Many different species of flies can cause problems for cattle. In this chapter we will briefly cover the two most important fly species currently affecting cattle - the house fly (Musca domestica) and the stable fly (Stomoxys calcitrans).

Both flies breed in manure and are therefore also referred to as filth flies. Other fly species presenting a risk to cattle are the blow fly (Calliphora spp), face fly (Musca autumnalis), and horn fly (Haematobia irritans) among others. A practical estimation of the economic effect of different fly species under normal conditions is very difficult due to the large fluctuations in the economic parameters of animal production. There are, however, some data that illustrate the damage that flies can cause to livestock.

Animal health needs environmental health

Controlled studies in dairy farms in the U.S. have shown that an infestation of house flies results in a 3.3% reduction in milk yields and that stable flies cause a 9.3% yield reduction. U.S. studies of 27 cattle ranches (feedlots) over two years involving some 14. 905 head of cattle found that stable fly problems led to a reduction in weight gain of between 2.3 and 3.5 kg per animal per season.

Stable flies can be very disturbing to animals; they stamp their feet and swish their tails to try to get some relief from these biting pests. All this effort costs energy and distracts the animals from feeding. This loss could be overcome for the most part if the animals were fed additional feed concentrates, however, this practice incurs in higher expenses for the farmer.

Fly problems result in reduced daily gains

In addition to these direct losses there are other potential indirect losses that must be considered. Flies are known carriers of many different animal and human diseases such as pinkeye, anthrax, brucellosis, tuberculosis and mastitis as well as Streptococcus and Staphylococcus wound infections. In addition, they can transmit Salmonella, Shigella and Escherichia coli pathogens as well as some protozoan diseases.