Cymraeg

Health and Welfare of Farm Animals
Session 3 - The Principles of Immunity

This resource is suitable to support Level 2 Agriculture courses.

The Principles of Immunity

Livestock have two mechanisms which protect them from disease:

  • White blood cells engulf foreign bodies such as bacteria; these are not specific to any particular disease causing organism.
  • Antibodies in the blood are produced to fight specific diseases.
graphic of antibodies / white blood cells

Antibodies

If an animal is infected by a disease, then it will produce antibodies to fight that disease. However antibodies arise in the bloodstream from other sources.

  • Therefore immunity may be categorised in several ways:
  • Active
  • Passive

    • Active Immunity

    Active immunity occurs when the animal produces antibodies either in response to natural challenges from disease, or as a result of vaccination.

  • Once an animal has produced a specific antibody, it can produce more antibodies of the same type rapidly in response to infection.
  • This is why there are some diseases that tend only to be caught once in a lifetime.
    • Image of cow being vaccinated

    Passive Immunity

    This occurs when an animal receives antibodies from another source rather than producing its own.

  • The protection from passive immunity doesn’t last long (a few weeks) because the antibodies are gradually used or broken down by the animal.
    • Image of lamb with ewe

    Colostrum - An Example of Passive Immunity

    Pregnant animals produce antibodies which are moved from the bloodstream to the colostrum (first milk).

  • It is very important that newborn animals are given colostrum as their first feed because they can absorb antibodies from the gut into the bloodstream.
  • The colostrum will only contain antibodies to the diseases that the dam has been exposed.
    • Image of newborn lamb with mother

    Vaccines

    Vaccines contain weakened strains of a disease causing organism (live vaccines), or attenuated (killed) disease causing organisms.

  • Vaccines are given so that the animal can develop an active immunity to a disease without suffering from the disease.
    • Image of cow being vaccinated

    How Are Animals Vaccinated?

    Animals are given vaccines in several ways, for example:

  • Clostridial diseases by injection.
  • Orf by scratching the skin.
  • Lung worm as an oral dose.

    • The vaccinated animal will produce antibodies in response to the vaccine.

    Vaccination Programme

    The levels of antibodies will rise gradually after vaccination; many vaccines have a programme that need to be followed to ensure the best level of protection.

  • Example: Clostridial vaccines the primary course consists of an initial vaccination then a booster after six weeks, this is followed by an annual booster to maintain protection and stimulate antibody production for the colostrum so that that lamb gains passive immunity for the first few weeks of life.
    • line of cows
    Graph of injection cycle = First Injection > 6 weeks > Booster Injection > Annual Booster Injection > Lamb develops passive immunity through receiving colostrums in the first six hours > back to the first injection

    Important Points When Vaccinating

    Vaccination will only work well if the treated animals are healthy and receiving sufficient food.

  • Care must be taken not to give too many treatments at once as this may hamper the development of immunity e.g. if a lungworm vaccine has been given, dosing the animals with anthelmintics (wormers) will kill the live lung worm in the vaccine and the animal will not be stimulated to develop its own immunity.
    • Cow being given treatment

    Care of Vaccines

    For the vaccines to work they must be correctly stored and administered.

    • Vaccines can be easily damaged or destroyed e.g. by heat or by killing live vaccines by using sterilizing chemicals on the vaccination equipment.
    Cow being given treatment
    Back to MenuNext Session ▶