DairyTalk 228: Why Good Cows Look Worse Over Time: The RZG Illusion - by Helmut Demmelhuber

Many breeders observe RZG values declining over time and
mistakenly question genomic reliability. This article explains
why that conclusion is misleading. A cow’s genetic potential does
not change; what changes is the reference population due to
annual base shifts. Older animals are continuously compared to
genetically stronger younger generations, causing a statistical
decline of four to five RZG points per year. The piece puts this
effect into context, introduces a simple rule of thumb for
realistic interpretation, and argues for focusing on true
performance, longevity, and breeding logic rather than purely
relative index figures.