Reports from farmers and vets highlight an increased risk of a spike in worm burdens in lambs.
Hatching of worm eggs is likely to have paused during the prolonged period of dry weather and relatively high temperatures with eggs lying dormant in dung and on pasture.
The rainfall which followed will have triggered these eggs hatching out into infective larvae quickly, completing their lifecycle.
Many farmers report a significant jump in worm egg counts despite, in many cases, an absence of any visible challenge. The reports are greatest in the east of the country with sporadic rainfall along the west coast meaning worms were in many cases completing their lifecycle leading to a continual but lower challenge.
Highest risk
The greatest risk from 1 June onwards is generally from strongyle worm species, sometimes referred to as roundworms, although depending on the lambing date and previous dosing regimen there may still be flocks faced with a threat of nematodirus.
The lifecycle of strongyles is pretty straightforward – eggs hatch and develop into infective larvae.
Once ingested by susceptible grazing lambs infective larvae develop in to adult worms.
These lay eggs which are passed on to pasture and the cycle begins again.
Worm counts therefore give a good indication as to the level of worms present.
The small limitation that exists is where a mass hatch occurs with a high number of larvae causing a significant loss in performance before this becomes evident in the worm count.
The characteristic signs of a worm burden are reduced performance in terms of weight gain and flesh cover and while scoring can be evident of a worm burden it is not a reliable measure.
Therefore, the best approach is a combination of worm counts, monitoring lamb performance and keeping informed as to the risks from reports from other farms.
The process of carrying out a faecal egg count is relatively straightforward.
A random sample of 10 to 15 lambs should be penned together, leaving time for them to defecate.
Samples should be collected and stored in suitable containers.
These can be obtained from the lab or vet carrying out the faecal egg count.
It is important that samples are submitted for analysis quickly.
Where posting, they should be posted on the day of collection and this should be timed so that samples are not in transit over the weekend. If samples are being retained they should be stored in a cool area and stored in a fridge if retaining overnight.
When interpreting results a faecal egg count of 600 eggs per gram or above for strongyles generally indicates a need for treatment. Treatment of lambs with a low egg count is wasteful of resources and can advance the rate of anthelmintic resistance occurring.
Unfortunately, anthelmintic resistance has limited the active ingredient that can be selected to treat lambs with resistance common to the three main classes – benzimidazoles (white), levamisole (yellow) and macrocyclic lactones (clear).
For this reason, it is becoming increasingly important that you know if anthelmintic resistance is an issue on your farm and the efficacy of products used.
This can be determined by carrying out a faecal egg count reduction test.
This is treating animals the day that you carry out the faecal egg count and carrying out a follow-up faecal egg count to see if it delivered the desired effect.
The timing of carrying out the second faecal egg count is important. For white and clear wormers the post-treatment samples should be collected two weeks post-treatment while for yellow wormers the follow-on faecal egg count should be collected one week after treatment.
Remember, faecal samples must be collected from the same lambs so it is important to mark these clearly on the first day.
Product selection will be closely aligned to knowing what products work on your farm.
Where there is resistance to the three common anthelmintic classes described above, it is important to consult your vet or adviser to develop a programme that will deliver the best possible outcome. This may include sequential treatment using two different active ingredients.
In such cases, there will be greater cognisance taken of the species of worm presenting the challenge.
The two new wormers, Zolvix (amino-acetonitrile derivatives – orange wormer - 4-AD) and Startect (spiroindoles – purple wormer -5-SI) were launched in 2010 and 2012, respectively. These products are prescription-only medicines with Startect unavailable in Ireland in recent years.
Their use should be restricted to safeguard their efficacy and most dosing programmes combine their use in biosecurity /quarantine treatments and possibly as a targeted treatment later in the season to give all animals a clean bill of health.
The rate of resistance developing can also be slowed by adopting the following practices which were discussed at the recent Sheep 2023 event in Gurteen Agricultural College.
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