A. Permin and M. Bisgaard

Poultry production has undergone rapid changes during the past decades due to the introduction of modern intensive production methods, new breeds and improved biosecurity and preventive health measures. Moreover, these intensive production methods place high demands on proper health, hygiene and management and require only a small, but very skilled labour force. In developing countries, however, adoption of this type of production has been limited due to the high inputs as listed above. The progress in industrial poultry production methods has thus had little effect on subsistence poultry production in the rural and peri-urban areas. In these areas access to poultry meat and eggs depends on village-level poultry production. Although poultry production is considered as secondary to other agricultural production systems it has an important role in supplying villagers with additional income and high quality protein. This system provides valuable protein through a low input system, now representing 30% or more of the protein consumed (FAO, 1998).

Almost all families in developing countries keep a chicken flock with an average size of about 10 adult chickens, varying from 5 to 50 animals. The majority of these animals are kept in free-range scavenging systems, where the birds scavenge around the house during daytime. Primitive housing of the birds during the night, however, often takes place. Supplementary feed consists mainly of household wastes, insects, larvae and seeds (Minga et al., 1989; Kabatange et al., 1990; Aini, 1990; Pandey, 1992).

Mortalities observed are in the range of 80 - 90% within the first year after hatching (Matthewman, 1977; Wilson et al. 1987). For the same reasons the owners never include chicks when they refer to the flock size. The mortality is believed to be caused by mismanagement, lack of supplementary feeding, predators and diseases (Aini, 1990; Pandey, 1992). Little research has been published on rural poultry health, despite the fact that up to 80% of the poultry population in Africa and Asia is kept by the households as free-range chickens (Minga et al. 1989; Aini, 1990).

Although solid data have not been published, Newcastle Disease (ND) is regarded as the principle factor limiting rural family poultry production in all African and Asian countries. ND may kill up to 80% of household poultry in Africa (Minga et al. 1989; Aini, 1990; Bell, 1992), but is not expected to account for the high early mortality rate according to the authors. In addition, detailed epidemiology of the disease in the village situation is largely unknown (Yongolo, 1997). Furthermore, recent studies have shown that other diseases are present in scavenging poultry communities (Bell et al. 1990; Cumming, 1991; Bell, 1992; Chrysostome et al., 1995; Permin et al., 1999). Since most of our knowledge relies on seroprevalence studies, solid longitudinal studies on causes of mortality are strongly needed to improve our knowledge on the prevalence and significance of the single diseases under village conditions. The following data therefore mainly reflect experience obtained under backyard conditions in developed countries.

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According to Jordan and Pattison (1996) and Calnek et al. (1997) poultry diseases can be divided into five groups, namely bacterial (Table 1), viral (Table 2), fungal (Table 3) and parasitic (Table 4). Besides there are various non-infectious diseases affecting chicks and growers. These are mostly associated with nutritional deficiencies (i.e. vitamins A, D, E, etc. as well as minerals and amino acids). Only the diseases of expected importance under village conditions, e.g. those causing high mortality rates in chickens are mentioned in these Tables.

Table 1: Important bacterial diseases in free-range poultry and the age group where the disease is most often observed

Table 2: Important virus diseases in free-range poultry and the age group where the disease is most often observed

Table 3: Important fungal diseases in free-range poultry and the age group where the disease is most often observed

Table 4: Important parasitic diseases in free-range poultry and the age group where the disease is most often observed

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Approximately 80% of the world poultry population is kept as free-range poultry (Minga, 1989; FAO, 1998). The free-range poultry production system has also been designated as the 'low input - low out' system (Pandey, 1992). Mortality in this system is in the range of 80 - 90% within the first year after hatching (Matthewman, 1977; Wilson et al., 1987) and is believed to be caused by mismanagement, lack of fresh water and supplementary feed, predators and diseases (Aini, 1990; Pandey, 1992). Of these, diseases are believed to be the main limiting factor to the production of indigenous chickens (Aini, 1990). Among causes of early mortality nutritional diseases might be expected to dominate due to shortage of supplementary feed before and after hatch. In addition, the quality of hatching eggs might be questioned under the climatic conditions present in these countries. Avitaminoses and lack of protein weaken the chicks and make them vulnerable to other diseases and predators. Diseases are also easily contracted under free-range conditions due to the scavenging habits of these birds (Soulsby, 1982; Pandey, 1992). With an unconfined type of management, disease control is very difficult to carry out and is therefore rarely practised by the owners.

As mentioned earlier, Newcastle Disease is believed to be the most important disease in free-range systems (Minga, 1989; Aini, 1990; Bell, 1992). During outbreaks of the disease up to 80% of the population may die. This, however, is dependant on different factors including the virulence of the strain causing the outbreak (Alexander, 1997). A recent study in Nicaragua (Kyvsgaard, 1999) has, however, shown that in ND-immunised birds mortality is still high. The majority of the mortality is found in chicks and growers up to 3-4 month of age. In these groups up to 52.5% of the animals died due to causes other than ND. Similar studies in Mali by Wilson et al. (1987) have shown that chick mortality is in the range of 60% within the first 3 months after hatching.

A study in Morocco (Bouzoubaa et al., 1992) has revealed that up to 58% of the village chickens had antibodies against Salmonella gallinarum and S. pullorum. Similar findings were reported in Nigeria by (Adesiyun et al. 1984). Chryosostome et al. (1995) also reported that 10% of the village chickens had antibodies against S. pullorum and that 62% had antibodies against Mycoplasma gallisepticum. Furthermore, 65% of the animals had antibodies against ND. In Mauritania, Bell et al. (1990) found that 17.5% of the birds had antibodies against S. pullorum and that up to 46.2% of the birds had antibodies against Gumboro disease. In the same animals 7.5% had antibodies against ND.

In Tanzania, Permin et al. (1999) examined 600 live chickens and found the presence of a range of diseases. All animals were parasitised with one or more (up to 14 species) species of endoparasites. In total 29 different species were detected in the study. Furthermore, 65.7% of the animals were parasitised with Cnemidocopt-es mutans, Dermanyss-us gallinae and/or Echidnopha-ga gallinacea.

The animals were also infected with a range of haemoparasites, the most common being Plasmodium juxtanucleare and Aegyptinella spp. Antibodies against Newcastle disease was seen in 7.3%, against Salmonella enteriditis in 2.0%, against Salmonella gallinarum/pull-orum in 52.7%, against Infectious Laryngotracheitis in 58.3% and against Gumboro disease in 42.3%. Similar studies have, to the knowledge of the authors, not been carried out in Asian countries. The significance of all these diseases, however, remains to be investigated. In addition, it should be noted here that a general trend for these studies is that they have only looked for antibodies against selected diseases.

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Long-term cohort studies, examining the causes of death, have to date not been carried out in the free-range production systems. Important knowledge on the proportion of the individual disease of the overall mortality is thus not known. It is consequently postulated that diseases other than ND are present in free-range poultry production systems and that a successful development of this production system is only achieved when the exact causes of death is known. Since publications on disease prevalence based upon post mortem examinations are not expected to be accepted by existing international peer-reviewed journals the WPSA (World's Poultry Science Association) should be addressed to establish an international journal dealing specifically with problems relating to scavenging/family poultry. Establishing such a journal would ensure a rapid implementation of research results obtained.

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Adesiyun, A.A., Bishu, G., Adegboye, D.S. and Abdu, P.A. (1984): Serological survey of Salmonella pullorum antibody in chickens around Zaria, Nigeria. Bulletin of Animal Health and Production in Africa 32: 81-85.

Aini, I. (1990): Indigenous chicken production in South-east Asia. World’s Poultry Science Journal 46: 51-57.

Alexander, D.J. (1997): Newcastle disease and other avian paramyxoviridae infections. In: Diseases of Poultry (Calnek, B.W., Barnes, H.J., Beard, C.W., McDougald, L.R. and Y.M. Saif, Y.M., Eds.), Iowa State University Press, Ames, Iowa, pp. 541-569.

Bell, J.G. (1992): The village chicken and disease control. Tanzanian Veterinary Journal 12: 44-47.

Bell, J.G., Kane, M. and Le Jan, C. (1990): An investigation of the disease status of village poultry in Mauritania. Preventive Veterinary Medicine 8: 291-294.

Bouzoubaa, K., Lemainguer, K. and Bell, J.G. (1992): Village chickens as a reservoir of Salmonella pullorum and Salmonella gallinarum in Morocco. Preventive Veterinary Medicine 12: 95-100.

Calnek, B.W., Barnes, H.J., Beard, C.W., McDougald, L.R. and Saif, Y.M. (1997): Diseases of Poultry. Iowa State University Press, Ames, Iowa, pp. 1-1080.

Chrysostome, C.A.A.M., Bell, J.G., Demey, F. and Verhulst, A. (1995): Seroprevalences to three diseases in village chickens in Benin. Preventive Veterinary Medicine 22: 257-261.

Cumming, R.B. (1991): Village chicken production: Problems and potential. In: Newcastle Disease in Village Chickens (Spradbrow, P.B., Ed.), Proceedings No. 39, ACIAR, Canberra, Australia, pp. 21-24.

FAO (1998): FAOstat. Statistical database of Food and Agriculture Organization of the United Nations, Rome Italy.

Jordan, F.T.W. and Pattison, M. (1996): Poultry diseases. W.B. Saunders Company Ltd, London, UK

Kabatange, M.A. and Katule, A.M. (1990): Rural poultry production systems in Tanzania. In: Proceedings of an International Workshop on Rural Poultry Develop-ment in Africa (Sonaiya, E. B., Ed.), Ile-Ife, Nigeria, pp. 171-176

Kyvsgaard, N. (1999): Personal communication.

Minga, U.M., Katule, A.M., Maeda, T. and Musasa, J. (1989): Potential and problems of the traditional chicken industry in Tanzania. Proceedings of the 7th Tanzania Veterinary Association Scientific Conference, TVA Vol. 7, Arusha, Tanzania, pp. 207-215

Matthewman, R.W. (1977): A Survey of small livestock production at the village level in the Derived Savanna and Lowland forest zones of south-west Nigeria. University of Reading, Department of Agriculture and Horticulture, Study No. 24, pp. 40-41.

Pandey, V.S. (1992): Epidemiology and economics of village poultry production in Africa: Overview. In: Procee-dings of an International Workshop on Village Poultry Production in Africa (Pandey, V.S. and Demey, F., Eds.), 7-11 May 1992, Rabat, Morocco, pp. 124-128.

Permin, A., Magwisha, H., Kassuku, A.A., Minga, U.M, Yongolo, H.M., Jørgensen, P., Nansen, P., Bisgaard, M. and Frandsen, F. (1999): Diseases in rural scavenging poultry in the Morogoro Region, Tanzania. (In preparation).

Soulsby, E.J.L. (1982): Helminths, arthropods and protozoa of domesticated animals. Bailliére Tindall, East Sussex, UK.

Wilson, R.T., Traore, A., Kuit, H.G. and Slingerland, M. (1987): Livestock production in central Mali: Reproduction, growth and mortality of domestic fowl under traditional management. Tropical Animal Health and Production 19: 229-236.

Yongolo, H.M. (1997): Epidemiology of Newcastle disease in village chickens in Tanzania. M.Sc. Thesis, Sokoine University of Agriculture, Morogoro, Tanzania.
 

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