Lamb Health – Vaccinations

Stock Journal Feature Article - May 2024

As the saying goes, prevention is always better than a cure. This really highlights how we should think about vaccinations and their place in a sheep health program.

Many of the diseases we vaccinate against are incurable, so preventing the disease is often the only way to tackle it. This includes diseases like:

• The ‘clostridials’ (Pulpy Kidney, Tetanus, Malignant Oedema, Black Leg and Blacks Disease) – each of these is caused by a different clostridial bacteria and is characterised by a short period of illness (often 24 hours or less) followed by death. Clostridial vaccines usually contain either two (pulpy kidney and tetanus) or all five of these in one dose, such as the 3in1, 5in1 and 6in1s.
• Cheesy Gland (caseous lymphadenitis or CLA) – A bacterial infection that causes incurable abscesses in the lymph nodes that can result in significant trimming at the abattoir. It is included with the clostridial vaccines.
• Arthritis – swelling of the joints that results in poor performance, culling and trimming or condemnation at the abattoir. The vaccine for one of the most common type of arthritis, Erysipelas, comes either on its own (Eryvac® or Eryguard®) or in combination with a clostridial vaccine (Glanery®)
• Ovine Johnes Disease (OJD) – A prolonged disease that causes wasting and eventual death in affected sheep. Gudair® is the vaccine used to prevent OJD. Read the manufacturer’s instructions carefully as there are a few restrictions regarding its safe use.
• Scabby Mouth – While animals recover from a scabby mouth infection, treatment is often not viable and the disease is left to run its course. This can create production losses or missed marketing opportunities.

For an animal to gain protection against a disease, their body needs to produce proteins called antibodies, which attack and neutralise foreign substances. Exposure to the foreign substance must occur before the body can be capable of producing the specific antibodies to fight it.

Lambs are born with a naïve immune system which must learn to produce the antibodies needed over time. This is where vaccinations come in. The vaccine contains either an inactive or weakened form of the disease-causing agent, allowing the lamb to start producing antibodies without the risk of a significant health challenge.

Most vaccinations work by the animal receiving two doses in the first year, followed by an annual booster. The first of these doses is called the primer, which introduces the disease to the lamb’s immune system. A small immune response is achieved but this usually only provides protection for a short period (around 4 weeks). As this immunity wanes, a second dose (the booster) is administered, ideally 4 to 6 weeks after the priming dose. Having had previous exposure, the lamb’s immune system is now able to mount a large response which, in most cases, provides protection for the next 12 months.

The best time to give a priming dose of a vaccine is at marking. The aim of this timing is to allow the maternal antibodies levels delivered from the colostrum to drop so that the vaccine can work appropriately, while limiting the time that a lamb is unprotected. Booster doses often fit in with weaning.

Marking and weaning also represent high risk times for infection and spread of disease, making vaccination programs even more important.

There are exceptions to the above timing and dosages of vaccine, so it is always important to follow label instructions carefully. Both Scabigard® for scabby mouth and Gudair® for (OJD) are a single dose vaccination, with no further boosters required.

Pulpy Kidney is another exception. The vaccines for this disease (3in1, 5in1, 6in1 etc) often only provide protection for three months when animals are faced with a high-risk challenge, such as a sudden change onto a richer diet. An extra booster may be required in these cases.

Timely and well implemented vaccination programs are a key component to maintaining the health of lambs and contribute to a productive and profitable enterprise.