At this time of year store lambs should be at least maintaining condition, though with the recent very wet weather they may have had a set back. However if they are failing to thrive it is worth investigating the reasons as to why. It could be a combination of factors that are involved such as liver fluke, worms, trace element deficiencies or inadequate nutrition.
For example in a batch of bought-in store lambs that we investigated last month there was a high worm egg count in the group, despite the lambs having been wormed about three weeks before, and there were also cobalt and selenium deficiencies. The high worm egg counts could have been due to either re-infection on heavily contaminated pasture or due to resistance to the wormer that was used. The lambs were not heavily stocked, had plenty of grass and at this time of year they shouldn’t be picking up high levels of worm challenge. It is therefore likely that the roundworms had resistance to the white drench used, which is a common occurrence in flocks across the country. The lambs have now been dosed with another class of wormer and are going to be dosed monthly with a cobalt-selenium drench.
If you are concerned about the effectiveness of the wormers that you are using in your flock it can be checked through doing worm egg counts 7 or 14 days after treatment (depending on the wormer used). Speak to one of the farm animal vets if you are concerned about the growth rates in your store lambs.
In the last few weeks we were involved with another flock which had lost over 30 bought-in store lambs, most of which were sudden deaths. In this case the lambs were thriving but on-farm post-mortem examinations found that the losses were due to pulpy kidney. This is one of the most common causes of deaths in growing lambs and it is often the better lambs that die suddenly. A vaccination course e.g. two doses of Ovivac P Plus given 4-6 weeks apart provides protection to lambs against pulpy kidney. It also gives cover against Pasteurella infections which are another common killer of lambs.
Catriona Ritchie BVMS MSc MRCVS Buchan Vets Large Animal Team