The term "crop out" is used to refer to colored horses that appear unexpectedly in breeds usually considered solid-colored. Crop outs of all kinds have been occurring in the Quarter Horse breed since its earliest days, and contrary to the registry's position that the unusual colors indicate infusions of "outside" blood, often the color is coming from the horses used by early breeders.
A study was done on crop outs in the early 1970s, tracing the distant ancestors or 100 crop out overo Quarter Horses. Unfortunately, the study was done before it was known that overo was a dominant gene, so the researcher was only looking for horses that repeatedly appeared in the pedigrees, mistakenly believing that conservatively marked horses could be carrying the "recessive" overo gene.
So the study found that Peter McCue was found in the pedigrees of 96 of the 100 crop outs, and Traveler was found in 86. But the researcher was looking for a recessive gene, so it was believed that the color was coming from linebreeding to one individual, concentrating the recessives that horse carried. Because the gene is dominant, what he should have looked for was a single individual that could have passed the color down in an unbroken line to the current crop out. This individual (and the horses that came after) would probably be flashy-marked horses that were genetically overos, but didn't appear to be "Paints" because they didn't have enough white to be obvious. Because the horses were traced so far back, complete records of the ancestors were not always available- particularly the mares- and the color may well have come from one of these unknown animals.
In the case of Peter McCue and Traveler, the stallions that consistently appeared in the backs of crop out pedigrees, it probably wasn't they who gave the color, but rather the mares they were bred to. In Peter McCue's case, he was a dark bay horse with no white markings of any kind; not the kind of horse to be considered a minimal overo! But he was owned in his later years by Coke Roberds, who owned many colorful horses, including the stallion Old Fred. Old Fred pre-dated the registry, and under the current AQHA standards, would be considered a crop out himself. But he was an influential sire in the early days of the Quarter Horse, and many of the mares Peter McCue bred while owned by Rovers were Old Fred daughters. Mary McCue (dam of Ding Bob), Buck Thomas II and Squaw were all by Peter McCue out of Old Fred mares, as was Sheik. Sheik, who had a white blaze, white muzzle and stockings, was used in both the Peavy and Weiscamp breeding programs (both known for producing horses with "extra color").
Traveler was also a conservatively marked horse- chestnut with a narrow strip and one hind sock- that was often bred to more colorful mares. After purchasing Traveler, the Shely brothers put together a broodmare band made up of Rondo-bred mares. The Rondo horses traced back to Old Billy, great-grandsire of Old Fred. An Old Billy grandson, Barney Owens, was described as having "white under his stomach, glass eyes, and a skunk tail." One of the Rondo mares bred to Traveler was Jenny (Sykes Rondo x May Mangum), full sister to the glass-eyed stallion Blue Eyes. Jenny went on to produce Little Joe, who in turn sired Cotton Eyed Joe, a sorrel with a bald face, one glass eye, and two white feet. Little Joe also sired Joe Moore, a name often seen in crop out pedigrees.
A similar situation exists in the Tennessee Walking Horse breed, where the foundation sire, Allan F-1, is often credited with the sabino roan color that was prevalent in the early days of the breed. In truth, the color came from the Copperbottom and Brooks family mares native to the area when Allan stood at stud. These mares, often unregistered and unrecorded, were usually flashy-marked sorrels or sorrel roans, and they consistently passed on this color to their Allan foals.
One stallion that did show up in the study that may well have been a minimally marked overo was Joe Reed. His name appears in 65 of the 100 horses in the study. Joe Reed was a chestnut with a wide blaze and four stockings. His dam Della Moore often appears in crop out pedigrees through her other son, Joe Moore.
Appaloosa crop outs are by far less common then Paint crop outs, but they have occurred. Usually one of the Quarter Horse parents was registered as a "roan" Quarter Horse when in truth they were unspotted varnish roans, and they provided the gene that resulted in their more obviously spotted offspring.
One well-known Appaloosa crop was Joker B. Joker B. was bred by famed Quarter Horse breeder Jack Casement. Born in 1941, his sire was the solid sorrel Red Dog (Balleymooney x Cinnabar by Old Joe), But his dam, Blue Vitrol, was a blue roan. Her sire, Brown Dick (Derring Doe TB x La Bold daughter) was 7/8 Thoroughbred and solid colored, but her dam was called Leopard and she traced through her dam line to the Roberds stallion Arab, who was said to be a leopard. Like so many of the crop out Appaloosas, Joker B. was born blanketed, but later roaned out in a varnish pattern.
Other Appaloosa crop outs to carry similar breeding were the blanketed Wapiti (Gold Heels x Quadroon by Song Hit TB), the palomino blanketed Ding Bob II, who was a full bother to Wapiti's grandsire, Si Ding, and Peavy Bimbo (Little Joe Jr. x Chipeta). All three horses traced through their dam lines (and Wapiti through his sire as well) to the Roberd stallion Arab through Blue Mare. Many of the descendants of Arab were registered with the AQHA, especially those that were born with marginal, or no color. Ironically, when the American Quarter Horse Association was formed in 1941, Coke Roberds declined to register his own horses with this registry that prohibited "painted or spotted" horses.
There is even an Appaloosa line that is responsible for Paint crop outs. That's the Mighty Bright line. Mighty Bright was linebred to Old Fred, the same horse responsible for the color on The Gambling Man. Mighty Bright himself was a dun with a bald face, blue eyes, and high stockings, and's lacy blanket. Occasionally, linebred Mighty Bright Appaloosas will have extra white on the sides or belly due to the splash-white gene they are carrying, and when large enough, the horses are denied parents.
Regardless of the pattern involved, it is likely that the mare lines, which were often poorly recorded in the early days of horsebreeding, were responsible for the color in today's crop outs. These mares from the early days of the registry, when color rules were less strictly enforced, passed along their flashy color to many of their offspring- though often in a moderate enough form that they continued to be registered in the American Quarter Horse Association- until a surprise foal was born that was undeniably colored. When this happened in the early years, these foals were considered "accidents" and proof of impure blood, but today they are often recognized as inheritors of a very old legacy. And while the AQHA many not accept them, they are usually embraced by their respective color organizations.
Breeds beside Quarter Horses where crop outs are known to have occurred:
Overos (various types):