EnviroHorse

Horse Urine and Implication for Trails
By Adda Quinn
Rev May 2001

Abstract

Ammonia and nitrogen in horse urine rapidly volatilizes into the atmosphere or adsorbs to soil when deposited on the ground. Horses have unique behavior involving urination. Most horses urinate in their paddocks or pastures. Simple management practices can avoid urine deposition in water bodies by trail horses. Unless there is direct deposition in water, the risk of horse urine excreted on trails providing nutrient enrichment to weeds on trails or contaminating streams will be extremely small. This is a companion piece to Horse Manure Aging and Nutrient Content and Implications for Trails by EnviroHorse, and many of the same references apply. 1

Background

Some have speculated that horse urine on trails can provide nutrient enrichment for weed seeds. The presence of ammonia in water bodies, even in very small amounts, has been shown to be harmful to some aquatic life, particularly salmonids. However, not all species are as susceptible to ammonia as salmonids. Cattle frequently urinate in stock ponds and these same ponds are often found to be the homes of red-legged frogs and tiger salamanders, which are, endangered species. 2 Ammonia is not ambient in aquatic environments. 3 Livestock excrement is coming under increasing scrutiny as a potential non-point source of nutrient enrichment from ammonia and nitrogen.

Nitrogen is needed to produce ammonia. In horses, nitrogen comes from the protein fraction of the horse's feed. Horses absorb protein in the form of amino acids in their small intestines where it is transferred to the blood stream as urea. In the large intestine, unprocessed protein is converted into ammonia that is absorbed by the intestinal wall, converted into urea and picked up by the blood stream.4 Urea is carried by blood to the kidneys and bladder where it is processed out and stored until excreted. Urea is highly unstable once excreted and coverts immediately to ammonia/ammonium and back to nitrogen compounds (all highly volatile and readily adsorptive). 5

Horses consume 20-30 L/day of water. Depending on a number of variables such as diet, temperature, illness, work being performed (exercise) and the conditions in the environment where deposition takes place, the average horse will excrete 5-22 L/day of urine. 6 The number of urinations will vary daily per animal, but ~3 may be expected. These ranges are large, making discussion about the "average horse" difficult.

We have not been able to find studies specific to horse urine on trails. Because of the immense variability in soil composition and soil microbial contents, such studies would be difficult to generalize from and are probably unwarranted given the risk factors discussed below. At this point in time, allegations regarding the environmental risk of horses urinating on the trails and providing nutrient enrichment to weeds are only speculative and not supported by science or experience.

Environmental Risk Assessment
of Horse Urine on Trails
By Adda Quinn

Horse Behavior and Water Bodies

While horses can readily defecate on trails, they do not as readily urinate on trails. 2,6
Most horses urinate in their paddocks or pastures. 7 Because of their physiology, horses under saddle generally signal riders of their need/intent to urinate. They are allowed to stop walking. Horses then stretch their bodies out in a rather awkward position to urinate, often standing on the front edges of all of their hooves simultaneously in a splayed posture. This places them in a vulnerable position if attacked by a predator. 60 million years of evolution and survival means this is an activity not undertaken lightly by the horse. Because of this unique behavior, it is easy for the rider to spur the horse out of a stream to avoid urination in a water body. Another effective management practice is for trail riders to pause and allow the horse to relax prior to a water crossing. Because the urination posture is difficult to achieve during locomotion, it will be more apt to occur with a relaxed horse at rest.8 Urination can be readily managed to avoid elimination in water bodies.

Those of us who perform hundreds of hours of volunteer equestrian patrol for local land managers annually can attest to the fact that horses prefer to urinate in safe, secure locations (like in their horse trailer while on the way home!). As a trail rider who often spends 4-6 hours/day on the trail in three seasons with three separate breeds of horses, trail urination will occur in perhaps 20% of the rides. Particularly when working in warm temperatures, the horse will attempt to preserve its liquids.

Weed Seeds

Horses in the wild used to roam up to 25 miles a day for food, water and shelter. Their continual movement dispersed manure and urine. Immediately after deposition, the dung, particularly if associated with urine, has been observed to "scorch" the area immediately surrounding it due to high immediate nitrogen levels. 9

However, since horses today are primarily confined to paddocks or pastures, it is unlikely that decomposition of the small amount of horse urine left on trails provides any significant nutrient enrichment to the trail environment compared to either ambient detritus decomposition from trailside flora or atmospheric deposition. Horses generally are restricted to hardened trail treads or fire roads that do not provide attractive habitat for plant growth.

According to a Gallop Pole, 22 million US homeowners spent more than $14.6 billion in 1997 on professional lawn and landscape care (and this number is growing annually). One study found that from 5-60% of nitrogen applied to turf grass leached to groundwater. In another survey, 84% of homeowners applying fertilizer had not tested soil prior.10 What is more likely to be the source of ammonia/nitrogen pollution to our water bodies? Horses that rarely urinate on trails or the backyard gardener? Automobiles are a known non-point source of air borne NOx emissions. To put this into perspective, which should we be more worried about: air borne nitrogen deposition from 133 million private automobiles in the United States11 or nutrient enrichment for weeds from ~2 million horses that occasionally frequent hardened trail systems across the entire country?12 The occasional urination of one of my three horses on any given trail ride pales compared to the frequency of my aging husband engaged in what he calls "fire prevention". Perhaps it is the elderly we should ban from trails if urine is a feared nutrient.

Conclusion

The risk of horse urine providing nutrient enrichment for weeds on hardened trail treads is virtually insignificant. Evidence suggests urine may in fact be toxic to some weed seeds initially exposed to it. Animal wastes should not be allowed in or on the margin of water bodies and management practices exist that can help to keep this from occurring.

Disclaimer

These materials have been prepared by EnviroHorse for information purposes only and are not legal advice. Subscribers and online readers should not act upon this information without seeking professional counsel. Every attempt has been made to assure that the information contained in this publication is accurate. EnviroHorse assumes no responsibility and disclaims any liability for any injury or damage resulting from the use or effect of any product or information specified in this publication.

About the Author

Adda Quinn was employed with a nationally known research institute for 21 years prior to her retirement. She has done research both on global climate change and contaminated soil and groundwater issues. As a trail advocate, she has provided research results in a variety of regulatory debates, both nationally and locally. She is a founding member and on the Board of Directors for EnviroHorse. If you have any scientific studies that you think would be helpful, these papers are a work-in-progress and EnviroHorse would love to have copies of them. Please contact us at envirohorse@yahoo.com If you have found these citations helpful, please consider a donation to EnviroHorse to help us find and sponsor more research. Papers are housed at www.californiastatehorsemen.com/envirohorse.htm

References Cited

1. See references cited in Horse Manure Aging and Nutrient Content and Implications for Trails by Bob Griswold of Envirohorse www.californiastatehorsemen.com/envirohorse.htm
2. Dr. Larry Gosselin, DVM, pers. comm. 4-10-01
3. Dr. Michael Rugg, Toxicologist, Calif. Dept. Fish and Game in personal communication to Adda Quinn and Alistair Bleifuss (RCD TAC), 1998.
4. Nutrient Requirements of Horses, 5th Ed. P8. p.43
5. Urea rapidly hydrolyzes to ammonia and is the major N component of urine. Phosphorus is only present in livestock urine in trace amounts. Potassium is present in urine, but in small amounts relative to N and P. Nutrients Available in Manure (for Nitrogen) from Dev. Doc. For Prop. Revs to the NPDES Reg and ELGs for CAFOs. EPA-821-R-01-003. Jan. 2001. Pp. 8-144/146.
6. Dr. Larry Wolford, DVM specializing in equids, pers. comm. 4-5-01
7. "Horses spend most of their time in pastures or paddocks where the majority of their excrement is deposited, collected and managed." Personal communication with Dr. Deanne Meyer, UCDavis Manure Management Specialist, February 1997
8. Toby Horst, Chairman BackCountry Horsemen, pers. comm. 2000.
9. Putnam, R., 1983. "Carrion and Dung: the decomposition of animal wastes". The Institute of Biology's Studies in Biology No. 156. Pp. 6 and 28.
10. www.epa.gov/owow/info/NewNotes Nov. 1998: Maryland Law Brings Lawn Care into Nutrient Management, and Jul. 2000: A Survey of Residential Nutrient Behavior.
11. 1998 World Almanac data on total US cars.
12. American Horse Council 1996 estimate of horses in the US was 6.9 million about half of which are in racing or showing and do not leave home. About a quarter of the remainder are likely to be too old, or infirm to leave home (manure study results from San Mateo County January 2001). This puts about one quarter of horses potentially on the trails. The average trail horse in California, ridden by an employed owner from an urban area, would likely not be present on public trails more than 12 to 16 hours per week- a maximum of about 10% of a week. Winters are difficult to ride on trails, so most riding occurs between April and November. Many more people use trails than horses. For example, in San Mateo County, the human population is nearly 700,000 compared to 4,000 horses. While all citizens and all horses may not be trail users, the horse subset that uses trails is probably very small. We believe that such small numbers of horses on urban trails and the brief time spent on them constitutes very little true environmental risk in terms of volume or contents of horse excrement.

(Return to Envirohorse)