If an animal is infected with disease organisms, particularly a bacterial or viral infection, it produces antibodies in the blood which engulf and destroy the invading bacteria or viruses. When all bacteria or viruses are destroyed, the animal recovers. The antibodies remain in the blood. If the animal is later exposed to that same infection, it may show slight signs of illness or no signs at all. This ability to withstand infection is called immunity. There are four kinds
- NATURAL ACTIVE IMMUNITY
This is the type of immunity acquired by an animal that has been infected by disease organisms and has recovered. Antibodies remain in the animal and it has a natural immunity to that particular disease, often for the rest of its life.
- ARTIFICIAL ACTIVE IMMUNITY
This is produced by giving an animal a very mild dose of an infection and allowing it to produce the antibodies to combat the disease. It is done by injecting the
animal with a small amount of the bacteria or viruses which cause the disease. The organisms injected into the animal can be alive, using what is called a live vaccine, or they can be dead, using a dead vaccine.
- NATURAL PASSIVE IMMUNITY
This is the type of immunity acquired by a calf when it drinks its mother’s colostrum. The antibodies pass from the mother’s blood into the colostrum where they are ingested by the calf and pass into the calf’s blood giving it immunity. This type of immunity is effective only for a short time.
In the case of a calf, immunity against scours acquired through the mother’s colostrum lasts for about the first 10 days of its life. After that, it begins to build up a natural active immunity against scours.
- ARTIFICIAL PASSIVE IMMUNITY
If an animal is injected with a low level of organisms of a disease, it will produce antibodies to combat that disease. After a few days it will be able to receive a larger dose of the disease organisms without being seriously affected. This process can be repeated over a period of time until the animal is receiving doses of the disease organisms that would normally kill it. The animal has developed immunity to the disease, but because this immunity has been acquired by infecting the animal in the first place, it is called artificial immunity.
If blood is taken from animal that has built up an artificial immunity, and the serum from its blood is injected into another animal, that animal will also develop immunity to that disease. Antibodies in the blood of the first animal have been transferred to the second animal and can be used to destroy the same disease organisms. This transfer of antibodies from the blood of one animal to the blood of another is called passive immunity, as in the case of the cow and its calf. Due to the immunity having been induced by artificial means, by taking blood from the first animal and injecting it into the second, the immunity induced is called artificial passive immunity. Passive immunity is effective only for a short period; in fact, for as long as the antibodies live in the blood of the receiving animal. No new antibodies are produced so that the immunity acquired lasts for about 1 – 2 weeks.
Unfortunately, not all disease organisms or the toxins (poisons) produced by them will produce immunity. In some cases lasting immunity can only be obtained after recovering from an infection. An example of this in humans is the immunity which people develop after having diseases like chickenpox or mumps as children (natural active immunity). Artificial active immunity can be obtained by giving the animal a mild dose of the disease, and an example of this in humans is vaccination against smallpox. In other cases of disease, results are variable, and in some cases, immunisation is produced.
The injections of either live or dead organisms used to produce artificial active immunity are called vaccines and the process is called vaccination. Vaccines will each work for one disease and sometimes only for a single strain of a disease. There are seven strains of Foot and Mouth Disease and a different vaccine is needed for each strain. Vaccines are prepared in laboratories and should be used according to the instructions on the bottle. They should be stored in a refrigerator and used before the expiry date on the bottle. Vaccines will remain effective for a limited period only and should not be used after that period has expired. Read the instructions carefully, and always inject the vaccine into the animal using a sterilised needle and syringe.
An example of a vaccination programme for a sheep flock is given below. It has been taken from the Sheep Producers Handbook. A more comprehensive programme is in the Sheep Lectures.
Pulpy kidney vaccinations
Lambs Two months of age
Older Sheep Annually
Purchases Prior to movement on to the farm
Vaccination September/October annually. Pregnant ewes must not be vaccinated.
Rams should be vaccinated prior to mating.
Vaccination of ram lambs at four months of age. Ensure that any ram purchased has been vaccinated.
VACCINATIONS WHICH MAY BE NECESSARY
Rift Valley Fever/Wesselbron
Vaccination required if disease is present in the country. The two vaccines can be combined.
Pregnant ewes and lambs under the age of one month must not be vaccinated.
QUARTER EVIL/MALIGNANT OEDEMA
Vaccination is required for individual flocks on veterinary recommendation.
Vaccination as required for individual flocks on veterinary recommendation.
The vaccines used in this programme are dead vaccines, and the dead organisms injected into the animal stimulate the production of the antibodies. In some cases a live vaccine is used, and an
example of this type of vaccination is the injection to prevent Redwater and Gallsickness disease. The animals are injected and develop a mild attack of the diseases, but they have to be observed very closely in case they become very ill. The normal procedure is to take the temperatures of the animals every morning and evening, and if an animal’s temperature becomes too high, e.g. 41 – 42°C, it would have to be treated for the disease. Unfortunately the effects of the vaccination would be
destroyed and the animal would not receive the desired immunity to the disease.
VACCINATION OF YOUNG CATTLE AGAINST REDWATER AND GALLSICKNESS
Vaccine is supplied for use on calves up to 9 ½ months of age. This age limit is imposed owing to the greater risk of fatal reactions developing as a direct result of inoculation in older stock.
The vaccine is a live one and its effectiveness is of a short duration, hence it must be used in the minimum possible time after dispatch from the laboratory.
DIRECTIONS FOR USE:
Sterilise the syringe by boiling – do not use disinfectants – and inject 5ccs. of vaccine under the skin of the neck.
Redwater should develop 7 – 10 days after inoculation and Gallsickness 4 – 5 weeks later. These reactions may be so mild as to go undetected or may be severe. It is advisable to take the temperature twice a day of at least a proportion of the inoculated cattle. By doing so, reactions can be detected before they become too severe and require clinical treatment.
Due to the Redwater disease, the animal’s temperature should start rising in approximately 7 – 10 days, remaining high for a couple of days and then subsiding to normal and remain normal until the Gallsickness commences on about the 25th to the 35th day after inoculation. If the Redwater temperature remains high, and especially if the animal shows signs of clinical distress, i.e. off food, dull, rapid breathing, purging or finally passing blood-coloured urine, it should be treated.
There are several drugs on the market for the control of Redwater. Check with a Veterinarian about which one to use.
The Gallsickness reaction is normally so mild in young stock as to cause no trouble. Going off feed and developing constipation may occur – in such cases try any tempting succulent diet and control the constipation with soapy water enemas; (handful of salt in a bucket of warm water with soap rubbed in to form slight foam). Enemas can be repeated several times a day if necessary, and a Friesland calf of 9 months of age would take about 4 – 6 litres at a time.
To ensure that reactions are in fact occurring, prepare blood smears from at least some of the animals when temperature reactions occur. In the absence of any reaction, do a blood smear on the 7th, 9th and 11th day for Redwater and the 25th, 30th and 35th day for Gallsickness.
Keep the calves in their normal condition after inoculations and feed as usual. The manufacturers of the vaccine do not accept any responsibility in the event of untoward results following use of these vaccines.
This is the serum obtained from the blood of an animal that has been infected with a disease and which contains the antibodies necessary to combat that disease. This serum can be injected into an animal in quite small quantities, e.g. 10ml, and if the receiving animal has been exposed to the infection, the serum will protect it or even kill off the dangerous organisms if it is caught early enough. However, as the immunity produced is passive immunity, the effect of the serum will only last for 1 – 2 weeks. This procedure is used for animals that have been exposed to infection by tetanus.
2. FIRST AID
As there is shortage of veterinary surgeons in most parts of Southern Africa, and the remoteness of many of the farms, farmers treat their animals for injury or disease more often than farmers in Europe or America. All farms should have a veterinary cupboard in the farmer’s house or farm office. This should be used to store medicines and first aid equipment and any vaccines stored on the farm should be kept in a refrigerator. The contents of the veterinary cupboard should include the following items.
AIDS FOR DIAGNOSING DISEASE:
- Clinical thermometers for taking the temperature of sick animals.
- Box of glass slides for taking blood smears.
- Box of small bottles with screw tops for taking blood and milk samples.
- Glass jars with screw tops (0,5ml size) or plastic bags for sending specimens to the veterinary laboratory.
- Bottle of Formalin (40% Formaldehyde solution) for preserving specimens.
- Scalpel with detachable blades.
- Scissors, one pair with curved, blunt blades and one pair with straight blades.
- Suture needles for stitching wounds and nylon or silk thread.
- Hypodermic syringes, 5ml, 10ml and 20ml sizes, together with 14 gauge needles.
- These can be metal syringes or disposable nylon syringes that are used once and thrown away.
- Trocar and cannula used to puncture the rumen in cases of bloat.
- Flutter valve for injecting large doses into an animal, as in the case of milk fever.
- Funnel and hosepipe for giving an enema to an animal.
- Nylon calving ropes.
- Long rope, 12mm thick, for restraining animals and casting cattle.
- Burdizzo for castrating calves.
- Rubber gloves for carrying out post mortems on carcasses.
- A supply of bandages, sticking plaster, gauze, cotton wool and plaster of paris.
- A bottle of surgical spirit, for sterilising the skin of an animal before administering an injection, and a bottle of mild disinfectant such as Dettol or TCP.
- Common vaccines These should be kept in the veterinary cupboard or in a refrigerator – check the instructions on the bottle.