Agriculture Reference
In-Depth Information
conditions, the ratio reverses, with 95 percent of the worm population in the
grass and 5 percent in the sheep. It is possible to worm the sheep but impos-
sible to worm the pasture. Logic, then, dictates that the most opportune time
to deal a severe blow to the new season's worm population is before the sheep
begin grazing the pasture, so they cannot transfer or “seed” the pasture with
a new worm population. The sheep should be wormed 2 or 3 days before
turning out on pasture so that the eggs are left in the feces in the barn or lot,
where the larvae cannot survive.
Many people practice a double drenching with an oral worm medication
in the summer in dry climates, which they say reduces the worm burden for
the season. They worm the ewes during dry weather and follow up with a
second worming 6 weeks later; this normally reduces the worm burden below
harmful levels. Hot, dry weather signifi cantly reduces the larval population in
the pasture, thereby reducing the infection rate in the ewes. It is also helpful
to move sheep to a clean pasture 24 to 48 hours after each worming to help
keep the pasture clean.
External Parasites
Most external parasites are more of a nuisance than a major health threat
for sheep, but there are some exceptions. The following external parasites
can all have substantial economic effects on a shepherd's operation, and may
occasionally be deadly.
■
Sheep keds (a.k.a. sheep ticks)
■
Lice
■
Maggots
■
Nose bots
■
Scab mites
Sheep Keds
Sheep keds used to be known as sheep ticks, but they are not true ticks. A
sheep ked is a wingless parasitic fl y that produces little brown eggs that are
white inside; the eggs hatch into almost mature keds in about 19 days. These
keds pass their whole life cycle on the body of the sheep, so the best way
to avoid this problem is never to buy sheep infested with them. Be sure to
inspect closely animals you are considering purchasing for any sign of keds!
Sheep keds suck blood and roam all over the sheep, puncturing the skin
to obtain food. These puncture wounds cause development of fi rm, dark nod-
ules that damage the sheepskin and reduce its value. (These defects are called
