It is widely agreed that a single copy of the cream allele located at the MATP locus dilutes the red horse to a palomino, and a bay to a buckskin. Yet, it is frequently debated whether it dilutes a black horse. In truth, this recurring debate is rather futile as the answer is simple, for those who are willing to learn instead of remaining defiantly persistent to their own incorrect opinions.
Misinformation has been increasingly common when it comes to this topic, with a fair majority believing, incorrectly, that a single cream dilutes the black horse to a smoky black. Those who believe this describe the smoky black as having pale inner ears, paler eyes, and more browner coloration, with less shine than that of a ‘normal’ black. However, this is incorrect. While a black horse carrying the cream allele is known as a smoky black, there is no phenotypic difference at all.
Many people are adamant that smoky blacks are phenotypically different from a normal black. They support their claims by saying that there is no research to prove the opposite point. While that is true, it is because there has been no research done on the normal shade variations in horses. Therefore, there are no research papers to support the claims of either side. However, the paper published when the cream mutation was originally discovered mentions, “… but has no or little effect on the black colour.” in regards to the cream mutation. Many people, however, disregard this line, or claim the little effect mentioned is what causes the supposed phenotypic differences.
With the lack of solid research proving or disproving either theory, we must turn to direct evidence to look for the truth. To disprove the theory that the shade of the coat differs or fades quicker as opposed to a normal black, we simply have to look at the statistics of normal shade variation, regardless of cream.
There are many horses who display all of the differences associated with smoky blacks, yet tested to not carry cream. Similarly, many horses display none of the characteristics, yet carry cream. Therefore, any incidents where a horse displays some, or all, characteristics and carry cream are simply coincidence.
To further prove our theory that a single cream has no effect on a black, new research and statistics suggests that almost all of the supposed traits of a smoky black, i.e. pale inner ears, pale eyes, easily faded coat, and a softer, browner shade of black the coat can be associated with nd1, an allele on the same locus as dun, which can often cause primitive markings, but no dun dilution. In many instances, nd1 has no characteristic effects at all. It is an interesting case, and worth further research.
Lastly, there is a fairly suggestive piece of evidence, which cannot be explained if one believes that a single cream does dilute black. We all know that a bay horse has a uniform red body, with black points (mane, tail, forelock and lower legs). Yet, what color are a buckskins points?
A buckskin has a clearly diluted body, which is a pale tan color as opposed to red. However, the points remain black. If black pigment can really be diluted by a single cream, then why do the points of a buckskin remain clearly undiluted?
One may argue that dominant agouti, the allele responsible for causing the bay phenotype, somehow restricts the single cream from diluting the points. While that is a possible scenario, it has also been disproven by the fairly common occurrence of frosting in the mane of a buckskin.
Bay horses often have red guard hairs along their manes and tails. In a buckskin, these a diluted, like the rest of the body, and are pale all along. So, the single cream very clearly does have an effect on the points.
Some people may say that cream only affects black ‘sometimes’. Genes do not, however, have effects sometimes. They either dilute or they do not.
Summary
There is copious amounts of conclusive evidence to completely disprove the theory that smoky blacks are anything phenotypically different from a normal black. We can safely consider the other theory to be the truth. While there may not be extensive research done on this subject, nor the normal shade variation in a horse, the amount of direct evidence is enough to consider it no more a theory or opinion, but fairly correct factual data.