Calving difficulty evaluations: New figures explained

As part of the January 2020 genetic evaluation, there has been a significant update to how calving difficulty is displayed.

Up until this year, each bull had a single calving difficulty PTA (Predicted Transmitting Ability) and reliability.

This provided an indication of the expected incidence of calving difficulty, irrespective of the type of female that a bull was mated with – i.e. a heifer or a cow.

With the new update, the calving difficulty PTA % will be split into four and these will reflect the truer incidence of on-farm calving difficulty.

Dairy heifer calving difficulty %;
Dairy cow calving difficulty %;
Beef heifer calving difficulty %;
Beef cow calving difficulty %.

To help with the change-over to this new method of displaying calving difficulty, the Irish Cattle Breeding Federation (ICBF) has developed a ‘Ready Reckoner’ that will aid farmers in the transition from the old single calving difficulty PTA to the new traits.

With the main breeding season fast approaching, AgriLand caught up with ICBF geneticist, Siobhán Ring, to get a better understanding of why and how these changes came about.

Why have these changes been made and why are they important for farmers?

This is important because whenever a farmer is going to buy a bull – whether that be a stock bull or whether it’s AI – the first thing they’re going to look at is: ‘Is this sire suitable for my herd in terms of calving?’. ‘Am I going to be able to calve them or is it going to be too difficult?’

We used to have one calving difficulty PTA value and reliability. So basically, what that tells you is the percentage of calvings that are expected to result in a difficult birth.

Ross Evans [ICBF] has been doing a lot of work on that in the last couple of years. Basically, what he was seeing was that the percentage of calving difficulty that we were showing was not really reflective on every dam type – whether that be a heifer or a cow, and whether that heifer or cow be in a dairy herd or a beef herd.

Siobhán Ring speaking on FarmLand in 2019

When we separate them, what we do see is that the most difficult calving bull on a beef heifer will very likely be the most difficult calving bull on a beef cow, but that won’t be the case when you come to a dairy cow.

For example, say you’ve got a Limousin bull and he comes up with an easy calving figure – around 3% – so you can definitely use him in the beef herd, as he’ll likely have many records from beef dams. This bull could be promoted for the dairy herd because he’s assumed to be easy calving.

But, because the relationship is not the same, because they’re not the same trait when you use them on different animals, you could potentially end up with an easy-calving bull on beef cows, but that same bull could have much more difficult calvings on dairy cows.

With the new evaluation, has there been much movement on individual bulls or sires in terms of calving difficulty?

Yes. Most of the calving records were coming from cows. That means that our old calving difficulty evaluation was mostly reflective of cows – whether that be dairy or beef cows.

So, with the new system, the cow figure is very similar to what farmers saw before, but when you look at the heifer calving difficulty, there will be a big jump.

For example, dairy farmers that have been using a Friesian bull on heifers that was under 2.4% – that would’ve been considered a safe threshold, they’re now gone to 5.2%.

New calving difficulty evaluations for the Friesian breed

But, it will differ depending on the breed as well, so if you’re talking about Aberdeen Angus, for the old system, that’s about 7.3%.

New calving difficulty evaluations for the Aberdeen Angus breed

This can be described like a currency change. When we moved from the pound to the euro, it was a big shock all of a sudden. This is a change in mindset and once we get over the initial shock, it will show farmers what is actually truly happening on farms.

With the new evaluation, what should I be looking out for when picking bulls or sires for heifers?

The PTA value (%), the reliability and the breed.

The lower the PTA value, or %, the fewer incidents of difficult calvings you should have. The higher the reliability, the more confident you can be that the PTA % is a very likely reflection of what you will see at calving.

In terms of the breed, we know some breeds have more variability in calving difficulty than others – for example, there is more variability in the Charolais than the Angus breed.

So, choosing bulls can be a complicated process, but we’ve tried to simplify it by generating a ‘Ready Reckoner’ to get to grips with the new PTA values and also providing a tool for dairy farmers that takes all of these metrics into account.

For dairy farmers, we now have a risk category associated with each bull for dairy heifer calving difficulty – low, moderate or high risk.

We are advising farmers to use bulls categorised as ‘low risk’ on dairy heifers. These bulls will have a low calving difficulty %, a high reliability and come from a breed that isn’t likely to change that much; these are the new ‘safe bulls’ for use on dairy heifers.

On the beef side, we don’t have three risk categories for heifer calving difficulty; we just have the old scale moving to the new scale and we have the ‘Ready Reckoner’ to help with that.

Generally, farmers would have used bulls that had a PTA value under 5% on beef heifers. So, if you are a beef farmer using Limousin bulls under 5%, the new figure is 8.1%.

Once farmers come to terms with this new single figure, that’s where your base is now; there’s nothing else behind it. Remember, if you are picking a bull for heifers, use the heifer figure; if you are picking a bull for cows, use the cow figure.

New calving difficulty evaluations for the Limousin breed

Will there be three risk categories for beef heifers in the future?

Potentially, in the future we may go down that road, but it won’t be as straight forward.

For example, if you use a double-muscled bull on a double-muscled female, that is a very risky mating, but if that same bull were mated to a female with no double-muscle genes, it could be a very different story; that’s not an issue we have to worry about on the dairy side.

Also, beef farmers have a varying level of tolerance to difficulty on heifers compared to dairy farmers. So, it will be a trait to consider for the future.

How have farmers reacted to these changes?

We now have four different groups of animals [mentioned above] that a bull could be potentially mated with to show farmers a truer reflection of what is expected to happen on-farm.

Even though there are four traits, we’ve been very careful in the way we’ve presented all of the information, because we know there can be an information overload.

If you’re a dairy farmer, you will only see the information relevant to a dairy heifer or dairy cow; if you’re a beef farmer, you will only see a beef heifer or beef cow.

In general, the response has been quite positive. We had received a lot of calls initially and there was an initial shock, but farmers now see it as a way forward and they are happy with more information.

We carried out a survey on 650 farmers and asked did they want to keep the old system or would they prefer to move to the new system where, yes it might cause a little confusion initially, but it will give more information; the vast majority wanted to move to the new system.

The challenge is to get used to the new scale. Heifers have a higher range now, so when you’re picking bulls, farmers need to have a look at what kind of bulls they are happy with.

How long was this research going on?

I would say five or six years.

The ICBF has issued a ‘Ready Reckoner Wheel’ (see below) which helps farmers to visualise the change from one single calving to two (heifer and cow) and how this varies.

For example, if dairy farmers were previously selecting a Friesian bull to use on dairy heifers with a calving difficulty of 1.8%, this figure will now display – on average – as 5.2% for dairy heifers and 2.3% for dairy cows.

For example, if suckler farmers were previously selecting a Limousin bull to use on beef heifers with a calving difficulty of 4.3%, this figure will now display – on average – as 8.1% for beef-bred heifers and 3.4% for suckler cows.