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, public health concerns of borders being shut down, and 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 influenza A virus and its severity depend on the strain of the virus. It is transmitted through direct contact with infected birds, contaminated areas and airborne droplets.
Common signs are sneezing, coughing, decreased egg productivity and swelling of the head and wattle; some birds can experience twisting of the necks 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 misshaped, and have poor shell quality.
Flock exposed to IB are susceptible to secondary infections, leading to mortalities.
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 a watery white diarrhoea, which sticks behind 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, which poses a potential risk to humans if contaminated poultry products are consumed. Salmonella is caused by different types of bacteria. Transmission occurs through ingestion of contaminated feed, water, or eggs.
Signs are diarrhoea, which can contain blood and mucus, dehydration, weakness and paralysis, and common respiratory signs like 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. Parasites infestations There are two types of parasites: internal and external.
Internal parasites include roundworms, flukes and tapeworms, where chickens ingest the larvae from contaminated water. External parasites are mites and lice, which 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 chickens suffering from various adverse effects on health, growth, and overall productivity. 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 other additional factors as chickens are more susceptible to heat stress than other livestock species because they lack sweat glands and rely on evaporative cooling to regulate their body temperature. High temperatures and humidity can compromise the immune system, and increase disease susceptibility. 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, poor air quality, reduced growth and productivity, fast spread of diseases within a flock and increased mortalities. A poor biosecurity programme can have significant adverse effects on a farm, which leads to increased risks of diseases spreading and financial losses.
In an attempt to minimise diseases during the wet season, farmers should implement biosecurity measures to prevent the introduction of diseases to the flock from the outside of each coop and 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 need more vaccination frequencies against fowl pox, compared to poultry raised in dry areas. Consulting technical advisors and staying informed on diseases-prone areas can contribute to effective disease control management.
* Beata Mudjanima is Feedmaster’s technical advisor in the communal northern regions of Namibia. She can be reached at bauala@feedmaster.com.na