Check a Pairing
Understanding COI
COI (coefficient of inbreeding) is the chance that a kitten inherits the exact same copy of a gene from both parents because they share an ancestor. 0% means the parents are unrelated, a full outcross.
| COI | What it means | Our use |
|---|---|---|
| 0% | Full outcross, no shared ancestors | Preferred default |
| 1.6% to 3.1% | Distant linebreeding, great-grandparent level | Fine when the shared line is healthy |
| 6.3% | First-cousin level, the common ceiling for deliberate linebreeding | Acceptable, but use sparingly and only on lines with clean health history |
| 12.5% | Half-sibling or grandparent-to-grandchild level | Do not pair |
| 25% | Parent-to-offspring or full siblings | Never |
What happens past the safe threshold: every cat carries a few hidden faulty gene copies that cause no problem while paired with a normal copy. High COI raises the odds a kitten gets the faulty copy from both sides at once, so problems that were invisible in the parents start appearing in the kittens. In practice that shows up as:
- Smaller litters and more failed or absorbed pregnancies
- Lower kitten birth weights and higher kitten mortality
- Weaker immune systems, more infections that linger
- Higher odds of expressing recessive disease carried in the line (in Maine Coons, the ones to watch are HCM, hip dysplasia, SMA, and PK deficiency)
- Reduced fertility in the next generation, which compounds the problem
These effects are not a guarantee in any one litter, they are odds that climb with the number. They also stack across generations, which is why a one-time 6.3% breeding is reasonable while repeating the same line generation after generation is not. The working rules for this program: aim for 0%, cap deliberate linebreeding at 6.3%, never double a line on a queen who is already linebred on it, and follow any linebred generation with an outcross.
Stud by Stud
Existing Linebreeding in the Program
| Cat | COI | Where it comes from |
|---|---|---|
| Tallulah | 12.5% | Tobias is grandsire on both sides; her parents (Victor and Abigail) were half siblings |
| Neverland | 12.5% | His dam Heaven Im The Clouds is also his sire's granddam |
| Davinity | 3.1% | Gus Nobabyglare sired both of her granddams (Farfalla and Ginevra) |
| Abbi x Calvin kitten (if kept) | 6.3% | Tonni on both sides |
COI (coefficient of inbreeding): 0% is a full outcross. Up to about 6.3% is generally considered acceptable linebreeding. 12.5% is half-sibling level. 25% is parent-to-offspring or full-sibling level.
Who Everyone Is
| Cat | Role | Sire x Dam |
|---|
Open Items
- Gold Rush Tilly's parents. Tilly is Tallulah's granddam and her parentage is unverified. This decides whether Aydan x Tallulah is a clean outcross or an overlap (Aydan's granddam Behold Mango is also a Gold Rush cattery cat).
- Sariah Rose's certificate. Bronwen's numbers assume Sariah is a Tobias daughter; worth confirming from her papers.
- Scarcelli's registered pedigree lists Sassy Lady as his dam; his actual dam is Honey Rose (unregistered import). This guide uses the actual parentage. Geralt's and Oliver's printed pedigrees inherit the same paperwork error.