At this time of year flies can often be a nuisance on livestock farms resulting in compromised welfare and performance. Hannah Noble looks at chemical-free solution to helping control fly populations.
Horn flies, head flies, face flies and stable flies are the most common species found irritating livestock on farms in the UK.
Tom Jackson, of LLM farm vets, says flies not only cause annoyance to animals, but are vectors for the transmission of numerous diseases.
He says: “In calves, flies mostly cause a nuisance, irritated calves will spend less time lying down and eating and generally unsettled, this can impact welfare and have a detrimental effect on growth.”
However, infectious bovine keratoconjunctivitis, also known as New Forest Eye, can spread quickly in calf groups if there is a substantial problem with flies. It causes painful lesions on the eye leading to corneal ulceration and temporary blindness, some severe cases may even call for the removal of the affected eye. This condition also causes welfare concerns, reduced intakes and ultimately reduced growth rates.
Summer mastitis can also be spread by flies, and can occur in both cows and in-calf heifers. Mr Jackson says getting summer mastitis in heifers at this age can often mean they calve down with three quarters.
He says: “AHDB quotes the average cost of summer mastitis is between £250 and £300 in treatment, lost milk and performance, in addition to compromised welfare, pain and irritation to the animal.”
The conditions associated with disease caused by flies may require treatment with antibiotics, and in a time where farmers are facing pressure to reduce their use of antimicrobials, alternative methods of prevention could prove valuable.
Most farmers will routinely use pour-on insecticides to treat the animals directly or with chemical sprays in the parlour to kill the flies as and when it becomes a problem throughout the whole season. However, most pour-ons have a lower age limit, which can make it difficult when treating calves.
Mr Jackson also says it is not just the welfare of the livestock which is compromised with the presence of a large population of flies, humans are also affected and he says people do not want to work in sheds that are filled with biting and nuisance flies.
He says: “A lot of the chemicals used to control flies are quite unpleasant and are not great for human heath, sometimes they can cause breathing difficulties.”
For most farmers treating flies using chemical methods is usually a reactive response – treating a problem once it already exists. Parasitic wasps however, are used by some farmers to proactively reduce and prevent the problem before it gets out of control.
Mr Jackson says these parasitic wasps have been shown to reduce population of stable flies by between 25 and 50 per cent, with some data showing a reduction of 90 per cent.
Biological pest control may seem like a relatively new practise in the UK, but for several years it has proven popular on cattle, pig and poultry farms in the USA.
Mr Jackson says: “Parasitic wasps, which are only a couple of millimetres long and harmless to livestock, parasitise the eggs of the nuisance flies.
“They actively seek out fly eggs and lay their own eggs inside. When the parasitic wasp eggs hatch, the young eat the fly egg and then go on to lay more eggs of their own.
“The wasps do not travel more than 30 to 40 metres once they hatch but they will seek out fly eggs in the area.
"More importantly they will not parasitise any other species so they are no danger to beneficial insects or honey bees.”
In the UK, Defra and Natural England have granted permission for the release of two indigenous species, Muscidifurax raptor, which has a life cycle of 18 to 24 days and Spalangia Cameroni which has a lifecycle of 21 to 28 days. During their lifetime each wasp produces between 30 and 60 eggs.
Mr Jackson explains the parasitic wasps are imported from Texas as pre-parasitised fly pupae, and are then distributed around the farm in 12 to 20 targeted areas identified as fly breeding sites, typically muck heaps, slurry lagoons and straw yards.
The amount of fly parasites required depends on several farm factors such as the number of cows and muck build up. As a rule of thumb one bag of parasites should be distributed per 100 cows but this may need to be increased if there is a heavy muck build-up or severe fly problem on the farm during the summer months.
Mr Jackson says the application of the parasitic wasps should take place from April through to September and needs to be repeated every two weeks to keep up with the speed of fly reproduction.