* This is the Veterinary Version. *
Pasture for Horses
Horses should have ample time on good quality pasture. The opportunity to graze and exercise improves condition, prevents boredom-related behaviors (eg, cribbing and weaving), and reduces the risk of large-intestinal impactions. Grazing on grass also helps reduce the incidence of gastric ulcers. Reducing the time spent in poorly ventilated barns reduces exposure to many inhalant allergens incriminated in development of recurrent airway obstruction. 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 elevated feeders off the ground reduces ingestion of sand, infective parasite eggs, and animal excreta.
Safe, durable fencing should be used for pastures and paddocks to reduce the risk of self-trauma. Double fencing between paddocks minimizes transmission of contagious 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 potentially toxic plants.
Excessive dust increases the risk of respiratory infections among young horses by inhalation of soil saprophytes, such as Rhodococcus equi (see Rhodococcus equi Pneumonia in Foals). The risk of this potentially fatal bacterial pneumonia on farms where the disease is enzootic can be reduced by minimizing exposure of young (<4 mo old), susceptible foals to aerosolized R equi using environmental control strategies such as decreasing dust formation on pastures and paddocks, housing foals in well-ventilated areas, rotating pastures, reducing the size of mare-foal bands, irrigating and planting dirt areas with grass, and removing feces frequently from stalls, paddocks, indoor arenas, and pastures. Breeding mares earlier in the season to ensure foaling during colder weather may reduce 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 reduced with preventive administration of 1 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 caused by 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 reduced by feeding psyllium at regular intervals and by providing trace mineralized salt with equal parts of bone meal.
Horses grazing on pastures near water may be at increased risk of contracting certain diseases such as Potomac horse fever, caused by Neorickettsia risticii and disseminated by aquatic insects and snails (see Potomac Horse Fever). Pastures and paddocks should be kept free of standing or stagnant water to reduce the breeding grounds for mosquitoes carrying infectious equine viral pathogens, including West Nile virus and Eastern and Western equine encephalomyelitis viruses (see Equine Arboviral Encephalomyelitis).
* This is the Veterinary Version. *