Registrations

Increasing levels of inbreeding can result in inbreeding depression, where performance can suffer; though it can be argued that any animal is only one mating away from being outbred.

The lower the level of inbreeding the better, though a threshold value of 6.25% has been determined to be an acceptable level of inbreeding within a breeding programme. The estimate of inbreeding is based on the relatedness of individuals in a pedigree, examples of inbreeding values for different matings are presented below.

Relationship	Inbreeding coefficient (F)
Father × daughter or mother × son	25.0 %
Brother × sister	25.0 %
Grandfather × granddaughter or grandmother × grandson	12.5 %
Half-brother × half-sister	12.5 %
Uncle × niece or aunt × nephew	12.5 %
Great-grandfather × great-granddaughter or great-grandmother × great-grandson	6.25 %
Half-uncle × niece or half-aunt × nephew	6.25 %
First cousins	6.25 %

Members looking to limit the impact of inbreeding can use the iTexel Mating Predictor.

iTexel Mating Predictor

Members are encouraged to use the Mating Predictor that is available on all devices through iTexel to manage levels of inbreeding within their flocks. Ewe / ram combinations cannot be assessed by eye. The Mating Predictor estimates the inbreeding values of lambs produced from a mating of any birth notified or registered ram in iTexel and any ewe in your flock, plus any registered alive ewe up to five-years old.

Mating decisions

Home-bred ram lambs may be your best source of genetics. If usually sold as shearlings they may also provide a cost-effective mating solution. You will know more about these stock than bought in stock.

Consider using at least one well-recorded (high ranked and medium to high accuracy) sire too. The performance of their progeny will enable more accurate comparisons to be made with other flocks. This may involve exchanging or sharing rams with other flocks or purchasing frozen semen and use of artificial insemination (see the ‘Technical Services’ section on this page that has guidelines on the use of advanced breeding technologies).

Only those ewes that are accurately in the Top 25% of your flock are likely to produce a future stock ram worthy of use in the home flock – genotyping is a quick way to improve accuracy and have more confidence in their rank. It is vital these ewes are mated to the right sire. Putting all high-ranking ewes to a new unproven sire is a risk that may not pay off.

Test unproven sires as fairly as possible by ensuring their progeny are born at the same time as those by other well recorded sires, and that they produce at least 10-15 fully recorded progeny in any year, more in large flocks.

Replacement females

Some flocks draft the ewe lambs they like the look of into a pen and deselect those that rank poorly; others identify those that rank highest and then sell or cull those they don’t like. Both approaches will achieve the same objective.

In established flocks the regular replacement of older, low-ranking stock ewes with high-ranking shearlings will greatly increase rates of genetic gain. In new flocks, culling stock ewes on their figures should be carried out with more caution, as less may be known about their true breeding potential, particularly for maternal traits.