I. Aini

Duck farming in south-east Asian countries mostly consists of backyard or subsistence type of rearing. The ducks are provided with poor quality feed and exposed to poor husbandry, thus subjected to non-infectious and infectious diseases. However, recorded information on diseases affecting these ducks is rather scarce. Commercial duck farms are as advanced as in other developed countries.

Duck farming in south-east Asian countries mostly consist of large number of small farms and very few intensive commercial farms. Traditionally, the duck industry in the south-east Asian region was mainly a backyard activity. Ducks were mainly raised by small farmers to supplement the family income, similar to the rearing of indigenous chickens. The ducklings were hatched by traditional methods of incubation using charcoal or by individual brooding. Most of these ducks were raised in paddy field areas, near lakes, used tin-mine ponds, canals, streams or along coastal areas, because supplementary feed came from leftover rice bran and broken rice after harvesting season as well as shrimps, snails or cheap thrash fish. Sea-shells were also used as a cheap source of calcium.

In countries such as Vietnam, Philippines, Thailand, Malaysia, Hong Kong and Korea, ducks are important cuisines. In Malaysia, the main outlets for broiler ducks are Chinese restaurants and stalls selling roast ducks. The consumption of duck meat is limited; it is not common on the daily household menu. Eggs are mostly consumed as salted or preserved eggs rather than fresh eggs (Awang, 1993).

Though the duck industry has advanced much since late 1950s, the progress is not as rapid as the progress in chicken industry. The scavenging system of duck farming is still important in many south-east Asian countries. This type of free-range practice exposes the ducks to different weather changes, non-infectious and infectious diseases. The husbandry practice is generally poor and disease control is unheard of. Besides other reasons such as poor husbandry and poor feed quality, diseases bring about one of the major economic losses to the industry. The statistics on the disease outbreaks, incidence, morbidity and mortality are either not available or not reliable, as farmers do not usually report any disease outbreaks.

The other two groups of farming practice are the smallholder semi-intensive and the commercial intensive farms. The intensive commercial duck farms are increasing in number. This paper highlights the common disease problems associated with the backyard and smallholder duck farms.

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Non-infectious diseases are mostly associated with environmental effects and nutritional deficiencies. Leg weakness associated with calcium deficiency is one of the common conditions reported (Awang, 1993), besides vitamin D, phosphorus, nicotinic acid deficiencies, and physical injuries.

Aflatoxicosis is also a common cause of mortality in ducks especially when feed is not properly stored. Aflatoxicosis is important in that it affects the bird•s immune system directly and indirectly.

Most of the farmers either feed the leftover food to the ducks or home-mixed feed; thus storage and quality control are very poor. Thrash fish especially tends to putrefy easily when proper storage is not provided. Wet environment encouraged mouldy growth.

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The most common infectious diseases reported are as follows:
Viral Diseases : Duck virus hepatitis
Duck virus enteritis
Bacterial Diseases : Cholera
Duck Septicaemia
Colibacillosis/Colisepticaemia
Fungal Diseases : Aspergillosis
Parasitic Diseases : Endoparasitism

It is not uncommon to have ducks that succumbed to multiple infections, especially when the husbandry is poor. Low-grade intercurrent diseases together with stress usually result in increased susceptibility to pathogenic organisms. When mixed infections do occur, it is often difficult to treat.

Duck virus hepatitis (DVH)
DVH which is caused by picornavirus, is a highly infectious, acute disease in ducklings less than 5 weeks old. This disease has been reported in all south-east Asian countries. Though vaccine is available, small farmers seldom resort to vaccination as a method of control.

Duck virus enteritis (DVE)
DVE is also known as duck plague. It is caused by herpesvirus, which can result in an acute, highly fatal disease, or it can be a chronic infection in carrier ducks. It is often thought that migrating waterfowls are involved in disease transmission. This disease has been reported in all south-east Asian countries (Seri Masran, 1996; Tran Dinh Tu, 1995). Although vaccines are available, vaccination is commonly not practised by small farmers.

Cholera (Pasteurellosis)
Pasteurellosis is an acute or chronic disease causing severe economic losses in ducks. It is caused by Pasteurella multocida and spread by contaminated equipments or carrier birds. The disease can be prevented by vaccination or treated with antibiotics. Similarly with other diseases where vaccine is available, vaccination is seldom carried out. Pasteurellosis is one of the common diseases encountered in ducks in Malaysia (Aini, 1993).

Duck Septicaemia
Another name for duck septicaemia is Anatipestifer syndrome, which is caused by Pasteurella anatipestifer. It can cause sudden death in young ducklings, with losses due to mortality or retarded growth. It is sometimes confused with colisepticaemia, except that nervous symptoms may be present in duck septicaemia.

Aspergillosis
Aspergillosis usually causes respiratory problems in ducklings. Mouldy environment or feed is very favourable for the growth of Aspergillus.

Parasitic problems
The feeding habits of the ducks expose them to many endoparasites, such as Eimeria anatis, Tracheophilus sisowi and Hymenolepsis anatina (Jan Nari, 1979). Other diseases, which are not commonly reported, include paratyphoid, botulism, coccidiosis and leucocytozoonosis.

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Ducks, which are reared under scavenging or extensive systems, are susceptible not only to infectious but also to non-infectious diseases. Adverse environmental conditions also contribute to the poor health condition of these ducks. However, the actual disease status in family ducks is unknown due to the scarcity of information. Except for DVE, DVH, pasteurellosis and colibacillosis, not much has been reported about other diseases of ducks under backyard system.

The author would like to thank Ms Normadiah Sukaimi for typing the manuscript.

Aini, I. (1993): Poultry diseases in the Asia Pacific Region. Proceedings, 10th World Veterinary Poultry Association Congress, Sydney, pp. 41-46.

Awang, I.P.R. (1993): A study of layer duck farming in Malaysia. DVM Dissertation, Universiti Pertanian Malaysia.

Higgins, D. (1993): Infectious diseases of ducks - 1. Poultry International, September 1993, pp. 28-34.

Jan Nari (1979): The situation of poultry disease in Indonesia œ control and eradication. Proceedings, Second Poultry Science and Industry Seminar, Bogor, Indonesia, p. 130.

Seri Masran, M.S. (1996): Malaysia œ Country Report. Proceedings, Ninth Asean Seminar on Poultry Diseases and their control, pp. 23-29.

Tran Dinh Tu (1995): Poultry diseases and control in Vietnam œ an overview. Proceedings, First Vietnamese œ Hungarian Workshop on Small Animal Production for the Development of Sustainable Integrated Farms, pp. 143-147.

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