Drenching our grazing animals is often seen as the single solution to dealing with internal parasites (worms). However, resistance of internal parasites to drenches is an increasingly serious issue facing not only large commercial sheep farms, but anyone who grazes animals. Resistance is now an issue on most farms, and in most species, including cattle, horses, sheep and goats.
Therefore, any use of drench should be considered as part of an overall control plan, rather than a single solution. Many of you will be aware of the strategies below, but this is one situation where it’s important to get the basics right. Unfortunately, there is no simple recipe to suit everyone and you should seek advice specific to your property.
- Adult animals (except goats) generally have good immunity to worms and can be used to “clean up” pastures grazed by younger animals that haven’t yet had time to develop sufficient immunity. Avoid having only young stock repeatedly grazing the same paddocks year after year.
- Cows are affected by different worm species to sheep and goats or horses or alpacas so different animal groups can be used to “clean up” worms of other animals on the property by alternatively grazing paddocks.
- Effective drenching involves targeting treatments to animals that require treatment and good drench selection and technique.
- The need for treatment can be monitored by collection of dung samples and assessment of the number of eggs present (faecal egg count). Faecal egg counts can also be used to monitor the effectiveness of the drench used.
- Adult stock generally have good immunity and don’t require routine drenching. The exceptions are barbers pole worm (Haemonchus) which can affect adult sheep and alpacas typically in summer/autumn, and goats which tend to be susceptible to parasites throughout their lives.
- Time drenching to when high numbers of worms are likely to be present. Worms grow best in warm, wet conditions so numbers on pasture are highest during spring and autumn.
- Select a combination drench that contains two or more active ingredients and help to slow the development of drench resistance to the individual ingredients. (Beware: praziquantel doesn’t count as an action family here)
- Ensure animals receive the correct dose for their weight and are not under-dosed.
- Check drenching equipment is delivering accurate doses.
There are a huge number of drenches available on the NZ market, and not all are created equal! It is important to seek the right advice as to which product is right for your situation, and how best to control parasites on your property. Talk to the team at your Franklin Vets clinic.