The star rating system (1-5 stars) was incorporated into the Euro-Star Index to make it easier for farmers to interpret – 5 stars being good, 1 star being poor. This concept has been largely successful in its adoption by the industry, but there are some important points to remember:
There are within and across breed stars. It is very important to know the difference. Within breed stars rank an animal only against other animals within its own breed. Across breed stars rank an animal against all animals across all breeds. An animal that ranks highly on a particular index or trait within its own breed might only be average or poor when ranked across all breeds.
There are multiple indexes and traits that have a star rating. A bull could be quoted as a “5 star bull”. But 5 stars for what? 5 stars on a certain trait or on one of the overall indexes? 5 stars within or across breed? Farmers need to ask these questions.
Look at the index or trait PTA first, then the star rating. It is easy to overly rely on the star ratings. While they are important and do tell you where an animal ranks, it is important to focus on the actual index or trait PTA value first. Currently, an animal with a Replacement Index of €100, for example, will be 5 stars across breed. A bull with a Replacement Index of €200 will also be 5 stars across breed. If compared on stars alone, one would think the bulls are equal (5 stars), but there is a vast difference in their actual Replacement Index figures.
In both tables 1 and 2 you will see there is a column giving the trait emphasis percentage. The trait emphasis basically means the average contribution of each trait to the index of the average, proven AI bull. For example, carcass weight makes up 41% of the Terminal Index. This means that, on average, proven AI bulls are getting 41% of their Terminal Indexes from carcass weight. This is an average and some bulls will be getting more than 41% and some bulls will be getting less. Every bull will be different. Again, this is why it is important to look at the PTA values of each bull when looking at an index.
Understanding reliability is an important element to interpreting the €uro-Star Index of any animal. Put simply, the reliability figure gives an indication as to how confident ICBF can be that an index or trait figure will not change in the future as more data is recorded. Where low reliability bulls are being used, it is important to use a team of bulls to protect against future fluctuations. Where bulls are being used on maiden heifers, it is important that they have a low calving difficulty figure (90%). Bulls with low reliabilities on calving difficulty should never be used on maiden heifers.