Scientists from the International Potato Center (CIP) and Vietnamese collaborators from various institutions and disciplines have been working together since 1997 to improve the sweetpotato-based pig feeding systems in northern and central Vietnam. The avenues for improving this system consist of three approaches:
Sweetpotato varietal selection involves conducting on-station and on-farm trials to select varieties most suitable for pigs. On-farm trials are conducted in various locations in north and central Vietnam where sweetpotato is an important crop for pig feed. Two types of varieties are selected: 1) dual-purpose varieties, and 2) forage varieties. For dual-purpose varieties, both the vines/leaves and roots are taken into consideration because roots provide starch while leaves provide protein and soluble carbohydrates. In this case, fresh yields are not used to determine the quality of sweetpotato as a feed stuff. Instead, the starch yield (fresh yield x dry matter (DM) x percent starch in DM) in roots and the protein yield (fresh yield x dry matter (DM) x percent protein in DM) in vines and leaves are used as indicators of the nutritional value of the varieties. Dual-purpose varieties are planted in paddy fields of northern and central Vietnam as a winter-spring crop, and this is the best season for root production. During the other seasons, the growing period for sweetpotatoes is shorter, and the sweetpotatoes are also planted on uplands at these times but there is a lack of sufficient soil moisture for harvestable roots to form. Therefore, during the spring, spring-summer, summer, and summer-autumn seasons, vine and leaf production is often more important than root production. During these seasons, forage varieties, which contain abundant proteins, are the priority. For forage varietal trials, various cutting regimes (e.g., cutting intervals and cutting ratios) are also tested to determine the best cutting methods to produce the greatest amount of vine/leaf harvest. When a variety contains a high amount of total dry matter in both roots and vines, it is recommended as a dual-purpose variety. Such a variety may also contain a high amount of total protein in the leaves when vines are cut at regular intervals of 10,15,20, or 25 days, thus it can also be recommended as a forage variety. In this case, the variety can be recommended for both dual-purpose and forage.
Farmers face three constraints after harvest of their sweetpotatoes: 1) storage, 2) high labor demand for daily processing of sweetpotato roots and/or vines for pigs, and 3) the need to cook the sweetpotato roots because they contain high levels of trypsin inhibitor. Without adequate storage facilities, farmers are often forced to feed large quantities of sweetpotato to pigs immediately after harvest in order to minimize loss during storage due to weevils, rats, rotting, or other factors. Pigs can only benefit from a certain amount of feed sources each day and over-feeding only results in wastage. Those farmers who do not over-feed during the post-harvest period, however, usually encounter loss during storage due to damaged roots or vines. Trials are conducted to find simple and low-input ensiling methods to conserve roots and vines so that farmers may process during the off-season and then feed the resulting silage during the busy field seasons reserved for rice planting and harvesting. Ensiled roots and vines can also be stored for at least five months so that farmers can ration the roots and vines based on balanced feeding formulation. Most importantly, the silage process minimizes the trypsin inhibitor in roots and eliminates the need to cook the feed. This saves two to three hours of labor per day and the fuel necessary for cooking the pig feed.
On-farm pig-feeding trials are conducted using the ensiled roots and vines in conjunction with a base feed which mainly consists of crops available on-farm to minimize additional investment. These trials have three objectives: 1) to determine the optimal proportion of each ingredient within the balanced feed, 2) to examine the best ensiling method, and 3) to examine the best proportion of sweetpotato silage in the daily diet. The results of these trials show that sweetpotato silage has three advantages: 1) improved pig growth rate, 2) reduced cost per kilo of weight gain, and 3) saved labor and fuel for cooking. The use of ensiled vines also improves growth and reduces cost while eliminating the need to chop vines daily.
Although the focus has mainly been on nutritional aspects of the pig-raising system, disease management is essential in order to take full advantage of improved nutrition. More importantly, without disease management, the results of feeding trials would be inconclusive because it would not be possible to differentiate between the effects of nutrition and illness on growth. No trials are conducted on disease management; nevertheless, participation of a veterinarian is an integral part of the project. The vet makes sure that the trial pigs are property vaccinated, looks after the pigs' general health, and treats the pigs as soon as symptoms arise in order to minimize any potential impact of illness on pig growth during the trials. At the same time, farmers are advised on general disease and illness identification, prevention, and treatment.
This book provides a summary of these four programs that CIP personnel and Vietnamese collaborators have been conducting since the beginning of 1997. Accordingly, the book is organized along the lines of these four programs, for each of the agro-ecological regions in northern and central Vietnam where sweetpotato serves as an important source of pig feed. Southern Vietnam is not included in the book because most pigs in this area are raised on commercial feed and sweetpotato is mainly a cash crop. The book provides information for, and will be of interest to, sweetpotato-pig farmers and agricultural extension workers who have responsibilities in rural household crop and pig production.
A Vietnamese-language version of the book is available specifically for the farmers and extensionists in northern and central Vietnam. This English-language version of the book is produced for non-Vietnamese readers, because it is expected that the integrated methods of crop and feed production and processing explored in this manual will be of interest to agriculturalists and livestock specialists in general. Some contextual information on sweetpotatoes and pigs in Vietnam is provided below to facilitate the understanding of these readers.
There are seven agro-ecological regions in Vietnam; this book targets the three major regions in northern and central Vietnam where most of the sweetpotato is grown during two or three seasons a year between rice crops. Due to climatic and soil variations among these regions, the crops grown are somewhat different, and the requirements for each crop, particularly for sweetpotato which is highly variable also differ. Since pigs are crop-fed, the available feeds also vary among these regions. In order to provide specific, useful information for farmers in each agro-ecological region, the book is further organized by agro-ecological region. For each region, information on sweetpotato varieties is provided for each season, both for human consumption and pig feed. Each region also requires somewhat varied agronomic techniques; therefore, information on agronomic techniques is also region-specific. Likewise, information on pig-feeding rations and daily formulations are all organized according to the available feed in each region. Information on pig disease prevention, identification, and treatment, however, is not as site-specific and is presented in general for all three regions. This health section is included in the Vietnamese version as a guide for farmers; it is not included in the English version since no research was actually conducted on illnesses and diseases.
The English version was reviewed and revised based on comments provided
by Dr. Danilo Pezo, animal nutritionist with the International Livestock
Research Institute (ILRI), to ensure the technical quality of the book.
Asection on "Some principles of pig nutrition in the tropics"
was consequently supplied by Dr. Pezo to strengthen the book by providing
a technical context for feeding sweetpotato to pigs in the tropics.