04.12.2023: Flies are often considered to common parts of a farm as dung beetles are of the dung heap. But the stable fly (Stomoxys calcitrans), also known as the barn fly, is a harmful blood-sucking pest. The present study by the University of Veterinary Medicine Vienna describes a case of massive stable fly overpopulation that resulted in severe harm to the pregnant sows on a pig farm in Austria. The researchers call for greater attention to be given to this harmful insect in order to improve the health and welfare of pigs.
In October 2021, the responsible herd veterinarian of a pig farm in Austria contacted the Swine Clinic at the University of Veterinary Medicine Vienna, reporting of numerous pregnant sows with bloody crusts over their entire bodies with bleeding skin lesions. This had been preceded by a massive increase of flies in the stable, but neither the farmer nor the veterinarian had been able to determine the species.
Thirty-three of 55 sows were affected by moderate to severe skin lesions, reproductive performance decreased during the time of the stable fly overpopulation, and pregnant sows exhibited defensive behaviour before resigning to being bitten at some point. Following control of the fly population, reproductive performance improved and even exceeded the performance before the infestation.
Risk to animal welfare and health of pigs
“Stable flies represent a serious danger to pigs and should be kept in mind for improved animal health and welfare,” says the study’s first author, Lukas Schwarz from the Swine Clinic at Vetmeduni. “Restlessness, pain due to biting, stress, loss of blood, reduced feed intake and local skin inflammation after biting are direct influences affecting the bitten host,” says Schwarz, summarising the immediate health impacts.
Knowledge about how to identify Stomoxys calcitrans and early recognition of an increasing stable fly population in pig farming systems, followed by proper insect control measures, are necessary to reduce losses caused by this harmful insect.
Other mammals, birds and humans also directly affected
The stable fly occurs in pig-producing countries worldwide. But while the impact of this blood-sucking insect is quite well-described in cattle, its role in pig production has been poorly investigated so far. The biology of the stable fly is quite different from that of the commonly known house fly, despite their similar appearance, and reproduction is linked to decomposing organic matter such as plant materials.
The stable fly may also act as a vector transmitting various pathogens through the bite. Humans may also be directly affected, as the stable fly feeds on human blood as much as it does on other mammals or birds.
The article “Bleeding skin lesions in gestating sows of a piglet producing farm in Austria” by Lukas Schwarz, Flora Hamar, Tanja Bernreiter-Hofer, Igor Loncaric, Mirjam Arnold, Thomas Voglmayr and Andrea Ladinig was published in Porcine Health Management.