Gastric ulceration common in NZ racehorses, study shows

April 13, 2007

by Neil Clarkson


The veterinary study on gastric ulcers in racehorses found 88% of horses had some evidence of gastric ulceration. Findings showed little difference in the occurrence of ulceration between horses that were stabled fulltime and those spending some of their time on grass.

A recent veterinary study of 171 New Zealand racehorses revealed that 88% of the animals had some evidence of gastric ulceration.

The study, reported in the February 2007 issue of the New Zealand Veterinary Journal, revealed little difference in the occurrence of ulceration between horses that were stabled fulltime and those spending some of their time on grass.

The study, one of three major articles in the journal on the subject, aimed to establish the prevalence of gastric ulceration in New Zealand racehorses, and any factors influencing the rate and severity of the problem.

It focused on 171 racehorses in work with 24 trainers. Thoroughbreds totaled 133 (78%), with the remainder being standardbreds. The animals were examined using gastroscopy during 2003 and 2004.

Evidence of gastric ulceration was present in 151 (88.3%) of the horses.

Ulceration was evident in 89% of the horses kept at pasture for at least four hours a day, in all 13 (100%) of horses kept at pasture full time, and in 16 out of 17 (94%) of horses stabled full time.

The prevalence and severity of ulceration did not differ between horses stabled full time, kept at pasture for part of the day, or kept at pasture full time. The severity of ulceration did not vary significantly with the quality of the pasture, nor with the duration of training.

The authors - Robin Bell, Janene Kingston, Tony Mogg, and Nigel Perkins - concluded that the prevalence of gastric ulceration in racehorses in New Zealand was similar to that reported elsewhere in the world for horses in active training for racing.

Despite the high prevalence, the cause of gastric ulcers in adult racehorses remains unknown.

The horse is a grazing animal and it is suggested that the constant flow of saliva and feed material into the stomach acts as a buffer for gastric acid. When horses are put into training they are usually stabled for prolonged periods and have little access to grazing, which may remove this important buffering mechanism, a 2003 study suggested.

A 1999 study of the issue said it would be interesting to compare ulceration in racehorses that spent time in a paddock grazing, as opposed to being stabled fulltime.

The New Zealand study did just that, but found no evidence that pasture grazing affected the rate of ulceration in horses in active race training. "We hypothesized," the authors said, "that daily access to pasture and grazing would be protective against gastric ulceration, resulting in a lower prevalence in New Zealand compared with other countries where racehorses are housed more intensively.

"In our study, there was no evidence to support this hypothesis, as all horses kept at pasture full time showed evidence of gastric ulceration ... and there was no difference in the prevalence or severity of gastric ulceration between horses grazed for different amounts of time or on pastures of different qualities. The majority of horses in the study were kept in paddocks, where the quality of pasture was subjectively assessed as either average or good."

The authors noted, however, that all horses in the study were receiving significant amounts of grain and supplemental feeds, which may have reduced the amount of time they spent grazing when out at pasture.

The authors noted a 2002 study that suggested other dietary factors, and the physiological stresses of training, may be sufficient cause for gastric ulceration.

"As the prevalence of gastric ulceration did not vary significantly between trainers, it is likely that one or more factors common to all trainers in the study contributed to the development of gastric ulceration. This finding may serve to focus future research away from variability between trainers and towards factors common among racehorses."

More work was needed on the causes of the problem, they said.

The journal also carried a review of literature on the subject, conducted by Drs Bell, Mogg and Kingston. Summarising, the authors noted that in recent years, gastric ulceration has been recognised as a common, possibly performance-limiting disease of adult horses.

Its prevalence in racehorses has been reported to be as high as 100%. In general, horses in active training for racing tend to have a prevalence of around 90%, whereas pleasure horses in full work have a reported prevalence of about 60%.

One small study of competitive mixed-breed horses showed that only 4 out of 23 (17%) had superficial ulcers before starting competitive work. However, after three consecutive days of travel and competition, 13 (56%) of the horses had ulceration, 36% of which had superficial lesions and 54% had deeper lesions.

In a preliminary study into the prevalence of gastric ulcers in endurance horses, ulcers were found in 23 out of 37 (67%) immediately after competition. It was suggested that the ulcers observed in those horses were acute; that is, had formed during the competition itself, and not the result of long-term management or training factors.

The review traversed emerging diagnostic tests which could obviate the need for gastroscopy, current treatment options, the healing process, and risk factors, which include diet and the amount of roughage, exercise, and stress.

Exercise, the authors noted, has been said to contribute to ulceration either due to decreased gastric action or increased gastric pressure. "The latter may be the result of action of the abdominal muscles or increased respiratory effort."

In their conclusion, the authors noted that it was difficult to compare the effectiveness of treatment methods between studies. They noted that the effect of gastric ulceration on racing performance is unknown, and that the significance of low numbers of small, localised lesions was questionable.

"Excess acidity in the stomach is the primary cause of this condition, though it is likely that other factors such as exercise and dietary change contribute to the development of the excess acidity. Until more is understood about this disease, its pathogenesis, and its significance, treatment will continue to be symptomatic."

The journal also carried a third report on gastric ulcers by the same authors, entitled "A comparison of two scoring systems for endoscopic grading of gastric ulceration in horses".