Effect of different protein levels derived from mixtures of water spinach and fresh sweet potato vines in basal diets of broken rice or cassava root meal and rice bran for growing pigs

Thim Sokha, T R Preston^* and  Khieu Borin**

Royal University of Agriculture,

Faculty of Animal Science and Veterinary Medicine

Sokha_rua@yahho.com
^* TOSOLY-UTA,  AA #48, Socorro, Santander, Colombia
**CelAgrid, Phnom Penh, Cambodia

Abstract

Thirty two crossbred pigs (mean initial weight 11.33 kg) were housed in individual pens and allocated to 8 treatments according to a 2*4 factorial arrangement. The factors were two sources of energy: broken rice compared with cassava root meal mixed with rice bran; and four levels of crude protein (10, 12, 14 and 16% in dry matter (DM)). The source of supplementary crude protein was a mixture (50:50 as DM) of water spinach with sweet potato vines. The duration of the experiment was 150 days, from July 02 to December 02, 2006.

There were curvilinear relationships between dietary crude protein concentration and live weight gain and feed conversion with the optimum point at 14% crude protein in the diet DM. Growth rates were the same but feed conversion was better when the energy source was broken rice rather than cassava root meal and rice bean. Growth rates and feed conversion improved with time on the experiment.

Key words: Broken rice, cassava root meal, feed conversion, growth rate, pigs, rice bran, sweet potato vines, water spinach

 Introdution

Pig production plays an important role as a major source of income of the rural poor farmers; moreover it also provides manure as the fertilizer for cropping. In Cambodia, 75% of the total pig producers are farmers who live in the remote areas (Khieu Borin et al., 1996). As the human population grows, there will be a need for more food to meet the increasing demand. The production of meat from non-ruminants (pigs and poultry) is increasing faster than from the ruminants because of the quick turnover of the capital and the ease of access to the market. However, the traditional feeds for pigs are cereal grains and soya bean which are also eaten by people. Therefore it is important to develop pig feeding systems which are non-competitive with humans. The most common non-conventional feeds which are used for pigs in the country are rice bran, banana stems, sweet potato vine, water spinach, water hyacinth, duckweed, cassava and dried fresh water fish.

Water spinach (Ipomoea aquatica) is traditionally used in Cambodia as a vegetable for both humans and animals. It has a short growth period and is resistant to common insect pests and diseases; it can also be cultivated either in dry or flooded soils. It responds dramatically to fertilization with effluent from biodigesters charged with pig manure (Kean Sopea and Preston, 2001). The yield was up to 24 tonnes/ha of fresh biomass achieved in a growth period of 30 days. The leaves and stems of water spinach contain more than 20 % crude protein in dry matter basis (Le Thi Men et al., 1999; Le Thi Men et al., 2000; Kean Sopea et al., 2001; Göhl, 1981; Ly et al., 2002). Water spinach has been used successfully to replace part of the protein in a diet of sugar cane juice for breeding sows (Le Thi Men and Bui Hong Van, 1993). Prak Kea et al. (2003) reported that there was a linear increase in growth rates in pigs fed water spinach, palm oil and broken rice when up to 6% fish meal (in diet DM) replaced equivalent amounts of water spinach, which they attributed to an improved amino acid balance, especially in terms of the sulphur-rich amino acids. Chhay Ty and Preston (2006) reported that water spinach was more palatable and had higher digestibility than cassava leaves. 

Sweet potato (Ipomoea batatas L. (Lam)) is the third most common crop in Cambodia after rice and maize and is a valuable pig feed. The roots provide energy and the leaves provide protein, and both can be used fresh, dried or fermented into silage (Woolfe, 1992). It is a common feed for pigs and also has high biomass yields of both tubers and vines (Le Van An et al., 2003). Traditionally, sweet potato is used as human food; however at present it is also used as feed for farm livestock, especially pigs. The biomass yield of sweet potato is high and can reach up to 50 tonnes of foliage and 30 tonnes of roots/ha/year according to Hoang Vu Tuyen et al. (1993). Sweet potato vines can be harvested several times throughout the year (Dahniya, 1981; Hoang Vu Tuyen et al., 2003; Le Van An et al., 2003)

Sweet potato leaves are reported to have a crude protein content of 25.5 – 29.8 % in DM, which is almost double the level in the stems (10 to 14% in DM) (Woolfe, 1992; Ishida et al., 2000).  The leaves can be used fresh, dried or as silage, and can replace fish meal and groundnut cake as a protein source for growing pigs (Le Van An, 2004). Growing pigs fed sweet potato leaves with addition of synthetic lysine had daily live-weight gains of 536 g per day, which was similar to that of pigs fed a control diet with fish meal as the protein source (542 g/day) (Le Van An, 2004). Men Le Thi et al. (2000) and Duyet Hoang Nghia et al. (2003, 2004) reported  that the most suitable proportion of sweet potato leaves in the diet of  sows is from 30 to 40 % (in DM) in pregnancy, and 20 to 30 % in lactation.

Rice bran is one of the main by-products used in pig raising (Rozemuller, 1998). However, the rice-bran produced by traditional mills in Cambodia is of low energy density. Broken rice is another by-product of rice milling but with the advantage of a high energy density as it is almost free of fibre. Cassava root meal is another energy source available in Cambodia. However, it is low in protein. According to Eusebio (1980), the inclusion of more than 50% cassava root meal in the ration decreases the live weight gain and the feed conversion of pigs.

The aim of the presented study was to determine the effect of different levels of crude protein, derived from combinations of sweet potato vines and water spinach in diets, on intake, growth rate and feed conversion by crossbred pigs fed basal diets based on broken rice or cassava root meal mixed with rice bran.

Material and methods

Location and duration

The experiment was conducted at the ecological farm of the Center for Livestock and Agriculture Development (CelAgrid) located in Preah Theat village, Rolous commune, Kandal Steung district, Kandal province, about 25 km from South of Phnom Penh city, Cambodia. The average annual temperature in this location is from 26 to 31 0C. The experiment was started on 02 July and finished on 02 December, 2006.

Experimental design

Thirty two crossbred pigs (Local*Yorkshire or Local*Landrace) were used in the experiment which was carried out as a 2*4 factorial arrangement. There were 4 replicates arranged as 4 blocks; 2 blocks had 16 castrate male pigs with average initial live weight of 11.7 kg and 2 blocks had 16 females with average initial live weight of 11.0 kg. The factors were four protein levels (10, 12, 14 and 16% in DM) and two energy sources (Broken rice alone or rice bran mixed with cassava root meal).

Energy source

 ·        Cassava root meal plus rice bran (CRM-RB) or broken rice  (BR)                           

Level of crude protein

 ·        10 ,12, 14 and 16 % in DM

Animals and management

The pigs were housed in individual pens with concrete floors and were provided with drinking nipples. All the pigs were vaccinated against hog cholera, pasteurellosis and salmonellosis diseases. They were also treated with an anti-parasitic drug (Ivomic given by injection) once after the vaccination.

Housing, feeding and management

Broken rice and rice bran were purchased from a local rice mill. The cassava root meal was purchased from the local market. Sweet potato vines were harvested initially from plots in CelAgrid (Photo 1). However, because of flooding in the Centre, it was later purchased from farmers in Kandal and Takeo provinces. The water spinach was bought from traders who harvested it from lagoons receiving waste water from Phnom Penh city (Photo 2).

 The water spinach and sweet potato vines were chopped into 1-2 cm lengths and mixed in the ratio of 50:50 (DM basis). The forages were given as the first feed at 07.00h.  The energy component was given at 12.00 and 16.00 h.

Measurements and data collection

The pigs were weighed in the morning before feeding, at the start of the experiment and then every 10 days. Individual daily weight gain was calculated by the regression of live weight on time in days. Individual feed intake was calculated from weight of fresh material offered minus the residue collected the next morning. Feed offered and feed refusals were recorded daily. Feed conversion ratio was calculated from individual daily DM intake and live weight gain. Samples of feeds offered and refusals were analysed for DM by microwave radiation (Undersander et al., 1993) and N following the methods of AOAC (1990).

Statistical analysis

The data were analysed statistically using the General Linear Model (GLM) option of Minitab (version 13.31) ANOVA software Minitab (2000). Sources of variation were: protein level, energy source, interaction between foliage* energy source, blocks and error.

Results

Feed intake 

The composition of the dietary ingredients is shown in Table 1.

 DM intakes of the forages were higher on the CRM-RB diet than on the BR diet (Table 2) at all stages of the experiment. There were significant interactions among treatments for intake of the forages and the total DM intake (Figures 2 and 3). On the CRM-RB diet the total DM intake increased with increase in protein content of the diet up to 134 g crude protein/kg diet DM and remained at the same level at the highest concentration of crude protein. On the BR diet the maximum DM intake was also reached with a protein level of 134 g/kg DM, but decreased significantly at the highest crude protein level. The intake of forages increased with crude protein of the diet on the CRM-RB treatment; in contrast, on the BR diet, intake of the forages showed no increase between 134 and 152g crude protein per kg of diet DM.

Growth rate and feed conversion

The mean live weights of the pigs at 150-days intervals during the experiment are shown in Table 5.

There were no differences in growth rate between the CRM-RB and BR diets at any stage of the experiment (Table 6 and Figure 4)  As expected there were differences in growth rate due to protein level at all stages of the experiment (Table 7; Figure 5). There were no interactions between sources of energy and levels of protein. Growth rates increased with time on the experiment (Tables 6 and 7). On the basis of the growth curves (Figure 5) the optimum crude protein level would appear to be about 14% in diet DM. The curvilinear relationship between live weight gain and crude protein concentration (Figure 6) also indicates little improvement in growth rate when the crude protein exceeded 14% in the diet DM.

Feed conversion was better on the BR diets than on the CRM-RB diets (Table 8) and improved as the protein concentration in the diet increased, in all stages of the experiment (Table 9). The relationship between protein concentration in the diet and feed conversion was curvilinear, indicating there was little improvement in conversion when the crude protein exceeded about 140 g/kg diet DM (Figure 7).

Discussion 

Diet composition

 The DM (16.0%) and crude protein (16.6% in DM) of the sweet potato vines were similar to the values reported by Brown and Chavalimu (1985) (18.1% DM and 17.2% crude protein in the DM). Similar values were reported by Dominguez (1992). The DM  and crude protein values for the water spinach (8.9 and 28.8%) differed slightly from those reported by Chhay Ty et al. (2006) (DM 11.2 % and  crude protein 25.6 %)  but were similar to results of Bruemmer and Roe (1979) (8.0 % DM and 29.0% crude protein) and Le Thi Men et al. (2000) (crude protein DM o f 28%). The crude protein values of the broken rice, cassava root meal and rice bran were similar to literature reports (Göhl, 1971).

Feed intake

The higher DM intake for the diets containing CRM-RB may have been a response of the pigs to the lower energy density (higher fibre content) of this energy source compared with broken rice which contains no fiber. A similar difference was reported by Chiv Phiny et al. (2007) comparing cassava root meal and rice bran diets with broken rice and sugar palm syrup. The absolute values for DM intake in our study for the CRM-RB diets were lower than in the experiment of Chiv Phiny et al. (2007) because the initial weights in our study were lower (11kg compared with 20kg).  There is no obvious explanation for the decrease in DM intake in the BR diet when the protein level was increased from 13.4 to 15.2% in the DM, since this depression was not observed for the CRM-RB diet. On both basal diets the major increase in intake when the crude protein was raised from 7-8% in DM to 11% almost certainly represented a response to an improved balance of protein to energy in the diets.

Growth rates and feed conversion

There appear to be few reports on the effect of protein levels on growth of young pigs given diets in which the major part of the protein was derived from vegetative sources. Nguyen Thi Hoa Ly et al., (2003) compared crude protein levels from 12 to 18% in the DM of diets for pigs (initial weight 20kg) give diets based on rice bran and maize with the protein derived from increasing proportions of sweet potato leaf meal and fish meal. There were no significant differences in the growth rates among protein levels and the authors concluded that the economically optimum level was 14% crude protein in the diet DM for the growth phase from 20 to 50kg.  Gonzaley et al. (2003) used a design in which sweet potato vines were given free choice and the protein level of the diet was varied by changes in the concentrate supplement in which the range of crude protein was from 13.2 to 25.1% derived mainly from soybean meal. Best results were with the supplement containing 17% crude protein with an overall crude protein in the diet of 17.3% in DM. This level is much higher that the optimum in our study which was with about 14% crude protein in the DM.  Prak kea et al. (2003) reported a liner increase in growth rates in pigs fed water spinach, broken rice and palm oil when the level of fish meal was raised from 0 to 6% partially replacing the water spinach which decreased from 50 to 29% of the diet, the overall content of crude protein falling slightly from 16.8 to 15.4% in DM.

The implication of inferior protein quality in sweet potato vines and water spinach is supported by the finding that when these feeds were major components of the diet of growing pigs there were improvements in growth rate from supplementation with lysine in the case of sweet potato vines (Le Van An 2004) and with methionine in the case of water spinach (Ly et al., 2002).  Similarly, Du Thanh Hang et al. (2007) recorded significant improvements in growth rate to methionine supplementation in pigs fed ensiled cassava roots and cassava root meal when the protein supplement was mainly as fresh cassava leaves.

Conclusions

• The optimum crude protein concentration for young growing pigs, given diets with low protein sources of energy (mixture of cassava root meal and rice bran or broken rice) and with the protein mainly from high protein forages (water spinach and sweet potato vines), was 14% in the DM.

• Growth rates were similar for basal diets derived from a mixture of cassava root meal and rice bran, or broken rice; however, feed conversion was better on the broken rice diets.

Acknowledgements

This research thesis was carried out at the ecological farm of the Centre for Livestock and Agriculture Development (CelAgrid) in Cambodia during the period 150days from July 02, 2006 and to December 02, 2006.

The authors would like to express my sincere gratitude to the MEKARN Project with the support from the Swedish International Development Authority (Sida) and Swedish Agency for Research and Cooperation (SAREC) to make this study possible.

Thanks are due to Mr. Chhy Ty for help in analysis the samples in the laboratory and to all staff of CelAgrid, especially Mr. Narum, Pearun, Savy and students Kampong Cham National school of Agriculture for their assistance during the entire experiment for taking care of the feeding and management of the pigs.

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