Treating only underperforming lambs for worm burdens has seen a Welsh sheep farm cut its wormer use by more than 45% while maintaining weights and performance.
Glyn and Chris Davies introduced Targeted Selective Treatment (TST) into their system at Awel y Grug.
This parasite management approach involves administering treatment solely to lambs failing to meet specific performance benchmarks, primarily daily liveweight gain (DLWG).
Historically, the Davies’ would have routinely treated all lambs within the affected group if intervention was deemed necessary.
The Moredun TST protocol was trialled on their farm at Cefn Coch, Montgomeryshire, as part of a Farming Connect ‘Our Farms’ project.
Independent livestock advisor Matt Blyth, who provided support during the year-long project alongside sheep consultant Kate Phillips, says that in TST system performance targets are based on the minimum daily liveweight gain a lamb should be able to achieve between two weighing points.
These targets consider previous recorded weights, the quality of feed and its availability, feed conversion ratios, weather conditions at that time, and which stage the lambs are at in their production cycle.
Matt says the expectation is that when those conditions allow lambs should exceed the minimum growth rate targets, but even those that only just achieve it are unlikely to need a wormer drench either.
“Research has shown that lambs consistently achieving at least the minimum target are generally coping with their parasite burden and do not require worm treatment at that time,” he explains.
Cutting wormer use has multiple benefits, Matt adds, and some that are harder to quantify such as the flock having less exposure to anthelmintics and the environmental benefits of using less chemicals in agriculture.
“By identifying and treating animals that didn’t meet their target weight, Glyn and Chris saved around 52% of the cost of the drench they would normally use if they were blanket treating all animals in a group,” he says.
Lambs in the project’s control group were dosed four times on average; those animals weighed an average of 15.3kg at the start of the trial and 27kg at its conclusion.
In the TST group, doses averaged 2.2, those lambs weighing an average of 16kg initially and 28.4kg when the final weights were recorded.
Lambs were weighed every three to four weeks and their performance assessed against set growth targets.
Those that were on target or had exceeded it weren’t drenched. “Even if there was a parasite burden, it was not significant enough to be limiting growth,” says Matt.
Lambs that failed to hit target weight were flagged up for closer investigation, he adds.
“They were more likely to require treatment as poor growth could have indicated a higher internal parasite burden that could have affected their performance.”
Other possible causes such as lameness, trace element deficiencies, external parasites, poor nutrition, and other health issues were also considered.
For these reasons, TST should not be used in isolation, Matt advises.
“Close collaboration with a veterinary surgeon or a livestock consultant is essential to correctly interpret performance data and understand what is happening within the wider farm system,” he says.
A small number of lambs were treated consecutively - three had to be treated every time they were weighed which suggested there was an underlying problem, Matt adds.
These lambs might have been reared by a younger ewe, their mother suffering from mastitis or had rejected them, or the lambs may have had other health issues.
“If there had been a higher number of lambs that had to be treated every time, further investigation would have been required to understand why they were not able to meet the minimum target weight throughout the five weighing sessions,” says Matt.
Throughout the project drench efficacy was tested by routine faecal egg counting using FECPAK.
This system monitors worm resistance and worm burden and should be used in conjunction with advice from a vet or other animal health professional, Matt recommends.
When those samples were taken was dictated by the active ingredient in the specific drench, either seven days after treatment when the yellow wormer 2-LV was used, and 14 days after the clear wormer 3-Ml.
Cost savings are an obvious positive outcome from using less drench but there are also other positives although these are harder to quantify - reduced exposure to anthelmintics and environmental benefits among them.
The uncalculated costs are the labour and time diverted into weighing every animal.
One of the challenges at the start of the project was getting the technology working efficiently together but once it was up and running it worked and there were positive outcomes for livestock and savings for the business, although it required significant support and intervention, Matt says.
Another cost that was not factored into the savings and other benefits was the financial outlay for handling equipment, software and hardware.
Matt says this equipment would have had additional uses on the farm though and not only been used for this work. “The capital investment of this equipment is however a significant cost to a business.”
Glyn and Chris opted to buy a high-spec setup, including a combi clamp, which allowed the process of implementing the TST policy and administering the correct dose for each lamb's weight to be streamlined.
But for others considering TST, the system isn’t reliant on top-tier technology, says Owain Pugh, Farming Connect Red Meat Sector Officer for mid Wales, who supported the Davieses with the project.
“TST can be implemented by using entry-level weigh heads and EID readers that are compatible with third-party apps, alongside a standard crate weigher,” says Owain.
“Drafting lambs into groups for treatment is a practical and budget-friendly approach that still allows for accurate recording and handling.”
For Glyn and Chris, the project has been so transformative that they will never revert to blanket treating lambs.
“I plan to use TST for the rest of my farming life,” says Chris.
Establishing the exact weight of each lamb and administering a corresponding dose makes sense in many ways, he adds, recognising that guessing lamb weight by visual assessment is unreliable.
“We have had 52kg lambs recording FECs of 1000 eggs per gram but are gaining 350g a day off grass without drenching so it looks as if they are building resilience.”
One of the reasons he was keen to trial TST is that the farm has developed a resistance to white drench as historically it was the only type of wormer used at Awel y Grug.
By avoiding blanket treatments, he hopes to prevent building resistance to other drenches.
TST has also seen Chris closely scrutinise the flock’s breeding as some ewe lambs that were frequently drenched in 2025 only gained 50-60g a day.
“I have been monitoring genetic lines as lambs from those lines are never going to grow into big strong ewes, we don’t want those genetics in the flock.”
TST is just one of the tools available to sheep farmers to help with parasite management.
If using, Matt recommends taking FECs and doing a FEC reduction test to confirm that the anthelmintics used on farm are working efficiently.
Farmers should also monitor nematodirus forecasts, visually assess lambs, and get professional guidance from the farm vet or advisor, he adds.
FARM FACTS
129ha owned land farmed
Land rising to 366m
Rotational grazing
800 Welsh Mules, Texel-cross and Nelson-type Welsh ewes
Lambs sold through Welshpool livestock market