Mr Forlong says at least seventy percent of the stock on his farm have never been drenched.
"Sooner or later drenches will fail and it's proving to be the case now where as instead of taking 20 years to fail, some of them are failing very much sooner and there's not likely to be new drugs researched," he says.
Farmers and experts have long known the effects over-drenching can have. It's an ongoing issue for the rural sector.
Veterinarian, Ben Hodgson says the animal health community is starting to better understand how incorrect drench use can be detrimental in the long term.
"We're starting to get more complex resistance where we have worms that are resistant to two or even three different drench chemicals. So even the triple combination drenches which are relatively resistant are no longer effective on some parasite species combinations," Mr Hodgson says.
That's why Mr Forlong says he puts pressure on the stock.
"They can go into a contaminated pasture, get a challenge and deal with it."
"I believe the parasite's job from my point of view is to stimulate the immune system - because all we're looking for are sheep with a very good immune system that can deal with parasites and whatever else," Mr Forlong says.
Over in Mahoenui, Russell Proffit breeds his stock for eczema tolerance and says weather has a part to play in his decision to drench stock for protection or not.
"If I had a choice and didn't have to drench I wouldn't, but there's a fine line. You've got to make an economical call and an animal health call," Mr Proffit says.
He says farmers manage their properties in different ways, but ultimately all farmers want to see the same thing, healthy productive stock.
"Every day I go outside, I want to see healthy stock. Why would I want to go and see a sick animal? We live outside, we enjoy what we do. If you're dealing with healthy stock it's far more enjoyable."
Mr Proffit's neighbour, Anna Nelson is also a registered vet. She says managing parasites is a balancing act.
"I think that we all need to use drenches. We need to use them very wisely, not overuse them, because we want to be here farming in another 20 years, and we need the drenches to still be working for us.
"So when the animals are requiring treatment we need to do it, to ensure that they stay healthy. We want our animals to be really thriving and doing well, because in turn we will do better when they are," she says.
Mr Hodgson says "the ideal solution is to prevent them getting parasites in the first place and we can do that with good feed management, rotation grazing and strategic use of drench. You can farm without drench. It's just more difficult and tends to be less productive."
Mrs Nelson says farming on a larger property with more stock makes it difficult to individually monitor all sheep.
"There's obviously people that have made good progress trying to breed animals that are resistant to worms, and that is a really useful thing to be able to work towards, but it is really slow progress," Mrs Nelson says.
According to Dave Leathwick of AgResearch, internal parasites cost New Zealand sheep, beef and deer farmers an estimated $700 million per year in lost production and treatment costs in 2015.
Mr Leathwick says there's not a lot of data showing the level of drench resistance in New Zealand, and more funding is needed to provide that information.
"Things are not getting a lot worse really fast like they are in some other countries. We have to take some credit for that in New Zealand, that we've gotten on top of the problem faster than most other places around the world."
The last national survey of drench resistance was completed in 2005.
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