On-farm evaluation of the effect of different fertilizers on water spinach (Ipomoea aquatica) yields, and of including water spinach and catfish oil in diets for fattening pigs in the Mekong Delta of Vietnam

Le Thi Men, T R Preston*, Tran Thi Thao, Bui Van Cong and Dang Ngoc Hoi

Department of Animal Science, College of Agriculture,
Cantho University, Vietnam
ltmen@ctu.edu.vn
* UTA Foundation, TOSOLY AA#48, Socorro Santander, Colombia
trpreston@mekarn.org

Abstract

Water spinach (WS) yield was estimated on 6 farms in the Mekong Delta. On 3 farms the WS was fertilized by pig manure compost and on 3 farms by using digester effluent. On each farm 120 m² of land was divided into 30 plots for growing and harvesting water spinach during 2 growth cycles.

The WS fresh biomass yield (29.8  tonnes) on pig compost was higher than for biodigester effluent (25.4  tonnes) in cycle I. However, the contents of DM and CP of WS were not different  between the two types of fertilizers. The yield of WS and the nutritive values showed the same tendency in cycle II. The content in dry matter basis of lysine was 0.97% vs 0.89%, threonine 1.09% vs 0.96% and methionine 0.45 % vs 0.57% for whole plant WS cultivated by pig compost or biodigester effluent, respectively.  There was higher level in total lipid of linoleic acid (C18:2) (15.9% vs 14.1%), but lower a-linolenic acid (C18:3= 42.7% vs 43.2%) in WS cultivated by pig compost compared with  WS given biodigester fertilization.

An on-farm trial was carried out using locally available feed resources to improve the current low income of farmers. 36  Yorkshire-type pigs, comprising an equal number of castrated males and females with initial mean live weight of 54 kg were used. The trial was designed as a randomized block with six households and three dietary treatments. The basal feed was the same for the three treatments and was based on rice-by products, a protein concentrate and included: catfish oil 5% (CF5); catfish oil 5 % with water spinach 5% (CF5-WS5) and water spinach 5% (WS5).

The daily weight gain (ADG) and feed conversion ratio (FCR) were not affected by dietary treatment. The feed cost per kg weight gain, and economic gross income were improved in WS5 (11%), and CF5WS5 (9%) in comparison with the CF5 diet. Overall, these results indicate that usage of locally available feed resources as supplements in pig diets can be recommended, especially in the practical smallholder situation.

Key words: Biomass, catfish oil, fattening pigs, fertilizer, local feeds, water spinach

Introduction

The Mekong delta with a large water surface area on the Tien and Hau rivers is suitable for aquaculture, especially for the Mekong catfish cultivation in floating houses. Large factories produce frozen white river cobbler filet for export. Of the abundant residues, the belly is pressed to give raw fish oil, which mainly consists of the fatty acids C16:0 (30.1%), C18:1 (38.3%) and C18:2 (13.2%) and has an energy content of 37.6 MJ/kg (Le Thi Men et al. 2003). With 5% of catfish oil included in growing pig diets based on rice by-product or dried cassava root waste, daily gain and feed cost per kg gain were improved. The CP content (20%) of the pork was not changed and the Iodine index (60) of pig fat little affected (Le Thi Men et al 2003).

Water spinach (Ipomoea aquatiac) or swamp cabbage with short growth cycles (4 weeks each one) has crude protein (26%  in DM), a balanced array of essential amino acids (Lys 1.3%, Met 0.4%, Thr 1.1% in DM), β-carotene and ME of 10.6 MJ/kg in dry matter basis. It has been studied for replacing a part of protein in diets in pig feeding in the Mekong Delta (Le Thi Men and Bui Hong Van 1994; Le Thi Men et al 1999, 2001, 2002 and 2003).

The HAT is one cultivar of water spinach this is cultivated from seed and gown in the soil. It has high fresh biomass yield after 3-4 weeks from sowing  (Duong Hong Dat 2002), and is rich in protein content. The crude protein content in the leaves and stems can be as high as 32 % and 18 % in dry matter basis, respectively (Ly Thi Luyen 2003). This vegetable can be widely used for human food, and given to rabbits, pigs and poultry (Hongthong Phimmmasan 2003).

Animal manure is a potential replacement for chemical fertilizer and is traditionally used by poor farmers in Vietnam. However, it is not properly managed so that the efficiency of utilization of the manure is not high. The introduction of low-cost biodigesters in Southeast Asia (Bui Xuan An et al 1997) has made it possible for small - scale farmers to convert manure into   biodigester and a nutrient-rich effluent.

The hypotheses

• Water spinach can grow well in land areas fertilized by pig manure compost or biodigester effluent and produce a high fresh yield in a recycling model for small holders in the Mekong Delta.

• Catfish oil at 5% can be combined with fresh water spinach in diets as a nutrient and energy supplement for fattening pigs and give improved performance and benefit to farmers.
   

Materials and methods

Water spinach cultivation

The trial was conducted during February and May 2004 in Tan Phu Thanh village, located around 20km from Cantho city. The economy of the village is based mainly on agriculture, of which fruit production ranks in first place, and rice production is the important component of the farming systems. In addition, livestock production includes pigs and fishery and other water resources are vital to the well-being of the village. Based on the practical situation, 6 families raising pigs were selected and divided into 2 groups, the first has plastic bio-digester (3 farms) and another 3 farms do not have biodigester. Each household had 120 m² of soil divided into 30 plots for growing water spinach from seed. The fertilizer used was pig manure compost or digester effluent. The fresh biomass was harvested after 30 days by turn for two cycles. The proportion of leaves and stems was measured in every cycle. The whole plants or leaves and stem separated were measured and the content of DM analysed by micro-wave radiation (Undersander et al 1993), crude protein and amino acid concentration (AOAC 2000). Fatty acid composition in the WS samples was determined by the method described by Jacobs et al (2000).

Feeding trial

The 36 Yorkshire-type pigs comprising equal numbers of castrated males and females had 54.3 ± 6.6 kg mean initial live weight . The experimental design included 3 dietary treatments, replicated in 6 farms, within which pigs were allocated to the treatments. There were 2 pigs (male and female) in each pen, and they were given the experimental diets three times daily. The daily allowance was restricted to about 3.5 % of body weight. There was free access to drinking water.

Samples of each feedstuff were taken in each farm, and the contents of DM, CP, CF, EE were analyzed according to AOAC (2000); ME was estimated according to NIAH (1995). All pigs were weighed at the initial, and final time point of the trial. Feed refusal in every pen was corrected every day.

Statistical analyses

Data were analyzed by ANOVA using the Basic statistics and General Linear Model of Minitab Statistical Software version 13. Sources of variation were treatments and blocks. The Tukey Test for paired comparisons was used to separate means when the differences were significant at the 5% level.

Results and discussion

Water spinach yield

Fresh biomass yield of water spinach was higher with use of pig compost than with biodigester effluent in both cycles I and II (Table 1).

The proportion of leaves to stems was similar in both cycles and for both types of fertilizer (Table 2). .

The content in dry matter basis of lysine was 0.97% vs 0.89%, threonine 1.09% vs 0.96% and methionine 0.45 % vs 0.57% for whole plant WS cultivated by pig compost or biodigester effluent, respectively (Table 3).  There was higher level in total lipid of linoleic acid (C18:2) (15.9% vs 14.1%), but lower a-linolenic acid (C18:3= 42.7% vs 43.2%) in WS cultivated by pig compost compared with WS given biodigester fertilization.

Pig feeding

Crude protein and crude fibre were similar for the three dietary treatments (Table 5), but the EE and ME content of the WS5 was lower than the others with added 5% catfish oil.

Growth and feed conversion did not differ among diets (Table 6). Feed cost per kg weight gain was lower for  WS (7,616 VND) than for  CF5WS5 (7,884 VND) and CF5 (8,115 VND). Sale price per kg live weight of finished pigs was slightly lower (14,500 VND) for CF5 because of the fatter appearance compared with the other diets (15,000 VND). As a result, the gross income per total weight gain was  higher in WS5 than in CF5WS5 and lowest in CF5 (Table 7). Thus, net economic benefit was higher in WS5 (11 %) and CF5WS5 (9%) compared with the CF5 diet.

Picture 1. The 'HAT' water spinach (WS) cultivated in the households of the Mekong Delta by using compost and biodigester effluent
Picture 2. Collecting WS	Picture 3. Feeding WS
Picture 4. The raw catfish oil used in the pig diets

Conclusions

• It is suggested that small holder farmers should cultivate vegetables as supplements for pigs, using effectively animal waste residues.

• Diets with 5% catfish oil gave better results when combined with 5% water spinach (DM basis) than when the oil was given alone.

References

AOAC 2000 Official Methods of Analysis. American Association of Analytical Chemists. Washington, DC.,USA

Bui Xuan An, Preston T R and Dolberg F 1997 The introduction of low-cost polyethylene tube biodigesters on small scale farms in Vietnam, Livestock Research for Rural Development, 9:2  http://www.cipav.org.co/lrrd/lrrd9/2/an92.htm

Duong Hong Dat 2002 Cultivated  Vegetables Manual. Hanoi Publishing House. 180 pp.

Le Thi Men and Bui Hong Van 1994 Evaluation of diets based on simulated sugarcane juice and water spinach for breeding sows. National Seminar Workshop Sustainable Livestock Production on Local Feed Resources. Hanoi/Ho Chi Minh city, Vietnam. Nov.22-27,1993

Le Thi Men, Brian Ogle and Vo Van Son 1999. Evaluation of water spinach (Ipomoea aquatica) for Baxuyen and Large White sows. Proceeding in National seminar-workshop. Ho Chi Minh City, VN. January 18-20 of 2000
http://www.mekarn.org/sarpro/lemen.htm

Le Thi Men, Huynh Huu Chi, Ngo Vi Nghia, Nguyen Thi Kim Khang, Ogle B and Preston T R 2003 Utilization of catfish oil in diets based on dried cassava root waste for crossbred fattening pigs in the Mekong delta of Vietnam Livestock Research for Rural Development (15) 4 Retrieved May 3, 2004, from http://www.cipav.org.co/lrrd/lrrd15/4/men154.htm

Le Thi Men, M. Yamazaki and R. Takada 2002 Determination of Amino Acids in Animal Feed Stuffs with High Performance Liquid Chromatography (unpublished)

Ly Thi Luyen 2003 Effect of the urea level on biomass production of water spinach (Ipomoea aquatica) grown in soil and water. Retrieved, from MEKARN Mini-projects http://www.mekarn.org/MSc 2003-05/miniprojects.htm

Hongthong Phimmmasan 2003 Water spinach (Ipomoea aquatica) as a low-cost feed resources for growing rabbits. Retrieved, from MEKARN Mini-projects. http://www.mekarn.org/MSc 2003-05/miniprojects.htm

Undersander D, Merten D R and Thiex N 1993. Forage analyses procedures. National Forage Testing Association. New York.