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9th November 2008

Risk Factors for Gastric Ulceration in Thoroughbred Racehorses

By Guy D Lester, Ian Roberston and Cristy Secombe

Rural Industries Research and Development Corporation

May 2008

RIRDC Publication No 08/061

What the report is about?

Gastric ulceration represents an important health concern to the performance horse industries. Economic impacts of this disease are difficult to quantify but include the costs associated with diagnosis, cost of medication, and labour involved in administering treatment. Perhaps of even greater economic significance are the costs attributable to reduced athletic performance. Superimposed on any economic impacts are the emerging industry concerns regarding the welfare of performance horses. The reported high incidence of disease across the world is of concern given the common lay opinion that peptic ulcer disease in humans is commonly correlated with emotional stress. The focus of this report is to identify specific factors that may be involved in the development and maintenance of gastric ulcers in racing thoroughbreds.

Who is the report targeted at?

The primary target group of the report is the thoroughbred racing community. It is however likely that risk factors will be common to other industries where animals are performing high levels of exercise. The information will also guide attending veterinarians with respect to identifying horses at risk of ulceration.

Project Aims

As stated above the principal aim of the project was to elucidate specific risk factors that may predispose racing thoroughbreds to gastric ulceration. The ideal outcome would be to identify factors that could be easily manipulated through management to reduce the risk and/or severity of disease. This should be of benefit to both trainers and owners. Another aim was to investigate associations between disease and clinical signs, as well as disease and athletic performance.

Study Methods

Data were collected from 402 thoroughbred horses over a 10 month period in 2006. There were 37 trainers enrolled in the study and they were based from the following regions in south Western Australia: Albany 420 km south of Perth; Mandurah/Larkhill 60 km south of Perth; Swan Valley 60 km northeast of Perth; Bunbury 170 km south of Perth; and Ascot/Belmont located within the metropolis of Perth. Endoscopy was performed in fasted free-standing horses and the squamous mucosa of the stomach was evaluated for ulcer disease. The gastric squamous mucosa was scored using a simplified system that ranged from 0 to 3. Grade 0, normal – intact mucosal epithelium with or without reddening or hyperkeratosis; Grade 1, mild – single or multiple small ulcers; Grade 2, moderate – single or multiple large ulcers; and Grade 3, severe – extensive ulceration with coalescing of ulcerated areas. Horses graded as 0 or 1 were classified as not having ulcers and those graded as Ulcer score 2 or 3 were classified as having ulcers. Trainers were then asked a series of questions pertaining to each horse. All variables were then assessed independently for association with gastric ulceration and those with a significance of P ≤ 0.25 in the univariable analyses were considered eligible for inclusion in the logistic multiple regression.

Key Findings

The overall prevalence of ulcer disease was 53%. This was reduced to 33% of the entire population when the definition of ulceration was restricted to horses having either moderate (grade 2) or severe (grade 3) disease. As anticipated, there were highly significant differences between trainers with respect to ulcer prevalence. The time that an animal had been in training was significantly associated with the prevalence of ulcers, with the odds of a horse developing moderate or severe ulceration increasing by 1.7 times for every week that the horse was in training. The location of exercise was also important with animals exercised at a track on the property where they reside being 3.3 times less likely to have ulcer disease than those that were not. Animals that the trainer reported as having difficulty in maintaining adequate body condition were more likely to have moderate or severe ulceration than those where no problems were reported. Interestingly, this was closely correlated with the time in work and quality of appetite. A poor appetite in response to gastric ulceration may be the critical response that leads to problems in maintaining body condition and reduced athletic performance. As would be expected these problems are accentuated with the length of time in work when caloric demands would be at their greatest. There is some evidence that psychological stress may also be a key factor in the development of squamous ulcer disease. Animals demonstrating stereotypic behaviour were more likely to have disease; the most significant vice was crib-biting or wind sucking. It could be argued that this vice could lead to ulceration or conversely could arise as a relief mechanism for on-going gastric pain. Alternatively crib-biting, along with other stereotypic behavioural traits, may simply be a marker for environmental stress, which in turn may independently increase the risk of ulcer disease and increase the likelihood of developing an abnormal behavioural trait. Horses that had access to some turnout were less likely to have ulcer disease; perhaps more importantly horses that not only had access to turnout but were turned out with other horses were even less likely to have disease. This indicates that horse-to-horse contact may be an important preventative strategy against ulcer disease. Playing of the radio within the barn was associated with increased risk of ulceration, indicating that this may be a form of stress for some animals. Of interest was the fact that we were unable document any direct link between aggression, diet, gender or age with ulcer disease.

Implications and Recommendations

The prevalence of ulcer disease is greater in metropolitan stables than in rural or semi-rural stables. Location by itself is not the critical factor; rather it appears that features common to these environments are increasing or decreasing the risk of ulcer disease. It may be that the focus of reducing disease is in evaluating the environment and making appropriate adjustments to reduce any stress on the animal. It appears that direct horse contact is an important protective strategy.

It is also clear that the generation of ulcer disease is multi-factorial and therefore adjusting any one factor may have negligible impact on overall disease prevalence. It is also important to consider what impact ulceration has on the individual horse. We would contend that horses, as individuals, differ widely in the expression of clinical signs that result from ulcer disease. Some horses with severe ulceration appear to demonstrate little to no outward signs of disease and continue to perform successfully, whereas in other animals ulcer disease appears to be highly debilitating and has a dramatic effect on appetite, body condition, and therefore athletic performance. Many of these animals can be effectively managed with anti-acid drugs, but may also respond to radical changes in their training environment.

The full report can be found at www.rirdc.gov.au/fullreports/index.html or purchased at www.rirdc.gov.au/eshop