Chris Gregory BVSc MRCVS, Molecare Veterinary Services
Over the last two articles we have looked at how to define the risk of liver fluke infestation in your herd, and the considerations around choice and timing of flukicide treatment at winter housing. The final article is intended as a round-up of the remaining factors influencing a fluke control plan.
Other considerations when building a fluke control plan
Giving the dose
After heeding all the advice and purchasing the correct product for the correct timing, the practicalities of giving the dose come in to play.
Yes, drenches invariably end up redecorating your handling system and staff; pour-ons get splashed around and injectable products are an open invite for pinched fingers and needle stick injuries. The point is, is that all the methods have pros and cons, but there must be a consistent methodology to accurately apply the correct dose.
- Solid handling system:
99% of anything to do with livestock revolves around safe, systematic, sympathetic handling. I guess the other 1% involves a bit of luck!
For example: head-scoops for drenches; good crush side-access for injections; slow handling to ensure pour-ons are applied consistently; and a million other examples according to the intricacies of each handling system.
- Well maintained dosing apparatus:
Without doubt the most common pitfall. Leaks, blockages, air ingress, perished washers can all lead to variation in doses administered. Always check and calibrate the equipment before use and wash out between uses. A simple measuring jug, old 50ml vet syringe or proper measuring cylinder will do the trick for checking calibration.
- Selection of appropriate dose:
Weighing animals pre-dosing allows for the most efficient use of product. However, it is vitally important to double check the accuracy of the weigh scales themselves and always allow for a percentage of dose wastage when calculating. If weigh scales are not available, I would still advocate some empirical method to estimating weight rather than eyeball e.g. weigh tape. This is mainly to reduce variability in dose rate and more importantly, to prevent under-dosing.
Under-dosing will not only be a waste of time due to lack of efficacy, it could also promote flukicide resistance. Sub-lethal doses select for the most naturally resistant flukes being treated, these survivor’s resistance traits become more concentrated either by repeated exposure to the same active or miss-use of the product (i.e. under-dosing).
Overdosing mainly risks unnecessary cost, though going over-board could mean straying off-label into veterinary cascade territory or even potential side-effects of overdosing.
The key to a good herd fluke plan is to reduce the pasture risk (i.e. risk of re-infection) as well as treating the animals.
All the usual recommendations to avoid ‘flukey’ ground:
- Fence off permanent wet spots
- Avoid excessive poaching of pastures
- Clean drinking water sources
Bear in mind that fluke ‘eggs’ (metacercariae) can survive on pasture for months under wet and mild conditions. Whereas periods of drought and higher temperatures will kill fluke eggs off.
As flukicides have no persistent activity, cattle out-wintered could re-infect post treatment if grazed on the same pasture. Use faecal egg counts/coproantigen to assess burdens later in the season to justify late winter/early spring follow-up treatments with the correct product, before moving to prime grazing.
Similarly, if cattle have been successfully cleared of their fluke burdens during housing, be mindful of the risk level of the pasture they will be turned out to. Tactical grazing of low risk pastures early grazing season could prevent build-up of fluke ‘eggs’ and slow re-infection, allowing time for higher risk pastures to undergo fluke egg kill-off.
Remember, the same fluke affect sheep and cattle so cross grazing can be risky with regards to ramping-up pasture contamination.