Effects of Standardized Exercise Tests on Plasma Thyroid Hormones’ Kinetics in Standardbred Racehorses.

This research article examines the influence of standardized exercise tests on thyroid hormone levels in trained Standardbred racehorses, with special consideration to the age and gender of the animals, in order to evaluate their performance and training adaptations.

Participants and Methodology

• The study involved twelve well-trained Standardbred racehorses, which included six stallions and six mares, and were further divided into three age groups (2, 3, and 4 years old).
• Each group comprised of two male and two female horses, to ascertain the impacts of age and gender on hormonal responses to the Standard Exercise Test (SET).
• The horses executed the SETs till their blood lactate concentration reached 4 mmol/L, a point where the speed of each horse (V) was evaluated under defined conditions.
• Blood samples were collected at regular intervals, including before the start of the SET, after each interval, and at the conclusion of the SET for analysis of thyroid hormones, particularly total and free triiodothyronine (T3, fT3) and thyroxine (T4, fT4).

Results and Analysis

• Analysis of Variance (ANOVA) portrayed that T3 and fT3 levels were significantly affected by the SETs.
• Horses at the age of 4 had higher T3 and fT3 concentrations as compared to the other age groups.
• Female horses showed higher levels of all thyroid hormones in their plasma compared to males.
• A correlation study divulged that an increased velocity (V) was negatively linked with all thyroid hormone responses, but exclusively in 2-year-old Standardbred females – a higher V led to lower hormone response.

Conclusion and Further Research

• The investigation concludes that the standardized exercise test used to calculate V resulted in an increase in certain thyroid hormones (T3, fT3) which was inversely related to V and was affected by the age and sex of the horses.
• The correlation between V and the thyroid exercise response can offer additional useful data for evaluating the performance of Standardbred racehorses and their training adaptation, according to their sex and age.
• However, it is necessary to undertake further studies in order to provide more concrete evidence on the worthiness of measuring thyroid hormones in Standardbred racehorses of varying sex and age.