In most cases, poultry diseases are an important problem for poultry farmers. Although farmers are familiar with the signs and symptoms of disease, the underlying causes are less well known. Almost every farmer and most extension workers hold Newcastle Disease (NCD) responsible for most deaths, and the disease has a local name in all languages.
Many causes of poultry diseases
However, not all infectious diseases are due to the NCD virus. Digestive problems resulting in slow growth and diarrhoea may be the result of rancid feed or too much salt, and may also be symptoms of diseases such as coccidiosis, salmonellosis, or Gumboro (Infectious Bursal Disease IBD). NCD often has the symptom of greenish faeces, which indicates a loss of appetite.
Poultry is extreme susceptibility to respiratory infections caused by a wide range of bacteria, viruses and fungi. These infections become more serious in increased stock density – even if only for overnight accommodation – because of increased risk of cross-infection. Inadequate ventilation of poultry houses results in a build-up of ammonia gas from poultry faeces, which contain urea. This can predispose the poultry to respiratory disorders, such as sneezing, running eyes and mucous discharges from the mouth. Providing good ventilation easily prevents this. More prolonged respiratory disorders are usually caused by diseases such as NCD, Infectious Bronchitis (IB), Infectious Laryngotracheitis (ILT), Chronic Respiratory Disease (CRD) and diphtheria.
Coordination disorders such as paralysis, limping, twisted neck and slow movement may be caused by a variety of factors, such as physical injury, nutrient deficiencies and diseases, including NCD (twisted necks or torticolis), Marek's Disease (paralysis), synovitis (tendon infections in which feet joints feel warm) and Avian Encephalomyelitis (AE).
Poultry health is also affected by nutritional and environmental factors, such as insufficient feed or feed deficiencies. A high mortality rate among chicks during the first days or weeks after hatching may be caused by insufficient feed and water. A high mortality in adult birds may be due to nutritional problems, such as salt deficiency.
Energy and protein deficiencies and imbalances can arise when the feed contains insufficient quantities of these nutrients, resulting in poor growth in young stock and a drop in egg production and egg weight in laying hens. Mineral and vitamin deficiencies may result in poor growth, low production or death. Vitamin D deficiency causes rickets (bone deformities) in young chicks and, if combined with a calcium deficiency, in chickens of all ages. A lack of manganese results in deformities of the feet of older chickens.
An excess of certain nutrients, especially minerals, can cause abnormalities. An excess of common salt (NaCl), for example, results in deformed eggshells as well as increased water consumption, and if drinking water is restricted (as is often the case with free-ranging birds), signs of toxicity may develop. Free access to feed of high carbohydrate and low fat, combined with lack of exercise, high temperatures and stress, can cause Fatty Liver Syndrome, which can result in high mortality.
Ingestion of toxic plant parts (such as leaves, seeds and sap) is a common hazard for freerange birds. Some toxins are produced by micro-organisms, such as those liberated by the bacteria Clostridium botulinum and C. perfringens, both found in the soil. C. perfringens causes necrotic enteritis, caused when the bacteria multiplies in the favourable conditions of the digestive tract and liberates a potent toxin that results in high mortality. Occasionally affected birds show anorexia, depression and diarrhoea, but most die without showing any clinical signs.
C. botulinum causes botulism disease, which is acute food poisoning. This is more common in ducks, which show the nervous symptoms of neck bent down and feathers falling out easily when lightly pulled. Botulism results from the bird eating rotting vegetable scraps, which contain the toxins produced by the C. botulinum. Household vegetable scraps which are not regularly removed are a potential hazard for botulism.