Grullo is a color of horses in the dun family, characterized by tan-gray or mouse-colored hairs on the body, often with shoulder and dorsal stripes and black barring on the lower legs. In this coloration, each individual hair is mouse-colored, unlike a roan, which is composed of a mixture of dark and light hairs. The several shades of grullo are informally referred to with a variety of terms, including black dun, blue dun, slate grullo, silver grullo, silver dun, or lobo dun. In the Icelandic horse, the grullo color is called gray dun, in the Highland pony it is called mouse dun, and in the Norwegian Fjord horse, grå or gråblakk (literally, "gray dun").
The word "grullo" originates from the Spanish word grulla, which refers to a slate-gray crane. Because of the origin of the name, some people will refer to a mare as a grulla and a stallion or gelding as a grullo, pronounced // GREW-yə and // GREW-yoh, respectively. (The original Spanish noun is pronounced [ˈɡɾuʝa] in American Spanish and [ˈɡɾuʎa] in Peninsular Spanish.)
In terms of equine coat color genetics, all of these shades are based on the dun gene acting as a dilution gene over the black gene. Because the grullo color is not due to the gray gene, a grullo horse remains the same basic color from birth, though some minor shade variation may occur from summer to winter coats. If a grullo also carries the gray gene, it will be born a mouse tan-gray shade, but then lighten and eventually develop a white hair coat with age. Because black is less common in general than bay or chestnut, grullo is likewise less common than red duns or bay (classic or zebra) duns. For example, only 0.7% of quarter horses registered each year with the AQHA are grullo.
The most obvious ways to tell a grullo are not only the existence of gray or tan-gray body color, but also its primitive markings, which include some or all of the following: dark face, cobwebbing around the eyes and forehead, dark mottling on the body, leg barring (sometimes called tiger striping), dark ear tips and edging, dark ear barring, dark shadowing of the neck, dark dorsal and transverse striping, and dark mane and tail guard hairs.
The appearance of grullo color among domestic horse breeds raises interesting questions about the tarpan, (Equus ferus ferus) a relative of the domestic horse that became extinct in the nineteenth century, which appears to have had dun or grullo coloration. The tarpan has been considered a true wild horse, an undomesticated relative or ancestor of the domestic horse. However, some authorities in the early twentieth century held the opinion that most equines called tarpans, in fact, were domestic or feral horses, not a separate species.
Several breeds with the grullo color have been developed in efforts to recreate ("breed back") the tarpan. These breeds include the Heck horse and Konik. One of the first experiments in this regard was published in 1906 by James Cossar Ewart, who obtained a "tarpan-like" horse by crossing a Shetland mare and a black Welsh pony.
- J. C. Ewart (1906). "The tarpan and its relationship with wild and domestic horses". Nature 74 (1909): 113–115. doi:10.1038/074113a0. "[F]or more than a century all the horses living in a wild state in Europe, which happened to be of a mouse-dun color, seem to have been regarded as tarpans."
Sources and External Links
- http://www.enloequarterhorses.com/inform1.php - Grulla Color Genetics and Photos
- Dun & Grulla horse genetics, color, and photos
- Dun Zygosity test from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web site accessed January 13, 2008.
- "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008