BY: VICTORIA O’SULLIVAN
Southland deer farmer and veterinarian Dave Lawrence of Tikana Wapiti was one of the first breeders to get on board with CARLA testing.
A self-professed ‘parasite nerd’, he was excited about the potential impact of the testing from the start.
He says parasitism in deer remains a critical issue in the industry because there are so many unknowns.
“If there’s something in an animal that can attach to a parasite and prevent further development once it’s ingested, it’s got to be a good thing.”
He started testing his fawns 10 years ago but says the introduction of an EBV for the test in 2016 was when they really gained traction.
Initial testing in 2010 showed only 10% of their fawns were in the medium-high category for CARLA antibodies. This year their fawns tested at 75%.
He says they have doubled the herd average for the test since 2016.
“That’s why it’s so exciting. If you are using DEERselect and EBVs, it gives you the power to up the ante.”
This year he’s stretched his drenching interval from four to six weeks. His liveweight results have been as good, if not better than previous years. “There’s been no negative impact, so that’s progress in the right direction.”
Extending drench intervals also contributes to achieving refugia on pastures by keeping parasites susceptible to drenching alive on pastures and slowing the build-up of resistant parasites. “It’s a double whammy of not only reducing the amount of drench, but the less time you expose a worm to a drench the less chance of developing resistance.”
Trait heritability is another positive for the industry. Buying terminal or maternal replacement sires high in the antigen means progeny will instantly inherit this as part of their genetic makeup.
“The latest [research] says not only is it a good idea to use a high CARLA sire, but you can test your own replacement hinds when they are 10 months old.”
He says selecting replacements high in the antigen will increase the whole herd level on the hind side. At a commonly used 20% replacement rate this benefit will be achieved in a five-year period.
He believes it’s a realistic option for all farmers to use as a tool. “It’s not only something for breeders to get into, it’s got some real scope for commercial farmers as well.”
He says combining good grazing practices, sensible drenching, timing and tools like dung beetles could have a real impact on the future of parasite control.
“I accept that we can’t stop drenching, but it’s inevitable that when we develop a high level of CARLA within our herds, we will be able to reduce our reliance on it.
The process of collecting samples and sending them for analysis is a simple procedure. A cotton swab is put in the mouth of the animal for 5-10 seconds to get a good coating of saliva, then enclosed in a vial and sent for testing.
“It takes a bit of time to do all the animals individually, but you only have to do it once and you’ve got a result that is potentially quite powerful,” he says.
Powerful tool in parasite war
It may be just a small saliva sample on a cotton roll, but the CARLA test is offering a powerful tool for deer farmers in the parasite management space.
CARLA, which stands for carbohydrate larval antigen, is the first tool available to deer breeders which allows selection for favourable immune responses to gastrointestinal parasites and lungworm – two of the biggest disease challenges in yearling deer.
AgResearch Farm Systems Scientist Jamie Ward presented his final research findings on the test at the 2020 Deer Industry New Zealand Conference in June. He noted that the testing offered a way to do things differently in the parasite control space, all while incorporating animal welfare benefits and increased production gains for farmers.
He said the antigen is a positive trait with no downside and all upside. To have the science prove it and be confident was a good step for the industry.
A breeding value for the test has been made available so breeders or farmers can use the information to make selections or buying decisions. Ward hopes that over time, active animal selection for higher CARLA estimated breeding values (EBVs) will provide opportunity to reduce the reliance on drench, particularly when used in conjunction with other management practices for parasite control.
Shifting to herds of deer with higher genetic merit for the antigen will increase the resilience of deer farm systems by producing animals that are more resistant to parasite challenges.
A reduction in drench reliance could have positive flow-on effects into the marketplace, where consumers indicated a preference for ‘low chemical input’ products.
“It’s good to have this to demonstrate the industry is serious about addressing issues that could arise or already do arise in the marketplace.”
Ward said animals that are more genetically resistant to parasites helped offer some peace of mind if mistakes were made with parasite management on-farm.
“If someone forgets to drench for a week then you are not going to end up with a whole lot of weaners really sick with lungworm because someone made an error.”
CARLA has a heritability of 0.45, meaning that good genetic progress can be made if selected for. No adverse effects on other estimated breeding values (EBVs) were observed and testing costs $10 per animal.
Ward encourages breeders and farmers to consider including the test in their breeding objectives or breeding plans as it offers a way to genetically increase the parasite resistance of their animals.
He said it was not a silver bullet to stop drenching tomorrow, but farmers can positively change their herd to reduce drenching requirements over time.
