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Friday 9 December 2016

Vaccination is the only answer to avoid greater disease incidences

Sheep

Andrew Kinsella

Published 23/08/2011 | 05:00

During the past few weeks, I have received a number of queries about the causes and prevention of pneumonia and coughing in sheep -- particularly lambs.

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I am at a loss to know why there are so many queries this year but it may be related to weather conditions, or that many farmers have omitted vaccinating against the disease. The high sheep prices may also be focusing the mind in relation to mortality and the impact this has on returns.

Pasteurellosis is the most common form of pneumonia in sheep. The bacterium responsible, Mannheimia haemolytica, is a normal inhabitant of the respiratory tract of sheep and has a large number of serotypes. It is assumed that environmental and management factors are pre-disposing causes of the disease. Some outbreaks can be linked to previously stressful situations such as changeable temperatures or wet weather. Over-crowding lambs in pens and sheds for prolonged periods during dosing or weighing, especially in warm weather, can also be a factor. Moving lambs from bare pasture onto lush aftermath, dipping, castration and transport are further stress-related events that can trigger disease.

The disease can occur at any time of the year and in any age of sheep but is most common during spring and summer. Often, the first sign of trouble is finding a dead animal followed by further deaths over succeeding days.

Lambs found alive are generally separated from the remainder of the group, are not grazing and often stand with their neck extended and head lowered. There maybe a discharge from the nose and eyes and froth from the mouth. Treatment is by antibiotics, such as oxytetracycline, but responses are generally poor unless detected early.

Prevention of pasteurellosis is a combination of good husbandry to prevent stressful situations and vaccination where there is a history of previous outbreaks. It should always be remembered that while vaccination prevents serious outbreaks from occurring, there may still be some cases of pneumonia even when vaccination is carried out. This is because not all pneumonia is caused by pasteurella. A further reason is that the vaccine, while containing the most common pasteurella serotypes, may not include the serotype responsible for the particular case in question. However, where there is a relatively high incidence of disease, sheep farmers should be asking why they are not vaccinating. A stronger case can be made for vaccination now that lamb price has improved.

Vaccinating the ewes pre-lambing with a combined clostridial and pasteurella vaccine, such as Heptavac P plus, will give clostridial protection through the colostrum to the lambs for about 12 weeks but will only give pasteurella protection for 3-4 weeks.

Where ewes have been vaccinated pre-lambing, lambs in high-risk flocks can be given the combined vaccine or a pasteurella-only vaccine such as Ovipast Plus anytime from three weeks of age. A second injection is necessary 4-6 weeks later to complete the programme. It will take two weeks after the second injection for the lambs to develop full immunity.

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Coughing can arise from any respiratory tract irritation or infection. There is a long list of bacteria, mycoplasmas and viruses that can cause coughing in lambs but probably the most common cause during summer and into the autumn is sheep lungworm (Dictyocaulus filaria). Lambs pick up infective larvae while grazing. These larvae bore through the stomach wall into the lungs where they mature. Female worms lay eggs that are coughed up and swallowed into the intestines where they hatch into larvae. These larvae then pass out through the faeces to complete the life cycle.

The presence of adult worms in the lungs causes chronic coughing that is most noticeable when the flock is being gathered. Young animals are mainly affected as adults develop immunity. The condition is generally worse during wet years.

Most of the common anthelmintics that treat stomach worms are also effective against lungworm. Where there is coughing, this should be verified by checking the indications on the dosing container.

Where damage has already been caused, it may take some weeks for coughing to cease. The majority of lungworm cases are relatively mild and it is generally considered to be of little economic significance.

Andrew Kinsella is a former Teagasc sheep specialist who now farms in Co Wicklow

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