One of the most important genes, which makes a Silver Fox rabbit's fur imitate the appearance of the Artic Silver Fox (a real fox), after which it is named, is the silvering gene. Overall, the genetics controlling Silver Fox fur colors are pretty uncomplicated and basic. In contrast, the silver gene is highly complicated and persistent.
Silvering begins to show up from 4 to 12 weeks and completes in about 4 or so months. Silvered hairs always are silver the full length of the hair shaft. I would like to explain here that silver guard hairs look white due to the contrast against the colored fur, but in actuality are truly light silver in color. In daylight, the silver can be seen on a Red-eyed White Silver Fox as slightly darker or silver in tint compared to the surrounding white fur.
I had read from several sources that a rabbit can only silver if it has two recessive "si" silvering genes. Recessive genes are easily hidden by a more dominant gene, typically. In the case of the silvering gene, the non-silvering dominant "Si" in combination with recessive "si" should cause the rabbit fur to not silver and I have read many sources stating:
- SiSi will not silver
- Sisi will not silver
- sisi will silver
However, this list is partially incorrect, in my opinion. The silvering gene is quite complicated and not well understood but it acts as if it is dominant more than recessive. When I personally crossed NZWs (non-silvered) with Silver Foxes, the F1 offspring always silvered. (F1 is the first generation from a cross breeding.) This more than suggested that it is possible for a rabbit to silver with just one silvering allele from only one of the parents.
This is a picture of a crossbred NZW/SF 75/25. Her father was a New Zealand White (non-silvered). Her mother was a SF/NZW 50/50 Gold-Tipped Black Steel with silvering and short, quick roll-back fur. This doe had longer fur with some roll back textured more like Silver Fox fur. She appeared to be a self black, but she also could have been a black Agouti super steel. She was in the process of silvering.
This is the sister of the above doe. She is an Agouti Black Gold-tipped Steel that was also in the process of silvering. She had short, fly-back fur. If you look at the golden color on her chest, which had not yet silvered, you can see the difference of the silvered long hairs sticking up on hip area. Keep in mind that silvering is not the same as steel and one has nothing to do with the other. In a steel, the gold or silver tips are seen as soon as the kit grows fur and the banding on the hair shaft is throughout the coat. Silvering begins to come in weeks later and the entire guard hair is silver.
Even though breeding a silver with a non-silver seemed to always produce some silvering to the same amount of silvering as the silvered parent in F1 rabbits for me and many other breeders, there are a few breeders who have done the same reporting that they had no silvering in the F1 offspring. (One breeder claimed to have the non-silvered F1 parent bred to a non-silvering breed produce F2 offspring that silvered! Seems highly unlikely, but not having seen the F1 parent in person, I cannot verify or deny the complete absence of silvering.)
What does all this mean? It is highly likely the silvering gene is an incomplete dominant gene we do not yet understand and may also have factors. In red breeds, the Rufus gene, which causes orange to deep red coloring, is said to have "factors" that can build to a deeper red or decrease or bright orange. Perhaps it is the same with the silvering gene. The combination of incomplete dominance and factors would explain the wide range of silvering variations with Silver Foxes.
What does all this mean? It is highly likely the silvering gene is an incomplete dominant gene we do not yet understand and may also have factors. In red breeds, the Rufus gene, which causes orange to deep red coloring, is said to have "factors" that can build to a deeper red or decrease or bright orange. Perhaps it is the same with the silvering gene. The combination of incomplete dominance and factors would explain the wide range of silvering variations with Silver Foxes.
Although it has not been determined in any resources I have found that there have been identifiable differences in the genes, some have categorized the amount of silvering when writing out the genotype, perhaps as a method to keep records but it is highly subjective in how one would categorize the wide range of variations:
I have bred two Silver Foxes with medium and even silvering from nose-to-toes, and I have gotten heavily to lightly silvered, but rarely a matching medium and even like the parents; in fact, the majority were more heavily silvered. If the parents were both "si2" with high factors who also had "si1", perhaps it is possible to have them appear as they did and throw a lightly silvered "si1si1" as well as "si2si2" with high factors. It may even be possible that these factors build up to looking like "si3" or that "si3" is in some Silver Foxes but tempered by "si1" or "Si". By the way, I have seen a pure Silver Fox that looked like a Champagne D' Argent so silvering can build, yet it also can decrease.
- "si1" for lightly silvered.
- "si2" for a medium amount of silvering.
- "si3" for heavily silvered, appearing nearly white even with a colored undercoat, like Champagne D' Argent rabbits.
Adding this concept to the theory of incomplete dominance with factors in mind, a rabbit with "Sisi2" could have any amount of silvering from lightly silvered to the amount expected with "si2si2" if the "si2" had high factors. Genetically speaking, "si1si1" bred with "si2si2" should result in offspring having "si2si1". Although it would be preferred to be simple that "si2si1" would mean that "si2" is the more dominant, both would be acting as incomplete dominants with their own factors. In such cases, the silvering on the offspring could range from what is expected on "si1" to "si2" with low to high number of factors.
I have bred two Silver Foxes with medium and even silvering from nose-to-toes, and I have gotten heavily to lightly silvered, but rarely a matching medium and even like the parents; in fact, the majority were more heavily silvered. If the parents were both "si2" with high factors who also had "si1", perhaps it is possible to have them appear as they did and throw a lightly silvered "si1si1" as well as "si2si2" with high factors. It may even be possible that these factors build up to looking like "si3" or that "si3" is in some Silver Foxes but tempered by "si1" or "Si". By the way, I have seen a pure Silver Fox that looked like a Champagne D' Argent so silvering can build, yet it also can decrease.
In conclusion, all this is just theory. In the end, you get whatever you get with silvering and it is largely unpredictable. The best you can do is breed rabbits and make note of tendencies in silvering from each. However, I will say that I am personally partial to changing the silvering genotype to be "Si" instead of "si" because most breeds do not have silvering and, in those that do, it acts more like a dominant gene than a recessive one.