BREEDING for polledness in a beef herd is a long-term proposition, and not without its challenges, an Australian Agricultural Co specialist told a recent Beef Connect webinar audience.
AA Co’s principal scientist Dr Matt Kelly provided a handy snapshot of progress in the company’s poll breeding projects, covering both its Mitchell composite cattle and Wagyu. His presentation was part of a recent Beef Connect* webinar.
As part of a Member Donor Company-backed extension and adoption project, AA Co has focussed on two challenges in its extensive northern breeding environments:
- How the company breeds for polledness, while still pursuing other breeding objectives, and
- Tackling some reproductive diseases that are often put in the ‘too hard’ basket, like trichinosis, vibrio and pesti (to be discussed in a separate, webinar being held in coming weeks).
In AA Co’s case there were a number of reasons to breed for polledness, Dr Kelly said:
- Reducing or eliminating the need for dehorning (economic loss due to bruising, as well as being safer for the animals, as well as staff)
- The future prospect of greater consumer pressure over the practise of dehorning.
He said the arrival of an accurate test for polledness had made the prospect more attractive, and it could be well integrated in normal stud practices, including the use of genomics.
He briefly explained the distributions that could be expected from homozygous and heterozygous polls, and horned bulls and females (click here to read an earlier genetics item discussing this topic).
Where once it was thought that only a single gene was responsible for scurs, it is now thought that two or more may be responsible, he said.
Progress in selection for polledness was discussed in two snapshots, covering AA Co’s Mitchell composite herd and its Wagyu herd.
Mitchell composite poll program
AA Co has been developing its Mitchell composite line since the 1980s, but genetic testing and greater selection for polledness has only happened more recently.
As this slide shows, back in 2017, just over 50pc of AA Co’s overall Mitchell composite program cattle were polled, and of those, just 12pc were PP homozygous polled animals.
As testing and selection gathered pace, from 2019 all stud bulls in the Mitchell composite program were PP animals. Two years later, all herd bulls were polls (either PP or PH), and by next year, the entire herd bull battery will be PP animals.
This year’s calf drop includes 60pc PP calves, and the objective is to see all calves produced under the Mitchell composite being natural polls by 2030.
Three years ago, AA Co started pushing full cohorts of PP bulls out to one of its commercial breeding properties.
“We’ve been watching to see how long it takes to start having a big impact on the rate of poll calves in that herd, with natural matings,” Dr Kelly said.
“Even though we started seeing big impacts from 2021 in the stud herd, females in the commercial Mitchell composite herd are a generation behind, and it also takes a generation to replace the existing herd bulls,” he said.
As the table below shows, it took three years to produce a really significant upkick in the polled female calf rate, rising from 47pc to 61pc from the 2022 calf drop to 2024. Steers rose from 31pc to 39pc phenotypically polled (not dehorned).
“The amount of heterozygous polls are the same in the male and female calves – the only difference is scurs that are needing to be removed in the branding process,” Dr Kelly said.
Wagyu poll program
Dr Kelly said AA Co’s Wagyu poll program differed in several ways from the parallel Mitchell program.
“With the Mitchells, when we started 50pc of the herd was already polled, which is quite different from the Wagyu herd. When we started this process back in 2017, worldwide there was not many Poll Wagyu bulls available.
“We could really only access a handful of (Purebred) polled bulls. Starting from a small base like that obviously presents a real challenge, with inbreeding and selection for genetic merit becoming an issue,” he said.
“And as the Poll Wagyu program rolls out, we will have to deal with scurs, just as we have had to in the Mitchell composite program.”
The graph below shows the index after two years of breeding for Poll Wagyu, running some AI programs. It shows the range of EBVs (grey bar) for horned animals, versus the polls. It indicates the presence of very few polls, and the fact they sat reasonably far behind the mean index for the horned Purebreds and Fullbloods.
Over the past five years from 2019 to 2023, however, as can be seen in the graphs below, AA Co has increased the number of Poll Wagyu to some extent. But the most important point is that the number of poll animals that are competitive with, and equal to the genetic merit of the horned equivalents has grown.
Dr Kelly said in executing its Poll Wagyu breeding program, the company would use genetic tools like MateCell and the Digital Twin predictive program (separate story to come) to help guide the project.
He provided a number of examples on why it was important to be ‘really careful’ when designing matings to achieve higher rates of polledness, from a small population.
Using one PP bull’s results, the example bull could not be used for a blanket mating, because 18pc of the poll breeding females in an example herd were his half-sisters, or related, causing inbreeding risk.
As a result, AA Co is working to develop more outcross PP Wagyu bulls, not as closely related to the females they will be mated to. In one example shown, the bull would have less than 2pc of a cow herd that he was highly related to.
Against this background, the entire Australian Wagyu cattle herd started from only a small population, given the restrictions placed years ago on genetic export by Japan.
Another example showed 6pc of females in a herd would be half sisters to a PH bull.
“The key message in all this is that in order to develop quality Poll Wagyu bulls, it’s a long-term process, requiring a lot of hard work and time,” Dr Kelly said.
“In the short-term, scurs will be an issue for us, and there remains some work to be done. We need to work with the universities to better understand how to interact with them better. It may be that we have to evaluate how we determine which animals truly need scurs removed, and which don’t.”
Questions
During a Q&A session at the end of the webinar, a viewer asked whether any trade-offs had been noted in the AA Co’s Poll selection work.
Matt Kelly said any time a new trait is added to a breeding program, compromises have to be made.
“We’re always having to compromise genetic gain in selection for polls – its always a multi-trait problem,” he said.
Another viewer asked whether a homozygous polled (PP) animal could exhibit scurs, or whether they were specifically related to the horned gene.
“In our experience in the Mitchell composite herd, it is so rare that its not significant. In the Mitchells, we’ll be breeding 300-400 PP bulls a year, and I don’t think we’ve seen any scurs. I’ve heard of very rare reports, but we haven’t seen any ourselves.”
Another question asked about inbreeding in Wagyu, and whether a coefficient of 7-10pc was the ‘cautionary level’ in a bull, or whether a higher level was seemingly OK to work with in a small herd of say, less than 250 cows.
UQ’s Dr Ben Hayes, who was in the audience, provided an answer, suggesting 10pc was ‘starting to get dangerous,’ because at that level, parts of the genone were probably coming down from the same grandsire or great grandsire.
“That means when you have identical bits of genome coming together, if there is a genetic defect present, you’re in trouble,” he said. “Getting two copies from the same grandsire or great grandsire means they will show that genetic defect – not just in Wagyu, but also within other breeds,” he said.
“Inbreeding is an interesting one, because it’s not really a problem – until all of a sudden it’s a really big problem,” Dr Hayes warned.
“You can track along at 10pc inbreeding coefficient for a little while, but when you really do start to get those chunks of genome coming through in the same animal from both sides of the pedigree, it can be very hard to get it out of the herd again.”
Even in Japan, Wagyu breeders were actively managing inbreeding, Matt Kelly said, because very intense selection pressure was being applied there as well.
Coming up: The role that the Digital Twin predictive model project is playing in AA Co’s Poll breeding work, especially in ensuring that other traits are not compromised, and the different rates of progress that can be expected through natural service, AI and IVF.
* Beef Connect is a collaboration between FutureBeef and Beef Central. FutureBeef is a collaborative project for the northern Australia beef industry involving Qld Department of Agriculture and Fisheries, NT Department of Industry, Tourism and Trade, WA Department of Primary Industries and Regional Development, and MLA. The aim of the FutureBeef project is to support sustainable and profitable productivity gains for northern beef producers.
Interesting to know whether/how much average weights have dropped by chasing a polled program?? Always a problem when you start single trait selection.