Being a small holder or a hobby farmer is hard work but can show many benefits. As a small holder or a hobby farmer, you do have a responsibility to use wormers in the most efficient and cost-effective way. But you are also responsible for doing your part to prevent any resistance forming.
What is resistance?
Parasitic worms are becoming resistant to the available treatments, so a control strategy based around mass usage of these worming products is not maintainable long term. They are important and useful products but, as with antibiotics, they need to be used with care to make sure resistance doesn’t occur.
So why should small holders and hobby farmers be worried about anthelmintic resistance?
Wormer resistance is the loss of sensitivity to a drug in a worm population, that was previously sensitive to the drug. This resistance is passed on through generations of worms, as a genetic trait, so once it is on your farm it is there to stay.
It is important to note that it is not your livestock that have developed resistance, it is the parasites themselves.
What are the different wormers?
There are three wormer classes in cattle:
- Benzimidazoles (white wormers)
- Levamisoles (yellow wormers)
- Macrocyclic Lactones (clear wormers)
In sheep, we have these three and a further two more: Amino-acetonitrile derivatives (orange wormers) and Spiroindoles (purple wormers).
What practices encourage wormer resistance?
Frequency of worming
Every time you dose a sheep or cow for parasites you increase the risk of wormer resistance on your smallholding. The more frequently that livestock are wormed, the more quickly and easily worms can build a resistance. This is because we only kill susceptible worms – leaving space for those resistant worms to breed and succeed.
If you find that wormer resistance is present on your small holding, you may be finding you need to dose more regularly, change products, or you might find products ineffective. Reducing reliance on these products and using them only when necessary is a proactive approach.
Dose and move
Dosing animals and moving them to clean pasture used to be common guidance – now we understand that it is better to leave treated animals on pasture for a short time. This is so the excreted resistant worms can breed with susceptible worms on the pasture reducing the risk of breeding only resistant worm populations.
Underdosing
Another area that can encourage resistance is underdosing your sheep or cattle with wormers. This is because worms only receive a small dose of product, not enough to kill them, but enough to encourage resistance.
It is really good practice to ensure all animals are weighed and dosed correctly as this can help reduce the risk of resistance. Another common way to do this is to weigh the heaviest in the group and dose for that weight. If there is a wide range of weights, split the group and weigh the heaviest in each smaller group.
Blanket treatment
This is when all animals in a group are treated with the same drug at the same dose. This is known as ‘blanket treatment.’ Blanket treatment is one of the main drivers of wormer resistance and is quite commonly seen.
How can I avoid resistance?
A really good technique is to use faecal egg count (FEC) testing. You get a sample of faeces from a certain amount of livestock and this can give an indication of the worm burden on your farm.
Wormer resistance does not suddenly happen, it builds up slowly and you may not notice production losses until there is up to 50% resistant worm populations. You may notice weight loss, milk yield and failure to thrive.
When buying in new sheep or cows, it is good practice to put them in quarantine to avoid any mixing of the livestock to prevent your original livestock becoming hosts to resistant parasites.
How do I use anthelmintics effectively?
Effective use of wormers is all about using the right product, at the right time, at the right dose and with the right technique.
The right time
It is really important to use wormers only when necessary, because using it more often than that will increase the selection pressure on the worms. This then means you will end up with a resistant population of worms.
The right product
SCOPS and COWS are two expert-led schemes which give excellent advice and any farmer or livestock holder should regularly go to their website for lots of information and advice.
On the SCOPS and COWS websites, you will find a comprehensive list of products, detailing which parasites they target, how to use them, what trace elements they cover and the meat withdrawal period. Your vet or the pharmacist or SQP at your local retailer should be able to advise too.
The right dose
Before treating, the group should be weighed, so that the correct dose can then be calculated from the guidelines on the product label. If you are in any doubt over dose, it is good practice to seek veterinary advice.
Using too little will expose the worms to the anthelmintic, but not necessarily kill them, ramping up the development of resistance.
The right technique
It is really important to check all equipment is in working order and, for the most common method of administering anthelmintic, a drench gun will need to be calibrated. SCOPS and COWS have lots of useful information, if unsure please speak to your veterinary surgeon or SQP.
A good way to calibrate your drench gun is to use a pot marked with measurements, or the tube of a syringe without the plunger to do this. Squirt the dose into the receptacle and check that the amount dispensed is what it should be, without any air bubbles.
It is also good practice to make sure that any livestock are properly restrained so that the whole amount given is swallowed. The nozzle should be slotted in the gap between molar and incisor teeth and over the back of the tongue.
Injections must be administered as per individual product manufacturers guidelines.
Subcutaneous injectable treatments should be given with a clean, sterile, 1.6cm needle, under the skin of the neck, 10-15cm below the ear.
Typically, intramuscular treatments should be given with a 2.5-4cm needle, into the mid neck, aiming inwards and upwards towards the head, but it is important to check for each product used. Injection sites should then be massaged gently to distribute the drug under the skin/through the muscle.
Can we not just use another product if we have resistance?
At the moment there are no new anthelmintic products being brought to market. Ultimately, for now, what we have is all that is available. Once the worms on your farms have built up resistance to all these products, it is likely that parasites may once again become a severe health risk to the livestock, this is why it is really important we monitor and continue to do FWEC on the farm to help to avoid any resistance.
If you have any concerns about worms, resistance, worm egg counts or how to administer a product, please seek advice from your veterinary surgeon or SQP.
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