Poultry production is a common activity in Southeast Asia, and is a major source of livelihood for over a million people in the rural areas. In the last two decades, Asian duck production has become more important, making up 87% of the world's duck population, and duck meat and egg production has increased more than four times (Chein Tai and Jui-Jane Liu Tai, 2001). This expansion has mainly come from the preservation of local breeds and strains, such as the local Muscovy duck and several Vietnamese breeds such as the Co and Tau duck (Duong Thanh Liem 2001), and imports of exotic and improved breeds. Improved ducks have become widely accepted and have increased in number, and are generally called “common ducks”.
Duck production is one component of integrated farming systems which are regarded as being part of a sustainable development in agriculture. Ducks (Anas platyrhynchos) can be integrated with rice, orchards, cash crops, livestock, and fish. Thus, the stakeholders not only can develop their livelihoods without accumulating debts, but also can get extra income through off-farm and non-farm activities (Le Thanh Phong et al. 2007). The Mekong Delta, located in the South of Vietnam, is considered as the country’s granary, accounting for 48% of the national rice production (followed by the Red River Delta). Besides, Mekong Delta has a warm ambient temperature and high annual rainfall that is suitable for duck production. Natural resources, including paddy rice fields, canal networks, and plant and grasses, for instance, are advantageous for ducks to increase in number. Ducks can effectively utilize low quality feed (agricultural residues, by-products and insects) and can produce highly nutritional foods for humans (Bui Xuan Men et al. 1998). Duck production is diversified into several raising systems according to economic criteria, for example, industrial integrated, medium to large commercial, medium to small commercial and mixed farming systems (integration of rice-ducks, ducks-fish or rice-fish-ducks) or spatial criteria, such as scavenging, semi-confined and confined systems (Edan et al. 2006). The large scale system has developed only recently in some areas of the delta. It is generally agreed that better breeds, together with improvements in management of stock health and using local feed resources, as well as other appropriate technologies should enhance sustainable small-scale duck production.
However, the free-raising of ducks in the rice fields or canals (scavenging system) without strict management of outbreaks of diseases is a risk for community health and also duck production. In order to deal with this important issue and create a sustainable duck production, semi-confined and confined systems are being introduced and widely extended, with the aim of limiting the spread of infectious diseases such as Duck Plague and Avian influenza.
An Giang Province, situated in the Mekong Delta is a well- known area for rice production, with 3,519,343 tonnes produced in 2008 (An Giang Statistical Yearbook 2009). The most common duck production system in this area is free grazing in the rice fields, utilizing the leftover rice grains, insects and snails as part of an integrated pest management system (Teo 2001). According to the An Giang Statistical Yearbook (2009), in 2008, there were 4,296,840 poultry, of which 3,437,129 were ducks, raised in An Giang Province.
Annually, rice mills produce large quantities of grain for export, as well as the by-products (rice husk, rice bran and broken rice). The broken rice is not as valuable as rice grain but it also can be exported or used locally for human consumption. Rice bran is the outer layer of the brown rice kernel (after separating the husk) which is removed while milling brown rice to white. Rice bran is a rich source of nutrients and a pharmacologically active compound and is currently used as livestock feed and for oil production (Tahira et al.2007). According to Houston (1972), rice bran often occupies 5-8 percent of paddy rice (whole grain). Commonly, in Vietnam, the rice mills have produced three kinds of rice bran: the initial bran (mixed with rice husk fragments) and two types of bran produced in the polishing process which are very fine and have higher nutritive value than the initial bran. In the Mekong Delta, rice bran is cheaper than rice grain and broken kernel so it is the most widely available feed resource for duck production.
Taro can be commonly found growing wild in the Mekong Delta, particularly on the banks of ponds and along rivers and canals. Traditionally, some taro species (Colocasia antiquorum and Colocasia gigantea ), which have a large corm or palatable stem, can be used for home consumption, while Xanthosoma sp., Alocasia sp., Alocasia cucullata and Alocasia macrorrhiza (giant taro/giant elephant ear) can be used both as human food and animal feed. Wild taro (Colocasia esculenta) originates from India and Southeastern Asia. It is a perennial herb 1.5 m tall, with thick stems, very small corms, and with leaf blades around 60 in length and 50 cm in width. Wild taro is very easy to grow, develops fastest in wet land and is highly resistant to pests and diseases. The wild taro leaf has a high nutritional value, with 22.5-26.3% crude protein in the dry matter (DM) (Malavanh Chittavong et al. 2008a and Chhay Ty et al. 2007). However, in common with other species of the Aracae family, an anti-nutritional substance, calcium oxalate, is found in all parts of the plant, causing irritation in the throat and mouth epithelium and indirectly affecting the feed intake. The influence of calcium oxalate can be reduced by ensiling with molasses (Malavanh Chittavong et al. 2008b), or by the addition of the stems without any further additive (Du Thanh Hang and Preston 2010; Nguyen Tuyet Giang 2008).
To investigate the opportunities to use taro leaves as an alternative to soybean meal as a protein source for growing ducks fed a basal diet of rice bran