Hormonal responses of Quarter Horses to a 6-week conventional Western-riding training programme

The aim of the research was to evaluate whether a 6-week conventional training programme for Western riding and each exercise training session can induce any different effect on changes of cortisol, total and free iodothyronine and oestradiol-17β levels of mature Quarter Horses. Eighteen Quarter Horses aged 16-20 years (six stallions, six geldings and six mares; mean body weight: 510 ± 70 kg) were recruited according to the level of competition experience, age and pre-training status and were divided into two groups paired by gender: group A, control horses (n = 9), and group B, trained horses (n = 9). For 6 weeks, group B horses performed a 5 days per week conventional training programme for Western riding, including 1 day of specific exercise session to simulate the different competitive events. Over the 6-week training period, blood samples from horses were collected once a week immediately before, under resting conditions and 24 h post exercise session.Two-way repeated measures analysis of variance (RM-ANOVA) showed a significant interaction between training and time for changes in triiodothyronine (T3) (P < 0.008) and cortisol (P < 0.002), as well as for changes in thyroxine (T4) and free T4 (fT4) (P < 0.0001). The effect of training was significant exclusively for changes in fT4 (P < 0.04) changes.A significant interaction between exercise session and time for T4 (P < 0.0027) and a significant exercise effect on fT4 (P < 0.0001) were also recorded.The results of this study might suggest the benefits of taking into account cortisol and iodothyronine changes to effectively monitor training in Quarter Horses.