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Stackyard News Jan 07
       

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    Guard Against Lice and Tick Threat at Lambing Time
18/01/07

Sheep producers are being urged to protect their flocks from lice and tick infestations this lambing season. Lambing time is often a pretty stressful time, but it can also be a period when lice and ticks are an added source of irritation for ewes and a health threat to young lambs, vets warn.

Sheep ticks live away from the host for most of their life cycle but pose a particular threat to flocks on rough and unimproved pastures where the natural increase in numbers coincides with the turnout of ewes and young lambs.

Sheep ticks

Lice outbreaks, in particular, are on the increase since the ending of compulsory dipping for sheep scab. “Although infestations by the biting louse Bovicola ovis do not cause the loss of body condition associated with sheep scab, they do cause considerable wool loss and make housed sheep very restless,” explains Schering-Plough Animal Health livestock veterinary adviser Paul Williams MRCVS.

Infested sheep not only rub, but also bite at their flanks and can often be seen with wool in their mouths. Unlike sheep scab, patches of bare skin are uncommon as the wool tends to regrow and there will also be no sign of scabs on the skin surface. Lice can be spotted clinging on to the wool of affected sheep – especially if a sample is held against a dark background – and they are typically brown in colour with elongated bodies and a definite head.

“Lice infestations can be eliminated by OP dips such as Coopers Ectoforce,” says Paul Williams. Pour-ons are also effective against lice, but they do not eliminate them. Pour-ons work best after shearing, but will also help control infestations in housed sheep providing they are not carrying excessively heavy fleeces. “Lambs should be treated at the same time as they can become heavily infested within weeks of birth,” he adds.

Since lice live permanently on the host animal, transmission is via infested sheep particularly when they are grouped together for housing or feeding in winter. “In addition to keeping existing stock lice free it is very important to isolate, inspect and, if necessary, treat replacement animals especially rams before they join the main flock,” Paul Williams advises. This procedure will also help to avoid the introduction of sheep scab to the flock.

Ticks in contrast, live away from the host for most of their life cycle but pose a particular threat to flocks on rough and unimproved pastures where the natural increase in numbers coincides with the turnout of ewes and young lambs.

As part of its life cycle the sheep tick, Ixodes ricinus, needs a blood meal from a host animal and the adult females are most likely to be found attached to the head, legs or other areas of skin not covered by wool. Their feeding can also cause abscesses in the joints, spine and internal organs of lambs resulting in a condition known as tick pyaemia.

“Badly affected lambs frequently die of starvation as they cannot keep up with the ewes,” Paul Williams says. “Ticks also transmit louping ill – a viral disease of the nervous system – and tick-borne fever, an illness characterised by a sudden high fever for 4-22 days. Abortion can occur in ewes not previously exposed to infected ticks. Most affected sheep become carriers and relapses of the disease can occur.”

Fortunately, the advent of effective pour-ons such as the only deltamethrin-based ectoparasiticide, Coopers Spot On, means heavily pregnant ewes and lambs can now be treated around lambing with minimal handling. “Adult and lambs can both be treated at the same time, with lambs able to be treated within a few days of birth at half the dose rate,” he advises.

link Farmers to question DEFRA minister over bovine TB fears
link Biosecurity on the Agenda for Agricultural Shows
link Farmers advised on employing foreign workers

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