Flies are notorious for causing a nuisance to cattle but are you aware they can be responsible for more serious issues, such as the transmission of disease between animals?
In the UK there are at least 20 species of fly which feed on cattle. Different species of flies feed on different secretions or tissues. Some pierce the skin and feed on blood; while others feed on secretions such as sweat, skin secretions, saliva, or tears. Some flies even feed on excretions such as urine or faeces.
There are two ways in which flies cause harm to cattle:
Animals which are exposed to a high fly challenge can become extremely aggravated and may cause injury to themselves, other animals or even those handling them e.g. kicking in the parlour. The evasive behaviour taken by the animals to try and alleviate the irritation caused by flies’ results in less time feeding, causing reduced productivity. The impact of such irritation on the welfare of the animals must be considered a priority.
- Disease- Spreading Vectors
Flies can act as vectors meaning that they have the ability to spread certain diseases between animals by biological or mechanical means.
Biological transmission occurs when the fly is carrying the pathogen, usually from a blood meal - for example Bluetongue virus carried by the Culicoides midge.
Mechanical transmission occurs when pathogens are passively transferred by the fly from one animal to the other. The spread of ‘pink eye’ bacteria from one animal to another demonstrates this form of transmission.
Vector Borne Diseases of Cattle
Summer mastitis occurs generally in non-lactating animals (cow and heifers) during the summer months. It is a bacterial disease caused by a number of bacteria acting synergistically. It is believed to be spread primarily by the fly Hydrotea irritans.
In cattle, large numbers of this fly cluster on the ventral abdomen and udder and the bacteria is mechanically transmitted from animal to animal.
The fly Hydrotea irritans lives in sheltered areas such as bushes/trees and only has the ability to fly in very calm, damp, humid conditions. As a result of this, the incidence of summer mastitis is highly variable and tends to be associated with ‘problem fields’ e.g. adjacent to woodland.
Disease may be present for up to a week before the animals appears systemically ill which is why it is important to check stock frequently during high risk periods. Be observant and look for swollen/enlarged teats - the consequences of summer mastitis are severe and animals may abort/die if untreated.
Infection Bovine Keratoconjunctivitis
This disease often goes by ‘New Forest Eye’ or ‘Pink eye’. It is a highly infectious disease caused by the bacteria Moraxella bovis. It can spread rapidly during the summer months and is more common in young stock. Head and nuisance flies act as mechanical vectors for the spread of this disease. The ocular lesions are very painful and disrupt grazing patterns resulting in poor performance and weight loss.
Blue Tongue and Schmallenberg in cattle
Both of these diseases have been shown to be transmitted by the Culicoides species of fly.
Bluetongue virus is generally not symptomatic in cattle. However, cattle act as reservoirs of infection which can be transmitted to sheep causing more severe disease.
Schmallenberg rarely shows clinical disease in adult animals and often the first suspicion of disease occurs when a deformed calf is born. Where it does affect adult cattle, it causes milk drop, fever and diarrhoea.
Medicinal products e.g. Deltamethrin pour-on are available which can help to control flies. Your local vet or SQP can help determine which is most appropriate to meet your needs.
- Target Larvae Development
Manure, spilled feed or any moist, organic matter can act as larvae development sites. Either ensure the prompt removal of such matter or use an insecticide growth regulator, such as cyromazine. It works by preventing larvae from developing into flies, thus reducing the overall fly challenge in the environment.
- Environmental Control
Avoid grazing ‘problem pastures’ at peak risk times where possible and consider the use of environmental approaches, such as fly paper of traps.
Your local vets and SQPs have a great deal of fly control knowledge so speak to them for advice and they can help you to design an appropriate strategy for your herd.
About the Author
Rachel Mallet is a Veterinary Surgeon, who now works as a Professional Services Vet providing technical support to vets, SQPs and farmers in the UK. Rachel is passionate about animal health and about promoting best practice and preventative medicine amongst farmers.
Use medicines responsibly. Noah.co.uk/responsible.
*Dectospot contains 10mg/ml deltamethrin and is a POM-VPS medicine.
The following active ingredients have indications for fly control in cattle: Deltamethrin, Alphacypermethrin, permethrin, cypermethrin cis 50: trans 50, moxidectin, doramectin, ivermectin.
Please consult your SQP or vet to determine which is the most appropriate for your herd and consult the SPC data sheets on the VMD website for further information on which species of fly are controlled and with which preparations.