1. IMMUNITY INTRODUCTION Definition : Resistance of an organism to infection, disease, or other unwanted biological invasion. The immune system consists of group of cells, molecules and organs that act together to defend the body against foreign invaders that may cause disease, such as bacteria viruses and fungi. There are 2 types of immunity: 1. Innate – first line of defence; skin, tears, mucus, saliva. 2. Adaptive – second line of defence; antibodies Immune system can be manipulated in farm animals to give protection against disease. Hyperfunction and hypofunction of immune system will affect farm animals. Both will retard growth.

2. Hyperfunction Occurs as a result of over-functioning of the immune system. For example, this manifests itself as a number of allergic diseases. Hypofunction Occurs as a result Increased incidence of diseases and these diseases are more severe. Development and maintenance Depends on thymus, lymph nodes, bone marrow and spleen. It operates in 2 parts: 1. Antibody product 2. Cell mediated immunity

3. Types of antibodies Antibodies or immunoglobulins are of several types though they are made of similar units. The antibodies are large proteins molecules specific for particular antigens. Anti bodies have 4 main types: 1. IgM – Most important( during early primary response) 2. IgG – Most important during secondary response. 3. IgA – Protects serromucous surface. 4. IgE – Protects against parasite, important in allergic reaction.

4. Passive and active immunity Immunity can be active or passive. Passive is one that introduces antibodies produced by another individual into the body of animal concerned. For example during birth, mother gives antibodies to new-born via colostrum and milk. In cattle, sheep, goat, pigs and horses, transfer is entirely from colostrum for Day 1 and Day 2 after birth. Passive immunity generally decreases in level along with time. Active Immunity usually occurs through introduction of vaccines in body developing resistance to a certain disease. Usually this form of immunity lasts for a long time.

5. Effects of disease on growth Disease in many cases can retard growth. Effects can be direct causing upset in metabolism and absorption which can lead to diarrhoea. An example of indirect response is animal consuming less feed. Some animal diseases can be transmitted to humans, and control of these types of diseases, known as Zoonoses, is vital to public health. Some diseases are: Salmonellosis, Feline Leukemia, Ringworm and Coccidiosis. If the animal has been exposed to sufficient strong challenge, vector may not be able to express itself. Therefore the growth rate is not affected. If vaccination has been done, it allows optimum growth rate to manifest. Oral immunisation in pigs and cows with enteropathogenic bacteria has given these benefits.

6. CONCLUSION The health of the body is dependent on the immune system’s ability to recognise and then repel or destroy these invaders. It is important to know about animal immune system because when the animals suffer from diseases, it affects their productivity and the economic well-being of many industries. In general, the functioning of the immune system is still a mystery. With incoming technologies and researches, we are looking forward to have more information on the topic.