Coloration of Texas Longhorn Cattle, Part 5

I once read about a breeder who tried to breed blue roan Texas Longhorns, but gave up after trying for several years with little success. He stated that the inheritance of color just wasn’t predictable in the breed. In truth, producing blue roans is not difficult, but the trick is that the best way to achieve this result is not by breeding two blue roans together. This month, I’ll discuss this topic as we examine the genetics of a few more white-producing genes, including Brockling and Roan, and I’ll also discuss some of the unusual ways that the various white-producing genes can interact with one another.

Technically, the Brockling gene is not a white-producing gene, but its effects are only seen in combination with the various white-producing genes. The dominant brockling allele (Bc) interacts with other genes to produce pigmentation on areas of the body that would otherwise be white (especially on the extremities, including the legs and the head). The most common pattern observed in Texas Longhorns is in animals that are homozygous s/s for the Spotting gene. Recall that this genotype produces animals that are spotted (with spots varying from large to small), and normally the legs and head would be unpigmented or spotted. But in the presence of the Bc allele at the Brockling gene, the animals appear to be wearing knee-socks (in other words, their legs are mostly pigmented) and a hood (a pigmented head and neck; see Figure 1). If the animal is homozygous for the normal recessive allele at the Brockling gene (e.g., bc+/bc+), then the legs and head will not be fully pigmented. The Bc allele can also produce pigmentation on other parts of the body, and often results in larger spots of coloration on the trunk.

Whereas alleles of the Brockling gene can increase the areas of coloration, alleles of the Roan gene can reduce overall pigmentation. The incompletely dominant R allele of the Roan gene restricts pigmentation (both phaeomelanin, or red pigment, and eumelanin, or black pigment). Texas Longhorns that are homozygous red (e/e at the Extension gene; see Part 1 of this series) and heterozygous R/r+ at the Roan gene will be red roans (a mixture of red and white hairs will be produced; Figure 2). Likewise, cattle that have at least one copy of the dominant black (ED) allele at the Extension gene and are heterozygous R/r+ at the Roan gene will be blue roans (a mixture of black and white hairs; Figure 3). Animals that have wild-type coloration (E+/e or E+/E+ at the Extension gene) and are also heterozygous R/r+ at the Roan gene are somewhat variable (typical of wild-type coloration), but normally exhibit some type of “wine colored” roan pattern (Figures 4 and 5). Wine roans are also called purple roans or mulberry roans, and vary from dark purple (as in Figure 4) to a lighter mulberry (as in Figure 5). This variation is typical of that produced by the wild-type allele at the Extension gene, and is related to the relative production of the two pigments (red phaeomelanin and black eumelanin; see Parts 1 and 3 of this series). The relative intensity of the purple roan coloration in these animals probably is related to interactions with other genes, although the details of these interactions are not fully understood. Although heterozygosity for the R allele at the Roan gene produces red, blue, and purple roans, homozygosity for the R allele produces an almost completely white Texas Longhorn (with pigmented ears), no matter which alleles are present at the Extension gene.

Figure 1. A Texas Longhorn cow (Golden Counter) that shows the effects of the dominant brockling allele (Bc). Notice the pigmented legs, head, and large spots of color on the body.

Figure 4. A wine roan (also called a purple roan or mulberry roan) Texas Longhorn bull
(Dalgood’s Mojo Rocket, photo courtesy of Malcolm Goodman).

Figure 5. Another (lighter) wine roan Texas Longhorn bull.
(Roundup’s Purple Sage, photo courtesy of Gary and Lisa Baugher).

However, as I briefly mentioned last month, all roans are not produced from the Roan gene. In addition, blue roans can be produced when animals have at least one copy of the black allele (ED) at the Extension gene and are heterozygous at the Color-sided gene (Cs/cs+). Therefore, there are two distinct genetic mechanisms for producing blue roans. The color-sided allele is common among Butler cattle, but true black Butler cattle are uncommon. Therefore, the combination of black with either a heterozygous Color-sided or a heterozygous Roan animal is relatively rare, at least compared to some other color patterns. Moreover, if the animal has both the R allele at the Roan gene and the Cs allele at the Color-sided gene, or both the R allele at the Roan gene and the Sp allele at the Spotted gene, or both the Cs allele at Color-sided and the Sp allele at Spotted, then it will be almost all white, except for pigmented ears and perhaps a few small spots of color (the White Park pattern). A mostly white animal is also produced if the animal is homozygous R/R at the Roan gene, or homozygous Cs/Cs at the color-sided gene. Therefore, there are a large number of genetic combinations that produce white animals with pigmented ears, which is why some people mistakenly think of white coloration as dominant.

Let’s now return to the problem of breeding for blue roans. It would be natural to attempt to breed for blue roans by selecting a blue roan bull and breeding it to roan cows (probably red roans, since initially a breeder might not have access to many blue roan cows). Table 1 shows the expectations of a cross of a blue roan bull (ED/e at Extension, Cs/cs+ at Color-sided, and r+/r+ at Roan) to a red roan cow (e/e at Extension, cs+/cs+ at Color-sided, and R/r+ at Roan). Note that we would expect to get a wide variety of colors and patterns of offspring, including blue roans, red roans, solid blacks, solid reds, white with red ears, white with black ears, and color-sided red animals! After a decade or so of breeding these two animals, we might expect to get a couple of blue roan offspring, but even these blue roans could have this coloration because of a different genetic basis from one another. It would be natural to now select a blue roan bull and a blue roan cow from this cross, and try again to breed for blue roan offspring. However, if we selected one of each of the two genotypes that produce blue roans from the first cross, then we would expect the results shown in Table 2. Notice that the expectations of this cross (now of two blue roans) still include blue roans, red roans, solid blacks, solid reds, white with black ears, white with red ears, and color-sided red animals. After all this effort, the frequency of blue roans has gone from one-quarter of the offspring up to only three-eighths of the offspring. At this point, most breeders would probably give up, after many years of attempts to breed for blue roans with only occasional success.

Table 1. The expectations of a cross of a blue roan bull (ED/e at Extension, Cs/cs+ at Color-sided, and r+/r+ at Roan) to a red roan cow (e/e at Extension, cs+/cs+ at Color-sided, and R/r+ at Roan).

Table 2.The expectations of a cross of a blue roan bull (ED/e at Extension, Cs/cs+ at Color-sided, and r+/r+ at Roan) to a blue roan cow (ED/e at Extension, cs+/cs+ at Color-sided, and R/r+ at Roan).

Despite this discouraging example, breeding for blue roans is actually quite simple. However, the trick is that the best success does not come from breeding blue roan bulls with blue roan cows. Instead, if we start with a bull that is all white except for black ears, and is homozygous ED/ED for the Extension gene, homozygous cs+/cs+ for the Color-sided gene, homozygous S+/S+ for the Spotted gene, and homozygous R/R for the Roan gene, and mate this bull to any solid black, red, or wild-type (e.g., brindle or Parker brown) cow, then ALL of the offspring would be expected to be blue roans! This is because all of the offspring would carry at least one black (ED) allele at the Extension gene (recall that black is dominant over the other colors), would be homozygous cs+/cs+ for the Color-sided gene and homozygous S+/S+ for the Spotted gene, and would be heterozygous R/r+ for the Roan gene, thus resulting in blue roan coloration. One of the reasons that blue roans are not more common is that many breeders are hesitant to select mostly white bulls for use as herd sires, because the breeders think that white bulls will not produce colored offspring. As this example shows, however, this belief is not necessarily correct. The color of the bull is not as important for herd sire selection as is its genetic basis for that color. Since there are many different genetic reasons why a given bull might be white, some knowledge of the ancestors of the bull and the colors that the ancestors exhibited is needed to predict the expected colors of the bull’s offspring.

As I mentioned last month, many breeders also avoid mostly white cows, and white cattle tend to bring lower prices at auction. However, as the example above demonstrates, some white cattle can produce a wide variety of offspring, including solid, brindled, roaned, linebacked, color-sided, and spotted calves. They can also produce white offspring, of course, especially if the selection of mates is not made carefully. For instance, the bull Classic had the reputation of producing many white calves, although he also produced many colored offspring (especially color-sided). This was because Classic was homozygous for the color-sided allele (Cs/Cs), which results in the White Park pattern. Since many breeders used Classic in combination with other Butler cattle, and since the color-sided allele is quite common in the Butler family, many of these offspring were also homozygous Cs/Cs, and therefore white. However, breeding Classic to solid colored (red, black, or wild-type) cows produces color-sided offspring (heterozygous Cs/cs+).

In this five-part series, I’ve attempted to present our current state of knowledge concerning the genetics of Texas Longhorn coloration. There are undoubtedly other genes, in addition to the ones that I’ve discussed here, that affect coloration, so I would welcome information on color patterns that do not seem to fit the genetic explanations that I’ve presented. In a future article, I plan to present and will attempt to answer any questions that I receive about Texas Longhorn coloration, and I will also present examples of additional types of coloration that readers bring to my attention. So, if you have questions or examples that do not seem to fit the genetic explanations I’ve presented in this series, please send me an e-mail or letter.

I’ve presented information on eight genes that are known to influence color variation in Texas Longhorns (Extension, Brindle, Dilution, Dun, Spotted, Color-Sided, Brockling, and Roan), and each of these genes has two or three different alleles that exist in Texas Longhorn herds. As I mentioned in Part 1 of this series, there are 26,244 different possible genetic combinations of these alleles. This helps explain why, as J. Frank Dobie so clearly noted in The Longhorns, that the colors of Texas Longhorns are “more varied than the colors of the rainbow”. I hope that a better understanding of the genetic origins of these varied colors and patterns will aid breeders who wish to breed for particular combinations.

Acknowledgements: I thank Gary and Lisa Baugher, Malcolm Goodman, and Rex Mosier for allowing me to use photographs of their cattle for this article.

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