THE NATIONAL BRITISH BELGIAN BLUE EVALUATION
what it does, how it works

BLUP

The performance and physical appearance of animals are the result of a combination of factors; the genes they get from their parents, management such as feeding, and other effects such as age and sex. To make genetic improvement breeders need to be able to assess how much of an animal's performance is controlled by its genes alone, i.e. its breeding value, and how much is due to everything else (the 'environment').

The BLUP (Best Linear Unbiased Predictor) computer programme, now adopted throughout the UK beef breeds, represents a major improvement over earlier methods of performance assessment and is recognised worldwide as being the best method of genetic evaluation available.

Beefbreeder calculations are carried out using multi-trait individual animal model BLUP:

Multi-trait
This means that instead of analysing information on each performance trait individually the traits are analysed simultaneously. This enhances the accuracy of the evaluation because performance traits are often associated ('correlated') with each other - e.g. 200 day growth is positively correlated with 400 day growth - so information on one trait helps to establish the animal's breeding value in other, correlated traits. These correlations are especially important when animals have a limited number of relatives with performance records.

The multi-trait analysis also helps to reduce the 'bias' which can be introduced by previous selection. For example, selection of heavier calves at weaning is expected to lead to higher 400-day weights. The fact that the remaining animals are expected to be heavier as a result of previous culling rather than because of a genetic effect is accounted for in multi-trait BLUP as long as the records on all the original animals are included.

Individual animal model
All the available records on the animal and its relatives are taken into account. These relatives may be ancestors, progeny, full or half brothers or sisters or any combination of these. The relative contribution of their performance depends on how closely related they are. For example, full brothers and sisters with the same sire and dam share, on average, half of their genes whereas half brothers and sisters share, on average, a quarter of their genes so provide less information about the genes of the animal being evaluated.

In order to 'disentangle' the effect of genes on performance from environmental effects there must be genetic links between contemporary groups (groups of animals that have been treated in a similar way). This is achieved when at least one animal in a group has one parent in common with an animal in another group. The greater the number of animals with common ancestors across contemporary groups the stronger the genetic links. These links are usually formed by the use of AI. In effect, BLUP compares the performance of the relatives of an animal with their contemporaries across many different herds. It then uses the fact that related offspring share genes and are therefore expected to perform more similarly than unrelated animals to account for differences in management between them.