A fresh look at pest resistance

WITH the range of worms attacking New Zealand sheep becoming ever more resistant to drenches, ram breeder Melvin Forlong said it is time to look afresh at breeding in more parasite resistance.  

Melvin and his family sell parasite resistant rams, with years of hard work and rigorous testing culminating in the fact that today 80 per cent of the sheep on their Ōhura property have never had to be drenched.    

The family has been breeding rams in the King Country for 90 years, beginning when Melvin’s dad, Houlton Forlong,  brought stud Romneys to his property in Tunanui Rd, Ōwhango, in 1933.

Houlton established the stud’s Fernleaf brand, which persists to this day, though in 2021 Melvin and his wife Carolyn sold the Owhango property to purchase a larger one at Ōhura, which they operate with son Justin and his wife Ananda.    

Meanwhile, Fernleaf rams have a following across the country, with the punters persuaded on their ability to sire parasite-resistant sheep and willing to pay a premium for them.

Despite this, Melvin said he had long been disappointed at the reluctance of vets and agricultural consultants to advocate genetics in combination with drenches to control parasites. And he warns that the time for a fair appraisal of genetics is long overdue.  

For example, he pointed to a December report from the national veterinary laboratory Gribbles Veterinary, which warned that 33 per cent of farms tested had Trichosytrongylus worms that were resistant to triple combination drenches. The report also revealed 18 per cent of farms had Teladorsgia species that were resistant to this mix of drugs.    

The commonly-used Moxidectin (popular for control of Barber’s Pole worm) was showing resistance in both these species – 38 per cent of farms for Trichostrongylus and 40 per cent of farms for Teladorsagia.    

But Melvin dreads further resistance to drenches from the pest commonly known as “Barber’s Pole”, as this could be devastating.    

Though not the only parasite that attacks the national sheep flock, the so-called Barber’s Pole parasite is perhaps the one most feared. Barber’s Pole, or haemonchus contortus, is named for its microscope image that resembles the traditional red and white-striped pole used to advertise haircuts.  

It can kill a previously healthy-looking lamb in a matter of days.  

In conditions favouring the parasite, adult worms lay eggs which pass out in the faeces of the host, and Barber’s Pole worms are the highest egg producers of all sheep worms. The eggs hatch within a few days and microscopic larvae emerge.

They migrate on to the pasture, where they may be ingested with the herbage grazed by sheep. In the sheep’s gut, larvae develop into adult worms in about three weeks.    

“Barber’s Pole worm is a blood sucker; it’s the vampire of the parasite world,” Melvin said.    

“The parasite infects sheep, sucking so much blood it causes severe anaemia. Checking a lamb, you will see the gums and eyelids normally red have gone white. Sheep with large burdens will be lethargic and pale. A sheep you thought was healthy can die in just a few days.”    

However, he added that his family had been successfully breeding rams with the aim of counteracting such parasites for 30 years.    

On a normal farm, the ewe lambs farmers kept to carry through as breeding stock in their first year of life would be drenched between six and 10 times.

“But last year we got 80% of our ewe lambs through without ever being drenched,” Melvin pointed out.  

He explained that the family business was not against drenching as such: “If sheep need to be drenched, of course we drench them, and we check them every week to 10 days to determine that.”    

A very basic observation has hastened the improvement of pest resistance Fernleaf could offer its clients.  

The results based on worm counts from an independent lab which has analysed “shit samples” over many years could not be ignored, Melvin said.  

“For years we took hundreds of shit samples and got them analysed and traced it back to their sires and bred our sheep from the ones whose sons had had the lowest worm counts. And that’s how we went at it.    

“In the early days we tested a lot of ewes as well, but we found that was pretty much a waste of time. Because we found on our farm that any sheep that shat marbles (instead of sloppy shit), or larger droppings we call “hand grenades” had the lowest worm count on average.    

“I think because we now have generations of sheep that are used to pharmaceuticals that’s how you end up with sheep who excrete the runny stuff.    

“So, with the female we just make sure that we don’t breed from anything that’s got sloppy shit, and that way you eliminate it from the female side.

“A lot of people dispute that this is so, but our testing is independent, and we can produce the data.  

“None of this means that you’re not going to get the odd marble producer that had a high worm count, or that occasionally you get a sheep that has sloppy shit that has a low worm count.

“But these are aberrations. We can provide overwhelming statistical evidence that the overall trend we have observed and measured here is irrefutable.    

“Some clients who have been buying off us over the last 12 years, many are only drenching their ewe lambs once (rather than the expected six to 10 times).    

“They are prepared to pay a premium; we get $5000 for our top rams and we averaged $1400 to $1500 for every ram we sold this year.”    

Melvin traces much of the success of breeding pest resistant sheep to the years of work by famous Wellsford sheep breeder, Gordon Levitt, who had supplied rams to Fernleaf.    

“In the 1990s Gordon noticed that some families didn’t have to be drenched as much as other families within his flock and so he started breeding from those sires and then he started taking shit samples to back up what he was observing.”    

He wished that vets would be more accepting of the work done by established ram breeders.    

At early Wormwise conferences he attended it was commonplace for one hundred per cent of the talk to be about drenching, with the value of worm resistant genetics left out altogether.    

“I’m pleased Ginny Dodunski is now leading Wormwise as she is sympathetic to what we are doing, having been our vet for a number of years, she has been very helpful.”

Prior to the mid-1950s there were no enthalpic drenches available and the national loss was around 20% (of sheep due to parasites).    

Then aerial topdressing came in and fertility surged. Stock numbers rose as farms were carrying 2-3 times as much stock than previously did.    

“And of course, every animal eats right next to where its best mate goes to the toilet, so the parasite problem exploded.    

“In the 1950s my father would lose about 20% of his lambs due to parasites.    

“Since then, we’ve had 20 to 30 generations of sheep that are totally dependent on drenches to get them through rather than their own immune system.

Here, thanks to superior genetics, we only drench 20% of our lambs (as opposed to 100% on most farms).    

“So I suppose we have come full circle from the 1950s, albeit with much higher stocking rates.”

Justin said improved genetics were in his view a matter of waking up in sheep a natural immunity to parasites which was always there.    

“Going forward, we will continue to push the boundaries on breeding worm resistant rams for farmers who purchase our rams. The idea is to increase their efficiency by reducing the need to drench and the workload of the farmer, who won’t need to get the sheep in every five weeks to do so.”    

Justin added that due to the warming climate, another aim was to introduce more eczema resistance into the flock.