Herd and flock health is a primary concern for stockmen and -women, as healthy, productive animals drive profits in livestock farming businesses, while meeting welfare concerns.
Disease risks can be significantly reduced when farmers practice sound stock management. This includes preventing contact with disease-causing bacteria, viruses and parasites, and increasing animal resistance to disease when contact with microbes is unavoidable. Animal vaccination to protect against vaccine-preventable diseases is a key strategy in the fight against livestock disease.
WHAT ARE VACCINES?
Vaccines are products containing live, weakened (attenuated) or dead micro-organisms (or parts of micro-organisms) that cause animal diseases. These microbes (or their products) are altered in a laboratory so that they keep their ability to stimulate the immune system without actually causing the disease. Vaccination is something like having a trained army, at the ready, in a country, in case of an invasion by foreign forces.
The true test of a trained army is often evaluated in the face of a challenge and the army must stay in training so that it is prepared for a possible invasion. Once animals have been vaccinated, annual booster vaccinations keep them fit to fight against the enemy – the microbes that cause disease.
Vaccines are sensitive biological products, effective for a limited time under recommended storage conditions and every batch of vaccines comes with an expiry date. It’s a good thing to bear in mind that vaccines can deteriorate sooner than the declared expiry dates if the manufacturer’s storage, transportation and handling recommendations are not met.
Vaccines contribute to the improvement of animal and human health, animal welfare, agricultural sustainability and to reducing our reliance on the use of antimicrobials to treat animal disease.
MAINTAINING THE COLD CHAIN
Animal vaccines have specific storage needs and a critical part of this is the maintenance of the cold chain. This is especially important in warmer seasons and in hotter areas. The recommended storage temperature for most vaccines ranges between 2°C and 8°C.
However, very little attention is given to the adverse effects of storing vaccines below the recommended temperatures and some vaccines are permanently destroyed by freezing. Vaccines that need to be stored at -70°C could quite easily be destroyed by a higher temperature which is still below 0°C.
A good example of this is in the storage of blood vaccines for anaplasmosis, redwater and heartwater. A standard household freezer operating at temperatures of around -15°C is not cold enough to store blood vaccines so they are stored and transported in dry ice or liquid nitrogen and thawed just before use.
Once a vaccine’s potency is lost, it cannot be regained or restored, and the vaccine will not provide any protection against the targeted disease. Vaccines are not like drinks in the fridge that can be rechilled and consumed after load shedding is over and the power comes back.
Vaccines must be kept at the recommended temperature and the duration of these temperatures varies between vaccines. The appearance of the drug does not change so the stockman (or woman) handling the vaccine cannot do a visual check to see whether it has lost its potency. The only way to be sure is to send the vaccine for laboratory testing.
CHOOSE THE RIGHT TOOLS
Handling infrastructure (the crush) has a major influence on the effective administration of vaccines. Poor handling facilities can make vaccination difficult and take up a lot more time than the stockman (or woman) may have anticipated.
This is a problem, particularly with vaccines that must be administered as soon as possible after opening to minimise the risks of compromising the cold chain and exposure to sunlight.
Most vaccines are injected subcutaneously (under the skin) so it is best to use short (1⁄2 inch) needles that will not bend or break. These needles are easy to use and will keep the vaccine subcutaneous even when the handler doesn’t have a lot of experience. Needle sizes from 15G to19G should be fine for most livestock vaccinations as vaccines are not usually thick. Farmers could consider using a narrower gauge in smaller calves and small stock.
Another practical challenge in the field is in the use of draw-off tubes attached to an automatic syringe. The longer the tube the greater the risk of air bubbles getting trapped along the tube. The vaccinator may not notice this and at the end of the run there is more vaccine in the vial and/or tube than there should be. This means that some animals have been injected with air and are therefore unvaccinated.
There is no way to tell which animals have received a full, partial, or even no vaccine dose unless the vaccinator picks up the problem immediately. It is better to go for a syringe that locks and secures the vaccine bottle on top or to use an automatic syringe that can deliver multiple doses. These syringes greatly reduce the chance of air bubbles taking up space and increase the probability of delivering the right dose of vaccine to the animals.
HANDLING LEFT-OVER VACCINE
It is best not to keep left-over vaccine after the vial has been opened. Try to share left-over vaccine with a neighbour and get it to him, or her, as quickly as possible once you have vaccinated your animals. The risk of contamination under field conditions is often difficult to manage, hence the recommendations to safely discard left-over vaccine.
Some vaccines, like lumpy skin disease vaccine, must be reconstituted before use and need to be used as quickly as possible after mixing. The recommendation is usually to use it within an hour, and sometimes less than an hour, of mixing before the actual live virus in the vaccine dies.
Covid-19 has put the importance of disinfectants and sanitisers into the spotlight but it is important to realise that certain vaccines (especially live vaccines) are killed by exposure to these chemicals. So never clean the area of the animal’s skin to be vaccinated with a disinfectant. As a standard practice farmers should boil needles to sterilise them and cool them down before use.
It may not always be practical to change needles between animals when vaccinating but there are times when a fresh needle must be used on every animal. For example, vaccinating against lumpy skin disease in a herd where some animals are showing signs of the disease, risks spreading the disease if the needles are not changed. Under these circumstances a new needle must be used on every animal and the animals should be healthy.
Animals that seem to be more at risk and appear symptomatic of the disease should be isolated and vaccinated at the end of the run to reduce the risk. This may not be helpful if the disease is already incubating in healthy-looking animals.
The best option is to vaccinate animals ahead of the high-risk period, for example during August and September for diseases transmitted to animals by insects. Breeding animals with slight reactions to the vaccine will then be fully recovered when the breeding season starts.
Farmers are strongly advised to use registered products. A registered vaccine will have a G. number and be registered in terms of Act 36 (Fertilisers, Farm Feeds, Seeds and Remedies Act, Act 36 of 1947). This is an assurance that the product has fulfilled the minimum safety, efficacy and quality requirements. There may be special circumstances where the authorities allow the restricted use of unregistered products.
The national animal health forum website (nahf.co.za) contains helpful information on animal diseases. Another valuable resource is the Ruminant Veterinary Association website (ruvasa.co.za), where veterinary practices throughout the country voluntarily report on diseases they encounter in the field. Make sure to read the accompanying package inserts on all vaccines (and other medicines in general).
Speak to your local veterinarian or animal health technician about customised vaccination pro grammes that can make a difference to your operation or contact me at firstname.lastname@example.org