NZ Animal Evaluation December updates

In the December Animal Evaluation (AE) run, NZ Animal Evaluation (a DairyNZ subsidiary) will introduce three important updates that may lead to some re-ranking of bulls and cows.

First, the Economic Values (EVs) used to calculate Breeding Worth (BW) will be updated. This is a routine, annual event to ensure the EVs, which form a key part of BW, reflect the latest farm economic factors.

The other updates are for two traits farmers can use to make selection decisions. They include an update to the Gestation Length (GL) breeding value, and an improvement to the Heifer and Cow Calving Difficulty (CD) breeding values.

All updates have been developed in consultation with breeding industry stakeholders and will be live in the Animal Evaluation run published on Friday 6th December 2024.

Economic Values update

Economic Values (EVs) form a key part of the BW calculation and are updated annually to reflect the latest farm economic factors. Last year, we introduced changes to the methodology which aimed to reduce unnecessary volatility for annual EV updates. As a result, this year's annual EV update showed modest changes.

The most significant EV change is due to the reintroduction of the capacity charge by Fonterra resulting in the EV for milk volume changing by 16%. The other EV’s experienced similar adjustments to last year with changes varying between 0-9%.

We expect little to no re-ranking of bulls due to the updates to EVs. For bulls enrolled in AE the correlation between the old BW and the new BW is 0.999. A correlation of 1 is no re-ranking and a correlation of zero is complete re-ranking.

Breeding Value changes

Calving Difficulty (CD) and Gestation Length (GL) are the last traits to be transferred to NZ Animal Evaluation and will be independently run through provider, The Helical Company. All other traits were migrated in 2021.

With this final migration, NZ Animal Evaluation, with key research partners AbacusBio and The Helical Company, have made updates to the evaluation for both BV’s. The evaluations take a stricter approach to data filtering, including more precise classifications of breeds into short, medium, and long GL categories.

Whilst improvements were not a goal of this work, they are a welcome result for the CD BVs. Importantly, the GL model is still just as accurate.

Improvements to Calving Difficulty

CD is now modelled with both direct and maternal effects. This means it considers not just the genes of the calf, but also the genes of the dam (the mother).

From a bull perspective:

• The direct effect refers to the likelihood of his calves experiencing a difficult calving when they are born.
• The maternal effect refers to the likelihood of his daughter experiencing a difficult calving when she gives birth.

These changes are reflected in both the heifer CD and cow CD breeding values for dairy bulls online.

With the change in breed classifications, the average CD breeding values (BVs) for Holstein Friesians have increased, while Jersey BVs have decreased. This is because the new model does a better job of separating out the effects of breed, with the BVs more accurately reflecting the relative incidence of calving difficulty in Holstein Friesians compared to Jerseys. This has resulted in a greater spread in the CD BVs, meaning the animals that are more prone to calving difficulty are more easily identified, while those that are less prone show clearer advantages.

Together, the stricter approach to data filtering, more precise classifications of breeds, and the inclusion of maternal and direct effects have resulted in significant improvements in the ability of CD BVs to predict a bull’s future daughters’ chances of experiencing CD.

Updates to Gestation Length

The new GL model has similar performance to the current model. The new GL model shows that the trend in GL is still decreasing, but at a slower rate than previously estimated. This means the BVs for recent animals (current animals in herds and bulls used in the last 10 or so years) are on average higher by about 1.5 days.

Summary statistics will be published in the Animal Evaluation run on 6 December and can be found on the animal and herd averages page.

What do these updates mean for farmers?

These updates, now all independently managed by NZ Animal Evaluation, mean you can have greater confidence in your breeding decisions going forward, to support a more profitable herd.

• The new EVs reflect the latest farm economic factors
• The BV updates maintain accuracy in GL and;
• Improve CD predictions

On average, across all breeds, BW has increased by $8.40. Come December, you might see a small increase in your herd’s BW, depending on the breeds you are currently milking.

The changes to CD won’t impact your herd’s BW as CD is not one of the traits that make up BW. However, you are likely to notice significant changes to the CD BVs of current bulls. For example, Holstein-Friesian bulls with a Heifer CD BV less than 0 represented the top 10% of bulls in the old evaluation. Now, thanks to the improvements to the CD model, the top 10% of Holstein-Friesian bulls will have an BV below 3.4. This represents a change in the BV values, rather than any actual changes to the likelihood of a bull’s future daughters experiencing calving difficulties.

This means that if you usually select Holstein-Friesian bulls with a CD BV less than 0 to use over your herd, you should revise your threshold to 3.4 to adjust for the change in values. Please see the table below for the translated CD Heifer BVs for specific breeds.

The new models are better at predicting CD, however, as with all selection decisions, it’s still essential to consider the reliability of each bull’s BV and the number of offspring in the evaluation to minimise the risks of calving difficulty.