Agriculture Reference
In-Depth Information
larvae migrate onto the moist sections of the grass and are ingested by the
sheep. Once swallowed, they invade the tissues of the digestive tract, where
they undergo a maturing stage and emerge as adult worms in about 21 days.
Eggs or larvae or both usually die during freezing temperatures or hot,
dry weather; in many parts of the United States, these weather conditions
tend to “sterilize” the pasture. However, nature has devised a diabolical sur-
vival mechanism for these worms that allows them to survive adverse condi-
tions: they hibernate as immature worms in the tissues and emerge weeks or
months later when conditions for survival are more favorable.
Internal Parasite Control
Sanitation is critical for internal-parasite control. Feed shouldn't be placed on
contaminated ground or bedding. Water tanks and creep feeders should be
kept clean and free of contamination by fecal matter.
On pasture, especially on set-stocked pasture, a main factor contributing
to heavy parasite loads is population density. A few sheep in a given area
deposit fewer eggs than lots of sheep in the same area. Thus, fewer infective
larvae will develop. Sheep that are set-stocked generally have lower-quality
feed, which weakens them. They're also forced to crop the grass too close to
the ground, which results in ingestion of more larvae, increasing the worm
load and aiding parasites in completing their life cycle. When you move sheep
from one paddock to another with managed grazing (see chapter 3), you gain
some measure of control by allowing time for the worm larvae to die. Sheep
managed this way are also generally better nourished, which in turn makes
them stronger.
The eggs and larvae of many worm species can survive as long as 9 months
in cool, damp weather but may die within a few days or weeks during dry,
hot weather. Thus, take these weather-related infl uences into account when
planning your sheep's movement. In moderate, humid climates, turn out the
sheep in the spring onto a paddock that was last used in the heat of summer
instead of the one they were on during the fall. If you live in the far north,
you can turn out your sheep in the spring on the last paddock they grazed in
the fall.
Malnourished sheep cannot tolerate as much worm burden as can well-
nourished sheep. Lack of proper nutrients, insuffi cient protein, and unbal-
anced nutritional elements, including lack of vitamins and minerals (such as
selenium), can leave them more vulnerable to worm damage.
 
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