On croplands, manure is spread before or after the growing season. On our farm, we spray fertilizer on the land, then till in the manure in early spring. This prepares the ground for planting. MacLean advises that farmers concerned about crops being stunted due to manure mixed with sawdust or wood shavings should add nitrogen fertilizer to the mix or to the soil. Spreading and harrowing manure on horse pastures should be done only in the coldest or hottest, driest weather to ensure larval kill, and should not be done during the season of parasite activity, says Douglas E. Hutchens, DVM, clinical assistant professor, University of Illinois.
Experts differ on how quickly horses can be returned to pasture after raw manure has been spread.
However, this might vary depending on the type of parasite load the horses carry. Consult with your veterinarian and cooperative extension service for recommendations pertinent for your situation. On large pastures, horses tend to graze in one part and defecate in another, so the elements of nature might take care of the manure problem as long as the horses are on a good deworming program and parasite load is at a minimum. Such is the case with the herd at Kansas State University, where stocking density is five or six horses per acre during the grazing season. Composting This is the process where manure and soiled bedding are heaped into a pile to decompose.