The Savannah cat, a hybrid breed born from the cross of a serval and a domestic cat, is classified using a unique system of filial numbers (F#) and letter designations. This system helps breeders and enthusiasts understand the cat's proximity to its wild serval ancestor and its breeding history. Each generation presents distinct characteristics and breeding challenges, particularly concerning fertility and the path to becoming a "purebred" Savannah.
Understanding these classifications is crucial for anyone interested in the breed, from its initial, difficult F1 crosses to the more established Stud Book Tradition (SBT) cats.
The Filial Number System: Tracing Serval Ancestry
The filial number (F#) directly indicates how many generations removed a Savannah cat is from its serval ancestor. An F1 Savannah is the direct offspring of a serval and a domestic cat, meaning it is approximately 50% serval. These F1 cats are known for being very large and often exhibit the most pronounced serval characteristics. However, producing F1s is challenging due to the significant difference in gestation periods between servals (75 days) and domestic cats (65 days), as well as incompatibilities in their sex chromosomes. This often leads to pregnancies being resorbed, aborted, or resulting in premature kittens. Furthermore, servals can be particular about their mates, sometimes refusing to breed with or even attacking domestic cats.
As the generations progress, the percentage of serval blood typically decreases. An F2 generation cat has a serval grandparent and is the offspring of an F1 female, with serval percentages ranging from 25% to 37.5%. The F3 generation has a serval great-grandparent and is at least 12.5% serval. It's important to note that male Savannahs are generally sterile until around the F5 generation, a phenomenon consistent with Haldane's rule for hybrid inviability, where the heterogametic sex (males in mammals) is most affected. Females, however, are fertile from the F1 generation, making them crucial for continuing the breeding lines.
Backcrosses and the Path to SBT
Beyond the standard filial numbering, breeders also utilize backcrosses to achieve higher serval percentages in certain lines. For instance, a Savannah backcross, termed BC1, can result in cats as high as 75% serval. This occurs when a 50% F1 female is bred back to a serval. Cases of 87.5% BC2 Savannah cats are known, though fertility at such high serval percentages can be questionable. More commonly, a 62.5% BC1 is produced when an F2A (25% serval) female is bred back to a serval. These backcrosses demonstrate the breeders' efforts to maintain and sometimes intensify the serval traits within the breed.
The F4 generation marks a significant milestone as it is the first generation that can be classified as a "stud book tradition" (SBT) cat, which is considered "purebred." This designation signifies that the cat's lineage has been consistently bred Savannah to Savannah for several generations. Savannah crosses are also referred to by breeders using the TICA code "SV × SV." The letter designators (A, B, C, SBT) further clarify the breeding history: 'A' means one parent is a Savannah and the other is an outcross; 'B' is used when both parents are Savannahs, with one being an 'A'; 'C' is used when both parents are Savannahs and one is a 'B'. Therefore, an A × (any SV) cross results in a B; a B × (B, C, SBT) cross results in a C; and a C × (C, SBT) cross results in an SBT. An SBT × SBT cross will always produce an SBT. F1 Savannahs are always 'A' because their father is a non-domestic outcross (the serval). The F2 generation can be 'A' or 'B', and the F3 generation can be 'A', 'B', or 'C'. SBT cats emerge in the F4 generation.
Fertility and Breeding Considerations
As hybrids, Savannahs often exhibit characteristics of hybrid inviability, particularly affecting male fertility. While male Savannahs are typically sterile until around the F5 generation, there have been observations by breeders of a resurgence in sterility in males at the F5 and F6 generations as of 2011. This is presumably linked to the higher serval percentage found in C and SBT cats. The issue may also be complicated by secondary non-domestic genes from Asian leopard cat outcrosses, which were extensively used in the foundational breeding of the Savannah breed. This ongoing challenge highlights the complexities of breeding hybrid animals and the continuous efforts required to maintain breed health and fertility.
Due to these fertility patterns, females of the F1–F3 generations are usually retained for breeding purposes, with the males primarily offered as pets. Conversely, in the F5–F7 generations, this trend is somewhat reversed, though to a lesser degree, with males being kept as breeding cats and females more often offered as pets. This strategic breeding approach ensures the continuation and development of the Savannah cat breed, balancing the desire for exotic traits with the practicalities of maintaining a viable breeding program.
