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News Article

Diet may impact hormone levels used to diagnose PPID in horses


Study reports that diet, and more specifically, a starch rich food, can influence ACTH levels.

ACTH concentrations are useful for the diagnosis of pituitary pars intermedia dysfunction (PPID). However, multiple factors (stress, exercise, and time of year) are known to influence ACTH levels. A study published in Domestic Animal Endocrinology suggests that diet may also impact ACTH concentrations.

The circulating concentration of ACTH is seasonal, peaking in the Autumn. It is also known to vary with stress, exercise and nutritional state (fasted or fed). When the results lie in the grey zone (between the maximum normal and the minimum disease level), a modified test can be used. This involves measuring the ACTH level before and after administering thyrotropin-releasing hormone (TRH). TRH stimulates the release of hormones from the pituitary gland for all horses. However, the subsequent increase in the circulating ACTH is much greater for those with PPID, even in the early stages of the disease, than healthy animals.

Researchers from Michigan State University, Massey University, University of Minnesota and WALTHAM Centre for Pet Nutrition investigated the impact of different factors on the level of ACTH. Sixteen horses formed two age groups; seniors (around 20 years old) and adults (around 9 years old). They were all fed grass hay and four complementary feed options, each in turn. The base diet was a low starch and sugar pellet fortified with vitamins and minerals. Horses were fed either the base feed alone or in reduced amounts with one of three options; feeds rich in sugar, starch or fibre. All diets provided the same amount of total energy. The effect of each of these on the ACTH concentrations at specific time points was measured.

As expected, the ACTH in the blood from the senior horses was higher than for the adults. Like previous studies, the level of ACTH was raised in October (Autumn) compared to March, May and August, regardless of age.

However, the results revealed that diet can also influence the ACTH levels in horses. The senior horses had much higher levels of circulating ACTH when fed the starch rich diet compared to the adult group at the same time of the year.

The researchers conclude, “In addition to age and time of year, diet is a potential confounder as animals on a starch-rich diet may be incorrectly diagnosed with pituitary pars intermedia dysfunction.”

Read article: Effect of dietary carbohydrates and time of year on ACTH and cortisol concentrations in adult and aged horses by S.I. Jacob, R.J. Geor, P.S.D. Weber, P.A. Harris and M.E. McCue, published in Domestic Animal Endocrinology (2018) vol. 63, pp. 15-22

Article details

  • Date
  • 09 January 2018
  • Source
  • WALTHAM Centre for Pet Nutrition
  • Subject(s)
  • Horses and other Equines