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Main diseases in sheep

The following provides a brief discussion on the main diseases in sheep for which vaccines are available. It highlights when vaccination is most useful and provides examples of appropriate programs.

Clostridial vaccinations are relatively cheap. They require two vaccinations approximately four weeks apart to provide strong immunity. A single shot at lamb marking provides only short-term protection and it is not until the second dose is given that lambs/sheep can be considered protected. To protect against tetanus at lamb marking, ewes must be vaccinated pre‑lambing.

Black disease almost always occurs when liver fluke is present. If your sheep have liver fluke, keeping sheep properly vaccinated is important. While immunity for tetanus and black disease are both long lasting (and probably after three doses lifelong immunity occurs), immunity to pulpy kidney appears to last for a much shorter period, and boosters should be timed to occur prior to a high risk period (grazing high quality feeds in rapidly growing lambs, lucerne or grain feeding). Generally, booster vaccinations 6-12 months apart should be sufficient, but there have been some suggestions that under continuous high challenge, more frequent boosters (every 3-6 months) may be justified.

Tasvax 8-in-1 provides extra protection for several less common clostridials (lamb dysentery) but does not cover cheesy gland. In general, where there is any risk of clostridial diseases, proper vaccination is extremely cost-effective and worthwhile. Rams should be vaccinated at least annually (after their initial two doses).

Cheesy gland has been identified as an unnecessary cost at processing, and while production losses are not always evident, where clostridial vaccines are being used it makes sense to always include cheesy gland (i.e. use 6-in-1), given the low extra cost (around $0.07/dose).

Scabby mouth vaccine (Scabigard®) is a live vaccine administered via scratching the bare skin. A small line of pustules form along the scratch line, which then encrusts, scabs and falls off. A sample of vaccinated sheep should be checked for ‘takes’ 10–14 days after vaccination. The scratch allows the virus to take hold, and a relatively harmless infection occurs that provides strong immunity.

Scabby mouth is a zoonotic disease (humans can catch it) so care must be taken when using the live vaccine, as exposure to the vaccine on an existing scratch can lead to a nasty infection for the operator. It is important the vaccine does not come into contact with disinfectant as this can kill the vaccine and make it ineffective.

The difficulty with scabby mouth vaccination is that it is believed the virus can live for many years in the soil, so by using a live vaccine, you are ‘introducing’ the disease, and then ongoing vaccination will be necessary. That said, it is probably already present on most sheep properties, and if you are considering vaccinating, it is usually because your sheep have already had an outbreak of scabby mouth. There is a specific declaration on scabby mouth vaccination on the National Vendor Declaration form (Q2).

Ovine Johne’s disease (OJD). The current vaccine (Gudair®) provides good protection against sheep developing OJD, and further assists in control by reducing shedding of OJD organisms for any infected sheep. The vaccine results in a reactive nodule in many sheep vaccinated, and some sheep can get a sterile abscess.

While Gudair® is a killed vaccine, it only requires a single dose for lifetime immunity (booster doses are not required). As young lambs are the most susceptible to infection, it is important on endemic properties that lambs being retained on‑farm for more than two years are vaccinated as young as practical, which usually means at lamb marking. The general recommendation is to vaccinate lambs between 4-16 weeks of age.

Despite most infection occurring when lambs are young, sheep are usually 2-4 years when they exhibit the clinical signs of weight loss and death. Lambs that are destined for slaughter before 1-2 years will not benefit from Gudair® vaccination. Similarly, vaccinating older ewes is not necessary.

Where OJD is present on a property, vaccinating lambs (at 4-16 weeks of age and preferably at lamb marking) that are staying on-farm for at least 1-2 years will assist in controlling OJD.

If non-Gudair® vaccinated sheep are brought onto an infected property from a known clean area, vaccination of young sheep (those retained for more than 2-3 years) should also be beneficial.

Gudair® vaccine must be handled with caution. Self-inoculation can lead to very nasty lesions in people, often requiring protracted multiple surgeries over several months. It is recommended that the safety vaccinator is used.

Campylobacter vaccination (Campyvax®) protects against abortion storms caused by campylobacter, and may also increase lambing percentage by decreasing foetal losses.

Campylobacter is believed to be quite widespread, and some reports suggest that vaccination can increase lamb marking percentages by about 10%, although a trial in southern NSW showed only one in six properties gained any benefit.

Vaccination should be carried out either pre-joining or the booster dose occurring when rams are removed (at the latest). Given the likely widespread nature of campylobacter organisms, young sheep lambing for the first time are at the highest risk to campylobacter, so producers should consider vaccinating ewe lambs/hoggets prior to their first lambing (two doses at least three weeks apart required).

While annual vaccinations pre- or post-joining are recommended, it is likely that ongoing exposure after the initial two doses provides a reasonable level of immunity, so revaccination of older ewes may not be worthwhile.

Erysipelas arthritis is mostly a problem in young lambs, and protection is best provided by pre-lambing vaccination of ewes so that lambs are protected via antibodies in the colostrum following birth and up until marking. Vaccination of lambs at marking and again at weaning will provide long-term protection, but it is important to note that if you are concerned of cases at lamb marking, then a pre-lambing vaccination of ewes will be the most effective approach.

Footrot vaccination may be a consideration in infected flocks, although vaccine use may be regulated in your state, requiring permission for its use. An excellent monovalent or bivalent vaccine is available, and appears effective where only one or two strains (serogroups) of footrot are present in a flock. There are 10 known serogroups and frequently multiple serogroups are present in infected flocks.

In July 2020, a ‘10 strain’ (actually nine strains, with no coverage of serogroup M) vaccine was reintroduced onto the market. Unfortunately, the duration of protection from multistrain vaccines is reasonably short, especially in Merino sheep. Footrot vaccine use should be discussed with your veterinarian (currently the monovalent/bivalent vaccine is not available).