Tools to use 

This year, and hopefully for the foreseeable future, I’ll be attempting to use a new tool on the farm; a microscope. I purchased this microscope last year after having trouble with parasites in the sheep. My idea is to use this microscope to monitor parasite levels in the flock to show when they need to be treated with a dewormer, and also to select rams with lower levels (more resistant to parasite infection) which will then lead to a more resistant flock over time. 

An example of a parasite egg seen through the microscope on the left. The large black circles are air bubbles.

In the past, recommendations were to deworm all your sheep at prescribed times of the year. While this helps prevent death loss and performance losses, it has led to the worms becoming resistant to the dewormers we can use. So over time, they become less effective, and eventually will no longer have much impact at all. The most up to date recommendations (to my knowledge) are to treat only when parasite levels reach a certain threshold, and preferably treat only the animals which themselves have high levels. Determining which individuals need treatment is not easy, as often parasite loads increase quickly, and the animals affected don’t always show clinical signs. In a perfect situation, you would take fecal egg counts of each animal, but with 1000 animals, it is not practical. There are some animals which generally are more susceptible, such as lambs compared to ewes, which you can focus on. This summer, I have been collecting and analyzing fecal samples from a few random lambs at key times, and before we have brought the animals in to handle. This gives me an idea of the parasite infection level in the flock and whether they need to be treated. This summer the levels have been low enough that I have only dewormed a few animals which show other signs such as anemia and poor body condition. This has cost and labour savings which has paid for the microscope several times already.

There is a lot of genetic differences in the susceptibility of individual sheep to parasites. In years that are dry such as this one, the parasites do not survive well so levels in all sheep are pretty low. In wetter years, the variability increases and susceptible animals are easier to pick out. My goal is that over time, by selecting more resistant rams, I will be able to continue to improve the flock and minimize the number of animals requiring treatment. 

I joined in a webinar just the other day which focused on genetic selection to improve resistance to parasites. The slide below shows the big difference a sire can make, especially in a wet year (2004 in this case). 

Sire differences. FEC stands for fecal egg counts, which give an idea of level of parasitism (higher numbers meaning more parasites) and PCV is packed cell volume, indicating level of anemia (lower numbers meaning more anemic).

This tool is something which with a bit of practice and training, any producer could use to reduce the parasite levels in their flock. It would lead to less reliance on commercial dewormers, meaning those would be useful for a much longer period of time.

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