In the last 2-3 weeks the national network of VI centres have diagnosed severe gutworm infections (otherwise known as parasitic gastroenteritis) in first grazing season calves in south-west Wales and south-west England, with diarrhoea, dramatic condition loss, and mortality of up to 10% reported.
Very high worm egg counts of up to 45000 eggs per gram of faeces have been identified. In these cases calves had last been wormed in July. Gutworms should always be considered in first season calves at pasture showing diarrhoea or condition loss.
Current outbreaks are likely a consequence of high rainfall in August/September allowing gutworm larvae to develop on the pasture, leading to high risk of infection. The hot, dry conditions in May-June likely reduced larval activity meaning development of immunity was reduced, making calves especially vulnerable this autumn.
Speak to your vet for further advice.