Farmers must be on high alert for worms in their lambs after a break in the weather is expected to cause a dramatic rise in the risk of worm larvae on pastures.  

Independent sheep vet Fiona Lovatt said the risk is usually a week or two following rain after a dry spell, with current warm and wet conditions creating perfect conditions for worms to 'get going'.  

She said: "When it's been incredibly dry, faeces remain compact when they fall and are not dispersed by rain, so the risk to lambs from worms is relatively low as the larvae are hardly able to escape onto the pasture. However, as soon as the rain arrives and it breaks up the faeces, it provides the perfect conditions for infective larvae to emerge from the dung and complete their lifecycle."  

And she warned that following rain, the risk to lambs can rise dramatically, but it may take longer for the Faecal Egg Counts (FECs) to catch up. 

She said: "If you saw high FECs earlier in the spring, there will have been contamination. The FECs may have gone low in the dry, but the chance is high they will suddenly spike again after rain. 

"The challenge can happen so suddenly there isn't always time for farmers to see a rise in faecal egg counts before there's a clinical problem, especially if they took a count just as the rain arrived. This is because there will be a lot of infective larvae but not yet adult worms laying eggs." 

"It's essential to be alert after rain and to take good advice, as the challenge could be sudden and devastating," she warned. "Generally, I like farmers to be both monitoring growth rates and taking general condition into account alongside relying on FEC tests." 

Low worm egg counts are currently being reported on most of the farms in dry regions involved in the Zoetis Parasite Watch Scheme, though, as always, there are regional differences. 

The network of 26 farms monitors worms and fluke every couple of weeks throughout the risk period, with results uploaded in real-time. However, it's a situation that Zoetis Vet Patricia van Veen expects will change suddenly.  

"As Fiona explained, worm egg counts are expected to rise quite dramatically over the next fortnight, especially on farms where high FECs were seen earlier in the year. The sudden change in weather will also provide optimum conditions for flies and maggots. You should speak with your health care professional now about the most appropriate parasite control for both worms and flies," she said.  

Keep abreast of the latest parasite data in your area using the Parasite Watch forecast at www.parasitewatch.co.uk