Sheep farmers can reduce worm burdens in lambs and improve their 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. This is known as the spring rise.

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

This is 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.

The group receiving the short-acting anthelmintic had low FECs initially, increasing from 4 weeks after lambing. The control group had a higher FEC than either the short acting or long acting treatment groups. Ewes and lambs in the control group required treatment for parasites at week 5 after lambing and week 7 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 could equate 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% but by controlling worms in lambs can add an extra 4.7kg livestock during the season.

The lowered egg output and ewes potentially ‘hoovering’ the pasture meant that throughout the season the 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.

Tackling the spring rise could mean potentially less worm treatments throughout the season.

Ashleigh Bright, head of science at FAI Farms said: “Periparturient ewes represent the major source of gastro-intestinal parasites for growing lambs and are therefore a priority for parasite control. The findings from this study suggest injecting ewes with long-acting moxidectin 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.

“Therefore, we advise it is used 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.”