A general Review on Some Important Diseases in Free Range Chickens

Anders Permin & Magne Bisgaard

Department of Veterinary Microbiology
The Royal Veterinary and Agricultural University
Bülowsvej 13, 1870 Frederiksberg C, Denmark
E-mail: ape@kvl.dk and m.bisgaard@post.tele.dk

Summary

Scavenging poultry is the most widely owned animal and the poultry suffer from a number of diseases as presented in this paper. However, long-term cohort studies, examining the causes of death, have to date not been carried out in the free range production systems. As knowledge on the proportion of the individual disease of the overall mortality is not available, it is postulated that other diseases than Newcastle Disease are present in free range poultry production systems and that a successful development of the system will be possible only when the exact causes of mortality are known. Post mortem examinations are not expected to be accepted by existing international peer-reviewed journals and it is proposed an international journal dealing with problems relating to scavenging and family poultry should be estab­lished as it would ensure rapid implementation of research results obtained.

Key words: Scavenging, poultry, diseases, causes, importance, developing coun­tries.

Introduction

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, the management methods place high demands on proper health, hygiene 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 developing countries. In these countries 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, is often seen. 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 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 of the prevalence and significance of the individual dis­eases under village conditions. The following data therefore mainly reflect experi­ence obtained under backyard conditions in developed countries.

Diseases

According to Jordan et al. (1996) and Calnek et al. (1997) poultry diseases can be divided into five groups, namely bacterial (table 1), viral (table 2), fungal (table 3), parasitic (table 4) and nutritional (table 5) diseases. Only the diseases of expected importance under village conditions, e.g. those causing high mortality rates in chickens are mentioned in these tables.

As seen a wide variety of diseases are expected to occur under village condi­tions. Some of these diseases are age specific, whereas others are encountered in all age groups.

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

Disease	Age group
Escherichia coli	All ages, but mainly chicks
Salmonella spp.	All ages, but mainly chicks
Salmonella pullorum	Chicks < 3 weeks
Salmonella gallinarum	Growers, adults
Pasteurella multocida	Growers, adults
Haemophilus paragallinarum (Coryza)	Growers, adults
Clostridium perfringens	All ages, but mainly growers
Mycobacterium avium	Adults
Mycoplasma gallisepticum	All ages
Mycoplasma synoviae	All ages

 

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

Disease	Age group
*Marek's disease	> 6 weeks
*Leucosis	Adults
Newcastle disease	Mainly growers and adults
Fowl Pox	All ages
Infectious Laryngotracheitis	Growers, adults
*Infectious Bursal Disease "Gumboro	< 8 weeks

*immunosuppressive disease

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

Disease	Age group
Aspergilloses	Chicks
Mycotoxicoses	All ages

 

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

Disease	Age group
Coccidiosis	Chicks, growers, (adults)
Histomoniasis	1-3 months
Nematodes	All ages
Haemoparasites	Chicks, growers
Ectoparasites	Chicks, growers

 

Table 5.  Important nutritional diseases in free range poultry and the age group where the disease is most often observed

Disease	Age group
Vitamin A, D & E	Chicks, growers
Other vitamins, minerals and amino acids	Chicks, growers

 

Discussion

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 output" system (Pandey, 1992). Mortality in this system is in the range of 80 - 90% within the first year after hatching (Matthewman, 1977; Wilson, 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. Lack of vita­mins and protein weaken the chicks and make them vulnerable to other diseases and predators. Diseases are also easily contracted under free range conditions due to scavenging habits (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; personal communication) has, however, shown that in ND-immunised birds mortality is still high. The majority of the mortality is found in chicks up to 3-4 month of age. In this group up to 52.5% of the animals died due to other causes 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 by (Adesiyun et al. 1984) from Nigeria. Chryosostome and his co-workers (1995) 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 Cnemidocoptes mutans, Dermanyssus gallinae and/or Echidnophaga 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/pullorum 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.

Conclusion

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 other diseases 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 W.P.S.A. should be addressed to establish an international journal dealing specifically with problems relating to scavenging and family poultry. Establishing such a journal would ensure a rapid implementation of research results obtained.

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