Explainer: How do proofs fluctuate in the ICBF Active Bull List?

Agriland

2 days ago

The most recent evaluation of the Irish Cattle Breeding Federation (ICBF) Active Bull List has sparked a bit of controversy among farmers as one of the most popular bulls in the country had his Economic Breeding Index (EBI) drop like a meteor.
So, naturally enough, the most recent evaluations caused debate among farmers, with many looking for a bit more clarity on how these evaluation are made.
Agriland highlighted these concerns among farmers with the ICBF, and asked for more clarity around how these evaluations are carried out and how bulls are assessed.
The bull causing the debate is Tankardsrock Teak (FR7929), who previously held the top position on the ICBF Active Bull List prior to the most recent genetic evaluation.
However, in the latest update, his ranking has dropped significantly as he fell 200 places to 201st. This decline is largely attributed to a reduction of €73 in his Fertility Sub-Index, which also impacted his Carbon Sub-Index, decreasing it by €8.
The bull – which is owned by the National Cattle Breeding Centre (NCBC) – was the most used bull in the 2024 season, which demonstrates why farmers are concerned about his sudden drop in EBI from €370 in March to €287 now.
How do proofs fluctuate?
It was highlighted by the ICBF to Agriland that Tankardsrock Teak moved from a Genomic Proof (GS) to a Daughter Proof (DP-Irl), as daughter performance data was included in his EBI for the first time.
Consequently, Teak's proof reliability increased by 13%. While daughter records are now directly contributing to his Milk Sub-Index, his fertility proof is still primarily driven by genomics and predictor traits.
Predictor traits are genetically correlated with economically important traits. For example, Milk Kilograms (Milk Kg) is used as a predictor trait for Calving Interval and Survival.
The ICBF highlighted that these traits serve as proxies to improve the reliability of evaluations—especially for young animals who have not yet expressed the target traits.
They are important tools for making early, informed selection decisions that enhance herd productivity and profitability.
So, for Tankardsrock Teak's latest evaluation, two new predictor traits were incorporated into his Fertility Sub-Index calculation for the first time, which was Age at First Calving (AFC) and Milk Kg.
Teak now has 257 daughter records for AFC and 127 daughter records for Milk Kg and on average, his daughters calve 0.65 days later than their herd mates and produce 152kg more milk.
While the increased milk production is genetically favourable, the strong negative genetic correlation between high milk yield and fertility contributed to the drop in his fertility index.
Combined with the slightly poorer AFC performance, these factors have significantly impacted his EBI.
Fertility genomics vs. reality
What we can take from this data is that genomic predictions for milk performance are proving accurate, which is evident in Teak's daughters' milk yields.
However, Teak's daughters will not yet have any calving interval and survival phenotypes, the traits that will make up the fertility sub-index.
The ICBF confirmed that first lactation milk recording data has been obtained and given the negative association built into the evaluation between milk and fertility have caused his fertility prediction to drop.
That said, there is still one remaining predictor trait yet to be included ahead of Teak receiving first parity calving interval and survival data later in the year: Calving to First Service (CFS).
Interestingly, this trait has a stronger genetic correlation to fertility than both AFC and milk kg and may help recover some of the decline in his fertility sub-index once it gets integrated, so, maybe not all is lost in terms of the fertility of this bull.
It is also worth noting that fertility records on later parities are also used where available so a sire will not be fully proven for fertility until his daughters that survive reach the start of their sixth lactation.
To accommodate the implementation of new economic values into the EBI and the introduction of a genetic base change, the next genetic evaluation will take place in late September.
Certainly, Teak is one to keep an eye on for the next evaluation as his CFS data will be incorporated and will give a better insight into his fertility performance.
ICBF advice
The only real practical way of overcoming these fluctuation in proofs and avoid having such a fluctuation affect the EBI and genetic merit of your herd, is to have a large bull team and not to overuse one bull in the team.
The ICBF highlighted that genomics has been proven to work and is accelerating genetic progress across the dairy industry.
While fluctuations in bull proofs can be concerning such as the recent changes seen with Teak, they are not unusual as similar adjustments have occurred in the past as more daughter data becomes available.
To minimise the impact of these fluctuations, farmers are strongly advised to use teams of bulls when breeding replacements.
No more than 15% of heifer replacements should come from any single bull. This strategy spreads risk and ensures a more balanced herd.
Despite the recent drop in his Fertility Sub-Index, Teak continues to demonstrate excellent genetic merit for milk production and may be suitable bull to use on your herd.
It's still too early to determine where his fertility figures will ultimately settle, particularly with additional data yet to be included in his evaluation.