However, because the performance of all animals is influenced by both genetic and non-genetic factors such as feeding, disease, climate and management, selection ‘by eye’ can be misleading. Consequently, until fairly recently, the genetic potential of animals could only be objectively compared if they were living in the same environment and being managed in the same way.

The development of powerful computers and sophisticated software in the form of BLUP (Best Linear Unbiased Predictor) has made it possible to disentangle the genetic from the environmental effects on the performance of pure-bred animals allowing animals within flock and animals in across flock breeding groups to be directly compared.

Although the majority of slaughter lambs in Britain are crossbreds, the purebred flocks have an essential role to play in the production of high genetic merit breeding stock for use in commercial flocks.

Mating and lambing records are kept on each animal born in Sheepbreeder flocks and performance data such as lamb weights, muscle and fat depths are collected on farm. Aspects of the animal’s environment such as month of birth and rearing group are also recorded.

In Sheepbreeder, EBVs are either calculated on a Breed or Breeding Group/SRS basis, or within-flock.

EBVs can also be combined into selection indexes for a specific breeding objective or set of objectives