If these precise variables are not met, the necessary temperature will not be reached, and bacterial control will not be effective. Keep in mind that the uninsulated earth foundation of a broiler house conducts heat away from the windrow piles, producing a sharp 50oF temperature gradient within the bottom five inches of the pile. The same will happen throughout the piles surface due to ambient air temperatures.
Poultry litter is not an inanimate object; It contains a complete ecosystem with physical and biological characteristics that are dependent on bird size, diet and litter handling during down time. Most used poultry litter has a low carbon nitrogen ratio of 10-15 making it difficult to reach the necessary temperature of 130-135°F within 48 hours unless the C:N ratio is raised to at least 15:1—which often requires the addition of upwards of 22 tons of fresh litter to each windrowing cycle.
If windrow composting is attempted without raising the C:N ratio, several undesirable events will occur:
Proof of Success?
Proponents of windrow composting often call on specific research to support their management decision. However, results from much of that data has been overstated, including the ideas that in-house composting: “eliminates E. coli, staph, aspergilla, Salmonella and respiratory virus; reduces aerobic and anaerobic bacterial populations, and eliminates/reduces cocci.” A study by D. Bautista showed that, “cocci oocyts were inactivated by the composting treatment inside the compost pile (1-foot depth) but not on the surface of the windrowed pile or at room temperature in the house.”
Also, research has brought to light concerns that, due to the nature of the spore, Clostridial spores may not be impacted by 130-135oF temperatures even though Clostridia in its vegetative state is sensitive.
So how should windrow composting success be defined? Bacterial reduction is assessed by looking at log 10 differences. A minimum of 3 log reduction is needed for bacteria to truly have been controlled.
In one study (Table 1), windrowing only produced a 0.5-1 log reduction so it was ineffective in reducing bacteria (Lavergne et al, LSU).
Table 1. Anaerobic bacterial reduction after in-house poultry litter pasteurization after three flocks