Viable Weed Seeds Widely Dispersed in Horse Manure

Horses may be responsible for spreading plants, many of which are considered weeds, over long distances, according to the findings of an Australian research project.

Catherine Pickering, an associate professor at Griffith University in Queensland, led a study to identify the germination capabilities of various weed seeds found in horse manure. After reviewing literature on germination of manure-dispersed seeds in Europe, North America, Africa, Central America, and Australia, Pickering found that a high number of plants can be spread in this way.

Many manure-borne seeds germinated well after passing through the digestive tract of a horse, and being deposited with manure meant that the seeds had a head start in growth because of the nutrients provided in the feces. Also, manure is often deposited in areas where the soil surface has been disturbed by the passage of horses, allowing seeds to take root in loose dirt.

Results of the research showed that from a list of over 2,700 nonnative plants growing in Australia, seeds from many were able to grow from horse manure. Some of the plants were designated as noxious weeds, meaning that they were considered harmful to humans or animals in some way. The spread of some types of plants might or might not be a problem, depending on the particular characteristics and the location where they were introduced.

Trail riding is a popular equestrian activity, and owners often transport their horses for long distances to engage in this recreational pastime. Pickering warned that legislators should consider the possible threat to agricultural activities and the environmental impact before opening parks and other public lands for equestrian use. Though some plants spread in horse manure are not inherently harmful, Pickering’s research found that 99% of the reviewed species were listed as weeds in at least one global location.