Page 70 - The Welfare of Cattle

CattLe eCtoParasItes 47

With adult flies typically on cattle for only a very short period of time, the application of
insecticides to cattle is generally of limited effectiveness for control of these pests. Horn flies
are the exception to this rule, as they spend most of their adult life on cattle and are there-
fore readily managed by application of insecticides to animals. Additionally, recent research
using insect repellents applied to cattle to provide short-term protection against horn flies and
perhaps other biting flies seems promising. Overall, these flies are best controlled by reducing
available immature development sites or by killing ectoparasites while they are concentrated in
development sites.
A somewhat unusual tick, the Pajaroello tick (Ornithodoros coriaceus), is found in animal
bedding sites throughout the California coastal mountain range and the foothills of the Sierra
Nevada Mountains. Unlike most other ticks of concern to cattle, this tick feeds multiple times
as an adult, with each feeding period lasting only 10–20 minutes. Since the 1950s, the Pajaroello
tick was associated with a condition of increased abortions in beef cattle called epizootic bovine
abortion or sometimes “foothill abortion.” Recently, researchers at UC Davis identified a bacte-
rium (Pajaroellobacter abortibovis) from these ticks that appears to be responsible for causing the
increase in cattle abortions.

eXteNSIVe VS. INteNSIVe SYSteMS: eCtOParaSIte MaNaGeMeNt

As mentioned earlier, a herd manager trained to recognize and control cattle ectoparasites
can reduce or even eliminate some ectoparasites, even when these ectoparasites are expected
based upon the type of production system. With respect to ectoparasite management, extensive
and intensive systems differ most importantly in the frequency and duration of interaction by the
herd manager and other facility employees with each animal, and in the ease by which animals
are gathered and treated for ectoparasites by topical application or injection of insecticides and
acaricides (see Table 6.2).
In intensive systems, the herd manager is expected to have much more frequent contact with
each animal as cattle are given daily care, to include providing feed and checking water sys-
tems. With the higher frequency of contact, herd managers should readily identify the presence
of ectoparasites while their abundance and impacts are low. Some extensive systems, such as
pasture-based dairies, may also require frequent contact between herd managers and cattle, thus
providing this same management benefit. But in many pasture systems, contact between the herd
manager and cattle is infrequent, limiting the ability of herd managers to recognize ectoparasite
problems until impacts to cattle production are noticeable. The importance of quickly recognizing
ectoparasite presence in the herd varies by ectoparasite. For example, early recognition that cattle
are infested with chewing lice may not be so important given their relatively low impact to cattle,
but recognizing that cattle are infested with New World screwworm when the number of infested
animals is small is incredibly important to avoid culling a large number of animals with gaping
wounds that are untreatable.
Cattle in intensive production systems are typically housed in pens allowing the herd manager
to easily quarantine parasitized animals or to efficiently administer insecticide treatments to all
or part of a herd. Cattle head gates, squeeze chutes, and alley stops built into intensive system
facilities make it relatively easy for herd managers to ensure treatment of all animals in a herd,
whether the treatment is an injectable, a topical pour-on, or a spray. In many extensive systems,
cattle are difficult to gather in one location and can be even more difficult to move through portable
squeeze chutes for treatment. The difficulty of treating animals in pasture systems is one reason
that insecticide-treated cattle ear tags have been widely used for many years for season-long control
of horn flies and face flies. Another recent improvement in treating pasture animals is the delivery
of insecticide to pasture cattle by firing an insecticide-filled gel capsule from a CO -powered gun
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