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Posted By: Bibby - Farm Vet

The Mystery of the Dying Lambs

I was asked to look at a group of lambs, these lambs were born the previous spring, some of the group had died and the remaining animals were in poor body condition, despite being feed additional concentrate and having access to hay. The owners of these animals were very worried about them.

We discussed the history of the lambs, this group were born in the spring of 2016, had been vaccinated with Heptavac P to protect them against clostridial diseases and Pasteurella Pneumonia. Over the last couple of months these lambs had routinely been treated with a benzimidazole group wormer. Despite the owners best efforts the lambs had still remained under conditioned and some still died.

When I visited the flock there was unfortunately another dead lamb. She was also in poor body condition and had faecal soiling around her back legs, suggestive of a case of scour. After discussion with the owner we felt that it would be a useful tool to perform a post mortem exam of the dead animal, to help determine the cause of death. In the hope that that information would be able to help save the other lambs.

Whilst on the visit we examined the other alive lambs, some of these lambs were also showing signs of scour with faecal matter around their back legs. We caught these animals and took sample to help identify the cause of their ill thrift.

There are a few very common causes of Ill thrift and scour in lambs, one being gastrointestinal parasites (worms), Protozoal parasites for example Coccidia and Liver fluke. These lambs were showing typical signs of sheep with a heavy gastrointestinal burden. However, their owner had been routinely dosing them to try and prevent infection. We chatted through when and how much the lambs were getting and by all accounts they were being treated perfectly, and with the right amount.

Back at the practice I looked at one of the sample and was able to identify a very high number of gastrointestinal worm eggs. We measure the number of eggs we see per gram of faeces. There is a scale: Below 250 Eggs Per Gram (EPG) being a low level of infection, between 250 and 700 EPG as a moderate infection and above 700 EPG as a high level of infection. These little lambs had a worm egg count of over 1000 Eggs Per Gram. So despite treatment these lambs were suffering from a very high worm burden.

The post mortem of the dead lamb also confirmed that the gastrointestinal parasites to be the cause of death, poor growth rate and scour. When the stomach of the lamb was opened up, hundreds of little worms were identified. These worms cause damage to the lining of the stomach, which means the lambs are not very efficient at digesting food, which result in the scour and weight loss seen.

Now we had identified the cause of the problem we needed to fix it. These lambs needed to be wormed with an effective anthelmintic. All the lambs in the affected group were wormed with an Ivermectin Group wormer, different to the one that had been previously used. I suspected that the worms that were infecting this group of lambs had become resistance to the previously used wormer. Benzimidazole resistance is fairly common in the UK. To ensure that the product we used on this occasion was effective, I asked the owners several days post treatment  to bring in another dung sample from the lambs. In the practice we performed a Worm Egg Count Reduction Test, this is to look for a reduction in the number of worm eggs per gram. To ensure that the treatment has been effective, we want to see a reduction in the number of eggs by 95%. On this occasion the worm egg count was 0 Eggs Per Gram. I was confident now that we had found an effective treatment.

The lambs are now a lot happier, they are starting to put on condition and are not scouring. Going forward we plan to monitor Worm Egg Counts to identify when we need to treat these lambs again.

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