A short time after the posts about Dominant White went out, I was contacted by someone about a family of seemingly white Miniatures. The stallion was advertised as a maximum white sabino, which is often how Dominant White horses are described. The writer wanted to know if I thought the horse was a White or a Sabino. She thought they might be Whites because of this quote from the Wikipedia entry about the color.
Horses with the W3 allele often retain interspersed flecks or regions of pigmented skin and hair, which may fade with time.
That quote was in reference to the third identified family of Dominant Whites, which began with the mutation in the Arabian stallion R Khasper. A few of the other Dominant White families – but not all – have this same tendency. Photos of the Freiberger horses in the original white study (W1, the Cigale family) show this phenomenon really well.
Here is a Cigale descendant as a foal.
Here he is as a mature horse.
(Both photos are from the original journal article by Haas and Brooks.)
The writer wondered if the same thing was happening with the Miniatures. Looking at the pictures, it was clear that whatever else was going on with the stallion, he was a tobiano because he was throwing a lot of tobiano foals from unmarked mares. The fact that some of those tobiano foals turned white really quickly was why Dominant White was suspected. Because the dark areas of their tobiano patterns looked to have uniformly dark skin, my own suspicion was that the foals at least were not White, but early greys.
Andrea Caudill sent the picture at the top of this post, and it is perhaps helpful in this case. The colt is two years old, and almost entirely white grey. His legs are muddy in the photos, but Andrea says they were also white. As a thin-coated race horse in what is probably a wet environment, it’s easy to see his dark skin. In my experience, it can be much harder to tell white greys with extensive markings or facial depigmentation from truly white horses when they are dry and have denser coats.
Some horses, like this colt, do grey really early. Famous white grey breeds like the Lipizzans and Kladrubers have been bred specifically for early and thorough greying. Conversely, breeds like the Percheron have been bred for later greying, so it would appear that greying speed can be manipulated by selective breeding. Perhaps even more interesting, and relevant to the situation with the Miniatures, is that early studies on the silver gene mentioned that pairing silver (Z) with grey (G) produced really rapid greying. I do not believe this was studied in-depth, but it is true that a number of Shetland breeders in the mid-twentieth century were attempting to breed “white” ponies that were in fact early greys. That might be what was happening with the Miniatures in question.