Keds cause cockle

22 March 2007

Summary Keds are insects that cause a defect commonly seen in sheepskins known as 'cockle'. The damage is often visible on both sides of the leather and can be difficult to conceal. They also stain the fleece causing it to be down-graded. However, their control is simple and effective. The Sheep Ked Sheep keds (Melophagus ovinus) are wingless flies that are found worldwide. Their brown body is approximately 4-6mm long and very hairy. They have strong legs armed with claws enabling them to crawl through the dense wool of the sheep more easily. Initially, they look similar to ticks, but they only have six legs instead of eight. Infestation is transmitted by means of direct contact, ie from sheep to sheep. Consequently, infestations spread quickly when sheep are housed together in winter. Very occasionally they will drop off and then climb onto another passing sheep. However, they cannot survive more than a few days off their host. These insects feed by sucking the sheep's blood through a barbed proboscis that they insert into the skin which causes intense irritation. Unlike ticks, keds do not feed in the same place for prolonged periods of time and so the area where the bite occurred does not develop a distinctive hole such as that seen with ticks. Unusually, female keds do not lay eggs; they are retained inside the female's body until they hatch. Approximately ten days after mating the female ked gives birth to larvae that are glued to the wool. Each female ked can produce up to 15 young. Within a few hours of birth, the larvae pupate and remain in this state for 20 to 35 days depending on the climatic conditions. Once the adult keds hatch from the pupae, they mate within a day or two and begin the cycle again. Damage caused by keds Keds are a significant problem for farmers since severe infestations cause weight loss and general ill-health in the animal and the fleece is downgraded because the ked faeces cause discolouration and staining that is difficult to remove. The irritation caused by the insects makes the sheep rub and chew at its fleece causing damage to the wool fibres. From the tanner's perspective, keds are bad news because they cause a problem known as 'cockle'. Small pea-sized hard nodules form in the skin that are often visible from both surfaces. On the grain side they may appear as a raised lump that gets flattened and polished during pressure treatments such as vacuum drying. On the suede surface cockle appears as a paler colour because dyes and other process chemicals are not able to penetrate into the denser fibre structure of the nodules. Often the nodules are confined to the neck area, but in severe cases they radiate from the backbone in lines and are then called 'rib cockle'. Control of keds Between 1948 and 1962 in the UK there was compulsory dipping of sheep against the sheep scab mite. Not only did this dipping regime control the Psoroptic mites that cause sheep scab, it also controlled many other ectoparasites such as keds. Once the compulsory dipping was lifted, there was a noticeable increase in cockle in domestic sheepskins. Ked population is drastically reduced when the sheep are sheared in early summer as many are removed with the fleece. This is also an ideal time to treat them with a suitable insecticide to eradicate any remaining parasites. However, the pupae are not very susceptible to the effect of many insecticides. Therefore, a fairly substantive insecticide or systemic product is more effective as it will kill the remaining keds as they hatch from the pupae.

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