How much does the horse’s back shape change over time?

Sue Dyson and Line Greve

Correct saddle-fit is important for optimal function of the equine back. A saddle that does not fit the horse may impair the structural development of the back and cause pain and muscle atrophy. There are a number of factors that may influence back dimension changes over time including skeletal maturation, nutrition, weight-control, season, conformation, duration and type of exercise, base-line muscle development, lameness, back pain and saddle-fit. Better understanding of back dimension changes over time is important for determining how often saddle-fit should be checked.

The aims of the study were to investigate changes in back dimensions over time in sports horses of variable age, from a range of work disciplines, working at different levels. The objectives were to quantify changes in back dimensions over time and determine the influence of horse-saddle-rider data and the association with a season, weight, work and saddle-management changes. We hypothesized that 1. changes in back dimensions over time were quantifiable; 2. seasonal variation would occur; and 3. fluctuations in weight, work history and saddle- management would influence the degree and direction of the back dimension changes.

One hundred and four sports horses in normal work were assessed prospectively in a longitudinal study using stratified random sampling within a convenience sampled study population. Thoracolumbar dimensions/symmetry were measured at predetermined sites every second month over a year; weight, work and saddle-management changes were recorded. Statistics were performed to assess the association between management changes, horse-saddle-rider factors and back dimension changes.

Complete data for the entire year was available for 63/104 horses (dressage [n=26], showjumping [n=26], eventing [n=26] and general purposes [n=26]). There were six horses within each work-discipline in three age-groups (3-5 years old; 6-8 and 9-12) and seven horses in one age group (>13). There were considerable variations in back dimensions over one year. In the multivariable analysis, the presence of gait abnormalities at the initial examination or asymmetry of back shape were significant; subsequently improved saddle-fit, work intensity, season and bodyweight retained significance.

In accordance with our hypotheses, there were quantifiable changes in back dimensions within a two month period and over a year. Seasonal variation did occur and fluctuations in weight, work history, and saddle-management influenced the degree and direction of the back dimension changes. In addition lameness and other gait abnormalities had a significant influence.

The seasonal changes are likely to have been influenced by diet; the majority of the horses were turned out daily with unlimited pasture available in addition to their usual source of nutrition. Muscle development is work-related. Although the quality of work was not assessed, horses in regular work had greater increases in back dimensions than horses in reduced work and horses ridden by expert riders had greater increases than horses ridden by less skilled riders. Horses which are lame often have compromised movement of the back, which is likely to limit muscle development and may result in muscle atrophy. The fit of the saddle was highly influential; improved fit of a saddle allowed the back dimensions to increase and highlights the importance of saddle fit for development of the thoracolumbar muscles and optimal performance.

In conclusion changes in back dimensions occur throughout the year. Pain elicited by palpation of the back may be an indicator that changes in back dimensions have occurred; saddle-fit should be reassessed. Saddle-fit should ideally be reassessed professionally several times a year, especially if there has been a change in work intensity.