Sheep farmers can reduce worm burdens in lambs and improve growth rates by treating ewes with a long-acting wormer prior to lambing, a recent study has found.

Around two weeks before lambing until six weeks, post-lambing ewes are more likely to shed worm larvae due to decreased immunity, which in turn is known as the spring rise.

However, trial work by FAI Farms in Oxfordshire last year (2017), found that injecting ewes with a long-acting moxidectin or clear wormer, led to low worm egg counts in lambs throughout the study period.

This was compared to ewes that were treated with the short-acting clear wormer; doramectin or were not treated at all (control group). Both of these groups showed higher worm egg counts in lambs, according to Ashleigh Bright, head of science at FAI Farms.

“The group receiving the short-acting anthelmintic had low FECs initially, increasing from four weeks after lambing. The control group had a higher FEC than either the short-acting or long-acting treatment groups," said Ms Bright.

"This meant ewes and lambs in the control group required treatment for parasites at week five after lambing and week seven after lambing respectively (FECs >250epg). The long-acting group also showed reduced pasture contamination and higher lamb growth rates compared to the other two groups."

Between shearing and weaning, when lambs are at pasture, lambs from ewes treated with the long-acting product had numerically improved growth rates; they outgrew the untreated control lamb group by 1.7kg and the short-acting group by 0.7kg.

This extra growth rate equated to an additional £2.94 per lamb, in a 60-day period, when comparing lambs from the long-acting treatment group and the control or an extra £1.21 per lamb when comparing the long-acting treatment group to lambs treated with a non-persistent product.

Other studies have found that worms can reduce growth rates by up to 47% and wool production by up to 21%, and controlling worms in lambs, can add an extra 4.7kg livestock during the season.

Lowered egg output and ewes potentially ‘hoovering’ the pasture meant that throughout the season, pasture contamination continued to reduce in the long-acting wormer treatment group, further reducing the risk to lambs. The other two groups showed a rebound due to ewe egg output.

Hence, tackling the spring rise could mean potentially less worm treatments throughout the season.

“Periparturient ewes represent the major source of gastro-intestinal parasites for growing lambs and are therefore a priority for parasite control," said Dr Bright.

“The findings from the study suggest injecting ewes with long-acting moxidectin (Cydectin) prior to lambing could be useful as part of a flock parasite control programme. This is in order to minimise the use of other anthelmintic treatments in that breeding year, and by reducing pasture contamination for those sheep which will graze the pasture in the next year.”

However, she warned that combatting parasites and the associated anthelmintic resistance that has developed in recent years, requires a multi-faceted approach.

“We advise using a long-acting moxidectin as part of a holistic parasite control programme, including genetic selection based on resilience to parasites, grazing management, nutritional management, targeted selective treatment, effective quarantine procedures and grazing plants with anti-parasitic properties,” she concluded.

The study also found that single-bearing ewes produced fewer eggs and therefore contaminated less pasture compared to twin, or triplet-bearing ewes.

This is because the twin and triplet-bearing ewes are potentially drawing more protein for milk production so they have a greater immunity drop compared to single-bearing ewes.

As a result, Zoetis vet, Dr Dave Armstrong suggested it may be worth leaving the single-bearing ewes untreated and instead monitor their worm egg counts.

“With the annual cost of stomach worms to the British sheep industry estimated to be about £84m, sheep farmers need to be looking at ways to reduce losses on farm due to worms, but in a responsible way.

“This study clearly shows the benefit of using Cydectin® long-acting injection for sheep, to control the spring rise and reduce lamb worm egg counts throughout the season,” he said.

However, he also warned that controlling the spring rise will not prevent the potential issue of a Nematodirus outbreak. “This is because this worm does not overwinter in the adult sheep and in fact, overwinters on pasture and hatches when temperatures are between 10-14oC.

“If you use a long-acting wormer at lambing, you will still have to monitor the Nematodirus risk on your farm and take necessary action, if the risk is there. Farmers should also consider using an “exit drench,” which effectively means using one of the novel group four or group five wormers such as Startect® , in order to minimise the impact of future anthelmintic resistance,” he added.