Disease is defined as a condition that impairs normal body functions. The severity of disease depends on the degree of impairment.
Various causes of poultry disease
1. Infectious: Bacterial such as salmonellosis, colibacilosis, pasteurellosis; viral such as Newcastle disease.
2. Parasitic: Endoparasite such as helminthiasis; Ectoparasite such as mite infestation.
3. Protozoan: Coccidiosis
4. Non-infectious: Nutritional such as deficiency diseases (vitamin deficiency); metabolic such as fatty liver syndrome.
Factors that influence occurrence of poultry disease
1. Host factor
-Age: Young birds are more susceptible to infectious agents than adult birds.
-Availability of various route of entry.
-Immune status of host
-Poor management condition
-Carrier status of birds
2. Environmental factor
-Wet litter
-Too hot or too cold conditions
-Dusty litter
-Poor ventilation
-High build up of chicken droppings
-Sharp wires in the cages.
3. Management practices
-High stocking density
-Chickens of mixed ages/varying species reared together
-Poor quality food and water
-Poor hygiene and inadequate cleaning program
-Leaking water bowls
-Rat and fly problems
-No security measures to prevent people and animals from entering the chicken house.
4. Causative agent
-Invasiveness
-Dose of causative agent
-Virulence of the causative agent
-Lifecycle of agents
Sources of infection to poultry flock
Spilled vaccines: Vaccine spillage is a source of infection because most live vaccines are live disease agents, so they should be properly handled.
Human beings: This involves farm manager, farm attendants, veterinarians, visitors and neighbors. They introduce infection and are potential disease transmitters to poultry flock.
Sick birds: These are birds that show clinical sign of disease but are not detected and removed.
Carriers: These are birds that have recovered from a clinical disease or did not show clinical signs of a disease but the causative organism is found in many parts of the body.
Vectors: These are animals that indirectly transfer infectious agents to the flock for example, rodents, flies, insects, pests and stray animals.
Live bird market: A lot of birds (healthy, sick and apparently healthy) are found in the live bird market which is a major source of poultry disease outbreaks thus the popular ALL-IN/ALL-OUT should be practiced.
Formites: These are inanimate objects that introduce infectious agents indirectly to a poultry flock. They include contaminated equipments, human shoes, clothing etc.
Laboratory exposure: Experimental animals and researchers are potential sources of infectious agent introduction in poultry flock in the absence of strict sanitary measure.
General signs of disease in poultry
Head held close to the body, tail and possibly wings droop, neck twisted with head held over back or between legs.
Combs and wattles are shrunken, pale or blue in color. Face parts are shrunken. Eyes are dull and may be held only partly open. Nostrils are caked and crusted. Eyes are watery. Sinus areas below the eyes are swollen or flutters with respiration.
Legs and feet are dehydrated with prominent tendons. Joints are enlarged and warm to the touch. Bottom of feet are cracked, crusted or discolored. Scales are enlarged and crusty.
There is loss of weight and strength. The muscle at the point of the keel and near crop cavity are shrunken resulting in a thin breast.
The manure or dropping is milky white, green, yellow or red. The droppings are very liquid or very sticky and not firm.
There is loss of appetite or excessive drinking.
Feathers are not preened. Feathers are fluffed out or broken. Staining is observed in areas of abdomen. Birds are generally ruff looking.
There is gurgling, rattling or snickering noise; gasping and obvious movement of abdominal wall.
There is reduced depth of colour. In adult hens, excess of yellow pigment may be associated with disease decreasing rate of lay.
Disease prevention
Healthy flock selection: Selection of viable and disease free chicks is necessary.
Adequate nutrition: Balanced nutrition should be given to poultry.
Adequate housing: Provide adequate housing for birds. The housing should be wild bird and insect proof, cross ventilation and foot dips at the entrance of the poultry house.
Adequate environment for the birds: This includes low humidity, good drainage system and adequate sunshine.
Sanitation: There should be regular cleaning and disinfection of housing, equipment, vehicles and people.
Preventing flock contact with reservoirs of infection: This involves removal of all animate and inanimate objects that transfer infection directly or indirectly to the flock. The inanimate objects that are reservoirs of infection include contaminated water, feed, dust, litter, soil, shoes and equipment including housing while animate reservoirs of infection include live reservoirs, sick birds, other domestic poultry, wild animals, feral birds, arthropods, snails, other domestic animals and humans.
Proper disposal of dead bird: This can be done through the following:
-Rendering: freshly dead poultry are rendered into fertilizer at a rendering temperature capable of sterilization.
-Incineration: smokeless and odorless incinerators are used for disposal of dead carcasses.
-Burying: deep hole dug and carcass buried so that animals cannot get to it.
-Pit disposal: well constructed hole in the ground were carcasses are dumped.
-Composting: compost mixtures of straw, whole poultry carcasses, manure and water in a definite ratio, compost heat rapidly and completely reduces soft tissue within 14 days.
Isolation or quarantine of sick birds: This can be done through providing separate housing for keeping sick birds pending recovery.
Vaccination: The process of injecting live attenuated or killed suspensions of an infectious agent in order to produce resistance against infectious agents on exposure.