Breeding value reliability
How reliable are genomic optimized breeding values?
Breeding values are an estimate, whether they are genomic optimized, or traditional, breeding values. As an estimate they have a certain reliability. This reliability is generally expressed as a statistical value (coefficient of determination, B) in percent. The reliability takes into account the fact that the breeding value could not be calculated on the basis of an endless number of progeny but could only be estimated on the basis of a restricted amount of information.
Another measurement that describes the reliability of an estimated breeding value is the 95% confidence interval. This expresses the range in which the true breeding value in 95 of 100 cases is around the estimated breeding value.
The number of daughters in pure progeny testing with which the same reliability would be achieved can also indirectly illustrate a breeding value.
The table below – using the breeding value of milk – indicates the confidence interval and a corresponding number of daughters for a stipulated coefficient of determination.
Further explanation
The traditional lineage breeding value of a calf has a reliability of about 35% which corresponds to the reliability of a progeny tested bull with 5 daughters. If the lineage breeding value of a calf is estimated at +800 kg, the true breeding value in 95 of 100 cases is in a range of +800 ±790kg, in other words in a range from +10 kg to +1,590 kg.
In American studies 70% reliability has already been achieved on a calf for the genomic optimized breeding value of milk. This reliability can only be specified for a proven bull with 24 daughters. If in turn an estimated breeding value of +800 kg is assumed, the true breeding value for this coefficient of determination is in 95 of 100 cases in the range of +263kg +1,337 kg.
With a traditionally progeny-tested Swissgenetics bull, a reliability of 85 - 90% is achieved through testing. If we assume a reliability of 90%, this corresponds to 91 daughters. With an estimated breeding value of +800kg milk, the true breeding value lies in the range of +490 to +1,110 kg. If the bull is put to secondary use on a large scale the breeding value can be estimated with a reliability up to 99%.
Conclusion
Genomic optimized breeding values of a calf achieve a reliability of 50% to over 70% depending on the trait and the number of proven bulls used to develop the system. This is significantly higher than a pure lineage assessment but not so high as with a proven AI-bull.