Last summer, biting midges caused obvious skin irritation and carcass downgrading on pigs farms across the region. To stop these costly consequences this year, farms have fitted insect screens on pig houses and they have made changes in manure management to discourage the pests.

Reports of biting midges are rare in the literature, Jesus Borobia-Belsue of MOSSVET reported, while the importance of parasitic arthropods in pig production varies, depending on the geographical location. No studies have been reported into the economic costs, which would be challenging as the effects are mainly in terms of reductions in performance and carcass value.

In May 2013, following a long winter in Northern Ireland, weather conditions suddenly improved. Four days after the start of this warmer and sunny weather, a routine veterinary visit to the farm revealed the first clinical signs of dermatitis in the pigs.

Within two weeks later, two slaughterhouses commented on the increased incidence of dermatitis, with 62 producers affected; prevalence ranged from 30 to 100 per cent of the pigs. One producer was penalised as more than 650kg of his pig meat was condemned.

Investigations revealed that the lesions in both live pigs and carcasses were multi-focal, slightly raised and hyperaemic and ranged from 0.5 to 2.0cm in diameter and distributed over the body. Affected animals appeared uncomfortable with pruritis (itching), which led them to rub themselves against the pen surfaces.

The symptoms eased after about three weeks.

As insect bites were suspected at the start, aerial traps were placed above the finishing pens on four affected farms for two weeks.

Species trapped were Musca domestica (house fly), Drosophila melanogaster (fruit fly), wood/window gnats of the Anisopodidae family) and Culicoides obsoletus. This is the midge linked to the spread of Schmallenberg disease in cattle and sheep.

Some of the Culicoides species [pictured above; source Agri-Food and Biosciences Institute of Northern Ireland, AFBINI] were found feeding on the live pigs and were sent for to a laboratory, which confirmed their identification.

The farmer also developed similar lesions on his arms and legs.

All affected farms had natural ventilation and no insect screens were fitted.

It is hoped that further outbreaks will be prevented by treating the slurry with insecticides to kill the larval stages, regular slurry removal, tidying up the area around the farm, application of insecticides to kill the adult flies and fitting insect screens to the houses.

These measures are accepted to eliminate the need for trimming of carcasses around the bite areas and future condemnations concluded Mr Borobia-Belsue. If used incorrectly, the use of ectoparasties on the pigs could produce residues in the tissues.