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Strategic Worming of Ewes at Lambing – what does this mean in practice?

Stephanie Patel BVetMed MRCVS

This is a question frequently asked and the reasoning not always well understood….

As most of us are aware, anthelmintic resistance continues to be a growing problem and with increasing cases of triple resistance being discovered on sheep farms, it is important that we are careful in how and when we use wormers. Remember that every time an anthelmintic is used, we are exposing that population of worms to the product and when some of the worms survive treatment, they will form a resistance and become dominant overtime. This is where resistance of wormers on farm develops and is something that needs to be carefully managed in order to reduce the negative impact this can have on effective worming treatments. It is therefore important that around lambing time a more strategic approach to worming is implemented to slow the growth of resistance. 

Unlike lambs and young sheep, adult ewes for most of the year have a good immunity to worms and should therefore not require regular worming. However, during late pregnancy and early lactation, this immunity dips due to the stresses on the ewe, also known as periparturient relaxation of immunity, which means that worm egg out-put can be increased from these ewes, therefore increasing the pasture contamination.

This is however dependent on the individual animal, and there will be cases where pregnant ewes do not have an increased egg output, and so the risk of significant worm burden is much lower. The variation in egg output within the pregnant ewe is determined by many factors, including but not limited to: how many lambs is she carrying, what other disease exposure has she had, nutrition, body score and quality of pasture. It is these varying factors that need to be identified and assessed in order to create a strategic worming protocol for your ewes.

Managing worm risks through husbandry and nutrition

Dietary protein in late pregnancy, specifically with bypass protein or DUP (digestible undegradable protein) is important as it will help to increase birth weights, improve colostrum and milk production as well as decrease egg production.  Combined with scanning the flock will mean more efficient (and cost effective!) targeted feeding. 

Keeping ewes in good body condition throughout pregnancy and in the run up to lambing will also help to put less stress on the immune system. The following body conditions should be aimed for at lambing time for ewes, (breed dependent) they are as follows: 3.0-3.5 lowland ewes (60-80kg), hill ewes (40-60kg) 2.5 and ewe lambs 3.0. 

How do you decide which ewes to worm?

It is important to build a clear picture of nutrition, body soring and fetal number for your flock. Once this has been identified, you should then be able to see which animals are under the most stress, which can predispose them to significant worm burdens during later pregnancy. Those at greater risk tend to be triplet bearing ewes, thin ewes, or the younger ewes in the flock.

Through targeting worm treatment, it is estimated that between 10 and 20% of the grazing stock will not fall into the treatment categories, therefore reducing the impact of worm resistance on farm. Combining this strategic, evidence-based approach to worming with faecal egg count testing for each group of ewes will also help to further reduce and target treatment where it is most needed and will be most effective.

For more information on strategic worming protocols, or for more advice on preventative healthcare for your flock please email [email protected]

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