Are you begging people to come take your horse manure for free—or perhaps even paying to have it hauled away? If so, it may be hard to imagine that your stable waste could be converted into something worth $30, $200, or even $1,000 per cubic yard.
The difference depends on how you compost it, says Rhonda Sherman, a solid waste extension specialist at North Carolina State University (NCSU). It’s not just heaping manure into a big pile and waiting for Mother Nature to do her job. Sure, this works. But the compost will likely be of the give-away variety, with weed seeds, pathogens, parasites, and chemical residues potentially contaminating it.
Not all livestock dung is created equal, Sherman points out, but horses that are eating good, balanced diets should produce compost-worthy waste. She is unconcerned about horses being fed beet pulp-based feeds. Although 95% of sugar beets grown in the United States are “RoundUp Ready”—meaning genetically modified to withstand the glyphosate herbicide found in RoundUp—this chemical readily breaks down in organic matter when U.S. Composting Council guidelines are followed.
“Persistent herbicides” are another story, she warned. Pasture, hay, and grain from fields treated with pyridine carboxylic acids are problematic. Chemicals such as aminopyralid, clopyralid, and picloram can pass through the horse’s digestive tract and persist in manure and compost piles for long periods without degrading. Tainted compost can kill plants and create liability issues for owners.
To transform livestock waste into high-value soil amendments, the top priority is making sure all the material undergoes a proper hot (thermophilic) phase. This is then followed by a slow cooling and stabilization period, during which the compost should be protected from contamination.
“As composters, we are essentially microbe farmers,” explains Sherman. “Our goal is to provide air, water, and nutrients in the right carbon-to-nitrogen ratio so microorganisms have what they need to break down organic matter efficiently.”
At 30:1, horse manure has an ideal carbon-to-nitrogen ratio for composting. Bedding within the mix will also impact the level of microbial activity. When heaped and moistened (about as damp as a wrung-out sponge), a cubic yard will heat up readily. For outdoor setups, the gold standard is reaching 131-150° Fahrenheit within the pile for a minimum of 15 days, with at least five turns during that period. Keep in mind, temperatures must reach 104° F to kill parasite eggs and larvae and 140° F to deactivate weed seeds. Turning helps cool and aerate the pile.
While the hot phase kills weed seeds, parasites, and pathogens, modulating the process preserves energy and nutrients. This is especially important when the manure is intended as fodder for earthworms. And it is composting with worms (vermicomposting) that converts organic matter into a biologically active, natural fertilizer worth upward of $200 per cubic yard. Because worms will die at temperatures above 90°, the mix must cool before it can safely be put into worm beds. This initial heating phase is known as “pre-composting.”
Horse dewormers are another concern. Ivermectin, for example, can be identified in the environment at 45 days post-deposit at levels harmful to beneficial insects and organisms. A Cornell University study shows that hot composting can speed chemical breakdown, cutting the time ivermectin remains in manure by half. The highest concentrations pass from the horse within days of deworming. But if you’re vermicomposting, it would be wise to withhold the manure from worm beds for 30-45 days, until it undergoes thorough hot composting—or simply skip the worms altogether.
Importantly, turning horse manure into high-value compost requires a beyond-the-basics approach. Sherman’s book, The Worm Farmer’s Handbook, offers practical advice, as do NCSU’s composting publications. For more how-to information, visit NCSU Extension’s online composting guide.