This post has been updated and reissued with more photographs.
This week will be a bit of a catch-all, covering a variety of patterns of white hairs that are neither grey, classic roan, face and leg markings, or associated with white spotting. (Varnish roan, for instance, is a leopard gene pattern.) The genetics of none are well understood. Following Sponenberg, I will list and describe them here. Sorry for the lack of photos, but I haven’t even seen all of these patterns myself.
The first, frosty, may be a variant of classic roan, as it is found in the same breeds. In this pattern, the roaning is most pronounced over bony areas such as the hips, and roaning may affect the mane, tail and head as well as the body. “Squaw manes” and “squaw tails” with white hair mixed in often indicate the frosty pattern. Although there is little doubt that the pattern is genetic, it is not well understood.
“Roaned” is used to refer to horses with a scattering of white hairs not due to the roan or grey genes. It is not always possible to distinguish them from minimal classic roans, but they do occur in breeds where roan does not occur.
White ticking is a much more specific pattern, involving the base of the tail and the flank. It is not progressive and may occur on any base color. Tails with the base white are sometimes referred to as “skunk tails” or “coon tails.” In Spanish the pattern is called rabicano—there are photos at the Wikipedia page. This pattern is one of the few “roan” patterns to occur in Arabians. Inheritance is thought to be dominant.
Birdcatcher spots are small white spots scattered over a horse’s body. They are named for a Thoroughbred horse, Irish Birdcatcher, who had such spots. They run in families so probably are genetic, but no studies have been carried out.
White striping is very rare in horses. The vertical white stripes may be a form of roan, as seen on the rabicano photo. Or it may simply be an accident of gestation. One striped Thoroughbred in Australia, Catch a Bird, is himself striped but is producing as a classic roan.
Finally, minor white markings may occur as a result of scarring. These are most common with freeze branding or saddle sores, but one pattern, called white lacing, is commonly due to a skin problem called reticulated leuktricia. Most often the growth of white hair in a net-like pattern over the hips and back is preceded by the formation of crusts in the skin, but not always. Both genetic and environmental causes seem to be involved. If you have an Amazon account, you may be able to see Sponenberg’s photos here.
Next week I’ll start discussing the patterns usually called paint or pinto.