The summer grazing period is a crucial time for sheep and cattle production, as farmers strive to make the best use of grass, the cheapest form of feed. Taking a targeted, informed approach to managing the impact of parasites during this time is vital to protecting future returns.

The July NADIS Parasite Forecast, sponsored by Merial Animal Health warns that July and August will be a crucial time for parasite control in lambs. Peak pasture larvae contamination will occur during the coming months, as lambs develop significant worm burdens, passing increasing numbers of eggs onto the pasture, and favourable climatic conditions hasten the development of these eggs to the infective larval stage. The risk will depend on pasture management and treatments early in the season. Control strategies should take into account these farm-level risk factors for maximal effect.

Unmanaged gutworm burdens in lambs can have a negative impact on growth rates, increasing finishing times and may lead to parasitic gastroenteritis which causes scouring and can result in lamb losses.

Sioned Timothy, veterinary adviser for Merial, says: “Worm control in weaned lambs can be complex, so taking advice on the most appropriate wormer and worm treatment is a good strategy. Discuss your specific farm setup and previous flock management with your vet or local animal health adviser (SQP) who will be able to suggest the best group of wormers for your situation, and how best to incorporate them into your strategic worming programme.

Targeted worm treatments based on achieving predicted liveweight gain ensures that only lambs with worm burdens sufficient to impair their growth are treated. Although weighing and sorting lambs may be more time-consuming than group treatment, there are considerable benefits; reduced treatments and medicine costs, and reduced selection for resistant strains of worms, because not all lambs will require treatment. For this approach to be effective, advice should be sought from a vet or SQP on the right product for the flock and parasites present.

Implementing treatment based on faecal egg counts (FEC) can also help achieve a balance between reduced selection for wormer resistance and minimizing the production impact of parasites. The decision to treat a group should be based on the FEC result from a pooled sample taken from at least 10 lambs.

Treating the whole flock or group at regular intervals, without the use of any diagnostic test (liveweight gain or FECs) is not recommended. This approach can reduce the effectiveness of wormers over time by increasing selection for wormer-resistant strains of parasites, especially when lambs are grazing relatively safe pasture. If this approach is used, measures should be taken to minimize the selection pressure, such as leaving around 10per cent of fitter animals within a group untreated.

Other issues during the summer months include tapeworms and blowfly strike. Tapeworm segments are commonly seen in faeces passed by lambs during July and August but are not generally of clinical significance. Blowfly strike is a major risk from June onwards which can be reduced through effective internal parasite control, to minimize scouring since this may predispose sheep to blowfly strike.

“Strike prevention is the best form of control,” says Ms. Timothy. “Spray-on products containing insect growth regulators (IGRs) will prevent infestation, but will not kill maggots that are already present.

“Where sheep have already become struck, farmers should use topical products containing a synthetic pyrethroid (SP), or a diazinon based plunge dip to clear the problem. These products may also provide protection against blowfly strike and treat other external parasites; farmers should consult their vet or animal health advisor to ensure they are using the most appropriate medicine for the circumstances”

In cattle, the NADIS Parasite Forecast reminds farmers to be alert for signs of lungworm in animals of all ages during July and August, especially in unvaccinated herds. Production losses occur from reduced milk yield in lactating dairy cows, reduced growth rates in youngstock, and the cost of replacements where individual losses occur.

“Strategic worming programmes using broad-spectrum wormers such as those containing ivermectin (IVOMEC® Classic, IVOMEC® Super - which also contains clorsulon) and eprinomectin (EPRINEX® ) to control gutworms, will also help prevent a severe lungworm infection,” says Ms. Timothy. “Achieving a balance between exposure to lungworm larvae to build immunity, and treatment to prevent disease is key to short and longer-term control of this damaging parasite.”

She continues: “Lungworm should be suspected in cattle of any age that are coughing at grass, and if diagnosed, farmers will need to treat the whole group. Ivomec classic (injection or pour-on) is suitable for beef cattle and dairy youngstock, whilst Eprinex (pour-on) has the benefit of zero milk withhold for adult dairy cows.”

Incidents of clinical PGE will peak in cattle during August and September if preventative measures have not been implemented. Where young cattle have receiving strategic treatments for gutworm, it is important that they remain set-stocked on the same pasture for the entire grazing season or are moved to safe grazing, such as silage aftermath. This will to ensure they are not exposed to additional worm burdens.