That is due to the peri-parturient relaxation in immunity of the ewes, leading to a rise in worm burden and faecal egg output around lambing time. In many situations drenching at this time is not only beneficial for the ewes but also for their lambs. However, the products available are not made equal.
For many obvious reasons it is not advisable to yard ewes any later than 2-3 weeks prior to lambing. This means short acting products, such as oral drenches, will simply not be persistent enough to have much of an effect on the peri-parturient rise. They do however have a place in treating existing infections. So if you have a problem with high winter worm burdens they may be beneficial at this time.
One option is long acting (LA) moxidectin based injections (e.g. Exodus LA®, Eweguard®). They can have a beneficial effect on the peri-parturient rise, are quite cheap on a per head basis and are easy to administer. However, they also pose the greatest risk to the development of drench resistance; being a single active and also having a ‘tail’ like effect of decreasing product levels in the animal. If you wish to use these products it is pertinent you know your farms drench resistance status so you can properly assess whether the product will actually work and that you follow our guidelines for the safe use of pre-lamb anthelmintics.
The other option is controlled release capsules (CRC’s). These are specially designed to deliver a constant rate of product at therapeutic levels over a 100 day period. They are far superior to oral drenches and LA injections when it comes to pre-lamb drench treatments. They have been proven to deliver results and aren’t as risky when it comes to drench resistance if compared with LA injections. There are many products available on the market with most being single actives, thus knowing your drench resistance status again is essential for these to be useful. If drench status is somewhat unknown the only option is the double active Bionic capsule which contains abamectin and albendazole.
A few guidelines for the safe use of pre-lamb anthelmintics:
- Good conditioned ewes and good pasture covers at lambing time are far superior to any pre-lamb drench treatments. If you can get this right then there is often no benefit in using pre-lamb drenches.
- Never drench all ewes in a mob. Even though trials have shown that no matter the body condition of the ewes all are affected equally by parasites, and thus all show a positive response to treatment; this benefit is probably more economical when applied to only the tail enders in the mob. For this reason we recommend targeted treatment, selecting only those ewes that require the extra help e.g. low BCS ewes (1’s and 2’s), in lamb hoggets, twinning 2-tooths and triplet bearing ewes.
- Maintain refugia! This goes hand in hand with number 2, a proportion of every mob should be left un-drenched so the worms they produce have never been exposed to the pre-lamb drench. This will help preserve your drenches and slow the overall development of drench resistance on your farm.
- Exit drenches should be used especially after using single active and long acting products.
- Monitor FEC’s during treatment to assess whether the product is working. This means doing FEC’s at roughly 60-80 days post capsule administration and roughly 30 days post LA injection.
- Consider whether trace element supplementation is actually all you need. Recent trial data has shown that on some farms a proportion of the production benefits seen from the pre-lamb drench treatments can simply be put down to the trace elements they contain. Supplementation could be a much cheaper way to increase the performance of your ewes this spring.