By Vet Dan Lawson
One of the main classes of wormers is macrocyclic lactone commonly known as ivermectin.
It is a very popular wormer type often used in its easy pour on preparation. However, research has shown that as much as 80-98% of this wormer passes out of the animal unmetabolized.
Once it is excreted it can remain in the soil for 180 days. Whilst this will obviously have consequences on aquatic and invertebrate life on the land it has also been shown to have a large effect on the grass yield itself.
Grass is the primary aspect to the majority of diets of ruminant species, therefore one of the most valuable commodities on farm, that a large amount of time and money is spent on to improve. With
research showing that such a large proportion of the wormer not being broken down before being excreted from the livestock, we must consider the large impact it has on the grass that is grown.
Research has shown that land that is spread with faeces contaminated with ivermectin showed a massive reduction in grass yield between 18-20%. This incredible effect on yield shows the large unintended effect that the use of ivermectin can have on grass yields, and therefore on farm productivity and profit.
This highlights the need to only use these products when necessary and not use a blanket approach to just worming when you “normally” would. Faecal egg counts are a vital tool to monitor the level of worm burden in your flock. As vets and farmers we have a responsibility to use all medications responsibly to avoid resistance.
Therefore, faecal egg counts play a key role in helping us to decide when and if the livestock need to be wormed and are used alongside the history from the farm and this has been a regular discussion point for many years.
They are typically used in lambs, as adult ewes in good condition with no concurrent infections will usually have good immunity due to previous exposure.
There is an increasing issue of resistance with the different classes of wormers due to unnecessary use in the past, therefore it is important to assess the current situation on your farm.
This can be done by a faecal egg count reduction test, it is used to assess whether the wormer has been effective. When taking samples you should take 10 individual samples or 10% of larger groups, this can be done by bringing the sheep on to some hard standing for a short time to ensure a fresh sample as possible. This test should be run as soon as possible, therefore we are able to run the test in house to ensure swift turnaround of results and prompt advice can be given.
The faecal egg count reduction test is done by comparing the faecal egg counts from before and after treatment. The second sample should be taken 7 days after treatment for levamisole (2-LV) and 14 days after for the other anthelmintic classes. This helps to monitor the effectiveness of the wormer and guide us to see any resistance issues on farm. There is suspected to be anthelmintic resistance if there is not a reduction in the faecal egg count by 95% or more.
Overall ivermectin, one of the most commonly used wormers, can remain in the soil a long time and have an incredible effect on the yield of grass, therefore we can use faecal egg counts to guide the correct time to worm the livestock to avoid unnecessary contamination of the land.