Review Article
Production and Environmental Implications of Equine Grazing

https://doi.org/10.1016/j.jevs.2013.05.004Get rights and content

Abstract

Horses' physical and digestive well-being is often enhanced when allowed to graze on pastures. Furthermore, a well-managed pasture can contribute to economic viability. Grazing can however have deleterious effects on the environment if not properly managed. Although equine grazing, defecating, and ground trampling behavior is unique from that of other livestock species, pasture management practices are often based on those derived from cattle grazing. This review summarizes the current knowledge of impacts of equine grazing on pasture quality and environment and identifies gaps where further information is needed to formulate and recommend sustainable grazing methods specific to equine.

Introduction

Horses assume a unique role in developing an ecological niche through their grazing behavior. They fertilize via urination and defecation and can modify soil structure by trampling during periods of exercise and turnout. Pasture is a good source of nutrition for the estimated 9.2 million equines in the United States, with over 90% of U.S. equine operations allowing resident horses access to pasture during the day [1], [2]. Grazing offers a myriad of benefits, however, poor manure and grazing management practices increase movement of sediment, nutrients, and pathogens into nearby surface waters causing a decrease in water quality [3]. It is important to acknowledge that these negative implications can occur when any animal is left on an area of land for too long. Horses are large bodied selective grazers; their very existence on pastures increases soil compaction, grazing intensity of forages, and manure deposition on pastures at an average rate of 18-22 kg each day. Although horse farm operators do not typically view themselves as stewards of the land, but rather as animal caretakers, almost half of horse farm operators surveyed in the northeast United States believe horse farms had a strong potential to impact the environment [4], [5]. In fact, horse farm operators in many parts of the United States are facing serious regulatory issues regarding horses housed on pasture [6]. It is therefore increasingly critical to educate horse farm operators on the best management practices (BMP) that foster management of the environment as well as health and welfare of their horses in order to bring them into compliance with regulatory agencies.

Although great advances have been made in the fields of equine nutrition, physiological, and veterinary sciences, very little scientifically based information is available regarding the environmental impacts of grazing horses on pasture. This review presents the benefits of pasture access and grazing on horse health, pasture quality and sustainability, summarizes the available information related to the environmental impact of horses grazing on pasture, and identifies knowledge gaps in the scientific literature.

Section snippets

Nutrition and Health Benefits of Pasture to the Grazing Horse

Depending on the geographical region, well-managed pastures may provide year-round ground cover and an economical feed source that can meet all of a horse's daily nutrient requirements. The digestible energy and crude protein provided by pasture can potentially meet the requirements of horses across several physiological states (e.g., maintenance, light work). Furthermore, well-managed pastures may also support mares during gestation and lactation [7]. The total acreage required per animal will

Benefits of Pasture to the Horse Farm Operator and Environment

The benefits of well-managed pasture are extensive, contributing to the well being of the horse and the land. First, a productive and properly managed pasture can meet most if not all of the horse's nutritional requirements during the grazing season, thus limiting the need to purchase additional forage or grains. Thus, supplemental hay feeding would be limited to only summer drought periods and times when access to forage is limited (winter). Furthermore, when horses spend more time on

Vegetative Damage

The act of grazing by animals, including horses, can cause irreparable damage to plant structures, and is influenced by grazing time in a restricted area, along with other factors including plant type, climate, and soil fertility. The effects of horses on pastures can be quite stunning if pastures or paddocks are overexposed to horses compared to areas where access has been limited (Fig. 1). Horses are selective grazers, consequently, they overgraze certain areas and ignore others, such as

Proportion of Time Spent Grazing While at Pasture

Horses are periodic grazers [52], and the health of their gastrointestinal tract is dependent on consumption of small, frequent meals [53]. When provided access to feed ad libitum, horses ingest feed frequently throughout the day and night. Mayes and Duncan [54] reported that equine grazing took place throughout the day, but peaks in grazing occurred soon after dawn and before dusk. Horses grazed between 63% and 75% of the daylight hours and 49% and 50% of the nighttime hours. Estimates of time

Grazing Systems

Grazing systems have been studied extensively, especially in relation to ruminant species [103]; however, few studies have been completed for comparative analysis using horses. Selection among grazing systems are often determined by the potential for pasture productivity to offset increased labor and equipment costs. Although environmental stewardship is rarely considered when designing grazing systems, such systems can greatly impact the environment. The two basic grazing systems usually

Stocking Rates

Little is known regarding proper equine stocking rates for pastures [114], [115]. Singer et al. [116] reported that appropriate stocking densities vary greatly, based on climate and region. Stocking rates are generally accepted to range from 0.4 to 0.8 ha per horse in temperate climates. In addition, forage growth rates are cyclic and have uneven growth over the course of a given grazing season, depending upon rainfall, temperatures and season. Therefore, when calculating stocking densities,

Evaluation of Horse Pastures

There are several methods to evaluate and monitor pasture conditions. The line-point transect method has been used for more than ninety years to quantify the amount and quality of plant cover at consistent and repeatable measurement points. This is accomplished by setting up specific transect lines in the desired area and choosing predetermined measurement points along those lines. At each point a vertical pin is used to identify species and measure the contact points and the parts of any

Current Management Practices

The management of grazing horses on pasture varies greatly. In the Northeast, there are a variety of management practices ranging from admittedly no management to monitoring of vegetative cover and implementation of rotational grazing [4], [5]. For example, in the North Central portion of the United States, several small acre farms are being formed from previously larger farms. Additionally, the number of small acreages in South Dakota (1-49 acres) increased 27% from 2002 to 2007 [121].

Basic

Conclusions

Research on equine pasture management and the environmental impact of grazing horses has been limited compared to other livestock species. Currently, management decisions regarding grazing systems and stocking rates are supported by data from other species with little information available for equine-specific systems. Equine-specific data are needed to develop pasture best-management practices and strategies, which can be implemented on horse farms. There is also a lack of regional research

Acknowledgments

This project was supported in part by US Department of Agriculture Multi-State project NE-1041, Environmental Impacts of Equine Operations, coordinated by Michael Westendorf, PhD. The authors thank Rachel Gilker, PhD, for consultation on soil dynamics and Cheryl Beste and Rozanne McGrath for editorial assistance.

References (125)

  • L. Clarke et al.

    Feeding and digestive problems in horses. Physiological responses to a concentrated meal

    Vet Clin North Am: Equine Pract

    (1990)
  • L.E. Dowler et al.

    Determination of pasture dry matter intake rates in different seasons and their application in grazing management

    J Equine Vet

    (2012)
  • A.V. Rodiek et al.

    Voluntary intake of four hay types by horses

    J Equine Vet Sci

    (2012)
  • S. McCown et al.

    Acceptability of teff hay by horses

    J Equine Vet Sci

    (2012)
  • A.C. Longland et al.

    Pasture nonstructural carbohydrates and equine laminitis

    J Nutr

    (2006)
  • G. Fleurance et al.

    Instantaneous intake rate in horses of different body size: influence of sward biomass and fibrousness 2

    Appl Anim Behav Sci

    (2009)
  • G. Fleurance et al.

    Influence of sward structure on daily intake and foraging behavior by horses

    Animal

    (2010)
  • N. Edouard et al.

    Does sward height affect feeding patch choice and voluntary intake in horses?

    Appl Anim Behav Sci

    (2009)
  • A. Naujeck et al.

    Influence of sward height on diet selection by horses

    Appl Anim Behaviour Sci

    (2005)
  • E.C. Glunk et al.

    Effect of restricted grazing on dry matter intake rate

    J Equine Vet Sci

    (2011)
  • A. Longland et al.

    Estimation of pasture intake by ponies from liveweight change during six weeks at pasture

    J Equine Vet Sci

    (2011)
  • S.J. Chavez et al.

    Horse intake estimation of AM versus PM grazing

    J Equine Vet Sci

    (2011)
  • S.J. Chavez et al.

    Intake estimation of grazing or stall-fed horses

    J Equine Vet Sci

    (2011)
  • J.C. Ince et al.

    Changes in proportions of dry matter intakes by ponies with access to pasture and haylage for 3 and 20 hours per day, respectively, for six weeks

    J Equine Vet Sci

    (2011)
  • A.C. Longland et al.

    The effect of wearing a grazing muzzle vs not wearing a grazing muzzle on pasture dry matter intake by ponies

    J. Equine Vet. Sci

    (2011)
  • S.E. Duren et al.

    Modification of ingestive behavior due to exercise in yearling horses grazing orchardgrass

    Appl Anim Behav Sci

    (1989)
  • American Horse Council. National economic impact of the U.S. horse industry....
  • USDA: APHIS: Veterinary Services. USDA National Animal Health Monitoring System (NAHMS). Baseline reference of 1998...
  • R.K. Hubbard et al.

    Water quality and the grazing animal

    J Anim Sci

    (2004)
  • Fiorellino NM, Wilson KM, Burk AO. 2013. Characterizing the use of environmentally friendly best management practices...
  • Swinker AM. Update of Nutrient Management Regulations and the Equine Industry, In: Zimmerman N, editor. Proceedings of...
  • J. Gallagher et al.

    The nutritional status of pregnant and non-pregnant mares grazing South East Queensland pastures

    Equine Vet J

    (1988)
  • Nutrient requirements of horses

    (2007)
  • Equi-analytical Laboratories. Common feed profiles. http://www.equi-analytical.com/CommonFeedProfiles/default.asp 2011...
  • Dairy One. Dairy one feed composition library. http://www.dairyone.com/Forage/default.asp. 2011 [accessed May,...
  • L.K. Warren

    Forage: the often overlooked source of omega-3 fatty acids

  • H. Boufaied et al.

    Fatty acids in forages. 1. Factors affecting concentrations

    Can J Anim Sci

    (2003)
  • F. Derksen et al.

    Airway reactivity in ponies with recurrent airway-obstruction (heaves)

    J App Physiol

    (1985)
  • J. Hudson et al.

    Feeding practices associated with colic in horses

    J Amer Vet Med Assoc

    (2001)
  • M. Murray

    Gastric-ulcers in adult horses

    Compend Contin Ed Practic

    (1994)
  • R.A. Bell et al.

    Daily access to pasture turnout prevents loss of mineral in the third metacarpus of Arabian weanlings

    J Anim Sci

    (2001)
  • S.O. Hoskin et al.

    Feeding value of pastures for horses

    NZ Vet J

    (2004)
  • A.B. Costin

    Runoff and soil losses from and improved pasture at Ginninderra. Southern Tablelands, New South Wales

    Aust J Agric Res

    (1980)
  • D.M. Butler et al.

    Ground cover impacts on nitrogen export from manured riprarian pasture

    J Environ Qual

    (2007)
  • L.B. Guo et al.

    Soil carbon stocks and land use change: a meta analysis

    Glob Chang Biol

    (2002)
  • M. Archer

    The species preferences of grazing horses

    Grass and Forage Science

    (1973)
  • M. Sanderson et al.

    Pasture monitoring at a farm scale with the USDA Natural Resources Conservation Service pasture condition score system

    J Soil Water Conserv

    (2009)
  • A.G. Matches

    Plant response to grazing: a review

    Journal of Production Agriculture

    (1992)
  • J.W. Singer et al.

    Equine stocking density effect on soil chemical properties, botanical composition, and species density

    Commun Soil Sci Plant Anal

    (2001)
  • D.A. Pyke et al.

    Rangeland health attributes and indicators for qualitative assessment

    J Range Manage

    (2002)
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