2. Feed crops and their processing and storage methods

Main available feeds include rice bran, corn, and sweetpotato (SP) vine; in addition, SP root, cassava roots, and cassava leaf are also very important feed resources for pigs.

2.1 Energy sources

2.1.1 Sweetpotato (SP) root

Like com meal and cassava meal, sweetpotato is also a readily available starch feed with high energy content in northern and central Vietnam. Similar to cassava meal, it has very low protein content. One major constraint of feeding sweetpotato roots as pig feed is the trypsin inhibitor which needs to be eliminated by bringing the feed to boil. Therefore, protein supplementation is also needed for sweetpotato root-based diet. SP root is very difficult to store for long because of its perishability and weevil attack. Hence, there is a need to process, such as ensiling, not only to reduce losses but also to improve quality by increasing nutritional level and decreasing trypsin inhibitor level, during long storage and use.

2.1.2 Dried cassava slices (chips) and cassava meal

Cassava root is also an available, common and cheap starch feed with high energy but low protein content. So protein supplementation is needed for the diets including cassava root meal. Fresh cassava roots contain high levels of hydrocyanic acid (HCN), which is toxic to animals, and cassava root cannot be stored in fresh form for a long time. It is better to store in form of dried chips or slices for later use.

To make chips or cassava meal, wash roots after harvesting. Then slice them (it is better when the brown peel is eliminated before slicing) and dry naturally in the sun on concrete floor until they become crispy dried and the moisture content gets below 14%. Drying time should not exceed 2 days. When it exceeds 3 days, quality may deteriorate. Put the dried slices in completely tight nylon bags for storage. The bags should be kept in a high, dry and cool place. They are milled only before feeding to pigs and they should be ground on a 1 mm sieve. Cassava meal prepared in this way has little risk of poisoning with hydrocyanic acid.

2.1.3 Corn meal

This is the most common and most available starch feed with high energy content. After harvesting, eliminating hairs, and shelling, the seeds are dried naturally in the sun on concrete floor and turned over regularly until reaching the moisture content of 14 % or below. The seeds are stored in a container to protect them from insects and rats. Before feeding to pigs they are ground to 1 mm.

2.2 Protein sources

2.2.1 Rice bran

This is the by-product of the milling industry. It is a good source of protein, fat, minerals and vitamin (B1). For pigs, rice bran Class 1 should be used because of its higher protein, fat and low fibre content.

2.2.2 Cassava leaf meal

Cassava leaf meal is a good feed source for animals because of its high protein, carotene and ash content. Fresh cassava leaves contain high HCN which can be eliminated by processing such as drying or ensiling.

After harvest, cassava leaves should be chopped not only because it helps to reduce cyanide, but also it shortens the drying time. Simple sun drying alone eliminates almost 90 % of the initial cyanide content. When combined with chopping, cyanide in the dried meal is reduced to levels which are safer for monogastric animals. They are then naturally dried in the sun by uniform distribution on concrete floor and turned over regularly as necessary. Once the moisture content reaches 14 % or lower, they become crispy and

become easier to break by hand. Drying takes two days in sunny and dry weather. After that they can be preserved in completely tight nylon bags for later use. The bags can be kept in the kitchen under the roof or in a high, dry and cool place. This procedure of preservation risks little chance of molding and insect infestation. Dried cassava leaves need to be ground on 1 mm sieve before feeding to pigs.

2.2.3 Sweetpotato vine

Sweetpotato vine is a good source of protein, ash and vitamins but rotting often develops, especially during the winter when it is cold and humid. Hence, it needs to be processed to improve quality, particularly increasing CP, and for prolonged use. Ensiling is a good method to process and store sweetpotato vine. For dual-purpose SP, vines are harvested in one cutting, which makes it convenient to irrigate, fertilise, and manage ensiling. The methods of ensiling sweetpotato vine and root have been discussed in an earlier section.

2.2.4 Fish meal

Fish meal contains high protein, fat, and ash content, and the animal protein source with high biological value makes it a particularly good feed.

Fish can be dried naturally in the sun or artificially in an oven. The dried whole fish can be preserved in completely air-tight nylon bags. Before feeding to pigs they should be ground. Fish is difficult to grind alone because of its high fat level, so they should be ground with dried com or soybean. For example, fish can comprise 10% of 100 kg of mixed concentrate feed. Or, 10 kg of fish can be mixed with 44 kg of com seeds and 10 kg of roasted soybean seeds before grinding them together.

2.2.5 Roasted ground soybean

Soybean is also a protein- and fat-rich feed. It provides plant protein with high biological value. Together with fish meal, roasted ground soybean is a good protein supplement for pigs when they are fed with cassava meal and sweetpotato root.

After harvest, soybean can be dried naturally in the sun as with corn. When drying is completed soybeans should be preserved in a container to protect from insects. Before grinding to feed to pigs, soybeans should be well roasted to eliminate trypsin inhibitor and to improve flavour.

2.2.6 Chicken manure

Although chicken manure is a waste product of chicken production, it is a very cheap source of protein and minerals. After drying it can be an additive for making silage of sweetpotato vines and roots. Ensiling has the effect of eliminating pathogens potentially present in chicken manure.

Two sources of chicken manure are available; The first source is from industrial chicken production including broiler and laying chickens, fed on balanced commercial feeds (feeds from the joint-venture companies or self making). The second source is from Free-ranging chicken raising, manure can be collected only when the chickens are inside the pen during the night. Industrial chicken manure has highest N content than Free-ranging one with, and the quality of boiler chicken manure is higher than the one from laying hens.

The chicken manure used for animal feed could come from broiler's manure cage floor system caught on a nylon sheet since its protein content is high while fibre and ash contents are lower. On the other hand, it is not contaminated with soil. It can be collected every 5-7 days before drying in the sun on concrete floor or on a nylon sheet. Drying takes about 2 days in hot and sunny weather. After finishing drying it should be kept in air-tight nylon bags for longer use. Before using for silage production it is ground on 1 mm sieve.

2.3 Concentrate feed mixtures (basal feed)

Concentrate feed mixture is a compound from various feed ingredients: from starch, energy source (com meal, cassava meal), protein and fat sources (rice bran, cassava leaf meal, soybean, fish meal) and mineral sources (mineral premix or dicalcium phosphate) to supply the basic requirement of the pigs diet.

After grinding on 1 mm sieve, the feed materials (com meal, cassava meal, cassava leaf meal, fish meal, soybean, rice bran) are mixed together according to the proportion shown in a later section. The ingredients can be mixed manually (by hand or by hoes) or by means of a mechanical mixer. If mixed manually it should be mixed and turned over 3-5 times until the mixture becomes well integrated.

2.4 Chemical composition and nutritive value of main feeds for pigs in Vietnam

Rice bran I:	High content of crude protein (13%) and low content of crude fiber (7.8%)
Rice bran II:	Medium content of crude protein (9.8%) and medium content of crude fiber (18.6%)
Ricebran III:	Low content of crude protein (7.6%) and high content of crude fiber(23.3%)
DM.	Dry Matter(%)
CP.	Crude Protein (%)
TP.	True Protein (%)
EE.	Ether Extract(%)
CR.	Crude Fibre(%)
NFE.	Nitrogen Free Extract (%)
T.ash:	Total ash (%)
Ca:	Calcium (%)
P.	Phosphorus (%)
ME.	Metabolisable Energy (kcal/kg).
Ch.manure CP1:	Meat purpose broiler chickens' manure from cage floor system caught on a nylon sheet, fed with CP group's feed.
Ch.manure CP2:	Meat purpose broiler chickens' manure from cage floor system caught on ground, fed with CP group's feed.
Ch.manure CG:	Meat purpose broiler chickens' manure from cage floor system caught on a nylon sheet, fed with Cargill's feed
Ch.manure KB:	Kabir dual purpose (a Chinese breed) broiler chickens' litter caught from deep litter system with rice husk bedding material, sieved to eliminate rice husk.
Ch.manure TH:	Tam Hoangdual purpose (a Chinese breed) broiler chickens' litter caught from deep litter system with rice husk bedding material, sieved to eliminate rice husk