Pig production in Cambodia is currently
characterized by small-scale free range systems, with some medium
and large scale production units. However, small scale pig
production so far dominates the supply of pig meat in Cambodia. To
a certain extent, human food residues, rice products and water
spinach (Ipomoea aquatica) and other foliages are major components
of the daily ration (Khieu Borin 1994; Cameron and Twyford-Jones,
1995). In general, small scale animal production is dependent on
locally available feed resources such as rice bran, sugar cane
tops, sweet potato vines, cassava roots, and agro-industrial
by-products from marine food processing and brewing. Commercial
feeds are rarely used because these are expensive. The proportion
of commercial feed used is about 20 % of the total, while the
remaining 80 % is mainly crop residues and farm by- products, which
are often of poor quality and low nutritional value (An et al.,
2003). The question is how to improve the nutritional quality of
diets in small-scale pig production systems and thus improve the
production capacity of the animals. It is also important to look
for simple and appropriate technologies which farmers can easily
adopt and which will lead to better income.
Fattening pigs is one of the sources of farm cash income for the
rural farmers in Cambodia. Devendra (1993) reported that there was
an average annual growth rate of 16.6% of the pig population in
Cambodia and that was the highest rate among the countries of
South-East Asia. Generally, piglets are purchased after the rice
harvest. The reason for buying piglets at this time is that farmers
will have enough money and feed available from rice by-products
(Khieu Borin, 1996). Rice bran is one of the main by-products used
in pig raising. Rozemuller (1998) reported that the rice bran
produced by traditional mills in Cambodia is of low energy density,
which limits its potential as an energy source to complement
fibrous sources of protein such as water spinach. Broken rice is
another by-product of rice milling but with the advantage of a high
energy density as it is almost free of fiber. Preston and Sansoucy
(1987) and Preston and Leng (1987) have suggested that one way to
achieve sustainable animal production systems is to match them with
the available local resources. Nevertheless there are also other
important factors that affect the pig production systems, such as
management, breeds and mortality caused by infectious disease and
parasites.
The large water surface areas in Cambodia have
brought advantages to farmers for crop cultivation particularly
water spinach which can be grown almost year round for use as human
food and feed for animals Water spinach (Ipomoea aquatica) grows
equally well in water or in soil and it responds dramatically in
biomass yield (24 tonnes/ha/cut) and protein content more than 20%
in DM when it is fertilized particularly with biodigester effluent
(Kean Sophea and Preston, 2001). Le Thi Men et al. (1999) reported
that the annual yields of water spinach can be as high as 455
tonnes fresh biomass (about 40 tonnes DM) per ha. The short
production cycles (25-30 day per cut) make water spinach a
potential crop in the Mekong region. The fresh leaves and stems of
water spinach have high crude protein content in the range of 18 to
31% in DM (Le Thi Men et al., 2000; Bui Huy Nhu Phuc, 2000; Prak
Kea et al., 2003). The plant is also rich in minerals with an ash
content of 12% in dry matter (Göhl, 1981). It has been used
successfully to replace part of the protein in sugar cane juice
based diets for breeding sows (Le Thi Men and Bui Hong Van, 1993)
and as the main protein source for growing pigs fed broken rice
(Ly, 2001; Prak Kea et al., 2003). The high yield potential enables
farmers to get a regular high income from harvesting water spinach
for their pigs and selling it to local markets.
Although water spinach has high protein content, its
digestibility is rather low. Ly et al. (2002) reported that the in
vitro digestibility of the crude protein was only 56% compared with
75% for duckweed. The low energy density in water spinach is a
limitation but could be corrected by supplementing energy-rich
feeds such as cassava root meal. The protein in water spinach is
deficient in sulphur amino acids according to Le Thi Men, (1999)
and Bui Huy Nhu Phuc (2000), while sweet potato vines are deficient
in lysine (Le Van An, 2004), thus there could be advantages in
combining these two forages as the protein supplement in basal
diets of broken rice and rice bran, available locally in
Cambodia.
Sweet potato (Ipomoea batatas (L) Lam) is a tropical crop with a relatively short vegetative cycle, the tubers of which are used for both human and animal consumption (Woolfe, 1992). It is among the five most important food crops in developing countries (Horton, 1988) and is the third most important crop after rice and maize, in many areas of Cambodia such as Kandal, Kampong Cham and Takeo Provinces. Sweet potato is planted near the Mekong river after rice harvesting and it is often used as animal feed. The tubers have a high carbohydrate content while the leaves are rich in protein, and both tubers and vines can be used as animal feed (Woolfe, 1992). The vines include the leaf and stem, with a crude protein content in the leaves of 260-330 g/kg DM compared with 100-140 g/kg DM in the stems (Ishida et al., 2000; Le Van An et al., 2003). It has been shown that the leaves make up approximately half of the sweet potato vines biomass (Woolfe, 1992; Le Van An et al., 2003). Thus, if the leaves can be separated from the stems a considerable improvement with respect to the dietary protein and amino acid supply would be expected (Le Van An et al., 2003). Sweet potato based pig production systems are very common in Cambodia and play an important role in the economies of small scale farmers (Peter, 1998). The productive potential of certain varieties of sweet potato can reach 24-36 tonnes/ha/crop of roots (Morales, 1980) while the foliage production varies from 4.3 to 6.0 tonnes DM per ha (Ruiz et al., 1980)
The primary reason for using forages is to save grain crops for
human consumption. Pig production systems serve as family savings
for short-term needs, such as school fees, books or clothing for
children. Moreover pig meat provides part of the dietary protein
for the rural family (Chantalakhana et al., 2002) Many alternative
feed resources are available in Cambodia but more research is
needed as to how best they can be used in pig feeding. It is also
important that the alternative feed resources can be grown on the
farm as this will directly benefit the poorer farmers, who do not
have cash resources to purchase supplements from outside the farm.
Diets for pigs based on broken rice or cassava root meal,
supplemented with water spinach and sweet potato vines, will have
an amino acid balance close to that in the "ideal" protein. The
optimum level of protein in the diet will therefore be less than
recommended for diets based on maize and soybean meal (NRC 1998).
When the protein is from forages, growth performance will be
better when the energy source is low in fibre (broken rice)
compared to an energy source higher in fibre (cassava root meal
plus rice bran).
To study effects on growth rate and feed conversion of
pigs of:
Different levels of crude protein derived from combinations of
sweet potato vines and water spinach
Energy sources derived from broken rice, cassava root meal and
rice bran