MODERN PROBLEM FOR AN ANCIENT BREED
A new study links an often-fatal disease in an ancient breed of Chinese horse to a thoroughly modern cause: a dietary deficiency related to management practices.
The Hequ horse, which has ancestry tracing back to the Tang Dynasty era, is native to the Qinghai Province of China. Used for a variety of activities from riding to light draft work, the Hequ is adapted to living at high altitude, where oxygen levels are low.
In recent years, a growing number of Hequ horses have developed a condition called edema pathema (EP), which causes a buildup of fluid under the skin, anemia, weight loss and involuntary muscle movements (dyskinesia). The increase in EP cases corresponded with adjustments in grazing management—including the fencing of grasslands that restricted access to some areas—leading researchers to suspect that the disease spike is related to changes in the horses’ nutritional intake.
To investigate, researchers from Guizhou Normal University in Guiyang, China, conducted a comparative trace element analysis of the soil and feed at two different
Hequ horse farms: One farm had a high incidence of edema pathema and the other, which served as a control, was a research facility that had no recorded EP cases.
The laboratory analysis showed a strong correlation between the occurrence of EP and low selenium levels. An essential micronutrient, selenium is needed for a number of body processes, including
The increase in edema pathema cases corresponded with adjustments in grazing management, leading researchers to suspect that the disease spike was related to changes in the horses’ nutritional intake.
metabolism, thyroid function and mechanisms that protect against tissue-damaging free radicals. Selenium levels in forage and soil, as well as blood and liver samples taken from resident horses, were all found to be low at the farm where EP incidence was high.
To further clarify the role of
selenium in EP, the researchers ran an experiment in which 1,576 Hequ horses received a daily oral selenium supplement. In the year after selenium, there were no cases of EP. In a separate study, 198 of 235 horses with EP recovered after they were given the same selenium supplement but in incremental doses.
The researchers conclude that it is possible that the edema pathema observed in the Hequ horses is caused by selenium deficiency in soil and forage.
Reference: “Studies on
Edema Pathema in Hequ Horse in the Qinghai-Tibet Plateau,” Biological Trace Element Research 2020
horses and some from horses with PPID, and then working out the numerical characteristics---means and standard deviations---of the two different populations, allowing them to be separated out,” says Durham. “The big advantage of this method is that you don’t have to rely on clinical examination to decide whether they have PPID---the math can do this.”
The statistical model ultimately yielded weekly thresholds---ranges of normal ACTH readings---for each week of the year. With this information, available online through the published paper, veterinarians can make more accurate PPID diagnoses generally, and especially during times of the year when ACTH levels naturally
The statistical model yielded weekly thresholds—ranges of normal ACTH readings—for each week of the year.
rise. A comparison of the thresholds generated by the calculations to clinical descriptions of the study horses confirmed that the mathematical method was accurate, says Durham.
“Apart from a different way of determining thresholds for diagnosis, the other novel thing that we did was present different thresholds for different scenarios,” says Durham. “Where there is a very strong clinical suspicion of PPID (for instance, an elderly, hairy, laminitic horse) then it is valid to use the lower threshold, and where it is a highly speculative test it is best to use the higher threshold. For most scenarios somewhere between the two the balanced threshold can be applied.”
Although the study was based on ACTH levels among horses in England, Durham says the findings should be applicable to those in the United States as well. “There is some debate about a possible small effect of higher or lower latitudes on ACTH values, although the timing would not differ. I seriously doubt that would have much, if any, effect.”
Reference: “Clinically and temporally specific diagnostic thresholds for plasma ACTH in the horse,” Equine Veterinary Journal, May 2020