On Tim and Richard Sheil’s farm on the Wexford/Carlow border, the lambs’ performance on grass was again somewhat disappointing and the brothers have attributed this to resistance to wormers.
o They ran drench trials of four different products to see what worked in their herd where lambs were weaned at 14 weeks.
Research shows that there is widespread resistance to dewormers (anthelmintics) on Irish sheep farms.
Treating lambs with products that do not provide the desired control is a waste of time and money and the resulting high worm load leads to poor performance.
do a drench test
The easiest and least expensive test to check if your dewormer is working is the drench test. This test measures the number of worm eggs in the manure before and after administration.
They cost €10-12 plus VAT per sample depending on which lab you use.
Generally, for a dewormer to be considered effective, it should kill at least 95 percent of the worms present.
■ The first step is to select approximately 20 lambs from the group to be tested, mark them clearly so you know which lambs need to be retested after the established time frame for the different deworming classes (see Table 1 below) and assign them to leave a clean pen for an hour or two to defecate.
■ Collect a sample (a teaspoonful) of at least 10 different fecal debris and place in a sealed bag for shipment.
■ Treat the lambs with the wormer to be tested – weigh the lambs and calibrate the dosing gun to ensure the dosing rate is correct.
■ Send the stool samples to a laboratory as soon as possible after collection, preferably the same day and at the beginning of the week so that they don’t sit in the mail over the weekend.
■ In the laboratory, the 10 faecal samples are pooled and the number of worm eggs in the total sample for the 10-15 lambs is determined as a group average.
■ After a specified number of days, repeat the process by collecting a second sample from the same group of lambs
– about 7 days after the first test when a yellow wormer was used and 14 days when a white or clear wormer was used.
The four products Sheils tested were Endospec (white dose), Chanaverm (yellow dose), Noromectin (clear dose of ivermectin), and Cydectin (clear dose of moxidectin).
In the case of Chanaverm and Noromectin, the worm count actually went up after treatment, so these products are considered totally ineffective on Sheil’s farm.
Endospec reduced worm counts by 70 percent, which is still considered a soak-through failure because the 95 percent target was not met.
Cydectin resulted in a 95 percent reduction and is therefore considered fully effective.
So now Tim and Richard know that Cydectin is pretty much the only effective vermifuge on their farm, they must try to protect its effectiveness for the future. Some simple steps you can take to support this are:
■ Use a white wormer earlier in the year to treat Nematodirus worms. Tim and Richard, like many farmers, now know that white wormers are not effective against intestinal worms on their farm, but there is no known resistance to white wormers in the treatment of Nematodirus.
■ Do not dose adult ewes. Older flocks have generally developed good immunity to intestinal worms, so adult ewes should not require routine treatment for these unless they demonstrate a need. This minimizes the amount of resistant worms that are returned to pasture
■ Quarantine dose – incoming sheep should be treated with one of the new anthelmintics (orange or purple) and held for 48 hours. They should then be moved to contaminated pastures recently grazed by sheep.
With previous use in the yard, there is no resistance to these products. They generally only require a prescription from your veterinarian; Trade names are Startect and Zolvix.
■ Continue to use fecal egg counts to determine when to treat and which classes of dewormers are effective on the farm.
In lambs, group faecal egg counts greater than 500-600 eggs per gram may impair performance and indicate the need for treatment for intestinal worms.
Lower egg counts usually do not require a regimen, saving time, labor and money, and prolonging the effectiveness of wormers working on the farm.
Tim and Richard spent a total of €123 including VAT to test the four products and are now equipped with important information.
For such a modest expense, this is something every sheep farmer should be doing.
At the Sheils’ farm, all lambs are raised on preferred grass such as aftergrass, reseeds. The ewes are used to clean up fields and paddocks that graze behind the lambs; 25 ewes were identified for culling after weaning for typical reasons such as mastitis, lameness and age to reduce stress on the turf.
Fertilizer is targeted to fields and paddocks that provide the best response at a rate of around 20 units of nitrogen – fresh overseeds/high ryegrass content/good soil fertility, etc.
Some high clover fields were skipped in the last round and have recovered quite well, with coverages of around 1,200 kg DM/ha now available for grazing.
James Doran is a Teagasc Drystock consultant based in Enniscorthy
https://www.independent.ie/business/farming/sheep/advice/how-drench-testing-can-save-you-time-and-money-and-boost-lamb-performance-41929610.html How drench testing can save you time and money – and improve lamb performance