Published October, 2012

A group of University of Kentucky (UK) College of Agriculture equine researchers published a study recently inVeterinary Parasitologyshowing that windrow composting is effective and practical for parasite control and waste management on horse farms.

The research team consisted of Jessica Gould, graduate assistant; Mary Rossano, PhD, assistant professor; Laurie Lawrence, PhD, professor; Rosalyn Ennis, research assistant; and Steffanie Burk, graduate assistant, all from UK's Department of Animal and Food Sciences, as well as Eugene Lyons, PhD, professor, from the Department of Veterinary Science.

According to the researchers, the study produced compelling evidence that windrow composting (the production of compost by piling organic matter or biodegradable waste into long rows called windrows) is an efficient and effective way of managing equine waste products while eliminating Parascaris equorum contamination. P. equorum is a parasitic nematode (worm) in horses that is abundant worldwide and is commonly referred to as the ascarid, or roundworm.

The parasite usually infests horses younger than 18 months old, and heavy infestations can be severe or even deadly. The infestation occurs when the young horse ingests larvated eggs (the stage that is infectious) present in pastures, paddocks, stalls, and on feeding and watering equipment. Eggs present in the environment can remain viable for years, so pastures and facilities used for foals and yearlings accumulate P. equorum and are a source of infestation for each new foal crop.

Anthelmintic (dewormer) use has long been a common and recommended practice on horse farms for parasite control. However, emerging drug resistance in parasites supports the need for alternative control methods that reduce environmental contamination with larvated eggs. Scientists have determined that a well-rounded control program for P. equorum should include maintenance of pastures, manure, stalls, the horse itself, and the equine traffic on the property. One practice that addresses most of these issues is waste composting.

Composting farm waste, both animal-derived and other expendable byproducts (bedding, landscaping waste, etc.), is a waste management practice for equine facilities that has become one of the most utilized and accepted technological alternatives for decreasing the overall volume of these materials. For some farms, composting this waste and subsequently using the final product as fertilizer and landscaping material might also be more cost-efficient than paying for its transport off the facility.

However, such practices might potentially increase contamination of the farm environment with P. equorum eggs and increase the risk of infesting animals. Foals exposed to pastures where caretakers used horse manure as fertilizer have been shown to have a significantly higher risk of testing positive for P. equorum in a fecal egg count evaluation.

Prior to the UK study, previous research had shown that within well-managed composting systems temperatures reach levels that inactivate pathogens such as parasites. Studies investigating the effects of temperature on sewage sludge, for example, indicated that for every 10°C increase in temperature above 20°C, there was a significant decrease in the amount of time to 99% inactivation of helminth eggs of the Ascaris genus, of which P. equorum is a member.

With that in mind, UK researchers set out to see if windrow composting was capable of killing P. equorum eggs in manure and stall bedding. Because composting is a themogenic (heat-producing) process capable of disinfecting or sanitizing its components of intestinal pathogens, the UK researchers theorized that it could be used to eliminate the viability of P. equorum eggs.

The goal of the study was to test a windrow composting system as it was normally used on a Central Kentucky horse farm. Under the farm's normal working conditions, past windrow composting piles decomposed completely on average between 10 to 12 weeks, without season of the year having a significant impact on the composting process.

Equine manure, soiled bedding, and other organic waste material used to build the experimental windrow were provided from stalls housing only horses previously confirmed negative for P. equorum eggs. Ingredients incorporated into the compost pile were balanced to create a 30:1 carbon to nitrogen ratio for optimum decomposition. Sealed packets containing P. equorum eggs were placed in the windrow under two different exposure conditions. Half were buried in the center of the windrow for the duration of the experiment and were only removed when the pile was turned. The other half alternated between the center of the windrow and resting on top. The alternating treatment was designed to mimic the way materials get redistributed when the compost is turned.

Typical daily windrow management by the farm staff included taking internal temperature and carbon dioxide readings from multiple locations across the same compost row. If temperatures were greater than 50°C (122°F) or the carbon dioxide readings were greater than 17%, the compost row would be mechanically turned and aerated with a specialized tractor-operated device. The farm management evaluated compost row moisture, and if moisture was deemed too low, they added water during mechanical aeration. Whenever the pile was aerated, sample of packets of P. equorum eggs were removed from the windrow and brought to the laboratory to be tested for viability. The study continued for 36 days while composting conditions and parasite viability were recorded.

The farm manager disclosed that while the recommended composting format was usually implemented, day-to-day farm operations occasionally limited the amount of attention given to windrow management. Thus, at certain times when aeration or additional water might have been necessary, it did not always occur. Because the researchers' objective was to test the composting system as it is used by the operation, the investigators did not interfere with the farm staff's management decisions regarding the windrow to insure it would best replicate their normal day-to-day operation. Rather, maintenance events were recorded as they occurred.

During the study, the high average temperatures, both minimum and maximum, produced inside the windrow in the first 16 days of the experiment indicated the high metabolic activity of microflora carrying out decomposition in the windrow. Mean temperatures within the first 16 days closely resembled the optimal temperatures for composting, which tend to vary from 45° to 50° Celsius (or 113° to 122° Fahrenheit). By Day 8 of the study, all the P. equorum eggs in both treatment groups were rendered nonviable. This was well before the composting process had slowed enough for the temperature to drop below the optimal range.

Both the width and the height of the windrow steadily declined over the duration of the composting process. The overall decrease in the material's volume demonstrated that the process accomplished one of the main goals of waste management: volume reduction. This was also consistent with typical compost production at the cooperating farm, indicating that the experimental windrow was representative of their method.

The results of the study demonstrate that under normal conditions at a working horse farm, windrow composting can be a very effective way to reduce P. equorumtransmission, manage waste, and utilize that waste as a safe nutrient source for pastures.

Holly Wiemers, MA, is communications director for UK Ag Equine Programs. Research information was provided by Jessica Gould, graduate assistant; Mary Rossano, PhD, Assistant Professor; Laurie Lawrence, PhD, Professor; Rosalyn Ennis, research assistant; and Steffanie Burk, graduate assistant, all from the Department of Animal and Food Sciences, as well as Eugene Lyons, PhD, Professor, from the Department of Veterinary Science