Monday, July 4, 2022

Sheep genetic potential holds challenges

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Growing pressure on sheep farmers over welfare concerns and climate change are demanding some shifts in what defines the ideal sheep. Richard Rennie spoke to AgResearch animal genomics scientist Patricia Johnson about her team’s work in trying to redefine sheep genetics in a shifting world.

AgResearch scientist Patricia Johnson says sheep farmers have to deal with many unproven claims about new breeds’ suitability to NZ farming.

Growing pressure on sheep farmers over welfare concerns and climate change are demanding some shifts in what defines the ideal sheep. Richard Rennie spoke to AgResearch animal genomics scientist Patricia Johnson about her team’s work in trying to redefine sheep genetics in a shifting world.

Patricia Johnson likens the recent review she headed on New Zealand sheep and the potential to improve them through genetics as something of a “genetic warrant of fitness” for the species here.

“The work has really been a chance to reflect on where we are going with our sheep in NZ. After generations of breeding for more production, the industry is having to consider the complexities of breeding now for climate change and its impact,” Johnson said.

She acknowledges the significant and world-leading advances made in identifying methane inhibiting genetics in sheep.

However, Johnson is adamant more work needs to be done in dealing with the consequences of climate change that are coming to bear in the here and now, regardless of future methane reductions.

“For example, there is evidence that Manawatū is likely to become the new Waikato, with huge implications for sheep populations there. Suddenly diseases like facial eczema are going to become a problem in Manawatū,” she said.

Parasites like Barber’s pole worm that dislike colder areas are also likely to become more prevalent in non-traditional areas.

Another challenge is to determine what proportion of sheep should be Wiltshire-type self-shedders, or have a hair-type coat, given that type of animal is better suited to some environments that are emerging in NZ as a result of the changing climate.

Wiltshires have had a major surge in demand over the past year, albeit more in response to lower wool prices and shearing costs than to climate change.

Other shedding or hair sheep breeds that could contain genetic promise include the US-sourced Katahdin, the Barbados Blackbelly, and the improbably named Cashmore Nudie, an Australian composite.

But bringing in new breeds to address one feature with genetics can impart a negative impact on other traits that undoes the new breed’s other good features.

“For example, New Zealand is the only place in the world that breeds for facial eczema resistance, any overseas breed coming here will not have that,” she said.

Sheep farmers seeking a new breed also face the tough task of sorting that breed importer’s marketing claims from reality.

“Historically, when new breeds came to NZ it was all very controlled, genetic merit was well-assessed before commercial release. Now it is a lot more ad hoc, often without objective evidence to back up claims being made,” she said.

A different future means consideration of traits like heat tolerance, but before you can commence any genetic improvement there needs to be a better definition of conditions like heat stress.

“You can’t generate objective data until you have defined exactly what constitutes heat stress and how you measure it; an area AgResearch is also working on now. It certainly does not have to be extreme before animals modify their behaviour,” she said.

Farmers here are also only ending up with genetics from overseas breeds that have effectively been filtered down before arriving here. Thanks to strict biosecurity rules, breeds from regions, including America and Africa, cannot be bought directly into NZ. 

“So, we have the likes of the Katahdin from the US potentially coming here after a select number going into Canada, from there to Australia and only then from Australia to NZ,” she said.

“Those bottlenecks mean by the time they get here they have a narrow genetic base, as happened with Texels early on.”

Ethical aspects of sheep management, including tailing, are also competing for sheep genetic composition, as consumers scrutinise practises more closely.

MPI’s changes around tail length have already prompted a flurry of breeders measuring tail length this season, with longer tails a blight for increasing dags and flystrike.

“There is potential there for some cross breeding with the likes of a Finnish Landrace, with their short tails, or the stubby tails of Texels and Dorpers,” she said.

Similarly, non-body wool with bare belly and bare breech, both heritable traits, is demanding more breed focus. 

A 1997 report proposed breeding sheep with a genetically stubby tail, with no wool on head, legs, belly or breech, but there has been little uptake from farmers.

Johnson said the ability to breed for shorter tails and eliminate wool from belly and breech brings some management advantages, as well as responding to climate change impacts like greater flystrike risk over summer.

“If we can show there are positives for you as a farmer, requiring less work, less shearing and less time, it means this is more than just a response to regulation,” she said.

With an assortment of more exotic sheep genetics available, the task in choosing which to include is also made tougher, given the relatively small amount of data available on many traits.

“Sheep Improvement Limited is the repository for recording most breeds in New Zealand, but not all exotic breeds are recorded in the repository, or for some traits there is very little data recorded, for example, intramuscular fat. It means we tend to have more marketing claims than we do objective data to back up those claims,” she said.

In the meantime, she is adamant the focus for sheep breeding needs to drill down into the here and now of coping with welfare and climate shifts.

“Adaptation to these challenges has tended to be underdone in New Zealand,” she said.

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