Adrenocorticotropic Hormone and Thyroxine Concentrations in Young Healthy Equids: Species Differences and Seasonal Variations.

Overview

• This study measured hormone levels of adrenocorticotropic hormone (ACTH) and thyroxine (T4) in young healthy horses, ponies, and donkeys across two seasons (autumn and spring) to identify species differences and seasonal variations.
• The findings highlight that hormone concentrations vary significantly between species and seasons, emphasizing the need for species- and season-specific reference ranges for accurate diagnosis of endocrine diseases in young equids.

Background and Motivation

• Endocrine diseases in equids (horses, ponies, donkeys) are increasingly investigated using hormone markers such as ACTH and T4.
• Most existing studies focus on adult or older horses, with limited data on young equids, particularly ponies and donkeys.
• Baseline hormone values and reference intervals for young animals and different species are necessary to avoid misinterpretations in clinical evaluations.

Study Design

• Population: 42 young healthy equids divided into three groups:
  • Horses
  • Ponies
  • Donkeys
• Timing: Hormone concentrations were measured in two distinct seasons—autumn and spring—to assess seasonal variation.
• Hormones measured:
  • Adrenocorticotropic hormone (ACTH)
  • Thyroxine (T4)

Key Findings

• Seasonal Variation:
  • T4 concentration was significantly higher in autumn compared to spring across all animals (p = 0.049).
  • ACTH concentration was significantly higher in autumn compared to spring across all animals (p = 0.00015).
• Species Differences:
  • T4 levels were higher in donkeys than in horses (p = 0.0046).
  • ACTH levels were higher in donkeys than in both horses and ponies (p = 0.001).

Interpretation and Implications

• Hormone concentrations vary substantially based on species and season in young equids, which must be taken into account when interpreting results.
• Applying reference hormone ranges developed solely for adult horses can lead to:
  • Overinterpretation of ACTH and T4 levels in donkeys and ponies
  • Incorrect diagnosis or misdiagnosis of endocrine diseases in these species
• The study highlights the importance of developing and using species-specific and season-specific hormone reference ranges for young horses, ponies, and donkeys.

Conclusion

• This research provides valuable baseline data on ACTH and T4 in young equids, showing clear species and seasonal differences.
• Veterinarians and researchers should apply adjusted hormone reference intervals to improve the accuracy of endocrine disease diagnosis in young donkeys and ponies.
• Future studies could expand sample sizes and explore other age groups or species to further refine these references.