Beata Mudjanima
Poultry diseases have significant effects on both the flock and the farmer. Their impacts can range from economic losses for farmers, including low productivity and high input costs, to public health concerns about border shutdowns and to environmental consequences.
Poultry diseases are caused by various factors, including viruses, bacteria, parasites, fungi, nutritional deficiencies, environmental factors and management practices. Below are some common causes of diseases.
Viral diseases
Avian influenza (bird flu) is caused by the Influenza A virus, and its severity depends on the strain of the virus. It is transmitted through direct contact with infected birds, contaminated areas and airborne droplets.
Common signs include sneezing, coughing, decreased egg production, and swelling of the head and wattle; some birds may experience neck twisting and sudden death.
Newcastle disease
The Newcastle disease virus is highly contagious and notifiable by law. It affects the respiratory, digestive, and nervous systems of birds.
It is transmitted through direct contact with infected birds and droppings.
Some of the signs are difficulty breathing, greenish watery diarrhoea, paralysis, twisting of the neck and death.
Infectious Bronchitis
A highly contagious viral disease which primarily affects the respiratory tract. It can spread rapidly within a flock, especially in poorly ventilated and overcrowded coops.
The virus can persist in the environment. Coughing, nasal discharge, wheezing and decreased egg production can be misshapen and have poor shell quality. Flocks exposed to IB are susceptible to secondary infections, resulting in mortality.
Infectious Bursal Disease (Gumboro Disease)
Infectious Bursal Disease is caused by a virus that targets the immune system of young chickens. Transmission occurs through contact with contaminated droppings.
Birds will have watery, white diarrhoea that sticks to the back and can lead to dehydration. The younger flock will have stunted growth, which can lead to poor uniformity and increased mortality.
Bacterial diseases
Salmonellosis is the most common bacterial disease and poses a potential risk to humans when contaminated poultry products are consumed. Salmonella is caused by different types of bacteria. Transmission occurs through ingestion of contaminated feed, water, or eggs.
Signs include diarrhoea (which may contain blood and mucus), dehydration, weakness and paralysis, and common respiratory signs such as sneezing and coughing.
Parasitic diseases
Coccidiosis is a parasitic disease caused by protozoa. The disease is more resilient in damp environments, increasing the risk of infection during the rainy season. Signs of coccidiosis are bloody droppings, ruffled feathers, anaemia and drowsiness.
Other signs of coccidiosis range from weight loss and decreased growth rate to a high percentage of visibly sick birds, severe diarrhoea, decreased egg production and high mortality.
Parasite infestations
There are two types of parasites namely internal and external.
Internal parasites include roundworms, flukes, and tapeworms, which chickens ingest from contaminated water. External parasites, such as mites and lice, cause skin irritation, decreased egg production, and feather loss.
Mosquitoes are good mechanical transmitters of Fowl pox, which can cause a drop in egg production by over 40%.
Nutritional diseases
Nutritional deficiencies can lead to various adverse effects on the health, growth, and overall productivity of chickens.
Poor growth and development can lead to stunted growth and reduced body weight. There will be reduced egg production and quality, and the flock will experience fertility issues.
Deficiencies in calcium, phosphorus, vitamin D or other minerals and vitamins essential for bone health can lead to skeletal abnormalities. A lack of amino acids can weaken the immune system and make birds more susceptible to infectious diseases.
Environmental factors
Heat stress and poor ventilation are additional factors, as chickens are more susceptible to heat stress than other livestock species, which lack sweat glands and rely on evaporative cooling to regulate their body temperature.
High temperatures and humidity can compromise the immune system and increase susceptibility to disease. Effects of heat stress include reduced feed intake and productivity, increased mortality, dehydration and respiratory distress. Poor ventilation in a coop can lead to the accumulation of ammonia, dust and pathogens, increasing the risk of respiratory diseases.
Management practices
High stocking density, overcrowding, and poor biosecurity can increase stress levels, lead to poor air quality, reduce growth and productivity, accelerate the spread of diseases within a flock, and increase mortality.
A poor biosecurity programme can have significant adverse effects on a farm, leading to increased risks of disease spread and financial losses.
To minimise disease during the wet season, farmers should implement biosecurity measures to prevent the introduction of disease into the flock from outside each coop and across the whole farm.
This can be done by controlling access to the farm and maintaining a clean and hygienic coop; the flock must be regularly dewormed and vaccinated against diseases.
Feedmaster’s layer guide illustrates a standard vaccination programme. However, consulting a veterinarian for a vaccination schedule that fits your flock is highly recommended.
Poultry raised near stagnant water will require more frequent vaccinations against fowl pox than poultry raised in dry areas. Consulting technical advisors and staying informed about disease-prone areas can contribute to effective disease control.
* Beata Mudjanima is Feedmaster’s technical advisor in the communal northern regions of Namibia. She can be reached at bauala@feedmaster.com.na