ICBF updates sire advice and TB data

Advancements in DNA screening of animals have led to new discoveries and given farmers better tools for breeding decisions.

Just like humans, cows can carry harmful genetic mutations.

These are called lethal recessive mutations, which only cause problems if an animal inherits two copies of the faulty gene.

If two carriers are bred together, there is a 25% chance their offspring will inherit both copies, leading to death—usually at the embryo stage.

Genotyping will identify these carrier animals, allowing farmers to avoid these risky matings. In Holstein-Friesian cows, two common lethal mutations are HH1 (Holstein Haplotype 1) and HH3 (Holstein Haplotype 3).

About 2% of Irish Holstein-Friesians carry the HH1 mutation, and around 5% carry HH3. This means that thousands of matings each year involve two carriers, leading to many cases where no viable calf is born.

HH1 mutation

The HH1 mutation is particularly problematic because it can cause pregnancy loss up to 200 days into gestation.

In seasonal calving herds, this often means a cow is found to be not pregnant at the end of the breeding season, reducing efficiency.

To address this, the ICBF sire advice system, which already prevents inbreeding, has been updated to avoid mating carriers of lethal mutations.

This improvement is expected to save the dairy industry about €2.2 million annually. The system can also be easily updated as new lethal mutations are discovered.

With a 5% prevalence of HH3, about 2.5% of dairy matings involve two carrier animals. If one million dairy cows receive an average of 1.5 artificial insemination (AI) services each, this results in approximately 3,750 HH3 carrier-to-carrier matings. Adding around 600 similar matings for HH1, the total comes to about 4,350.

If the cost of losing a heifer (after factoring in the cull cow value) is €1,000, then the financial loss from these 4,350 carrier-to-carrier matings (where half of the pregnancies won’t succeed anyway), adds up to around €2.2 million.

Other updates to Sire Advice:

Farmers can breed cattle that are less likely to become TB reactors by selecting cows and bulls for breeding that have the highest overall EBI as well as the lowest breeding value for TB resistance.

Genetic resistance to TB typically ranges from 1% to 15%, with an average of 8.5%.

This means that, on average, 8.5% of a bull’s offspring could become TB reactors if exposed to the bovine TB bacterium. In 2024, there were 41,000 TB reactors, with around 490,000 cattle exposed to TB (based on the average TB breeding value of 8.5%).

If this breeding value were to improve to 4.5% — a 4% unit increase in genetic resistance — the number of reactors would drop to 22,000, nearly half of 2024’s total.

By choosing bulls with stronger TB resistance, farmers can significantly lower the number of TB cases in their herds, reducing costs, stress, and workload.

To make selection easier, ICBF has introduced a traffic light system for TB resistance:

These colour codes are now visible in:

1.The ICBF Active Bull List.

2. Animal Search.

3. EBI Profile.

4. ICBF Sire Advice. The image on the right displays the Health Sub-Index traits for three high EBI bulls with good, average and poor resistance for TB.

Several updates are planned for the EBI and are expected to be implemented in the September evaluation, following the completion of research and approval by the Technical Advisory Group and the ICBF board.

Economic Values Update

To ensure the EBI accurately reflects profitability on Irish dairy farms, Teagasc has conducted a comprehensive review of the economic values used in the calculation of the EBI.

This update takes into account rising input costs (such as increased fertiliser and feed prices), higher output prices (including milk price adjustments), and future market projections, including processing costs.

Genetic Base Population Update

To ensure the EBI reflects current genetic and management standards and remains a relevant tool for breeding decisions, ICBF will be updating the genetic base population i.e. the starting line from which we measure progress in PTAs.

The genetic base population will be updated by shifting the base year to more recent genetics.

This helps keep genetic evaluations relevant as animals improve over time. The most recent update occurred in September 2016, shifting the base from cows born in 1995 to those born in 2005.

The change will ensure evaluations reflect the current population’s performance rather than an outdated standard.

It will highlight the improvements in traits like milk yield, fertility, and health.

Linear Type Update

ICBF will be updating how it evaluates the physical traits of animals, known as linear type assessment. The new system will use a single-step evaluation, the international standard, to provide more accurate results.

This update will better reflect the data used to score animals on traits like body size, mammary system, and feet and leg conformation.

Health and Management Update

Health and management traits, like Linear Type, will be assessed using the single-step evaluation.

This approach provides farmers with more precise tools to enhance cow health and management.