Environmental Quality², that evaluated commercial amendments in broiler litter. Untreated litter was the control in both cases. The Poultry Science paper looked at two dosage levels each of alum, ferrous sulfate, ferric chloride and phosphoric acid, and one each of sodium bisulfate and calcium/iron silicate coated with phosphoric acid (Study A). The other paper encompassed calcium hydroxide, alum, alum and limestone combined, ferrous sulfate, and a commercial product composed of ethylene glycol (Study B).

Alum emerged as the preferred amendment in this study because it had the broadest range of benefits (Table 1). Alum not only allowed the least amount of ammonia loss (Table 2), but it also maintained nitrogen content and limited runoff of phosphorus.

In terms of ammonia generation, ferrous sulfate and phosphoric acid allowed 50% or more ammonia to form than did alum. Ferric chloride allowed still more ammonia generation, while sodium bisulfate and calcium-iron silicate simply matched that of the control.

The study also considered nitrogen and phosphorus content to gauge the litter's effectiveness as fertilizer and potential for phosphorus runoff. Alum, ferrous sulfate and phosphoric acid increased the inorganic nitrogen content of litter versus the control, which can improve crop yields. This is to be expected, since less nitrogen was lost as ammonia with these compounds.

Alum and ferrous sulfate also reduced water soluble phosphorus concentrations, so litter treated with them should have less phosphorus runoff than the control. Phosphoric acid greatly increased soluble phosphorus concentration compared to the untreated control. Phosphorus runoff is a growing problem for the environment,as well as for agricultural productivity.

Although ferrous sulfate performs well in many ways, it can cause iron toxicity in birds and has led to die-offs in commercial day-old chicks. A study of cumulative mortality for broilers at four weeks showed a far higher mortality rate when they were grown on litter treated with ferrous sulfate than litter alone or litter treated with alum (see Figure 1)⁴. The lower mortality with alum was probably due to decreased ammonia, while the higher value for ferrous sulfate appears to be due to iron toxicity.

In looking at the economics of using alum, the paper notes that increased ventilation can solve most of the health problems caused by ammonia, but at a price. It cites data from a computer program that models the economic benefits of ammonia control in poultry houses⁵. Ventilation to lower ammonia from 80 ppm to 25 ppm for a house with 19,000 birds at an outside air temperature of 7 °C would cost $3,800 per flock. Alum can do the same and costs nearly 20 times less.

In summary, alum was the optimum litter amendment tested because it is a highly effective and non-toxic way to reduce ammonia, preserve nitrogen levels and reduce phosphorus runoff.

The results of this study reinforce that of Study A and show the effectiveness of high alum doses.

Litter treated with 100 and 200 g of alum/kg of litter had 36% and 99% less ammonia than the control. This reduction was well above that of the other compounds tested. Until the last week of the study, when available acidity began to drop, the ammonia level with the higher alum dose had been zero because alum held pH at 7.07, much lower than other treatments.

By contrast, ferrous sulfate decreased ammonia by 11% and 58% for the 100 and 200 g/kg treatment, while calcium hydroxide did not alter ammonia significantly. A commercial product that contained ethylene glycol actually increased ammonia.

The higher rate of alum use "resulted in a doubling of the nitrogen content of the litter, which would greatly increase the value of poultry litter as a fertilizer source." With regard to phosphorus: "Dissolved P concentrations at the end of the study were significantly lower with the addition of 200 g alum/kg than any other treatment..."

This paper cites another study⁶ that found that phosphorus concentration in runoff from small plots receiving alum-treated poultry litter as fertilizer was 87% less than those receiving normal litter.

Why this summary? It is nearly impossible to choose the most effective litter amendment to control ammonia given the many compounds available and the claims made for them. This summary condenses two papers by Dr. Philip Moore at the U.S. Department of Agriculture and his collaborators at the University of Arkansas that describe their investigations into ammonia

Cumulative mortality rates for broilers at four weeks.

1. Moore, P.A.,Jr., T.C. Daniel, D.R. Edwards and D.M. Miller, "Evaluation of Chemical Amendments to Reduce Ammonia Volatilization from Poultry Litter," Poultry Science, 75:315-320, 1996.
2. Moore, P.A.,Jr., T.C. Daniel, D.R. Edwards and D.M. Miller, "Effect of Chemical Amendments on Ammonia Volatilization from Poultry Litter," J. Environ. Qual., Vol. 24, No. 2, 1995.
3. In Europe, Control of Substances Hazardous to Health sets human exposure to ammonia at 25 ppm with 35 ppm for a 10-minute exposure. Also, F.S. Carlile, in his article "Ammonia in Poultry Houses: A Literature Review" (World's Poult. Sci. J., 40:99-113, 1984) suggests that ammonia should not exceed 25 ppm in poultry houses.
4. Moore, P.A.,Jr., Unpublished manuscript.
5. Attar, A.J. and J.T. Brake, "Ammonia Control: Benefits and Trade-offs," Poultry Dig., August 1988.
6. Shreve, B.R., P.A. Moore, Jr., T.C. Daniel, D.R. Edwards and D.M. Miller, "Reduction of Phosphorus Runoff from Field-Applied Poultry Litter Using Chemical Amendments," J. Environ. Qual., 24:106-111, 1995.

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