One thing’s certain about 2016 worm threat: It’s unpredictable!
From most areas of the UK, feedback suggests that last year was one with low to moderate roundworm burdens, according to Zoetis vet Dave Armstrong. “Where this was identified using good diagnostics,” he says, “economies from using fewer wormer treatments were possible with manageable risk rather than a fingers crossed approach.
“Looking ahead at the 2016 grazing season, price pressure on finished lamb and beef, or indeed milk, mean intense scrutiny on costs of production. It is important however to understand that cutting cost may actually have an impact on production, exacerbated if the parasite challenge is high.
“For example, fewer worm treatments because of known low parasite burdens on pasture can offer genuine savings. But it would be false economy in the face of moderate to high infection pressure due to the impact of roundworms on growth rates.”
Whichever of these may have applied in 2015, independent ruminant specialist Kate Phillips suggests that there is no guarantee of the same this year. “Despite Jaunary’s frosts, the warmest December since records began could help create much higher than usual over-wintering of worm burdens,” she says.
“This applies equally to sheep and cattle. Clearly, a balance must be struck between avoiding unnecessary use and cost of wormers on the one hand, and pursuing a growth rate dividend when worming is justified on the other.”
With the latter in mind, gastrointestinal worms can reduce summer growth rates long before signs start to show as loose faeces and dirty rumps, according to former SAC adviser Dr Basil Lowman. In growing cattle for example, he has said unseen worm infections could easily reduce growth by 0.1kg a day [ref ].
On good pasture, 1kg/day live weight gain should be possible, according to a factsheet published by Eblex (now AHDB Beef & Sheep) [ref ]. But a mere 10% shortfall could mean 20-30 days of additional feeding next winter to reach a target weight, or selling a 20kg lighter beast in the autumn. Either way, the likely extra cost is in the region of at least £40/head. Kate Phillips suggests that the same principles can apply proportionally to lamb growth rates post-weaning.
For further information, please contact your local veterinary surgeon or SQP.
 Dr Basil Lowman, 5 February 2007. Interview with author. SAC beef specialist. Comments re-validated by Dr Lowman 22 March 2011.
 Eblex press release (viewed 27 Oct 2010). Eblex challenges beef producers on grass performance. http://www.eblex.org.uk/news/beef-producers-on-grass-performance.aspx.