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October 1, 2022

In March 2022, we had Dr. Johan Greeff on the Head Shepherd podcast, discussing health traits in sheep.

This is the second half of this podcast transcript where Johan discusses fly odour, resistance vs resilience and breech strike traits.

Hopefully listeners are starting to get a feel for the depths that you've gone through over time to study all this stuff in huge detail. We'll move on from worms and onto flies. And this is already shaping up to be a long podcast, but it's fascinating, fascinating stuff. 

When I started my PhD, you were setting up your flystrike resistance trials. Could you lead us through what happened there and what you found.

The breech strike trial started off in 2006 and the idea was to identify what are the indicator traits that one can use to select animals indirectly for resistance to breech strike. A lot of work was done in the past in New South Wales and Eastern states on body strike, but there was not a lot of work done on breech strike because of the animals being mulesed.

So we set up the project at NWA and there was another sister project in Armidale in New South Wales, which was working on fine wool sheep.

We did the same thing. We set up the base foundation populations in such a way that we can generate as much variation between the indicator traits that we were aware of, like the dags and wrinkle. At that stage breech cover or bare breaches was very highly prominent- everyone was focusing on bare breeches

So we sourced animals from different flocks and we also sourced rams from a variety of breeders across the industry with big variation in their breeches and wrinkle. Not extreme wrinkles, but average wrinkles. So we set up the level of the scoring system that is now being generally used in the industry to score animals on a 1 to 5 basis for dags, breech cover, breech wrinkle in the fine wool breeds, urine stain etc.

Then we looked to see how the progeny of these different rams, that were under the same conditions, how they perform. The one thing that was really striking about this whole thing, that was a very important finding, is the huge difference that exists between sire progeny groups. There are huge differences in animals.

There were two phases. In phase one, there was no mulesing and no crutching. So the animals were challenged as much as possible. And then in the second phase the animals were crutched for a four week period.

But across both phases, every single year we found this massive variation between progeny of different sires. In some years some of the progeny of some sires had more than 100% strike rate. Virtually every one of them got struck, some groups had two or three strikes. And then the other rams, there were very few animals struck and that was quite a remarkable thing. And although we were interested in specific strains, we also quickly realized that there was more to breech strike than only those indicator traits.

So we evaluated the animals and we estimated the heritability of the different indicator traits to see which of them are best correlated with breech strike.

The ones that came up in our environment were dags. Dags were the most important ones. So it's a heritable trait in our environment and indeed is strongly correlated with breech strike. In the Eastern States, though, they don't have a dag problem there. Wrinkles were the biggest issue there.

And although there was a big focus on breech cover or bare breeches, that didn't play a big part. When we look at the amount of variation explained by the different traits that we've measured, the one thing that stood out absolutely was unmulsed and uncrutched sheep had dags.

In the second phase when we crutched the animals, by removing the dags, only then the breech wrinkle came out as being the second most important trait. And these two traits explained about 40% of the total variation of dags and wrinkles. Whereas breech cover, it plays a very small part with 5 or 6% the variation, so it doesn't play a big part. 

We also found that although there are these big differences, there was a fear that the plainer animals and the animals with no wrinkles, would be less productive than the others… But we didn't find that to be the case. There were animals that were plain, wrinkle score one and open bare faces and they really performed in the top 10-20% of the population. So it was just a matter of finding these productive animals who also have these favorable indicator traits. So that was a nice outcome.

We then started selecting animals for low breech strike. We were doing it because it was heritable- well it was not highly heritable because it's a trait depending on the incidence, but on the underlying scale it's quite heritable, but on the observable scale which we work on, it is not as heritable.

But the nice thing is that it is heritable, and breech strike is repeatable. And the same with breech wrinkle, which is heritable- About 30% and it is repeatable about 50%. And then the same with breech cover. Although it was not an important factor, it was all heritable and quite repeatable.

So those traits are the important traits that we focus on. And that allowed the industry to set up breeding values. And now breeding values for those traits are generally available on the sheep genetics website where people can identify the most productive animals and also the animals with favorable indicator traits.

Yeah and we have a number of clients that watch that very, very carefully and grab anything that turns up a bit sort of extreme in those traits, extreme in the right way. Urine stain was on the list as well. Did it show much in ewes?

Urine stain did play a small part, not a big big part. Off the top of my head I think it's around 5% as well, but it was not heritable at all. So it's no use focusing on urine stain. We were planning to do some research, because sometimes when you’re at the cradle at marking, you see some of these young ewe lambs that have got more urine stain than others. But the incidence was so low we couldn't get any results from them to say definitely that it makes an impact on the animal.

So at the end of the day, it is not a heritable trait. It might contribute to the animals being more susceptible but it's not important if you crutch them- you remove much of those animals defects.

I guess the somewhat frustrating thing for you in the team, and I guess it's par for the course, but those indicator traits explain roughly half of the variation and the rest was kind of left. I remember watching for years, you had various PhD students of various projects trying to work out what the other half was, or what it could be explained by. Did you ever get any closer to that?

Yes, where we looked at quite a lot, and the one trait that we were very interested in, was the odor. Because it was clear from our results if you looked at animals that got strike at hogget age or early weaning, they are more likely to strike in the remainder of their lifetime than other animals.

So we had these animals that were never struck at all and then these animals that were struck early in life as a hogget. And then they were struck subsequently again and again over their lifetime, because they were much more susceptible, because it's a repeatable trait

So we looked at some samples of these animals, and we wanted to see whether there are differences in odor. We contacted a sniffer dog company that were willing to train dogs to see whether they would be able to differentiate between wool from resistant sheep and wool from a susceptible sheep

We provided them regularly with wool and they trained the dogs. After they were satisfied that those dogs could differentiate, we tested them. The dogs were 100% accurate at identifying the samples on which they were trained- but, they knew the samples.

So the question was then how will the dogs perform on samples that they have not been exposed to. They were not exposed to Armadale, our sister breech strike trial so we sampled sheep from them. We exposed the dogs. They've never seen these fine wools in their life. One dog was particularly good and 82% of the time he could identify resistant sheep and he would ignore the susceptible sheep 92% of the time. So that showed us that these dogs were able to pick something up and that odor does play a part. But we don't know whether dogs and flies smell the same thing. So we needed to see whether or not the flies responded to it.

So we set up a fly colony and we started working on flies and seeing how the flies respond. And that was a lot of hard work to see how these flies behave with these different wool odors.

At the end of the day, to make a long story short, it's much more complicated. The flies don't only use odor to identify susceptible sheep, they also use sight which was clearly shown from working with different colored bottles and putting samples in different stuff.

They use sight and they look at the humidity also. They use the humidity of the wool before they make a decision to lay their eggs. And so they might do other things as well that we're not sure how they do it or what is happening.

We then see if we can get a profile of these susceptible animals. Do they have a unique odor profile? We put it through a gas chromatograph and we tested this odor. We used the electron telegraph detector where you put antennas from a blowfly in the detector. With the amplifier, you can see how the nerve cells of the antenna spark when it responds and identifies specific chemical components in the odor. 

Then we tried to identify which odors of the sheep the fly identified and then we looked to see how they correlated with breech strike. 

First let me say there's more than a thousand different chemical components, volatile properties, coming off of sheep. And among those thousands, there were five that played a part. One of those ones is a compound with the name of Octanal. The more octanal, the more the flies like that type of odor. 

But there was a complicated factor as well because during this process, when we looked at this odor profile, we found that there was a big difference in the odor profile between resistant and the susceptible sheep. The susceptible sheep has a narrow little odor profile, whereas the resistant sheep have a wide spectrum of different odors and we wanted to use that and promote it. But unfortunately that is where the money dried up. And there was a feeling that from the funding bodies, that odor is not worthwhile investigating. And so that's where we stopped.

Yeah. Right. The massive amount of work and a lot of detail to try to work it out. What's going through my head is that it's kind of like worms, and in my case that’s footrot…Can you see a mechanism where we can have flystrike breeding values generated from untreated animals that are carefully monitored?

Yes, I think the most powerful technology that we have at the moment that can be very effective is genomic breeding values.

Here at Katanning we have the old sheep CRC flock. It acts as a genomic resource flock where we progeny test industry sires and take blood samples and SNP markers and see which SNP markers are correlated with the trait of interest.

In the case of breech strike, that is the same sort of thing we can do. It's being used now for worm resistance as well. When you can progeny test the sire, you get to see which traits are correlated with worm resistance and then somebody else linked to the flock can then just bleed the animals in his flock and then see, using those markers, to predict which animals will be resistant. So that can play a big part.

And the same with strike, the only issue is that we have to do it in very controlled conditions and you have to set up a special flock that's specifically for breech strike. You can't do it where you look at production traits, because the struck animals' production will suffer. So you have to do it independently of that in a different place. 

But genomic breeding values are probably the most powerful technology that we have at the moment that will allow us to select for those traits that are different and expensive to measure. And I'm sure that that will make a big, big impact as they've done already in other breeds and traits already.

They have. I have a couple of questions I forgot to ask whilst we were talking about worms. So we'll cover them off. The interesting thing with worm resistance is that you can select them under a scour worm environment and they become resistant to barbers pole, is that true?

There is a cross-protection. We don't have a lot of Haemonchus in our environment. And when we have Haemonchus, it's in certain cases close to the coast. But we haven't actually found a strong relationship between resistance. Haemonchus is the dominant worm versus WEC from Trichostrongylus. But the time of the year might be a big factor. I know that it was done by Chris Morris. He showed the correlation between Haemonchus and some of these scour worms... That there is a positive correlation. So if you select from the one it does have a beneficial effect on the others or resisting the others. So they have a carry over effect.

But we haven't found it yet because we haven't actually looked to that extent the same way as what Chris Morris did.

Yeah. And the last question on worms which we get asked a bit… And just to be clear, I'm in the resistance camp, but resistance versus resilience? I guess we get a few people out there talking about resilience to worms rather than resistance. What's your thoughts on that?

Well, I personally am more inclined for resistance. With resilience you might find animals that can maybe tolerate them better than others but what the other work has shown is that although that may be the case, the moment we see suffering in terms of lower feed, there's a drought coming or there's a shortage of feed or something like it, then those animals are the first animals that don’t perform. They fall over. They don't last as long as the resistant animals. 

One thing about the resistant animals that I can mention to you is that the animals with lower WEC count, they are also the better animals with better staple strength. They were also the animals with more subcutaneous fat. So they carry more reserves. And I'm not sure anyone checked to see if this is the case in resilient animals as well. That might be the case, but I'm not sure.

But personally I prefer the resistant way. You do not contaminate the pastures and that way the resistant animals can protect the other animals, whereas resilient animals will contaminate pastures and put the younger animals under a lot of stress. They will not be protecting them. And so you don't get that holistic benefit from worm resilience. So my preference is to go for worm resistance.

Yeah, exactly and just add one more trait to the bow of worm resistance, we've found a slightly favorable correlation to footrot as well. There’s a correlation between footrot resistance and worm resistance. So there's just lots of good things that go nicely together.

The thing is with resilience is, how do you measure it? It’s a difficult trait to measure whereas with worm resistance a much, much easier trait and a much more beneficial trait. 

We have to clearly define what you think about resilience and how do you measure it? Because you have to challenge the animal somehow and you can't indefinitely challenge them, you have to measure them at some stage. And where do you draw the line? It makes it very difficult in how often you have to measure it. And that makes worm resistance much easier to work with than resilience.

Yeah. Fantastic. I have another question I want to ask you. There's a couple of graphs that you produced a million years ago, which I've used a lot, around the impacts of head cover on fertility. You did an analysis of one of your flocks and the less wool on the head of a sheep, the more lambs it had. Is that what you consistently found?

That's what we absolutely found. We just found exactly the same thing that was done many years ago in the 60s, just with DNA, where the animals with the open faces had much more weaned lambs than animals with muffled faces.

And we found the same thing, except that we focused on the bare breech. And the bare breeches are of course also correlated with their bare faces. They weaned more lambs per ewe than those with muffled faces.

And the same for the wrinkles- we found the same thing. The higher the wrinkle in the animal, the lower number of lambs weaned. And the same with breech cover. The higher the breech cover, the less lambs weaned. So the bare breeches with the open faces, the plainer animals, are much more fertile and produce more lambs than the others. And that was just a repeat of what was done in the 60s.

I guess if anyone's out there painting a picture in their head of what the future sheep looks like, it gets pretty easy with worm resistance and fly resistance and an open head and clean points. And we know, as you've already said earlier in the interview, that you can cut plenty of fleece wool with these open heads. The old adage of “You can’t strip all of the wool off kind of” was in a world of pre BLUP and pre breeding values… When you can actually achieve many things that might be slightly negatively correlated, but you can achieve them in a balanced objective.

Absolutely you can. Once upon a time, there was this belief that these plain sheep that have an open face are less productive. That's not the case today.

Yeah. You and your good friend and colleague Tony Schlink have done lots of work together over the years. But one of the things that you've done is study the genetics of processing properties. There was the felt wool work which was pretty really interesting. Do you want to just quickly talk about what you found there?

Yes, it was a privilege to work with Tony, who is now retired. And Tony was very interested to see whether we can breed specifically for fabric properties.

The problem at the moment is when you process wool… wool is just blended just together so you might lose some of those unique properties. So we actually started off and looked at the most important properties like pilling and the felting of wool.

And we found that felting and piling is quite a heritable trait, you can breed for it. And we also showed that when you make yarn from different individual sheep's fleeces, that some of the yarns actually shrink much more and that was correlated with the felt.

So there are some sheep out there who have a high propensity to felt and for wool shrink, much more than others. And we were really keen on progressing this to see if we can breed animals for specific markets. There were obviously animals that you could, if you go into ‘felting properties’, breed specifically for that. Or animals in the ‘fabric properties’ where you don't want to get the shrinkage or pillage.

And although they have those characteristics and you can breed from them, there was a strong feeling from the industry that to separate those animals and test for those characteristics down the track would be too difficult and therefore we didn't get support from them unfortunately. But there's certainly opportunities there for anybody else to take it further. 

If they want to breed for specific fabric properties/types, then you can do that. Especially now with genomic breeding values. If you use that genomic breeding with that characteristic, you will be able to identify animals with the specific fabric properties.

Yeah I think it's intriguing and something that maybe we're not ready for yet. I think you and the group that you work with were probably ahead of your time for a fair bit of your careers. Particularly yourself, John and Tony. And maybe in some time people will work out that we can get really specific with that breeding program and breed directly for a particular market and I think would be such an intriguing area. 

I guess I always talk about the fact you can breed for anything on a sheep and I think that that proves it more than anything. Who would have thought you can change the felting properties of wool just by selecting for it?

Yeah, it was quite remarkable. I was very privileged to work with those scientists. They were very motivated and passionate. I was very fortunate to do that but now it's time for somebody else to take it further. Hopefully somebody is still interested in those areas.

Yeah. And I think we'll probably wrap it up here. But yeah, just yeah. You and the team have been amazing. You’ve just done such important work for the industry. It set us up to be in such a much better place than we would have been otherwise.

Thanks hugely for your efforts over your career and the massive, massive amount of work. I think people listening today will have cottoned on to the fact that a lot of that work hasn't been that pleasant or hasn't been that glamorous. There's a lot of head down and bum up work to get the job done. Thanks for all that and many thanks for sharing all your thoughts today.

My pleasure. I had a lovely time and I really enjoyed it and that it was a privilege to do what I could do.

Sophie Barnes
Article by:
Sophie Barnes

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