WARM, wet weather may prompt rapid development and release of worm larvae onto pastures, increasing the risk of productivity-limiting parasite burdens in sheep this summer. 

Lambs grazing permanent pastures will become exposed to infective larvae as part of the ‘mid-summer rise’ that results from pasture contamination earlier in the grazing season. Warm, wet weather will speed up the process of worm development and the release of larvae from faecal pellets. But if conditions turn dry for a prolonged period this can delay larval challenge, with a return to infectivity when wet weather arrives.

Sioned Timothy, ruminant technical manager at Merial Animal Health, says: “It’s important to take a sustainable approach to worm control in lambs in order to limit selection pressure for anthelmintic resistance, but using the right approach, worms can be controlled effectively and growth rates preserved.”

“Moving weaned lambs onto aftermaths during July and August can reduce the risk of parasitic disease. This simple management practice reduces exposure to the high larval challenge that builds up on pasture and is one of the most critical components of sustainable parasite control.”

For worm control strategies to remain effective getting to grips with any resistance already present on the farm is critical – this will allow appropriate product selection, and allow a farm specific plan to be formulated. The use of targeted selective treatments (TSTs) in lambs can reduce the likelihood of selecting for resistant strains of worms. TSTs allow a pool of unselected parasites to pass out eggs onto pasture helping to maintain wormer efficiency in the longer term.

Regular weighing of lambs every three to four weeks and monitoring of lambs’ body condition helps to target selective treatments to lambs that are failing to meet expected growth rates. Lambs that are in good body condition and performing well can be left unwormed. In general only 40-60% of lambs require worming.

Not all parasite problems pose the greatest risk to young sheep. On affected farms, sudden outbreaks of haemonchosis can occur sporadically in sheep of all ages. High faecal egg counts and warm, wet climatic conditions that favour larval development, can lead to a rapid increase in challenge. The disease is characterised by anemia, sub-mandibular oedema (bottlejaw) and in severe cases sudden death. 

Notably, unlike other worm infections, diarrhea is not generally a feature. Many wormers, including Oramec® (ivermectin) and some flukicides, such as Trodax® (nitroxynil), are effective against this species of roundworm, and advice should be sought from a vet or animal health adviser on the most appropriate option. 

While in cattle, lungworm infection begins to pose a threat to unvaccinated and naïve young stock and adults from July onwards.In cattle, lungworm disease may appear from June onwards, especially in unvaccinated youngstock, cattle that have not received anthelmintic treatments, and naïve adults. 

Early signs of lungworm include coughing and an increased respiratory rate, and severely affected animals may experience sudden weight loss. 
Ms Timothy says: “On farms where lungworm is a recognised risk, first season grazers should have been vaccinated prior to turnout. However vaccination does not entirely mitigate the risk of lungworm, and farmers must remain vigilant for the early signs of disease. The prompt use of a fast-acting wormer as soon as lungworm is diagnosed, is recommended.”