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) (Pb0.008) and cortisol (Pb0.002), as well as for changes in thyroxine (T4) and free T4 (fT4) (Pb0.0001). The effect of training was significant exclusively for changes in fT4 (Pb0.04) changes. A significant interaction between exercise session and time for T4 (Pb0.0027) and a significant exercise effect on fT4 (Pb0.0001) 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.