The sheep ked, Melophagus ovinus, is one of the most widely distributed and important external parasites of sheep. There are also keds that parasitize deer in North America (Lipoptena cervi, L mazamae, L depressa, and Neolipoptena ferrisi).
Keds are wingless dipterans. The adult is approximately 7 mm long, brown or reddish in color, and covered with short, bristly hairs. The head is short and broad, and the legs are strong and armed with stout claws. (See .)
Lipoptena cervi (deer ked), a biting fly in the family of louse flies (Hippoboscidae).
Courtesy of ABOL/HP Fuehrer Vetmeduni Vienna.
The female sheep ked gives birth to a single, fully developed larva, which is cemented to the wool and pupates within 12 hours. A young ked emerges after approximately 22 days. Females live 100–120 days and produce approximately 10 larvae during this time; males live approximately 80 days. The entire life cycle is spent on the host. Keds that fall off the host usually survive < 1 week and present little danger of infestation to a flock (1).
Ked numbers increase during the winter and early spring when they spread rapidly through a flock, particularly when sheep are assembled in close quarters for feeding or shelter.
Pathology of Sheep Keds
To feed, sheep keds pierce the skin with their mouthparts and suck blood. They usually feed on the neck, breast, shoulder, flanks, and rump, but not on the back, where dust and other debris collect in the wool. Ked bites cause pruritus over much of the host’s body; sheep often bite, scratch, and rub themselves, thus damaging the wool. The fleece becomes thin, ragged, and dirty. The keds' excrement causes a permanent brown discoloration, which is likely to decrease the value of the wool. Keds also cause a defect in hides called a cockle, which affects the grade and value of the sheep skin.
Infested sheep, particularly lambs and pregnant ewes, can lose vitality and become unthrifty. Heavy infestations can considerably decrease the condition of the host and even cause anemia. Keds also transmit Trypanosoma melophagium, a nonpathogenic protozoan parasite of sheep.
Diagnosis of Sheep Keds
Close inspection of the damaged, dirty wool and underlying skin reveals infestation by wingless, hairy flies.
Treatment and Control of Sheep Keds
Chemicals and dips
Shearing, followed by insecticides with residual activity
Shearing removes many pupae and adult sheep keds. Thus, shearing before lambing and subsequent treatment of the ewes with insecticides to control the remaining keds can greatly decrease the possibility of lambs becoming heavily infested. Sheep are usually treated after shearing, and best results are obtained if an insecticide with a residual activity of ≥ 3–4 weeks is used so the keds that emerge from the pupae are also killed. Modern treatments to control lice also control keds.
Dipping is an effective method of treatment. Completely submerging the sheep in vats ensures the destruction of all keds present but, in most instances, does not kill the pupated larvae; a long-acting insecticide is required to kill newly emerging keds. Large flocks of range sheep should be treated in a permanently constructed dipping vat. Smaller flocks and farm flocks can be successfully treated in portable, galvanized-iron dipping vats or in smaller tanks, tubs, or canvas dipping bags.
Spraying can be as effective as dipping and is more convenient in some areas.
Shower dipping is also sometimes used; the sheep are held in a special pen and showered from above and below until the fleece is saturated. The run-off is returned for recirculation, and the concentration of insecticide used is the same as for dipping. The concentration of the insecticide can drop rapidly and become ineffective if the label instructions for replenishment are not followed explicitly.
Jetting involves the forceful application of insecticide by a handheld, multiple-jet comb drawn through the short fleece. Although a little slower and less effective than dips or sprays, jetting can be advantageous for smaller flocks because it is economical and does not require a permanent installation.
Spot-on or pour-on formulations of the newer pyrethroids are easy to apply and effective.
Powder dusting fits well into management practices at shearing time. It is rapid, economical, and avoids wetting the animals. Various types of equipment for dusting are available commercially.
For More Information
References
Small RW. A review of Melophagus ovinus (L.), the sheep ked. Vet Parasitol. 2005;130(1-2):141-155. doi:10.1016/j.vetpar.2005.03.005
