Tankardsrock Teak (FR7929) 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—falling 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.
Transition from Genomic to Daughter Proof
In this latest evaluation, Teak moved from a Genomic Proof (GS) to a Daughter Proof (DP-Irl), as daughter performance data was included in his Economic Breeding Index (EBI) for the first time. Consequently, his 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.
What Are Predictor Traits?
In genetic evaluations, predictor traits are traits that are genetically correlated with economically important traits. For example, Milk Kg is used as a predictor trait for Calving Interval and Survival. These traits serve as proxies to improve the reliability of evaluations—especially for young animals who haven’t yet expressed the target traits. They are important tools for making early, informed selection decisions that enhance herd productivity and profitability.
New Predictor Traits in Teak’s Evaluation
In this evaluation, two new predictor traits were incorporated into Teak’s Fertility Sub-Index calculation for the first time:
- Age at First Calving (AFC)
- Milk Kilograms (Milk Kg)
Teak now has 257 daughter records for AFC and 127 daughter records for Milk Kg. On average, his daughters calve 0.65 days later than their herd mates and produce 152 kg 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
Teak’s latest proof confirms that the genomic predictions for Milk performance are proving accurate, as evidenced by his daughters’ milk yields. However Teak daughters do not yet have any calving interval or survival phenotypes, the traits which makeup the fertility subindex. What they do have is some first parity milk records which 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). 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 integrated. 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.
Looking Ahead
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 therefore Teak’s proof will not be updated again until thenat which point the CFS data will be incorporated and offer better insight into his fertility performance.
Advice for Farmers
Genomics has been proven to work and is accelerating genetic progress across the dairy industry. While fluctuations in bull proofs—such as the recent changes seen with Teak—can be concerning, they are not unusual. 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. 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.