THE AMERICAN MUSTANG


removed from the range and held in corral facilities is infectious upper respiratory disease. Both bac- terial (Streptococcus equi and S. zooepidemicus) and viral (equine herpes and influenza viruses) agents are problems, but upper respiratory infections caused by S. equi and S. zooepidemicus, along with the less common sequelae of internal abscesses and immune mediated reaction (purpura hemorrhagica) associated with these bacteria, are most common. Exposure to both viral and bacterial respiratory agents has been documented in free-roaming wild horses and burros,14 but exposure levels and effec- tive contact rates for disease spread seem low in the wild. The real problems occur when animals are removed from the wild and congregated in captivity. Most of the animals are immunologically naïve to infectious respiratory disease agents when they are captured. Combined with the stress of adapting to captivity, this makes them particularly susceptible to infection. Complete isolation is very difficult in large dry-lot facilities and exposure to the agents that typically cause infectious upper respiratory dis- ease in the domestic world seems inevitable. While vaccines for these agents are commonly used, they generally are not highly efficacious in this situation. The best approach to controlling disease out-


breaks seems to be as follows: (1) isolate new ar- rivals as much as possible when first removed from the wild, (2) use a broad vaccination protocol (equine herpes and influenza as well as Streptococcus equi as soon as possible following capture depending on animal condition, and (3) allow many of the respira- tory conditions to “run their course” once they start to occur. Vaccination protocols that include peri- odic boosters for respiratory disease agents seem to keep outbreaks that do occur in check but, to some extent, such outbreaks seem inevitable, given the ecology of the disease agents involved and the sus- ceptibility of the large numbers of animals that must be handled during the transition from free-roaming to domestic life. Large-scale treatment of groups of animals with sulfa antibiotics added to drinking wa- ter is sometimes used to try to decrease the spread and severity of infection, but it is difficult to know how beneficial this is in practice. Fortunately, while morbidity may be high, these conditions are usually self-limiting without treatment, serious complications and mortality due to pneumonia or internal abscesses are rare. Treatment of individ- ual animals housed in a group setting is not without added risk and stress associated with handling, so this type of treatment is usually reserved for those individuals who appear to be suffering from compli- cations of the upper respiratory infections. Preventive healthcare and biosecurity measures


in place at BLM facilities include managing animals in groups according to their risk and exposure pro- files, to the extent possible, given the demands of moving large numbers of animals. For example, the most active centers for receiving animals fresh off the range have traditionally managed animals in


418 2014  Vol. 60  AAEP PROCEEDINGS


groups as they are gathered from different HMAs. To the extent possible, these facilities would usually be emptied and cleaned and handling facilities would be disinfected prior to the start of each gather season. Animals removed from the range are rou- tinely tested for equine infectious anemia and vac- cinated for eastern and western equine encephalomyelitis, tetanus, equine herpes and influ- enza viruses, West Nile virus, Strep. equi, and ra- bies. The diagnosis and treatment of animals is performed by or under the supervision of a veteri- narian and all surgical procedures are performed by a veterinarian. Specific protocols for diagnostics, treatments, and anesthesia are the responsibility of the attending veterinarian; however, it is BLM pol- icy that all castrations be performed by a veterinar- ian under general anesthesia. All animals moved interstate by the BLM do so with a Brand Inspection Certificate, where required, and an Interstate Cer- tificate of Veterinary Inspection.


Animal Welfare


Protecting the health and well-being of feral horses and burros begins with a healthy environment on the range. When range conditions provide ade- quate forage and water, the animals are remarkably hardy and do well, even in the harsh high desert environments typical in the Western U.S. During periods of drought or when forage utilization levels are too high, the ecology of the area suffers with decreased plant health and diversity. Ultimately, the animals suffer because of this. Excess numbers on the range above what the habitat can support is the biggest welfare problem in the Program and it has no easy solution.15 The natural condition where stallions, often more


than one different stallion, will breed a mare several times a day throughout estrus is a very effective breeding model. Foaling rates are high. Typi- cally, 60 to 75% of breeding age mares will foal each year and mares often foal well into their late teens and twenties. Unlike animals that may not twin or have larger litters in response to harsh conditions, horses generally invest heavily in just one offspring. In addition, where conception and birth are sepa- rated by several months, the grazing season that affects conception may be very different from that of the foaling season. Reduced fecundity is not often seen and the mechanisms of so called “self-limita- tion” are too often mechanisms of starvation. Star- vation usually means reduced survival of newborn and nursing foals in the summer and a higher than usual die-off of older adults over the winter. It is not uncommon for young wet mares and older


horses to show dramatic changes in body condition during the course of the year. Many horses will fluctuate from a body condition class of 5 (the Hen- neke 1–9 scale)16 following the peak of forage pro- duction in the spring to a body condition of 4 or even 3 in the fall or winter months, depending on drought and winter snow cover. This can represent a sea-


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