Deciding to vaccinate
To make the decision whether to vaccinate or not, you need to consider the:
- cost and impact of disease, including welfare implications
- likelihood of the disease occurring
- cost of vaccine
- efficacy of the vaccine.
- are not usually 100% protective, and even with vaccination some animals may succumb to disease.
- may not necessarily stop an animal being infected or transmitting the disease. In most cases, they stop the outcome of the disease, and they may or may not stop infection.
- may mask a disease being present.
These aren’t reasons to not use a vaccine, but they must be understood to get the best value from a vaccine.
Let’s look at two examples
1. Pulpy kidney in lambs
A producer is concerned about losses just prior to or after lamb marking. The producer vaccinates lambs at marking with 6-in-1 and is wondering if this is sufficient. The first-cross ewes have been joined to terminal sires and the producer is expecting to get $150 average for lambs straight off their mothers at 14–15 weeks of age. Replacement ewes are purchased with two 6-in-1 vaccinations administered prior to purchase.
To get effective protection around lamb marking, the producer needs to vaccinate the ewes pre-lambing. A single vaccination at lamb marking to the lambs will only provide a small level of protection 2–3 weeks post marking.
If a 5-in-1 or 6-in-1 vaccine is used pre-lambing, then a single pre‑lambing booster will cost approximately $0.30/dose plus labour (i.e. $30/100 ewes and just over $0.23/lamb if there is 130% lambing percent).
Assuming a 98% protection from vaccination and 5% of lambs get pulpy kidney, the gain from vaccination would be $925/100 ewes, or a return on investment of 30:1 or 3,000%.
The producer needs to save one lamb every six or seven years to pay for the vaccination.
2. Arthritis in sheep
There are a number of causes of arthritis, but if the main cause is erysipelas, then vaccination may be appropriate. A producer is concerned about arthritis in lambs, which is observed around marking. Last year, the producer had at least 20 lambs out of 500 (4%) affected and which could not be sold.
Erysipelas vaccine is given to ewes pre-lambing, and can be given at the same time as a pre-lambing 6-in-1.
The vaccine costs $0.70 a dose, and if approximately 20% of ewes require two doses, then allow $0.85 per ewe. If the loss associated with arthritis is the full value of the lamb ($150), the vaccine is 95% effective and the lamb marking percent is 130%, then there will be gain of $3,280 by vaccinating (a return on investment of vaccinating of over 7:1).
These scenarios emphasise the importance of assessing the likelihood and level of disease in the absence of vaccination, something always easy in hindsight but difficult in reality.
Where there is any risk of disease and a vaccine is available, vaccination to prevent or minimise disease will be a cheap and almost always worthwhile investment.