A longitudinal study of back dimension changes over 1 year in sports horses.

Major back dimension changes over time have been observed in some horses, the speed of which may be influenced by work type, skeletal maturity, nutrition and saddle fit. Currently, there are no longitudinal data quantifying changes in back dimensions. The objectives of this study were to quantify back dimension changes over time, to identify the effects of horse, saddle and rider on these dimensions, and to determine their association with season, weight, work and saddle management. A prospective, longitudinal study was performed, using stratified random sampling within a convenience sample of 104 sports horses in normal work. Thoracolumbar dimensions/symmetry were measured at predetermined sites every second month over 1 year; weight, work and saddle management changes were recorded. Descriptive statistics, and univariable and multiple mixed effects linear regression were performed to assess the association between management changes, horse-saddle-rider factors and back dimension changes. Complete data was available for 63/104 horses, including horses used for dressage (n= 26), showjumping (n= 26), eventing (n= 26) and general purpose (n= 26), with age groups 3-5 years (n = 24), 6-8 years (n = 28), 9-12 years (n = 24) and ≥ 13 years (n = 28). There were considerable variations in back dimensions over 1 year. In the multivariable analysis, the presence of gait abnormalities at initial examination and back asymmetry were significant and had a negative effect on changes in back dimensions. Subsequent improved saddle fit, similar or increased work intensity, season (summer versus winter) and increased bodyweight retained significance, having positive effects on changes in back dimensions. In conclusion, quantifiable changes in back dimensions occur throughout the year. Saddle fit should be reassessed professionally several times a year, especially if there has been a change in work intensity.