Michael Wildenstein says a variety of conditions that span the gamut from genetics, nutrition, management, environment, aging and past pathologies can bring on thin soles.
"Nothing is ever static when it comes to hoof health," says the certified journeyman farrier, who is also a Fellow with honors of the Worshipful Company of Farriers of Great Britain as well as a member of the International Horseshoeing Hall Of Fame. "Take an otherwise fit horse whose genetic lineage points to his having thin soles, then the likelihood is that he will as well. On the other hand, if a horse were to have no genetic predisposition, but is nutritionally compromised, the result could be the same."
Regarding the theory that there is a direct link between fungal disease and thin soles, whether due to health or trauma, he notes that fungal spores are everywhere. However, these are usually no cause for concern unless there is a systemic imbalance, topped by an external disruption, as in the case of the horse who is nutritionally deficient and then suffers a minor sole bruise.
"Because his immune system already is depressed and because fungi are opportunistic in nature, invasion will meet with little resistance as they overwhelm the healthy tissues, eating them as they grow," he says.
From a trimming perspective, he notes that the sole can be easily misread, which can contribute to the problem. He says it can be difficult to distinguish between what is healthy and needs to be preserved and false sole, which should be removed. Some sole that is shedding should be left alone so that new sole underneath can mature, but other sole that is shedding may need to be removed due to fungal infection.