Wednesday, June 13, 2012

External Parasites of Sheep and Goats


External Parasites of Sheep and Goats1

P. E. Kaufman, P. G. Koehler and J. F. Butler2
Arthropod pests limit production in the sheep and goat industry in many ways. External parasites feed on body tissue such as blood, skin, and hair. The wounds and skin irritation produced by these parasites result in discomfort and irritation to the animal. Parasites can transmit diseases from sick to healthy animals. They can reduce weight gains and milk production. In general, infested livestock cannot be efficiently managed to realize optimum production levels.

Lice

Lice are external parasites which spend their entire lives on the sheep or goat. Both immature and adult stages suck the blood or feed on the skin. Goat lice are host specific and only attack goats and their close relatives such as sheep.
Louse-infested animals may be recognized by their dull, matted coat or excessive scratching and grooming behavior. Sucking lice pierce the host's skin and draw blood. Biting lice have chewing mouthparts and feed on particles of hair, scab and skin exudations. The irritation from louse-feeding causes animals to rub and scratch, causing raw areas on the skin or loss of hair. Weight loss may occur as a result of nervousness and improper nutrition. Milk production is reduced about 25 percent. Also, the host is often listless and in severe cases the loss of blood to sucking lice can lead to anemia.
Lice are generally transmitted from one animal to another by contact. Transmission from herd to herd is usually accomplished by transportation of infested animals, although some lice may move from place to place by clinging to flies (phoresy). Lice are most often introduced to herds by bringing in infested animals.
Louse populations vary seasonally, depending largely on the condition of the host. Most sucking and biting lice begin to increase in number during the fall and reach peak populations in late winter or early spring. Summer populations are usually minimal, causing no obvious symptoms. Animals under stress will usually support larger louse populations than normally found.
Control of louse infestations is needed whenever an animal scratches and rubs to excess. Louse control is difficult since pesticides do not kill the louse egg. Since eggs of most species will hatch 8 to 12 days after pesticide application, retreatment is necessary 2 weeks after the first pesticide application.
There are 4 kinds of biting lice and 5 kinds of sucking lice that can attack sheep and goats in Florida.

Biting Lice

The angora goat biting louse, Bovicola limbata and Holokartikos crassipes are the two major biting lice species. The goat biting louse (Figure 1) and the sheep biting louse are of lesser significance.
Figure 1.  
Goat biting louse life cycle.
All four species live on the skin surface feeding on bits of hair and other skin surface debris. Egg hatch requires 9 to 12 days, and the entire life cycle averages 1 month. The biting lice of goats are world-wide in distribution with winter-time populations being most severe. In Florida high populations have been observed year round.
The best control of biting lice is an animal residual spray. Retreatment is recommended 2 weeks after the first pesticide application for most insecticides.

Sucking Lice

Five species of sucking lice attack sheep and goats. The following are of importance:
  1. African blue louse - Found in semi-tropical climates in the United States, India and Puerto Rico. They are found on the body, head, and neck. Heavy populations have caused the death of the host.
  2. Foot louse - This louse prefers the feet and legs of goats and sheep. Populations peak in the spring and at that time the lice may affect the belly area as well. Scrotum infestations on bucks are common. Lambs seem to have the highest infestations. Egg hatch for this species of louse takes longer than the other species. Therefore, retreatment should be applied after 3 weeks for most insecticides.
  3. Goat sucking louse - Populations (Figure 2) are dispersed over the animal's body. It is also found on sheep.
  4. The face and body louse and the long-nosed cattle louse - These are minor pests.
Figure 2.  
Goat sucking louse life cycle.

Nose Bot Fly


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