A piebald horse has a black base coat broken by large, irregular patches of white. The term is British in origin and describes the color combination only — black and white — not a breed or a genetic mechanism. The white markings arise from one or more white-patterning genes (frame overo, splashed white, sabino) acting on a horse that would otherwise be uniformly black, and they can appear anywhere on the body with no fixed arrangement.
In North American usage, piebald falls under the broader pinto category, which covers any horse with large white patches regardless of the base color. When the base is any color other than black, the combination is called the equivalent non-black-base pattern, not piebald. The genetic basis involves the same spotting loci that produce other white-patterning variations; the color of the base coat determines the classification.
Piebald coloring appears across many breeds and is not a breed-defining trait. In registries such as the American Paint Horse Association, horses with this pattern may be registered based on parentage and pattern requirements, but the pattern itself can arise in any breed that carries the relevant white-patterning alleles.
Among the white-patterning genes that produce piebald coloring, frame overo carries a specific health consequence: homozygous frame foals are born with lethal white syndrome, a fatal failure of intestinal innervation. Recognizing the signs in a white foal born from two frame-pattern parents is time-critical; when to call the vet covers the triage criteria. Brindle coloring, by contrast, is not a white-patterning gene variant — it arises from chimerism and other mechanisms entirely separate from the spotting loci that produce piebald.
Further Reading
For the genetics behind piebald patterning and its inheritance: