Amaranth (Amanathus spp.) as replacement for water spinach (Ipomoea aquatica) with or without paddy rice on growth performance of rabbits

Chhay Ty, Pok Samkol, Khieu Borin and T R Preston*

Center for Livestock and Agriculture Development (CelAgrid). Prah Theat village, Sankat Rolous, Khan Dangkor.
P.O. Box 2423 Phnom Penh 3, Cambodia
chhayty@celagrid.org
* Finca Ecológica, TOSOLY, AA #48, Socorro, Santander, Colombia

Abstract

The aim of this experiment was to evaluate foliage of Amaranth as replacement for Water spinach as the basal diet of growing rabbits. Twenty crossbred rabbits with an initial weight of 0.84±0.08kg were allocated to a 2*5 factorial arrangement in a completely randomized design with 2 replications. The first factor was level of Amaranth replacing Water spinach with ratios (DM basis) of: 0:100, 25:75, 50:50, 75:25 and 100:0%). The second factor was supplementation with paddy rice (20 g/day or none). Amaranth and water spinach foliages were hung separately inside of the cage. Paddy rice was fed in the feed trough.  The rabbits were weighed every 10 days during the 80 days of the experiment. 

There were curvilinear decreases in growth rate and poorer feed conversion as Amaranth foliage replaced Water spinach as the source of forage. Growth performance was improved by supplementation with paddy rice, but this did not compensate for the negative effects on growth and feed conversion attributable to the Amaranth. In the diet with Water spinach as the only forage the effect of the paddy rice was to increase growth rate by 25% but feed conversion was poorer by 24%, thus in practice there would appear to be little economic incentive to feed paddy rice when Water spinach is offered as the basal diet.

Keywords: feed intake, feed conversion, fiber

Introduction

Integrated farming systems play a crucial role for smallholder families in rural areas in terms of sustainability, while minimizing economic risks (Lukefahr and Preston 1999). Livestock including rabbits convert plant materials that are low in nutritive value into high quality products, such as meat and milk, and return nutrients to the soil in the form of feces (Pok Samkol et al 2007). Production of meat, milk and eggs by converting plant proteins into animal protein of superior nutritive value for humans is one way to match animal production systems with the locally available feed resources.  

Amaranth (Amaranthus spp.) has been cultivated for producing nutritious grain and foliage, and as a colorful ornamental (Brenner et al 2000). The plants are tolerant of heat and drought. Amaranth foliage is an excellent source of protein (Segura-Nieto et al 1994) and bio-available iron and vitamin A (Rangarajan and Kelly 1994). In Malawi, rabbits were fed Amaranth foliage as a supplement to a concentrate containing maize and oilseed meals. Reproduction and growth were satisfactory: 20 rabbits per doe/year; growth rate of 15 g/day from four to 16 weeks (http://www.mybunnyfarm.com/science/ ch2.htm).

The combination of fibre and starch in paddy rice appears to make this feed a valuable supplement to improve the feed intake and growth performance of rabbits fed forages of low nutritive value such as Guinea grass (Luyen and Preston 2012).  Paddy rice supported higher growth rates in rabbits fed leaves of cauliflower or cabbage (Tam et al 2009). Inthapanya and Preston (2009) used paddy rice to supplement mulberry foliage and reported higher feed intake and almost double the growth rate.

The aim of the present study was to evaluate the use of amaranth foliage (Amanathus spp.) as a replacement for water spinach (Ipomoea aquatica) which is known to be an excellent basal diet for growing rabbits (Honthong Phimmasan et al 2004).

Materials and Methods

Location

 The experiment was carried out from 19 September to 8 December 2012 at the Center for Livestock and Agriculture Development (CelAgrid) located in Prah Theat village, Sankat Rolous, Khan Dangkor approximately 25 km from Phnom Penh city.

Animals and experimental design

Twenty crossbred rabbits (Local x NZ White) with an initial weight of 0.84±0.08 kg were allocated to a 2*5 factorial arrangement of ten treatments n a completely randomized design with 2 replications (Table 1). The factors were:

• Level of amaranth replacing water spinach (% DM basis): 0, 25, 50, 75 and 100% (DM basis)  

• Supplementation with paddy rice: 20 g/d or none

Feed and feeding system

Amaranth, water spinach and paddy rice were purchased from farmers in Kandal province. Amaranth and water spinach were hung separately inside the cage. Paddy rice was fed in a trough at the rate of 20 g/day. Amaranth and water spinach were offered 2 times per day in the morning at 8:00 am and afternoon at 5:00 pm, while paddy rice was given once only in the morning.  

Photo 1. A bunch of water spinach hanging inside of the cage

 Data collection

The rabbits were weighed every 10 days during the 80 days of the experiment. Feed offered, refusals and proportion of leaves and stem in amaranth and water spinach were recorded and samples analyzed for DM and CP (N*6.25).

Chemical analyses

Leaves and steam of amaranth and water spinach were ground before analysis. The DM content was determined in an infra-red oven following the procedure of  Undersander et al (1993). CP was determined according to AOAC (1990). All analyses were performed in duplicate.

Statistical analysis

Analysis of variance was performed using the general linear model of the ANOVA program in the Minitab software (Minitab 2010). Sources of variation were:  with or without paddy rice, level of amaranth, interaction between paddy rice and level of amaranth and error. When the F-test was significant at P<0.05, pair wise comparisons were performed using Turkey’s procedure in the same Minitab Software.

Results and discussion

Chemical composition of feeds ingredients

Crude protein in leaves and stems was similar for Amaranth and Water spinach (Table 2).  However, there were major differences in proportions of leaves and stems with Amaranth having a high proportion of leaves and low proportion of stems, the exact opposite of the ratio of these components in Water spinach in which the stems predominated.  

Feed intake

Of the Amaranth component of the diet, selection was mainly for the leaves (Table 3; Figure 1); in contrast, for the Water spinach component selection was more or less equally divided between leaves and stems. The overall effect of raising the offer level of Amaranth was a linear decrease in DM intake (Figure 2).

Figure 1: Proportions of feed intake of rabbit fed amaranth as replacement for water spinach	Figure 2: Effect on feed intake as the offer level of Amaranthus was increased

Growth and feed conversion ratio

There were curvilinear decreases in growth rate and poorer feed conversion as Amaranth foliage replaced Water spinach as the source of forage (Table 4; Figures 3 and 4). Growth performance was improved by supplementation with paddy rice, but this did not compensate for the negative effects on growth and conversion attributable to the Amaranth. In the diet with Water spinach as the only forage the effect of the paddy rice was to increase growth rate by 25% but in contrast DM feed conversion appeared to be poorer by 24%. DM digestibility was found to be reduced when paddy rice was added to a diet of Water spinach (Huyen et al 2010) which could explain the poorer feed conversion with supplementary paddy rice. However, other researchers reported improved feed conversion when paddy rice was added to a Water spinach diet (Tam et al 2009; Huyen et al 2010).

Figure 3: Effect on growth rate of rabbits of replacing Water spinach by Amaranth foliage with or without paddy rice supplementation	Figure 4: Effect on DM feed conversion of rabbits of replacing Water spinach by Amaranth foliage with or without paddy rice supplementation

Theoretically there is more protein in Water spinach than is needed by growing rabbits, and balancing this with digestible carbohydrate would seem to be a logical strategy. However, the role of fiber  -digestible or not is a related factor. The classical recommendation (Lebas et al 1997) is that rabbits need from 13-14% fibre in their diet and that indigestible fiber should be 9-10%.

It would seem that paddy rice fulfills these requirements in that invariably there are positive responses when it is added to a high-protein forage diet (Inthapanya and Preston  2009; Tam et al 2009; Huyen et al 2010; Luyen and Preston 2012). By contrast, the fiber in Amaranthus does not seem to provide the right qualities, or else there are non-nutritional components present that lead to reduced intake and hence poorer performance.

Conclusion

• There were curvilinear decreases in growth rate and poorer feed conversion as Amaranth foliage replaced Water spinach as the source of forage for growing rabbits.

• When Water spinach was the only forage, supplementation with paddy rice (20 g/day; about 14% of diet intake) increased growth rates by 25%  but led to 24%  poorer feed conversion.

Acknowledgments

The authors would like to express their gratitude to the MEKARN project financed by Sida (Sweden) and to the Center for Livestock and Agriculture Development (CelAgrid), for providing resources for conducting this experiment.

References

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Received 19 December 2012; Accepted 30 December 2012; Published 4 January 2013

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