For the last 10 years, our national flock has been coming to terms with the issue of worm resistance. This is where the parasites (roundworms) are becoming resistant to the treatments (anthelmintics) we have used for decades.

The parasites are doing this because of an innate ability to survive and also because some of our own actions on farm which have enabled this process. They do this by genetic mutations which makes them resistant to the mechanisms by which these wormers previously paralysed or killed them. This is coupled to the fact that it’s over 35 years since we’ve had a new product in the market.

Last week, Teagasc published data on a study carried out into worm resistance in Irish cattle. They took 20 dairy to beef farms and used the three active worming agents we use or have. These are the white (benzimidazoles), yellow (levamisoles) and clear (macrocyclic lactones, ivermectins).

They discovered resistance to all three wormer groups across a number of farms. The level of this resistance varied but the key point was that it was clearly identified that we have resistance issues on our cattle farms.

This may seem alarming but is not surprising considering we know frequent use over time of these products on parasites means they adapt and become resistant.

Is this something to worry about?

While grazing grass is a unique advantage we have in this country, one of the key challenges in a grazing system is the control of parasites.

Over the last 10 years, I’ve increasingly seen this as a growing problem. We have more intensive grazing on short rotations and very favourable weather conditions most years for worms. To maximise grass utilisation, we look to graze down to 4cm the same place most of these parasites hang out.

When rotationally grazing, we have animals shedding eggs in their dung which leads to the build-up of parasites in those pastures. Mild, wet winters, springs, summers and autumns have also posed an increased risk. The parasites mostly have life cycles which are reliant on mild, wet conditions. So parasite numbers, which to this point we have managed with more intensive dosing protocols, are growing.

We have become very reliant on these products and use them frequently. This lends itself to the development of resistance. They have become very cheap and anything cheap often can be undervalued.

This has led, particularly with the ivermectins or clear drenches, to frequent usage. Often we see larger volumes being sold, sometimes with a free jacket as an incentive for the sale. There is nothing wrong with a free jacket for the winter, but it shouldn’t determine which type of dose you use.

I spoke with two farmers recently who had lungworm in dairy calves in May. Another farmer I met blamed the quality of the product because it didn’t seem to work. This is something I myself have queried but it’s possible that it was just resistance I was seeing.

Resistance can also develop through poor practices around application of products, particularly under dosing, which means the worms are exposed to smaller quantities, which speeds up the development of resistance.

The Tesgasc study found resistance (at varying levels) on all 17 farms where ivermectin was used. There was less resistance to yellow drenches, possibly due to them being used less frequently. The problem is that every farm might be different and I would say many farms are lucky to have no resistance yet.

So what can we do?

Firstly, it is no harm to know how to test for resistance on your own farm, particularly if in any doubt about how well products are working. You can use a FECRT (faecal egg count reduction test) where before dosing take a faecal egg count (measurement of numbers of worm eggs in the faeces), then worm dose and repeat the FECRT. The second FECRT is done at a certain time after dosing 14 days for clear/white doses and seven days for yellow doses.

What we should expect to see is >95% reduction in the numbers of eggs, meaning a dramatic kill of the adult parasites which produce the eggs. Anything less than a 95% kill rate can indicate a level of worm resistance once dosing has been carried out correctly.

There will be no “one fits all” model when planning dosing for farms. What does work is to sit down and plan out an on-farm dosing regime that can slow down this resistance.

For some farms, this may mean reduced amounts of dosing and for others it may mean changing products and timing. Like most problems, if ignored it will get worse and some tough decisions may be needed around prescribing of these products to put value back into them.

If the person selling you them doesn’t know what a worm life cycle is, the parasites it kills, how to use it and what worm resistance is, they shouldn’t be allowed to sell the product.

We really need to pull up our socks on this one and maybe forego the free jacket.

Worms and winter

In the third of our four-week series on beef health for the winter, we look at controlling worms at housing. Follow our video series online, where Adam Woods and Tommy Heffernan talk through worms for the winter.

In our beef herds, cold and wet spells for the last week mark the beginning of winter housing and also a key time to manage worms at housing. Worms have a life cycle which involves eggs being passed out in dung developing through a number of stages into infective larvae when eaten develop into adult worms.

The problem is every adult worm produces thousands of eggs which leads to build-up of parasites over time particularly these larvae in pasture. As they get older, animals can develop a resistance to most of the roundworms. This can only be done when exposed to small numbers over time, which doesn’t always happen in every farm.

Worm resistance is now something we need to have on our radar.

So when it comes to worming cattle at wintertime, the main parasites we are thinking about are gutworms and lungworms.

The symptoms for gutworms can be mild to poor thrive, scouring and coughing with lungworms. So even without these symptoms being present, often we will choose to dose cattle at this point to clear them out.

How can I work out the risk?

It is no harm in beef herds before winter housing to run some FECs to check for worm eggs.

The options for wormers seem massive, with nearly 150 brand names on the market. However, we only have a choice of three active agents – white, yellow and clear. When deciding on a wormer, look at what you have used previously and for how long. As a general rule, I recommend rotating wormers every two to three years. Next thing is to work out which route, which is often decided by product and also by handling facilities and time.

More and more we use ivermectin pour-ons for simplicity. Understandably, we are always looking for an easy life but generally depending on this method alone for many years is not sustainable. Watch our video as we chat through making decisions when choosing wormers.

A question that comes up every year is whether cows need a worm dose or not. I have said previously that cattle develop immunity to worms over time so the theory would be they don’t. This has been complicated by the fact though that parasite burdens seem to be increasing on some farms. We are also more liberal with our dosing in young stock on some farms, leading to this immunity not developing.

So to worm cows or not is very much a farm-specific question. I always recommend making that decision by taking a pooled worm sample from six to eight older, thin or cows we aren’t happy with. Use this as a gauge with your vet on dosing decisions.

As we now become more proactive around the use of wormers, a question that arises on some farms is – are there cases where we are using wormers where they are not needed?