Tankardsrock Teak - whose AI code is FR7929 - has suffered a major crash in economic breeding index (EBI), based on the latest evaluation by the Irish Cattle Breeding Federation (ICBF).

The NCBC-owned bull was the highest EBI bull in the country at the previous evaluation in March and was the most used AI bull in the 2024 season.

His new EBI is €287, down from €370 in March, meaning he drops from first to 202nd position on the active bull list.

Almost all of the reduction in EBI comes from his fertility proof, which has fallen from €182 to €109, while his milk proof remains consistent at €104.

The fall in EBI for fertility is surprising, given that Teak’s sire - OTS - is an older bull born in 2013 which has a very reliable and stable EBI.

The fertility sub-index for OTS actually increased at the May evaluation and he now has an overall EBI of €296, some €9 higher than his better known and widely used son.

Fall

Farmers that used Teak in such high numbers in 2024 and 2025 will be disappointed to see his proof fall by so much, as it means the EBI of his progeny will also fall.

In essence, it means that there are over 200 bulls that have a higher EBI than Teak, which, in hindsight, would have been better bulls to use, judged on EBI alone.

However, variability in a bull’s proof is nothing new and we have seen the EBI of a bull fluctuate up and down before.

It is not until progeny data for a bull comes through and reliability increases to over 95% that we will be certain of his proof.

As more data on Teak is gathered, his EBI could increase, although it is unlikely to increase by the degree to which he has fallen now.

The catastrophic fall in Teak’s EBI is a reminder that farmers should be using a team of bulls to minimise the impact of one bull’s EBI crashing, such as in this case.

It also demonstrates that the fertility proof of a bull is often overestimated by genomics, a problem geneticists recognise and try to remedy.