Fat-Free mass is one of the tests in our Sales Select test that we use to identify elite thoroughbred talent. Basically our findings have been that elite horses, even as yearlings, tend to be leaner, with less fat and more fat-free mass (it is also a great scale for cardiovascular dimensions). Its fairly easy to do once you know how, just an ultrasound over the rump to measure the depth of the muscle.
A paper this month appeared in the Equine Veterinary Journal with similar findings to what we have seen in the field. This was a large study taken over a number of years and included the intensity of training as an effect on the body composition.
Fat-free mass was greatest in males (P = 0.006) at all training stages. There were no interactions between training duration, intensity, gender and age (P>0.05); all effects were linear. Training duration had a negative effect on rump fat thickness (P = 0.0002), fat mass (P<0.0001) and % fat (P<0.0001) and a positive effect on fat-free mass (P = 0.01). Training intensity had a negative effect on rump fat thickness (P = 0.009), fat mass (P<0.0001), % fat (P<0.0001) and fat-free mass (P<0.0001). Fat-free mass was greater for elite versus non-elite horses at all training stages (P = 0.003) for males (P = 0.05) and females (P = 0.04) and 2 (P = 0.002) and 3-year-olds (P = 0.02).