Effect of different sources of supplementary fibre on growth of rabbits fed a basal diet of fresh water spinach (Ipomoea aquatica)

Khuc Thi Hue and T R Preston*

Goat and Rabbit Research Center, Sontay, Hatay, Vietnam
hienhue02@yahoo.com
^*Finca Ecológica, TOSOLY, UTA (Colombia)
AA #48, Socorro, Santander, Colombia
trpreston@mekarn.org

Abstract

The experiment was carried out at the Livestock Research Centre, Nam Xuang, Laos,  from 20 Sept to 20 Oct, 2005. A completely randomized design was used with 4 treatments: WS, water spinach only (control); WSS, water spinach + Stylosanthes foliage; WSG, water spinach + Guinea grass leaves; WSRB, water spinach + Rice bran. There were 3 replications with 12 weaned rabbits about 40 to 45 days of age and 400 to 550 g live weight housed in individual cages.

The intakes of dry matter (DM) and crude fibre, and the growth rates of the rabbits were higher when supplementary sources of fibre were offered together with the water spinach. The apparent digestibility of DM  and crude protein was high (>80%) in all treatments.

There would appear to be advantages in offering supplementary sources of fibre when rabbits are fed basal diets of fresh water spinach.

Key words: Guinea grass, rabbit, rice bran, Stylosanthes, water spinach

Introduction

In recent years, rabbit husbandry in SE Asia has developed quickly due to demand of fresh meat for human consumption. Furthermore, it is becoming a popular animal because of specific characteristics of feeding behaviour that favours its role in integrated farming systems.

The rabbit (Oryctotagus cuniculus) is a pseudo-ruminant, raised widely in developing countries such as Vietnam, Laos and Cambodia. Its production contributes to improved nutrition and economy in the family as a source of animal protein, as well as extra income by sale of animals. Rabbits can be fed many kinds of grasses (eg: guinea grass), legumes (eg: stylosanthes), vegetables (eg: water spinach, sweet potato vines), leaves from trees, fruits (eg: bananas), roots and tubers (eg: cassava, sweet-potatoes) and by-products from the kitchen.

Concerning the nutritional requirement of rabbits, they require diets with moderate to high levels of fibre (at least 15 to 20% in the DM), moderate levels of protein (12 to 15% in DM), low fat and physical attributes in the feed having an abrasive action on the teeth (Anon 2001). There are several kinds of available protein-rich forages in Laos such as water spinach (Ipomoea aquatica) and Stylo (Stylosanthes) which supported good growth in rabbits (Hongthong Phimmmasan et al 2004).Water spinach has been  reported to have a very high biomass yield (Kean Sophea and Preston 2003) with around 28% crude protein, 12% crude fibre and 19% ash in DM of fresh leaves and stems (Ho Bunyeth and Preston 2004; Ly Thi Luyen 2004). Water spinach has a short growth period and is resistant to common insect pests. It can grow both in soil and in water and it is very easy to grow by farmers. People and animals traditionally consume water spinach in tropical regions. 

Research in Vietnam showed that using water spinach as a protein source for Ba Xuyen and Large White sows gave good results in feed intake and digestibility (Le Thi Men et al 1999). In a study at the Goat and Rabbit Research Centre in North Vietnam, rabbits grew at 18 to 30 g/day when fed fresh water spinach and a concentrate supplement (Tran Hoang Chat et al 2005). In research reported by Samkol el al (2006), growth rates were between 12 and 18 g/day on diets composed only of water spinach. For these reasons, water spinach  is now considered a feed resource with high potential for rabbits.

The results reported  by Samkol et al (2006) indicated  that in a feeding system with high offer levels of fresh water spinach (leaves and stems), the rabbits selected a higher proportion of the leaves,  but this resulted in slower rates of growth. As the stems are higher in fibre the outcome was a positive relationship between levels of fibre consumed and the growth rate. 

The hypothesis that was tested in the present study was that growth performance of rabbits fed basal diets of water spinach would be improved when they also had access to feeds with higher levels of fibre. The sources of high fibre feeds that were selected were: Stylo (Stylosanthes guiensis), Guinea grass (Panicum maximum) and rice bran.

Stylo is a short-lived perennial legume (2 to 3 years) which grows into a small shrub with some woody stems. It can adapt to a wide range of soils and climates, especial growing well on infertile and acid soils (Hongthong Phimmmasan et al 2004). Guinea grass (Panicum maximum) grows well on a wide variety of soils and even under light shade of trees and bushes (and thus can be grown with other crops). It can survive long dry spells and quick-moving fires which does not harm the underground roots. It also responds quickly to fertilizers and watering. It grows well from sea level up to 1,200 masl. Rice bran in Laos is high in fibre as the mills used for processing the rice grain leave a considerable amount of husk in the bran.

Materials and methods

Location

The experiment was carried out in the Livestock Research Center, of NAFRI, in Nam Xuang village, Vientiane province, Laos, from 15 September to 15 October, 2005.

Animals

12 weaned rabbits (8 male and 4 female) were used in the experiment. The body weights ranged from 0.4 to 0.6 kg with the age about 40 days. The rabbits were housed in individual cages (Photo 1) with 3 rabbits allocated to each of the following four treatments in a completely randomized design

• WS-O: Water spinach alone
• WS-S: Water spinach + Stylo
• WS-GG: Water spinach + Guinea grass
• WS-RB: Water spinach + Rice bran

The basal diet was water spinach offered initially at 10% of body weight (dry matter basis), then increased so that there was always a residue of about 20% of the amount offered. The stylo, guinea grass and rice bran were also offered at about 20% over recorded intakes. The foliages were hung by a wire from the roof of the cage (2 to 3 cm above the floor) and were offered fresh 3 times per day at 6 am; 12 am and 6 pm after cutting and carrying them from the experimental area of the Centre.  Rice bran was bought in the local market and supplied once per day in the morning.

Measurements

 The rabbits were weighed at the beginning, the end and every 5 days for measuring daily live weigh gain by linear regression of live weight (Y = g/day) on time in the experiment (X = days). Feeds offered and feed refusals were measured daily for estimating total dry matter intake. The proportions of leaves and stems of water spinach were recorded every day in the feed offered and refused. Samples of feeds and refusals were taken every 5 days and analyzed for DM by micro-wave radiation (Undersander et al 1993) and crude fibre (AOAC 1990). The faeces of each rabbit were collected daily to determine digestibility. For each treatment, 10% of  the total faeces was stored in the refrigerator (-20°C) during periods of 5 days for later analysis of DM, N, crude fibre and ash.

Statistical analysis

The data were analyzed by ANOVA using the General Linear Model (GLM) option of the software of Minitab (Version release 13.31). Sources of variation were: treatments and error.
 

Results and discussion

Feed characteristics

The DM content of the feeds varied from 8.8% (water spinach) to 87.1% (rice bran) (Table 1).  The crude protein (CP) content of the DM was highest in water spinach leaves (21.1%), followed by Stylo (16.1%) and Guinea grass (11.1%). The lowest CP was obtained in rice bran and water spinach stems (8.88 and 9.94%, respectively). There were no differences in crude fibre content between the Stylosanthes, Guinea grass and rice bran (range of 26.6 to 29.0% in DM). The crude fibre content was lower in the leaves of water spinach (14.1%) than in the stems (20.2%).

Feed intake

The proportions of leaves in the offered water spinach were higher than in the refusals; on all treatments the rabbits consumed some 85% of the leaves offered but only 68% of the stems (Table 2 and Figure 1). This selection  for leaves over stems is similar to the findings of Samkol et al (2006). The  intakes of leaves and stems (as DM) of the water spinach were not affected by supplementation with the other fibre sources (Figure 2).  Total intakes of dry mater, nitrogen and crude fibre were highest when stylo and guinea grass were the supplements and lowest on water spinach alone with intermediate values for the rice bran treatment.  Remois et al (2000) also found that feed intake of rabbits  was higher when the fibre content of the diet was increased.

Figure 1: The proportions of leaves and stems in water spinach offered, refused and consumed

The maximum intakes of DM were on the diets with supplements of stylo or guinea grass (Figure 2).

Growth rate and feed conversion

Growth rates were higher on all the treatments with supplements high in fibre, than on the control of water spinach alone (Table 3). The growth rate in rabbits on the control diet of water spinach alone is within the range reported by Hongthong Phimmasan et al (2004), Samkol et al (2006) and Chiv Phiny  and Lampheuy Kaensombath (2006). When water spinach was supplemented with concentrates the growth rates exceeded 30 g/day in the study of Tran Hoang Chat et al (2005).

There were positive relationships between growth rates and intakes of DM (Figure 3) and crude fibre (Figure 4).

Faeces characteristics

The DM content of the faeces was highest on the diet with rice bran as the supplement (Table 4), while N content was highest on the control diet of water spinach alone. There were no differences in organic matter and crude fibre content between diets.

Digestibility

Digestibility coefficients for DM, crude protein and crude fibre were lowest on the diet with a supplement of rice bran (Table 5). In general the coefficients were high especially for crude protein with values >90% on the control and stylo-supplemented diets.  According to Gidenne (1996), Gidenne et al (1998) and Perez et al  (1996), an increase in fibre leads to a decrease of retention time and an increase of caecotrophe production because of increasing  bacterial fibrolytic activity which in turn results in a reduction of digestibility of the diets (Gidenne et al 1998; De Blas et al 1999). These relationships were not apparent in the present study, as there was no correlation between the crude fibre content of the diet, or the daily intake of crude fibre, and DM digestibility.

Conclusions

• Growth rates of rabbits fed a basal diet of water spinach were increased when they had access to supplementary feeds with higher content of crude fibre (stylosanthes, guinea grass or rice bran) which had an additive effect on DM intake.

• Digestibility coefficients were high on water spinach as the sole feed or when supplemented with stylosanthes or guinea grass but were not related to crude fibre intakes.

Acknowledgements

Thanks are given  to Sida SAREC - MEKARN program for funding this research. We also thank Ms.Lamphey; Mr Chhay Ty, and all staff in Nam Xuang Livestock Reasearch Center, Laos for assistance with the conduct of the study.
 

References

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Received 31 January 2006; Accepted 12 February 2006; Published 17 April 2006

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