Coefficient of inbreeding

Did you know that the BSBA Babydoll CloudLines registry software lets you look up extended pedigrees and automatically calculates a Coefficeint of Inbreeding (COI) for each registered sheep? The calculations use all the pedigree information in the registry. That's much more data than an individual breeder would typically have access to.

Our registry also has a handy tool where you can enter a proposed sire and dam to calculate the COI for their lambs.

If you are really keen, you can even ask CloudLInes to recommend a registered ram from any flock in the registry to suit a particular ewe based on COI!

So what does the COI tell you? Technically, it is the probability of inheriting two copies of an allele (trait) from an ancestor that appears on both sides of the pedigree. Remember it is just a guideline but it does indicate when things might be going to get a bit wobbly with your breeding program and heavy culling could be needed.

The COI result depends on the amount of pedigree information used in the calculation. Ideally, you want a full pedigree for at least four generations but more is even better. If parts of the pedigree are missing, the COI result can end up lower that it should be. When you register with BSBA, we work hard to trace as much pedigree information as possible. COI calculations should get more and more accurate as we record more generations.

Some research on COIs turned up the following information. Generally a COI under 5% (0.05) is considered desirable. Between 5% and 10% vigour and fertility will start to be lost. Over 10% is generally considered a problem although there may be times when line breeding is an appropriate option (for example to breed for a particular trait such as stripes when there are only a few sheep with that trait).

COI for full brother and sister is 25%
COI for parent and child is 25%
COI for grand parent and grand child is 12.5%
COI for uncle-niece or aunt-nephew is 12.5%
COI for first cousins is 6.25%
COI for great grandparent and great grandchild is 6.25%
COI for half uncle-niece or half aunt-nephew is 6.25%

These figures assume that these relatives are not already closely bred (in which case the COIs would be higher).

While Southdowns genetics in Australia appear reasonably diverse, many Babydoll breeding programs over the last decade have been based on using just a small fraction of those genetics. The COI calculator in our registry software is one tool that can help us to build a robust Babydoll breed rather than one that is heading towards extinction.