Water spinach (Ipomoea aquatica) and Stylo 184 (Stylosanthes guianensis CIAT 184) as basal diets for growing rabbits
 

Hongthong Phimmmasan,  Siton Kongvongxay, Chhay Ty* and T R Preston**

Livestock Research Centre, NAFRI, Lao
 hongthongp@yahoo.com
*UTA (Cambodia), PhnomPenh, Cambodia
chhayty@utafoundation.org
**UTA (Colombia), Socorro, Santander, Colombia
regpreston@utafoundation.org

Abstract

Two experiments were carried out to evaluate fresh water spinach (Experiment 1 in An Giang University, Vietnam) and stylo 184 (Experiment 2 in the Livestock Research Centre in Lao) as basal diets for growing rabbits. In each experiment graded levels of broken rice were used as supplements (0, 5, 10, 15 and 20 g/rabbit per day in Experiment 1 and 0, 4, 8 and 12 g/day in Experiment 2).

Growth rates on water spinach ranged from 18 to 23 g/day and DM feed conversion from rates 1.61 to 2.65, and were not affected by the level of broken rice.  DM digestibility coefficients determined by the insoluble ash technique ranged from 84.7 to 89.3% and were not affected by level of broken rice. The rabbits preferentially selected the leaves of the water spinach (70% of leaf DM consumed compared with 50% in the foliage offered). Levels of short chain fatty acid in the faces increased with level of broken rice, implying that gastric digestion of starch in the stomach was incomplete. Performance on Stylo 184 as the basal diet was much poorer with growth rates ranging from 5.54 to 6.67 g/day and DM feed conversion from 15.1 to 19.8.

Water spinach as the only source of feed for growing rabbits appears to support acceptable growth rates of close to 20 g/day with a DM feed conversion of 2.7.  This simple feeding system may be attractive for small-holder farmers in the tropics, due to the possibility to raise rabbits with a local resource (water spinach) that is easy to grow and needs no processing.

Key words: Broken rice, digestibility, growth, rabbits, water spinach

Introduction

In most developing, tropical countries as Laos, Vietnam or Cambodia, farmers keep livestock like cows, buffaloes, pigs, fish and poultry for their main source of income. Small animals like chickens, ducks and rabbits are used for home consumption. However, productivity is low and there is a lack of feed resources, particularly in the dry season.

Some approaches to solve the main constraint of feed scarcity in general and protein sources in particular, have been directed toward the search of local feedstuffs. Rabbit husbandry is not an exception in this context, and there are some recent reports concerning the use of tropical foliages as sources of protein for this specie (Akinfala et al 2003; Sarwatt et al 2003).

Two protein-rich forages available in Lao are water spinach (Ipomoea aquatica) and Stylo 184 (Stylosanthes guianensis CIAT 184).   Water spinach is easy to plant and has a very high yield of biomass, which is rich in protein. The crude protein content in the leaves and stems can be as high as 32 and 18 % in dry basis, respectively (Ly Thi Luyen 2003). It is widely used for human food, but at the same time this vegetable can be given to rabbits, pigs and poultry. For these reasons, it is considered that water spinach can be a low cost feed for rabbits at smallholder farmer level. Stylo 184 is a short-lived perennial legume (2 to 3 years) that grows into a small shrub with some woody stems. It is adapted to a wide range of soils and climates but is one of the few herbaceous legumes which will grow well on infertile, acid soils.  Unlike earlier varieties of S. guianensis (eg. cv. Schofield, Cook and Graham) Stylo 184 has shown good resistance to the fungal disease anthracnose in Southeast Asia. It is usually grown as a cover crop, which is cut every 2 to 3 months. It effectively suppresses weeds and is a good feed supplement for most animals, including chickens, pigs and fish. Stylo 184 can be fed fresh or dried for hay and leaf meal. It does not tolerate being cut close to the ground since there are few buds on the lower stem for regrowth. This can be improved by making the first cut at 10 to 20 cm to encourage branching close to the ground. Subsequent cuts must be made higher (>25 cm) to ensure good regrowth (Horne and Stür 1999). N concentrations of Stylosanthes guianensis range from 1.5 to 3 % in DM. DM digestibility of young plant material lies between 60 to 70%, but with increasing age and lignification this may be reduced to below 40% (Mannetje and Jones 1992).

The objective of this communication is to report preliminary observations concerning the use of water spinach and stylo 184 as the basal diet for growing rabbits, and to determine the effect of supplementing these forages with small amounts of broken rice as a readily digestible source of carbohydrate.

Materials and methods

Location

The experiment with water spinach was carried out from August through September 2003 at An Giang University, Vietnam, as one of the mini-projects in the MEKARN MSc programme (www.mekarn.org). Average air temperatures in the experimental area were: 6 am, 27.3 ± 1.55 ^oC, 12 am, 31.8 ± 2.92 ^oC, and 6 pm, 27.7 ± 2.37 ^oC. The experiment with stylo 184 was done in the Livestock Research Centre of NAFRI, in Nam Xuang about 44 km from Vientiane city, Lao PDR, from October through December  2003.

Experiment 1: Water spinach

Animals and treatments

Ten young rabbits in individual cages (average 416 g live weight) were allotted at random into five treatments consisting of fresh water spinach (Ipomoea aquatica) given at libitum and five levels of broken rice (0, 5, 10, 15 and 20 g/rabbit per day) to determine growth parameters and digestive indices during a 30 day trial. In view of observed digestive upsets and  mortality on the highest levels of broken rice, the trial was extended for a further 30 days to observe the performance with effects of reduced levels of broken rice (0, 4, 8 and 12 g/day) mixed with 100 g of fresh duckweed, the latter being included to slow down the rate of consumption of the broken rice.  The design was a randomized block with blocks being the replications.

Feeding and management of animals

The water spinach was bought from farmers in the neighborhood of the University. The broken rice was from the local market. The water spinach (leaves attached to stems) was hung in the cage, by tying the stem portion to a bamboo stick (Photo 1).

Photo 1: Hanging the water spinach from the roof of the cage

The foliage was offered to the animals at least two times a day beginning in the morning at 6:30 am. Observations, mainly at midday (12:00 m) and in the evening (5:30 pm), were done to ensure the permanent availability of water spinach. The broken rice was served to the animals in a small bowl every morning, when feed refusals from the previous day were recorded. The proportions of leaves and stems (fresh basis) in the water spinach were recorded daily in the feed offered and refused. The animals were weighed every five days during the trial.

Animal housing

The cages were made of bamboo strips and metal wire mesh (Photo 1), with an elevation from the floor of approximately 0.5 m. The dimensions of each cage were: width 25 cm, length 25 cm and height 25 cm.  Two batteries of five cages each were housed in an open shed at the University Campus.

Digestibility studies

Faeces were collected on days 10 to 15 to determine digestibility indices by the acid-insoluble ash technique (Van Keulen and Young 1977). Feed refusals were collected every day and kept frozen in plastic bags until analysis.  At the end of the collection  period, feed refusals and faeces were mixed thoroughly by hand and pooled, ground in a coffee grinder in the fresh state and, thereafter, representative samples were used for chemical analysis.

Chemical analyses

Chemical analyses of the diets and faeces were undertaken following the methods of AOAC (1990) for ash and N. The DM content was determined using the microwave method of Undersander et al (1993). pH (glass electrode) was measured on the fresh faeces, which were also analyzed for total short chain fatty acids (SCFA) by steam distillation in a Markham apparatus followed by titration of the distillate with NaOH 0.01 N.  Ash from feed and faeces was treated with HCl 2 N, then combusted in a muffle furnace at 800ºC for 4 h for the estimation of acid insoluble ash, following the method of Van Keulen and Young (1977) as outlined by Ly et al (2002). Digestibility indices were calculated by standard procedures using acid insoluble ash as inert marker.

Statistical analysis

The data were subjected to analysis of variance (Steel and Torrie 1980) using the General Linear Model (GLM) option of the MINITAB software (Release 13.31, 2000). Sources of variation were treatments and error. Growth rates were calculated from the linear regression of live weight (Y=g/day) on time in the experiment (X=days).

Experiment 2: Stylo 184

Animals and housing

Twelve rabbits (mean weight 860 g) were allocated in individual cages (30cm high, 30 cm length and 30 cm width) for the 56 day trial. The design was similar to those used in Experiment 1.

 Treatments and design

The four treatments were 0, 4, 8 and 12 g/day of broken rice added to a basal diet of fresh stylo 184 offered ad libitum, allocated according to a completely randomize design with 3 replicates per treatment.

 Feed and feeding system

Broken rice was bought from the local market. Stylo 184 foliage (leaves attached to stems) was harvested daily from plots in the livestock research center and suspended in the cage with a wire around the stems.  Fresh foliage was offered 3 times per day (Morning, afternoon and evening). The broken rice was fed only one time in a small bowl every morning, when feed refusals from the previous day were recorded.

Measurements

Amounts offered and residues of stylo 184 were recorded daily. Samples of foliage offered and refused were separated into leaves and stems and the DM and N content of each was determined. The animals were weighed every seven days.  Dry matter and N were determined following the methods of Undersander et al (1993) and AOAC (1990), respectively.

Statistical analysis

This was the same as in Experiment 1.

Results and discussion

Experiment 1

Feed characteristics

The broken rice used in the trial had a low content of ash and crude protein (Table 1). On the other hand, the leaves from the water spinach were rich in crude protein, nearly twice the value corresponding to the stems from this same plant. The leaves and stems from water spinach used in the experiment were the terminal branches and the crude protein (Nx6.25) ratio of leaves to stems in the dry material was 1.75:1.

Feed intake

The rabbits offered the higher amounts of broken rice did not eat all that was offered  (Table 2), and this was especially evident (P<0.001) when broken rice was given at levels of 15 and 20 g/day per animal. Intake of water spinach was reduced at offer levels of broken rice above 5 g/day (Figure 1). The rabbits selected more of the leaves than the stems (Figure 2) but the proportion was not affected by the level of broken rice.  The total DM intake was reduced at the highest level of broken rice supplementation. Total crude protein intake was lower with broken rice offer levels of 15 and 20 g/day, compared with levels of 5 and 10 g/day (Table 2 and Figure 3).

 

Figure 1: DM intake of WS leaves, WS stems and broken rice according to levels of broken rice offered

Figure 2: Proportions of leaves and stems (DM basis) in the water spinach offered and consumed according
to offer level of supplementary broken rice

Figure 3: Quantities of crude protein consumed as leaves and stems of water spinach and as broken rice

Growth and feed conversion

Neither final weight  nor mean daily gain (Table 3) was influenced by the inclusion of graded levels of broken rice in the offered feed. Feed conversion was similarly unaffected by supplementation. The pattern of growth was uniform (Figure 4). Values for both growth and feed conversion were at an acceptable level, and were superior to reported performance data for rabbits in Nigeria (9 to 11 g/day and 4.9 to 6.0 DM conversion; Akinfala et al 2003), Tanzania  (13 to 19 g/day and 3.8 to 4.2 DM conversion; Sarwatt et al 2003) and Vietnam (10.0 g/day and 7.0 DM conversion; Nguyen Quang Suc et al 2000; 16 to 22 g/day and 4.1 to 4.7 DM conversion; Dinh Van Binh et al 1991).

Figure 4. Growth curves of rabbits fed water spinach ad libitum and graded levels of broken rice (BR g/day)

Digestibility studies

Increasing the level of broken rice in the diet appeared to result in a lower pH  (Table 4) and a significant increase in the concentration of SCFA in the faeces (Figure 5). The implication from these observations is that the SCFA must have arisen from fermentation in the caecum and large intestine of the starch in the broken rice.  On the other hand, none of the digestibility indices examined in the current study appeared to be affected by the level of broken rice consumed by the rabbits.

Figure 5: Relationship between intakes of supplementary broken rice and concentration
of short chain fatty acids in the faeces of rabbits fed ad libitum water spinach

Mortality

One rabbit on the 20 g/day broken rice level developed severe diarrhoea and died after 2 weeks on the experiment. The symptoms and observations of higher levels of SFCA in faeces with increasing broken rice in the diet suggest that the cause may have been undigested starch reaching the large intestine, providing a substrate for bacterial fermentation.

Experiment 2

Feed characteristics

Feed intake

The broken rice was consumed completely at all offer levels. The rabbits offered high levels of broken rice ate lesser quantities of stylo leaves and stems (Table 6). Total DM and crude protein intakes were not different. DM intakes as a percentage of live weight were much higher in Experiment 2 (9 to 10%) than in Experiment 1 (4.2 to 6.4%). By contrast, the percentages of crude protein in the dietary DM consumed were much lower in Experiment 2 (15 to 16%) compared with Experiment 1 (21 to 28%).

 Growth rate and feed conversion

Growth rates were uniform (Figure 6) but low on all treatments (Table 7) and were not significantly influenced by the inclusion of graded levels of broken rice, while DM feed conversion appeared to be improved. These indices were very much poorer than those reported in Experiment 1.

Conclusions

The two experiments reported in this paper were preliminary attempts to develop feeding systems for rabbits based on locally available forages. The results must be treated with caution, as only small numbers of rabbits were used. Nevertheless it would appear that:

• Water spinach has a very high potential as a complete feed while stylo appears to be considerably poorer.
• For both forages little was gained by offering small quantities of broken rice.
• This simple feeding system with water spinach may be attractive for small-holder farmers in the tropics, due to the possibility to raise rabbits with this local resource that is easy to grow, has a high biomass yield and needs no processing

Acknowledgments

The authors would like to express their thanks to SidaSAREC for funding this research through the regional MEKARN project. The support of the staff of the Faculty of Agriculture and Natural Resources of An Giang University in Vietnam and the Livestock Research Centre, Lao is gratefully acknowledged.
 

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Received 10 April 2004; Accepted 30 April 2004