Effect of supplementation with sweet potato root and paddy rice on growth performance of local rabbits fed water spinach (Ipomoea aquatica) and paper mulberry (Broussonetia papyrifera) as basal diets

Sangkhom Inthapanya and T R Preston*

Faculty of Agriculture and Forest Resources, Souphanouvong University,
Luang prabang, Lao PDR
inthapanyasangkhom@yahoo.com
* TOSOLY, AA48 Socorro, Santander, Colombia
trpreston@mekarn.org

Abstract

Growth of young (45 to 50 days of age)  rabbits (n=48) was studied in a completely randomized 2*3 factorial design with 6 treatments: The factors were: basal diets of water spinach or foliage of Paper mulberry (Broussonetia papyrifera) and supplements of Paddy rice or Sweet potato root or none. The rabbits were housed in pairs in cages made from bamboo and wood.

Leaves and stems of Paper mulberry were higher in DM and lower in crude protein compared with water spinach. The proportion of the diet DM consumed as supplements was in the range of 27 to 31%. The supplements increased the growth rates on both forages, with no apparent differences between the two supplements. Growth rates were better for water spinach than for Paper mulberry. Feed DM intake was higher for the diets with Paper mulberry compared with water spinach but there were no differences among supplements. DM feed conversion was better on  water spinach than Paper mulberry and for the two supplement treatments compared with the un-supplemented control.

Key words: Crude protein, feed conversion, feed intake, tropical forages

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 basal diets for this species (Akinfala et al 2003; Sarwatt et al 2003; Hongthong Phimmmasan et al 2005; Pok Samkol et al 2006;  Nguyen Thi Kim Dong et al 2008)

Water spinach (Ipomoea aquatica) plays an important role for farmers in rural areas, because it is easy to plant and has a very high yield of biomass with a short growth period; it can be harvested in dry or flood period (Kean Sophea and Preston 2001). 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). Water spinach is widely used for human food, but at the same time this vegetable can be given to rabbits, pigs and poultry.

Paper mulberry (Broussonetia papyrifera moraceae) is a tree that is common in the northern area of Lao.

Photo 1. The Paper mulberry tree in Luang Prbang, LAO PDR. Note the large and abundant leaves

The leaves have a crude protein content from 22.6 to 28.5% in DM, according to Napaserth et al (2007). The leaves could be a potential feed resource for rabbits as some farmers say the leaves can be fed to pigs,  Presently the bark of Paper mulberry is used in the handicraft industry to make paper and envelopes. The leaves would thus be a by-product from this process

Sweet potatoes are widely grown in Lao. In 100g of sweet potato root there are 20g of carbohydrates including 4.2 g of sugar (USDA Nutrient database 2006).  It has been suggested that sugars may be a more appropriate source of carbohydrate for rabbits than starch (Leng 2006). So far, the most consistent results from carbohydrate supplementation have been with paddy rice (Nguyen Huu Tam et al 2008).

The present experiment aimed to evaluate the foliage of Paper mulberry as the basal diet for rabbits and to compare sweet potato root with paddy rice as carbohydrate supplements.   

Hypothesis

The hypothesis to be tested is that:

·         Supplements of paddy rice and sweet potato root can improve the growth of local rabbits fed water spinach or paper mulberry as the basal diet.
 

Materials and methods

Location

The experiment was conducted in the Experimental farm of Souphanouvong University, 7 km from Luang Prabang city, northern Lao PDR.

Experimental treatments and design

Two factors were studied in a growth experiment with rabbits was carried out for 60 days, with an extra 14 days for adaptation to the cages and diets.

The factors were:

Basal diet:

·         WS: Water spinach  

·         PM: Paper mulberry

Carbohydrate supplement:

·         PR: Paddy rice

·         SPR: Sweet potato root

·         NS: No supplement

The rabbits were assigned in a completely randomized 2*3 factorial arrangement of 6 treatments with eight animals per treatment.

Animal and housing 

Local rabbits (n=48), with initial live weight from 400 to 800g and 45 to -50 days of age, were housed in pairs in.cages made from bamboo and wood (Photo 2)  with dimension: width 0.5 m, length 0.5 m and height 0.5 m. There were spaces in the cage floor to let the faeces go through.

Photo 2: Hanging the foliage in the cage

Feeding and management

The rabbits were adapted to the experimental feeds for two weeks before collection of data. All feeds were offered freely so the rabbits could select the individual components. They were vaccinated against coccidiosis, pasturellosis and staphylocococosis and drenched against ear mange before the experiment started.

Paper mulberry (Photo 3) and the combined leaves and stems of the water spinach (Photo 4) were hung as a bunch inside the cage. Sweet potato root (Photo 5) was placed on the floor of the cage. Paddy rice (Photo 6) was put in a bowl inside of the cage. Both the paddy rice and sweet potato root were freely available, as was water. .

Photo 3: Leaves of Paper mulberry	Photo 4: Water spinach

Measurements

The rabbits were weighed at the beginning, at the end and every 5 days. Feeds offered and feed refusals were measured daily for estimating total DM intake. The proportions of leaves and stems of water spinach and Paper mulberry were recorded every day in the feed offered and refused.

Chemical analyses

Samples of feeds and refusals were taken every 5 days and analyzed for DM by micro-wave radiation (Undersander et al 1993) and crude protein (AOAC 1990).  

Statistical analysis

The data were analyzed by the GLM option in the ANOVA program of  the Minitab software (2003). In the model the sources of variation were: Supplements, basal diet, the interaction basal diet*Supplements and error. Weight gains were measured by the linear regression of live weight (Y=kg) on days in the experiment (X=days).

Results and discussion

Feed characteristics

Leaves and stems were higher in DM and lower in crude protein in  Paper mulberry than in water spinach (Table 1).

Feed intake

The proportion of the diet DM consumed as supplements was in the range of 27.0  to 30.3%  in the case of sweet potato for both forages. For the paddy rice range was 27.2 to 31.4% (Table 2; Figures 1 and 2).

Figure 1. Proportions of diet ingredients consumed by the rabbits (DM basis) fed water spinach as the forage source	Figure 2.  Proportions of diet ingredients consumed by the rabbits (DM basis) fed paper mulberry as forage source

Growth and feed conversion

The supplements increased the growth rates on both forages (Table 3; Figure 3), with no apparent differences between the two supplements. On average (Table 3), growth rates were better for water spinach than for Paper mulberry. Feed DM intake was higher for the diets with Paper mulberry compared with water spinach but there were no differences among supplements, as in the treatments with supplements, the rabbits ate less of the basal diet compared with the no supplement group. As a result, DM feed conversion was better on  water spinach than Paper mulberry and for the two supplement treatments compared with the no supplement treatment.

There appear to be no reports in the literature on the nutritive value of the leaves of Paper mulberry for monogastric animals, including rabbits. The results of the present experiment indicate that it is consumed readily and when combined with paddy rice gives similar performance to water spinach although as the sole diet supports poor growth rates. The positive effect on growth of a supplement of paddy rice is in agreement with the report of  Nguyen Huu Tam et (2008). However, in the report of those authors the paddy rice represented 56-58% of the diet DM compared with the levels of 27 and 38% in the present experiment. There is an urgent need to carry out growth response studies with varying levels of paddy rice, so that the appropriate level can be decided according to the relative costs of the paddy rice and the basal forage.

In this experiment, the sweet potato root was equally effective as paddy rice in the water spinach diet but slightly poorer with Paper mulberry. This contrasts with observations by Sen Sorphea (2008) that supplementing water spinach with sweet potato root supported the same growth rate as on water spinach alone. The explanation may be in the lower quality of the water spinach leaves in the present experiment (19.7% CP in DM) compared with Seng Sorphea’s experiment (29.9%).

Conclusions

• Water spinach was better than paper mulberry as the basal diet for rabbits
• Supplementation with paddy rice and sweet potato root at about one third of the total diet DM led to almost double the growth rate for both forages.

Acknowledgments

The senior author expresses his gratitude to the MEKARN program financed by the Sida-SAREC Project for providing the opportunity and the budget to do the research. Thanks are also given to Souphanouvong University, Faculty of Agriculture and Forest Resource for providing infrastructure support and laboratory assistance.  

Reference

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Received 6 September 2009; Accepted 16 September 2009; Published 1 October 2009

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