The Influence of Season on Endocrine Testing in Equids.

The study investigates how seasonal changes affect hormone testing in horses and related animals, emphasizing the influence of environmental and biological factors on interpreting these tests correctly.

Introduction to Seasonal Influence on Endocrine Function in Equids

• Equids (horses, donkeys, zebras) exhibit strong seasonal variations in hormonal activity.
• Photoperiod, or the length of daylight, is the principal factor driving these endocrine changes.
• Other factors modulating endocrine function include:
• Breed differences among equids
• Geographic location and its associated climate
• Age of the animal
• Nutrition status and diet composition
• These seasonal influences necessitate adjusting endocrine diagnostic test interpretations depending on the time of year.

Seasonal Variations in Pituitary Activity

• The pituitary gland’s activity exhibits circannual rhythms—yearly cycles correlated with seasons.
• One hormone notably affected is adrenocorticotropic hormone (ACTH), which varies predictably with season.
• This predictable variation allows for the development of seasonally adjusted diagnostic thresholds when testing for pituitary pars intermedia dysfunction (PPID), a common endocrine disorder in older equids.
• Using these adjusted thresholds enhances the accuracy of diagnosing PPID during different seasons.

Seasonal Influence on Insulin Dynamics

• Insulin regulation and concentration in equids are less well characterized in terms of seasonal effects compared to pituitary hormones.
• Emerging evidence suggests there is an increase in serum insulin concentrations during winter months.
• This winter-associated rise in insulin may have implications for diagnosing insulin dysregulation and related metabolic conditions such as equine metabolic syndrome.
• Understanding these patterns is important to avoid misinterpretation of insulin test results due to natural seasonal fluctuations.

Clinical Implications

• Recognizing and accounting for seasonal endocrine patterns is critical for veterinarians interpreting hormone tests in equids.
• Failure to consider seasonal effects may lead to misdiagnosis or inaccurate assessment of disease severity.
• Seasonally adjusted reference ranges and diagnostic thresholds improve clinical decision-making.
• Overall, this approach supports better health management and treatment planning for equids with endocrine disorders.