Vaccination and preventive treatments for sheep year

We all know prevention is better than cure and the effects of a disease outbreak can be devastating to a sheep flock. While the lamb price is struggling it may be harder to convince farmers to invest in preventive medicine, but when weighed against the potential cost of disease, can they afford not to?

With some vaccines being POM-VPS products it is important their use is discussed to ensure they are being used appropriately so they achieve their purpose within the flock and make the investment worthwhile (Table 1).

Clostridial disease

This well-known group of diseases typically causes sudden death in sheep, with nearly all cases being fatal. Postmortems are therefore usually the mean for diagnosis and if signs are seen, treatment is often ineffective. These bacteria form spores that can survive in the soil for years and so we cannot control this disease by any method other than vaccination as all grazing animals are potentially at risk.

Many of these diseases are caused by Clostridium perfringens, but others include C novyi, C tetani, C chauvoei and C septicum. Several multivalent vaccines are available for prevention against this group of diseases, but it is important to ensure farmers use the correct one for each production group. Those designed for breeding ewes are essential to protect the newly born lamb via colostrum as well as the ewe, and should be given four to six weeks before lambing to ensure adequate antibody levels in the colostrum.

Those designed for growing lambs are less expensive as some of these diseases are not protected against, but are adequate for animals that will not be kept as replacements.

Although these diseases are well known, beware of making assumptions, as we do sometimes still see outbreaks and often it can be traced back to inappropriate use or assumptions about bought-in animals’ history.

The vaccination protocol should be tailored to the individual farm. For example, if some animals may be kept as replacements, it may be wise to advise that as lambs they receive the same vaccine as the breeding flock so when they join the flock, they only require one booster annually and the second injection is not forgotten.

It is also imperative we educate our clients on the importance of correct use. One dose instead of an initial double dose will not provide adequate protection, neither will giving the booster too close to lambing, which may also trigger other metabolic diseases such as hypocalcaemia, due to the stress of gathering and handling so close to lambing.

Some flock owners only vaccinate their breeding stock routinely and the risks to their lambs after maternally derived antibodies wear off must be discussed due to the fatal nature of this disease and our inability to treat it effectively.

At an approximate cost of £58 to double-dose 50 lambs, you need only save one animal to pay for the vaccination of a group of 50 against clostridial disease and Pasteurella.

Pasteurellosis

Vaccination against pasteurellosis (Pasteurella trehalosi and Mannheimia haemolytica) is an important inclusion in a flock’s vaccination protocol and is included in many clostridial vaccines already, or can be vaccinated against on its own.

Pasteurellosis can affect all age groups and is most often seen over the summer, typically following predisposing factors such as bad weather, gathering or another disease outbreak. It has two presentations – septicaemia and pneumonia – and, in its acute form, can have a similar presentation to clostridial disease, with sudden death.

The difficulty in a Pasteurella outbreak is although antibiotic therapy should be an effective treatment, the stress of gathering and treating can cause significantly more losses and so potential outcomes must be discussed with the farmer.

Orf

Orf, or contagious pustular dermatitis, is caused by a Parapoxvirus and the disease can have a significant economic impact as well as being a zoonotic disease.

Although disease can occur in any age at any time, this is most often seen in young lambs and on the teats of nursing ewes, where it can lead to mastitis and ewes being reluctant to feed their lambs. This disease can be confirmed by submitting scab material for electron-microscopy. Although a relatively expensive test, it is important orf vaccination is only carried out in flocks where orf has been confirmed because it is a live vaccine. The vaccine is used in the face of an outbreak and it is administered by skin scarification.

Affected animals should be isolated to help prevent further spread and antibiotics may be necessary to treat secondary infections of the scab wounds.

It is also essential to advise farmers of the zoonotic risks, especially in farms that are open to the public. As this virus is resistant in the environment, it may survive in sheds or on equipment to become an issue again the following year.

Infectious abortion

Three causes of infectious abortion can be vaccinated against in sheep – enzootic abortion (Chlamydophila abortus), toxoplasmosis (Toxoplasma gondii) and Schmallenberg virus.

Despite one being a bacteria, one a parasite and the third a virus, all these diseases can be diagnosed in the same way using serology and postmortems of aborted fetuses/placenta.

In general, most of the vaccines available are not safe for use in pregnancy and are intended for use before the breeding season. An inactivated vaccine for enzootic abortion came back on to the market this year with a claim for use in abortion outbreaks and use in pregnancy if the prebreeding window is missed.

Footrot

Dichelobacter nodosus is the only cause of lameness for which vaccination can be used to reduce the prevalence of disease in a flock. It is important footrot is confirmed as the cause of the lameness, as other causes of lameness will not be reduced by its use and this could lead to assumptions the vaccine hasn’t worked when it may have been another condition causing the issue.

The vaccination protocol is flexible and can be adapted to meet the flock’s needs, for example, once a year if outbreaks are usually seen at a particular time, or as much as two doses six weeks apart and then a single booster at four to five monthly intervals if there is a year-round problem.

It should be noted moxidectin 1% injection cannot be used in animals that have been vaccinated for footrot.

Louping Ill

Louping ill is caused by an arbovirus and transmitted by Ixodes ricinus ticks. It is endemic in certain areas of the UK. Prevention is by vaccination and tick control, and it is mainly seen as a problem in young sheep, but can affect any age. The disease is mainly seen in spring and autumn when ticks are most active and vaccination should be given four weeks before the risk period.

Developments

Moredun Research Institute has developed a vaccine against Haemonchus contortus, which was registered for use in Australia in October 2014. This is the first vaccine in the world for use against a sheep nematode. It is not currently available in the UK, but was found to be effective against all Haemonchus worms, including those with anthelmintic resistance. Work is being done on developing a vaccine against Teladorsagia circumcincta, a significant contributor to parasitic gastroenteritis in the UK.

Routine treatments

Vaccination protocols are one of the main elements of any sheep health plan and something that should always be done, without fail. Recommendations on other routine procedures have changed over the past decade and it is often hard to convince clients to change their year-round routine.

With regards to worm control, we no longer recommend drench and move on to clean pasture, or blanket treatment at set intervals throughout the summer, as we now know this selects highly for anthelmintic resistance. Instead, faecal egg counts and history should be used to dictate worming treatments rather than the month of the year.

Several flocks still routinely drench the whole flock prior to tupping. Discussing the need for this, or lack of it, can help save the farmer money and avoid unnecessary treatments by only doing thin ewes or shearlings at this time of year.

Foot trimming is a routine task for many flocks, but it has shown unless sheep are lame, feet should not be trimmed as the overgrown horn will naturally fall off and we can do more damage than good by changing the shape of the foot or by over-trimming. Conditions such as footrot do not require foot trimming and this practice can increase the spread within the flock.

If farmers aren’t convinced, get them to leave a group untrimmed and see how the lameness compares to the rest of the flock.

Routine treatments or preventive medicine protocols for a flock should be discussed at least annually as part of a health planning meeting and reviewed throughout the year. As new challenges arise, protocols may need to be changed, but effective health planning can help to improve the health and welfare of the sheep and the performance of the flock.