Page 67 - The Welfare of Cattle

44 the WeLfare of CattLe

Host Contact by Ectoparasite Life Stage(s)
Contact with Cattle
Immature Adult
Permanent Ectoparasite
Intermittent Ectoparasite
Temporary Ectoparasite
Persistent feeding on blood or body tissues of one animal
Brief feeding on blood or exudates, no or limited host fidelity

Figure 6.1 Category of cattle ectoparasites and host association by life stage.

time spent off the host (intermittent ectoparasites), or they may contact hosts only briefly during one
or more life stages to feed on blood or body exudates (temporary ectoparasites). In addition, some
insect species may not feed on cattle, but can impact cattle production due to nuisance or transmis-
sion of pathogens acquired from animal feces (environmental pests).

Permanent ectoparasites

Permanent ectoparasites of cattle in North America include five species of lice and four species
of mites. The more damaging blood feeding lice are the longnosed cattle louse (Linognathus vituli),
shortnosed cattle louse (Haematopinus eurysternus), cattle tail louse (H. quadripertusus), and little
blue louse (Solenopotes capillatus). A single species of chewing louse, the cattle biting louse (Bovicola
bovis), feeds on skin rather than blood. Cattle mites feed on skin debris or lymph within the dermal
tissues and include the important scabies or “mange” mites Psoroptes ovis, Sarcoptes scabiei, and
Chorioptes bovis, as well as the cattle follicle mite (Demodex bovis). Feeding by lice and mites can
be quite irritating to the host, and may result in considerable physical damage due to dermatitis, tissue
destruction, and hair loss. Lice and mites can also cause damage to hides, particularly as animals rub
and scratch against objects in their environment to alleviate the itching caused by lice and mite feeding.
Heavy infestations of lice and/or mites can reduce weight gain and milk yield. Additionally, poor physi-
cal condition of heavily infested animals, often coupled with substantial hair loss, can result in death
of young calves and older cattle when exposed to severe weather conditions or low nutritional levels.
Management of lice and mites is commonly achieved by treating cattle with topically applied
insecticides and acaricides, and by limiting contact among infested and uninfested animals or herds.
Injection of ivermectin or related parasiticides may also provide control of lice and mites.

Intermittent ectoparasites

The New World screwworm fly (C. hominivorax) is intimately associated with the cattle on
which they live and feed during their immature life stages. The adult fly lays eggs in wounds of
cattle (and other animals) where the immature larvae (maggots) consume living tissue, a condition
called myiasis. Infested wounds often encourage additional egg deposition as wounds are expanded
by the feeding maggots. Damage to cattle caused by these flies can be severe, often resulting in
death of the animal when infestation is not promptly treated. The New World screwworm fly was
eradicated from North America by 1966 following years of mass releasing sterile male flies to mate
with wild female flies. This eradication effort is one of the greatest success stories of insect man-
agement by the U.S. Department of Agriculture! Unfortunately, New World screwworm flies persist
in South America and on some Caribbean islands, and a reintroduction of these flies to the Florida
Keys in 2016–2017 demonstrates that the cattle industry must remain vigilant. While release of ster-
ile males is the primary tool to eradicate these flies from a region, immediate control of screwworm