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 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