The Genetics of Coloration in Texas Longhorns: The Wild-type Color Variants. Hillis, Double Helix Ranch. This article is the third in a five-part series on the genetics of coloration in Texas Longhorn cattle. This article was published in Texas Longhorn TrailsVolume 16, number 6 If you have comments or questions about this article, please e-mail me. This article is intended for a general audience of Texas Longhorn breeders, rather than a technical audience.
However, some scientific jargon is unavoidable, so if any of the terms are unfamiliar, please see the Glossary. Everyone has his or her own preferences about color of Texas Longhorns. Black seems to have been a favorite over the past few years, perhaps because it is less common in Texas Longhorns compared to the various shades of reds and browns. Other people love Black and white longhorn cattle of any shade, and some people are enthusiastic about grullas. I enjoy a diversity of color, but I find the various modifications of wild-type coloration to be the most beautiful and interesting of Texas Longhorn colors.
For one thing, these are the colors that change the most through time; wild-type colored calves are usually born some shade of red, and then darken with age, and may appear almost black as adults Figure 1. However, the degree of expression of black pigment eumelanin varies considerably, and is influenced by additional genes. These combinations of genes together with the wild-type allele at the Extension locus produce some of the most striking colors in Texas Longhorns, including brindle, Parker brown, walnut, and wine-colored.
Many introductory books on cattle greatly simplify the discussion of the genetics of cattle coloration, and may only present information on black and red Black and white longhorn cattle.
This is because the explanation of the black and red alleles is relatively simple, and because many breeds of cattle are fixed for one or the other of these two colors.
There are, in fact, just two pigments that affect hair color of cattle, and these two pigments are black eumelanin and red phaeomelanin. Black cattle have both pigments, but they produce an excess of eumelanin, and this essentially masks the red phaeomelanin. Red cattle produce little or no eumelanin, and so their hair looks red. White cattle produce neither pigment in their hair.
It is doubtful if the red, black, or white colors were found among Black and white longhorn cattle ancestral aurochs the ancestors of modern European cattleat least in high frequency. These color patterns were selected by humans early during the domestication of cattle, as a way to ensure breed purity and because humans liked the diversity.
In contrast, the aurochs are thought to have had an allele that allowed differential and variable production of both eumelanin and phaeomelanin, which produced a brown coloration with areas of black essential like the Parker brown coloration of Texas Longhorns; Figure 2.
The males were probably more darkly pigmented than the females, and adults more darkly pigmented than juveniles. This occurred because the relative expression of the two pigments changes in response to the expression of other genes that are activated with maturation and sexual differentiation.
Texas Longhorns have retained all three of these basic colors black, red, and wild-type. The black allele is dominant over the other two, and the wild-type coloration is Black and white longhorn cattle over red, so individuals with wild-type coloration are either homozygous for the wild-type allele in other words, they have inherited the allele from both parentsor else they are heterozygous for the wild-type and red alleles they inherited the wild-type allele from only one parent.
Although all Texas Longhorns with wild-type coloration can express both pigments, the relative degree of black and red pigmentation is highly variable and is affected Black and white longhorn cattle several other genes.
For instance, there are two alleles at the Brindle locus a dominant allele that is abbreviated Brand a recessive allele that is Black and white longhorn cattle br. The Brindle gene has no obvious effects in true red or black Texas Longhorns, but if at least one copy of the Br allele is present in a wild-type colored individual, then that cow or bull will be brindled Figure 3.
The degree of brindling may vary in response to other factors, including sex differences, as males often show more extensive and typically darker brindling patterns than do females. In addition, complex brindle patterns can develop in response to interactions with the various genes that produce areas of white, roan, or reduced pigmentation Figure 4.
For instance, if the bull is heterozygous for both wild-type coloration and brindling, then he is expected to pass on both of these traits together only about one-fourth of the time half of the time he will pass only one of the two traits to his calves, and the other fourth of the time he will Black and white longhorn cattle neither trait to his offspring. Even if he passes both wild-type coloration and brindling to his offspring, they may show a lesser degree of expression of the trait because of the influence of sex differences or the effects of other genes including the various genes that Black and white longhorn cattle areas of white.
In addition, brindling typically develops with age, so the calves will not be brindled at birth, even if they are expected to develop this coloration as they age.
On the other hand, if a breeder wishes to breed all brindled cattle, then a bull that is homozygous for both wild-type coloration and the dominant brindle allele will always pass on both traits to his offspring. If this bull is mated to either red or wild-type cows, then all of the offspring are expected to show some degree of brindling.
The degree of brindling will be variable because of the effects of other genes, but some black striping within areas of red or brown coloration should be present. The only offspring that may not show any brindling are calves produced by mating this bull with a black cow, because if the cow passes the black allele on to the offspring then the calves will be black rather than brindled recall that the black Extension allele is dominant over the wild-type Extension allele.
There are two color variants produced in cattle with wild-type coloration that deserve special mention: They are usually born some shade of dark red or brown, and then become nearly black Black and white longhorn cattle they mature. However, unlike true black animals, they have a light-colored muzzle ring, and usually a dark reddish-brown streak across the top of the head and backline see Figure 5. Females with this coloration typically show a much greater degree of reddish pigment than do the males Figure 6.
Many people consider the walnut coloration to Black and white longhorn cattle one of most beautiful and striking colors that is present in Texas Longhorns, and the deepening saturation of color that comes with increasing age of the animals adds another dimension of interest.
Note the dark red hair on the poll, and the prominent muzzle ring. Females with the walnut coloration usually show less expression of black pigment than do males, and may appear deep red with only small areas of black. However, they may appear almost completely black as well. As with other Black and white longhorn cattle color variants, the muzzle ring on this cow Shadowette is clearly visible.
The wine roan coloration, another of the wild-type color variants photo of Delta Rockette courtesy of Malcolm Goodman. The wine or burgundy coloration is another variant of wild-type coloration that is considered highly desirable by many breeders Figure 7.
This coloration is also produced by a combination of eumelanin and phaeomelanin, but the two pigments are present in lower concentration, to produce a burgundy coloration. As the photographs that accompany this article illustrate, any of the colors of Texas Longhorns can appear with different patterns of white hairs that lack any pigment.
Additional Reading and References. The genetics of coloration in Texas Longhorns: Texas Black and white longhorn cattle Trails 16 3: Grulla, dun, and other reduced pigment patterns.
Texas Longhorn Trails 16 5: Spotted, lineback, color-sided, and White Park patterns. Texas Longhorn TrailsOctober Roan and brockling patterns. Texas Longhorn TrailsNovember The role of melanocyte-stimulating hormone MSH receptor in bovine coat color determination.