Seasonal variation in results of diagnostic tests for pituitary pars intermedia dysfunction in older, clinically normal geldings.

This research investigates whether the results of diagnostic tests for a particular disease in horses, pituitary pars intermedia dysfunction, change across different seasons in the state of Alabama. The study found that indeed some hormones do vary throughout the year, suggesting that the time of year can affect the diagnosis of this disease in older horses.

Research Sample and Methods

• The study involved 15 healthy mixed-breed geldings (a term for castrated male horses) with the average age of 14 years old. This study was running for a year, with samples collected each month from each horse.
• The hormone concentrations investigated were endogenous plasma ACTH (Adrenocorticotropic hormone), plasma α-melanocyte-stimulating hormone (α-MSH), serum cortisol, and serum insulin. These hormones were chosen because all four are associated with pituitary pars intermedia dysfunction, a common disease in older horses.
• As part of the study, the horses were also administered a drug called dexamethasone, and cortisol concentrations were measured at 15 and 19 hours afterward.
• A technique called radioimmunoassay was used to measure the hormone concentrations. This is a laboratory method designed for detecting the concentration of substances such as hormones in a sample.
• The recorded hormone concentrations were compared between each month’s data using a specific type of analysis known as repeated-measures ANOVA (Analysis of Variance).

Results and Conclusions

• The researchers found out that significant variations existed across different months in the concentrations of α-MSH and insulin. However, the variations observed in cortisol and ACTH levels did not exceed the existing reference ranges.
• There were also significant correlations noticed between the age of the horses and the observed ACTH concentration in several fall and winter months, and between horse age and insulin concentration in September.
• The conclusion of this research was that the time of the year does influence the hormone levels of older horses. The horses have higher ACTH levels in several fall and winter months and higher insulin levels in September than younger horses.
• Additionally, researchers also found that the reference ranges used for α-MSH and insulin concentrations also need to be specific to the season, with noticeably higher concentrations detected in the fall.
• Therefore, the study recommends that veterinarians should only submit samples to local laboratories capable of providing season-specific reference ranges for their respective geographical regions.