Wyoming sheep producers should be on the lookout for keds

By Whit Stewart

Wyoming’s premier wool clip is a major source of pride for the state’s sheep industry. The clip ranks second overall in total wool production, at 2.3 million pounds, with the greatest total value across all 50 states, according to the U.S. Department of Agriculture’s National Agricultural Statistics Service. 

Wyoming’s reputation as the wine country of wool is not fable, but a unique strength to the state’s sheep industry. Still, the external parasite sheep ked, also known as Melophagus ovinus, is the one perennial challenge threatening our wool clip reputation. 

The following article is intended to serve as a refresher in how producers can manage and eventually eliminate the sheep ked from their flocks. 

Background information

            We often refer to the sheep ked as a sheep tick, when in reality, it is from the insect order Diptera, which makes them a true but wingless fly. Being insects, they have six legs as opposed to eight legs found on adult true ticks. 

            Both male and female keds feed on sheep blood every 24 to 36 hours. Contact is the major mode of transmission across sheep because keds have no wings or ability to propel themselves very far. 

            Sheep keds cannot survive without their host. But, if environmental conditions are favorable, they can survive off a sheep for up to 24 days and will try to climb to the top of suitable objects, like corral posts, to infest a new host.

Sheep ked lifecycle

            What’s most important with ked management is understanding the life cycle and timing treatment options accordingly. With a lifespan of 100 to 130 days, the female ked can produce 12 to 15 larva over the course of her lifetime, whereas male keds can live up to 80 days. 

            Unlike the majority of insect species, the female keds retain a single larvae at a time inside their bodies, nourishing them with ked “milk” for about a week, when larvae are fully grown. 

            The keds then deposit and glue the larvae onto wool where they molt into the pupal stage, closely resembling a dark kernel of corn. The sheep ked will remain unhatched in this pupa stage for 19 to 30 days depending on ambient temperature.

 Remember, the 19 to 30 days rule-of-thumb, as this timeframe should guide retreatment. 

Ked treatment

            The adult sheep ked’s ability to survive is tied to its ability to move up and down the wool staple to thermoregulate. Generally, the warmer the temperature, the shorter the pupa stage, and the colder the temperature, the longer it will take to hatch.  

            Yet, the most important consideration is the unhatched puparia is not killed by insecticides on the first application. Thus, two and potentially three treatments post shearing are critical to target the new adult keds, which have emerged from the protective pupal case after the first treatment. 

            Unfortunately, unless producers regularly inspect their sheep closely, ked infestations can come as a surprise on the shearing floor, due largely to keds preferring the lower half of animals like the neck, ribs, abdomen and britch. 

            Researchers in the 1940s observed female keds artificially placed on sheep migrated to the britch, whereas males migrated to the neck and shoulder. The majority of unhatched puparia were deposited underneath the neck. 

Most research indicates the most probable mode of transmission is from the newly emerged keds that transfer from the ewe to the lamb. Thus, the time between shearing and lambing are critical in terms of treatment and eradication. 

            Sheep ked infestations create real wellbeing challenges to the sheep flock due to rubbing and scratching irritated areas from these biting parasites. It is well documented losses to pelt values are observed due to formation of hard nodules, or cockles, at the ked feedings sites. 

Ked impacts to clips

            Early research with Merino wethers indicated ked infestations reduced the amount of greasy wool produced, but no differences were observed post-scouring. Its speculated the infestations will decrease skin blood flow in addition to greater production of wool grease, such as suint and lanolin, resulting in potential discoloration and potential price deductions when selling the wool clip. 

            Still, many clips in the region do not exhibit this discoloration as a result of ked infestation and negotiated prices should be priced on objective information. In visiting with some of our major wool buyers in the region, they’ve mentioned unless excessive irritation to the sheep occurs resulting in discoloration and fiber strength issues, price discounts are rare.

            In the published literature, effects of ked infestations on lamb growth ranges from no differences in growth to an eight-pound difference at weaning. As with many parasitic problems in sheep, good nutrition can alleviate severity of production losses. Thus, the good nutritional management which should be a part of late gestation, can also help alleviate the stressors from ked infestations.

Best management practices

There are additional best management practices for sheep ked control. First, apply insecticide in the periods immediately after shearing, as keds in long staple wool can minimize contact with insecticides. Second, apply at least two applications – one at shearing and another 19 to 30 days after initial treatment to disrupt the life cycle of hatching pupa. Third, mixing untreated sheep with treated sheep can also be a source for re-infestation. In one study, after only six days of mingling treated sheep with untreated sheep, a 45 percent re-infestation rate resulted the following year. Lastly, producers should inspect purchased sheep on arrival for ked infestations specifically the neck, shoulder and britch areas. 

            Whit Stewart is the University of Wyoming Extension sheep specialist. He can be reached at whit.stewart@uwyo.edu.