13.1: How to measure genetic improvement?

Genetic improvement indicates how much better animals are genetically in the current generation as compared to the previous. To be able to determine the genetic improvement, it is required to know the genetic potential of the animals. The actual genetic potential cannot be measured. But if the breeding values of the animals can be estimated with very high accuracy, using information on many offspring for example, these EBV can be used as good approximation of the true genetic potential. Apart from high accuracy, the EBV also need to be estimated without bias of systematic effects. For example, animals that are fed with a high quality feed may perform systematically better to animals that are fed simple feed. If EBV are not corrected for this effect, the EBV of animals that were fed the high quality feed will be biased upwards. Their performance was better, but not because of their genetics. To get the best estimation of the EBV they need to be estimated using BLUP, which can take these systematic effects of feeding, housing, season, or other environmental influences into account (see chapter on ranking the animals).

Summarising, it is possible to get a good approximation of the genetic improvement across generations when EBV are estimated with high accuracy and using BLUP. The realised genetic improvement or realised genetic response can be determined by taking the difference between the average EBV in both generations.

This simple formula will give the best possible approximation of the realised genetic response. Remember that the predicted genetic response is calculated as

    The difference between the realised and predicted response is what requires evaluation.  The smaller the difference, the better the realisation resembles the prediction, and the less evaluation is required. However, if the difference is substantial, it is essential to find out what causes it.