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World Leading Ovary Scans in Heifers potential Game Changer

 

In the first fertility trial of its type in the world, a Beef + Lamb NZ Genetics project is close to identifying a new tool to predict a dairy or beef cow's potential fertility before she has her first calf.

Neil Sanderson, a North Otago angus breeder and veterinarian specialising in beef fertility, is excited about the prospect of being able to measure and predict a heifer's lifetime fertility by taking an ultrasound scan of her ovaries.

He says fertility is the number one trait that drives the profitability of both the dairy and beef sectors, particularly in a country like New Zealand with a seasonal grass-based pastoral system.

Sanderson believes New Zealand's average calving rate of around 83 per cent is dismally low and even a small improvement of a few percentage points could have a huge impact on this country's agricultural earnings.

His interest in predicting cattle fertility was raised at the World Ruminant Reproduction Conference in Alaska seven years ago, where two scientific papers presented explored the relationship between the number of follicles produced in a cow's ovaries and the potential fertility of that animal.

Initially Sanderson worked with AgResearch on a project which found positive links between antral follicle counts (AFCs) and the fertility of dairy herds on four South Island dairy farms.

"When we looked back at empty dairy cows in autumn we actually found consistently in every herd a much higher number of low antral follicles and hardly any highs," he says. "That's what really got me interested in this."

That research thread was picked up by Beef + Lamb NZ Genetics about three years ago and on-farm trials of 10 pedigree and performance recorded angus breeding herds confirmed that AgResearch's results were consistent and repeatable in beef breeds.

Sanderson says new high resolution ultrasound scanners with a skilled operator now make it relatively easy and inexpensive to see and count antral follicle numbers in the ovaries of cows with a skilled operator.

AFCs appear to remain consistent and repeatable through an animal's lifetime, clearly identifying her as a producer of low, medium or high numbers of follicles.

"We have proven in both beef and dairy cows that there is a correlation between antral follicle counts and pregnancy outcomes, so those with higher AFCs have a higher chance of becoming pregnant," he says.

"There is also a correlation between higher AFCs and a cow's ability to get in calf earlier in the season rather than later."

Sanderson believes antral follicle numbers have the highest heritability of any fertility trait, which means that by selecting for this trait breeders could make good genetic improvement.

The significance of this research is that it could provide the beef and dairy industry with a relatively simple tool to predict the fertility of a heifer before her first mating. Potentially farmers could identify animals with a more productive breeding life from a younger age.

"Ultimately, I guess the aim of this would be to find genetic links or even find some genes or gene markers that are associated with this trait we are looking at," Sanderson says.

Until now there has not been a direct means of measuring fertility in dairy or beef cows. At the moment farmers can only "look backwards" over a breeding cow's lifetime to gauge if it was fertile or not.

The beef industry's Breedplan uses a "days to calving" estimated breeding value, but Sanderson says that is measured in older cows, not heifers. This estimate of fertility is only seven percent heritable so breeders can't make much genetic progress by selecting for this trait on its own.

Beef + Lamb NZ Genetics has subsequently set up a beef progeny trial of 50 bulls at five different locations around the country to validate the beef industry's Breedplan system. The trial is now in its third season with between 600 and 700 R1 heifers on the ground.

All heifers are the progeny of known angus and hereford sires and commercial beef cows in a transparent, controlled trial that Sanderson says is very well run and will help identify sire links.

"We will be able to follow these animals through the first three or four years of their reproductive life to see if those with low AFCs drop out at some stage or take longer to get in calf.

"We've now got calving records on those animals so we're looking at correlating antral follicle numbers with calving outcomes, when they get in calf, early or later, to confirm any patterns."

An interesting factor is the huge variation between herds and management systems, he says, "which validates that we could well be on the right track, whereas in dairy herds there was hardly any difference between herds with high, medium and low AFCs.

 "We never expected that, which suggests the possibility of a genetic link because some beef herds are quite closely bred."

Sanderson says the next step for the Beef + Lamb NZ Genetics project is to link the phenotypic information on antral follicle counts into existing breed evaluation systems to try and find common links with sires.

"I think within a couple of years we should be able to transpose that information into a breeding value of some sort," he says. "Even on its own I think it's a good phenotypic indicator to exclude heifers with low antral follicle counts."

He believes many cattle breeders are already improving the fertility of their herds by default by mating heifers for two cycles and culling any empties or late calvers.

Sanderson believes the median national calving rate of 83 per cent suggests the range of calving rates in the commercial beef industry is spread between 65 and 95 per cent.

"That's the frightening thing. It's a huge opportunity lost," he says.

He would like to see the beef industry set a target national average calving rate of 90 per cent by 2020, a figure he believes is achievable by scanning heifers for fertility and linking that information with existing pedigree and performance recorded data.

"I think (the fertility trial) has the potential to lift that pregnancy rate quite quickly and I think it will do that," he says.

New Zealand has about one million beef cows. Lifting the national calving rate by 1 per cent could potentially increase the number of calves by 10,000, which as a rough rule of thumb would currently be worth up to $8 million to the industry for each percentage point increase in the national calving rate.

Beef + Lamb Genetics' manager Graham Alder says the initial trial work on AFCs looks encouraging and if it can be developed to predict fertility it would be a big leap forward for beef breeding in New Zealand and internationally.

He says conception rates in cattle have remained relatively static at around 82 to 83 per cent for decades, cow size has got bigger over the last 20 or 30 years, but average carcass weights have stayed the same at about 300kgs.

"The challenge is we are breeding bigger cows that are no more fertile and we're producing the same carcass weights, so cows are less efficient than they used to be," Alder says.

"So if a beef cow is less efficient it is less profitable and this research is looking at how the industry can improve that. If we can produce more accurate and easier to use breeding tools for the industry that can predict fertility, this work is pretty exciting."

The Beef + Lamb NZ Genetics project has attracted unprecedented funding support from Meat and Livestock Australia and has the backing of leading beef breeders and breed societies on both sides of the Tasman, which is seen as an indication of international interest in this research.