Understanding Girth Sensitivity in Horses

One of the interesting aspects of working in the McPhail Equine Performance Center is that researchers from all over the world visit the center to study different aspects of equine performance and veterinary care. Everybody comes with different interests and expertise that allows us to study a diverse range of topics. It’s not uncommon for researchers to return several times over a course of years to follow up on their projects. One of these returnees is Sandra van Iwaarden, a teacher at the Dutch National Equestrian College in Deurne. Sandra first appeared in the McPhail Center when she was an undergraduate student. She returned a year later to do research for her BSc thesis. This year, in Sandra’s third visit, she completed a research project for her MS thesis entitled "A descriptive study on the anatomy and sensitivity of M. cutaneus trunci in horses in relation to girth pressure."

Her project investigated resentment to girthing (girthiness) in horses and, specifically, the role of the cutaneous muscles in persistent girthiness. The cutaneous muscles form a thin sheet of muscle that lies just under the skin. The muscle fibers attach into the skin and their function is to twitch the skin to dislodge flies or other irritants from areas of the body that are difficult to scratch. If you lightly touch the skin over the horse’s chest, it elicits a reflex twitch response.

The hypothesis underlying Sandra's research was that girthiness represents a persistent skin twitch response to the pressure of the saddle and girth. The majority of horses become accustomed (habituated) to girth and saddle pressure but some horses continue to react adversely throughout their lives. Some horses will even collapse if the girth is tightened too abruptly.

We tested the horses' skin twitch response when pressure was applied by running the thumb down the skin in the girth region with a constant firm pressure. The horses varied greatly in their sensitivity and responsiveness to this. The most common signs of discomfort or irritation were pinning the ears, swishing the tail, turning the head toward the person applying pressure and threatening to bite. These are the same signs that many horses exhibit when you tighten the girth.

The horse’s reaction to the pressure of the thumb running down the girth region was tested repeatedly in a group of 2 year-old horses throughout the period of foundation training. Each horse’s reaction was recorded at the start of training (before introducing the tack), after introducing the surcingle and after introducing the saddle. Most of the horses became less responsive as training progressed. However, the two horses that were most reactive to pressure in the girth region at the start of training became more reactive as training progressed. This led us to believe that some aspects of the horse’s reactivity to saddling, and specifically girthing, are manifestations of the horse’s inherent sensitivity. In other words, some horses are just more sensitive than others; this not only affects their responses during the early stages of training but may also affect how they adapt (or not) in the longer-term.

The horses we used for this study were bred and trained at the university’s Horse Teaching and Research Center so the bloodlines and family histories were well known to the farm manager. After the study was completed, we learned that the horses that became more sensitive to girth pressure as training progressed belonged to families that were notorious for being highly reactive to various types of environmental and training stimuli.

Sandra’s thesis received an A+ grade from the University of Edinburgh and she will present her research at the upcoming International Conference on Equitation Science that will be held October 26-29, 2012 in conjunction with the Global Dressage Forum at Academy Bartels in The Netherlands.