Merck Manual

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Professional Version

Pasture for Horses


Allison J. Stewart

, BVSc (Hons), PhD, DACVIM-LAIM, DACVECC, School of Veterinary Science, University of Queensland

Reviewed/Revised Oct 2022 | Modified Nov 2022

Horses should have ample time on good quality pasture. The opportunity to graze and exercise:

  • improves body condition

  • prevents boredom-related behaviors (eg, cribbing and weaving)

  • decreases the risk of large-intestinal impactions

Grazing on grass also helps decrease the incidence of gastric ulcers. Decreasing the time spent in poorly ventilated barns decreases exposure to many inhalant allergens incriminated in the development of equine asthma syndrome Asthma in Horses Equine asthma is a chronic, nonseptic respiratory disease of adult horses. Although a heterogenous disease, all horses with asthma share common features of airway inflammation, airway hyperresponsiveness... read more Asthma in Horses .

Access to good forage provides a natural source of vitamins and fiber. If horses are fed in groups, sufficient space should be allowed to minimize competition and to ensure that even the most submissive horse has access to an adequate diet. Feeding hay and grain in feeders elevated off the ground decreases ingestion of sand, infective parasite eggs, and animal excreta.

Safe, durable fencing should be used for pastures and paddocks to decrease the risk of self-trauma. Double fencing between paddocks minimizes transmission of infectious disease between horses. Overcrowding should be avoided. Overgrazed pastures, which result from overstocking, lead to extremes in ground conditions (eg, dust or mud), contribute to increased parasite burdens, and favor overgrowth of weeds, some of which are potentially toxic plants.

Excessive dust increases the risk of respiratory infections among young horses by inhalation of soil saprophytes, such as Rhodococcus equi. The risk of this potentially fatal bacterial pneumonia Rhodococcus equi Pneumonia in Foals Rhodococcus equi is a gram-positive, intracellular bacteria that causes chronic suppurative bronchopneumonia with abscessation in foals 1–5 months of age. Clinical signs are mild and nonspecific... read more <i >Rhodococcus equi</i> Pneumonia in Foals on farms where the disease is enzootic can be lowered by minimizing exposure of young (< 4 months old), susceptible foals to aerosolized R equi via environmental control strategies such as:

  • decreasing dust formation on pastures and paddocks

  • housing foals in well-ventilated areas

  • rotating pastures

  • decreasing the size of mare-foal bands

  • irrigating and planting dirt areas with grass

  • removing feces frequently from stalls, paddocks, indoor arenas, and pastures

Breeding mares earlier in the season to ensure foaling during colder weather may decrease the number of susceptible foals exposed to dry, dusty summer conditions. On farms where R equi is endemic and foal morbidity and mortality rates are high despite attempts at pasture management, the incidence of disease can be decreased with preventive administration of 2 L of hyperimmune plasma containing high concentrations of antibodies against R equi to newborn foals within the first week of life, followed by a second dose 25 days later.

Overstocking in barns and pastures favors outbreaks of other contagious respiratory infections due to viral and bacterial pathogens spread between horses via aerosolization of respiratory tract secretions. Enteric infections with Clostridium difficile and C perfringens can become endemic on some farms. An increased incidence of Clostridium diarrhea in newborn foals has been associated with foaling on dirt, gravel, or sand surfaces, and with stall confinement or limited turnout on dry lots during the first 3 days of life.

Whenever possible, horses should not be pastured on sandy soils, because sand ingestion during grazing predisposes to colonic and rectal sand impaction, chronic diarrhea, and weight loss. If sandy pastures are unavoidable, the risk of sand colic can be decreased by feeding psyllium at regular intervals and by providing trace mineralized salt with equal parts bone meal.

Horses grazing on pastures near water may be at increased risk of contracting certain diseases such as Potomac horse fever Potomac Horse Fever Potomac horse fever (PHF) is an acute enterocolitis syndrome producing mild colic, fever, and diarrhea in horses of all ages, as well as abortion in pregnant mares. The causative agent is Neorickettsia... read more , caused by Neorickettsia risticii and disseminated by aquatic insects and snails. Pastures and paddocks should be kept free of standing or stagnant water to decrease the breeding grounds for mosquitoes carrying infectious equine viral pathogens, including West Nile virus and Eastern and Western equine encephalomyelitis viruses Equine Arboviral Encephalomyelitis .

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