Effect of Guinea grass on feed intake, digestibility and growth performance of rabbits fed a molasses block and either water spinach (Ipomoea aquatica) or sweet potato (Ipomoea batatas L) vines

Doan Thi Gang, Khuc Thi Hue, Dinh Van Binh and Nguyen Thi Mui

Goat and Rabbit Research Centre,
Sontay, Hatay province

Abstract

In the first experiment, thirty six weaned New Zealand White rabbits at 30 days of age, and with body weights ranging from 0.7 to 1.0 kg, were randomly allocated to 6 treatments, according to a 3*2 factorial arrangement. The factors were: Foliages (Water spinach, Sweet potato vines, mixture of Water spinach and Sweet potato vines) and Source of additional fibre: (access or not to Guinea grass). In addition all rabbits were offered a molasses block at 5% of live weight, consisting of: 15% soybean meal, 25% cassava root meal, 20% rice bran, 5% minerals and 35% molasses. The second experiment was a study of the digestibility of the same diets used in experiment 1.

Giving the rabbits access to Guinea grass resulted in significant increases in DM intake and growth rate but decreases in the apparent digestibility of DM and crude protein.

Key words: Digestibility, fibre, growth, Guinea grass, rabbits, Sweet potato vines, Water spinach
 

Introduction

Rabbits are raised almost in almost all developing countries, and contribute to improving the nutrition and the economy of smallholder families, both as a source of animal protein, as well as a source of extra income through the sale of animals. They can be fed different kind of grasses, tree leaves, fruits (bananas), roots and tubers (eg: cassava and sweet-potatoes), and by-products f(eg. rice bran). In particular they find vegetables such as sweet potato vines and water spinach very palatable.

Water spinach has a high biomass yield, and a short growth period and is resistant to common insect pests. It can grow both in soil and in water and produces high yield of biomass when fertilized with biodigester effluent (Kean Sophea and Preston 2001). People and animals use it traditionally in tropical regions for consumption. Results from a study in Laos showed that rabbits gained 18 g / day when fed only on fresh water spinach (Hongthong Phimmmasan et al 2004).

Sweet potato (Impomoea batatas L) can be planted for tuber or forage production, dependent on purpose and season; it can be planted once and cut throughout the year with subsequent harvests every days (Le Van An et al 2003).

Earlier research with water spinach as the basal diet of rabbits indicated that the fibre content may be too low for it's efficient utilization as the sole diet (Samkol et al 2006).

This study aimed to evaluate ways to improve the utilization of water spinach and sweet potato vine for growing rabbits.
 

Materials and methods

Two experiments were conducted at the Goat and Rabbit Research Centre, Sontay, Hatay Province, North Vietnam, in 2005-2006.

Experiment 1: Effect of a supplementary fibre source (Guinea grass) on growth of rabbits fed water spinach or sweet potato vines or a mixture of the two foliages

Treatments and design

Thirty six weaned New Zealand White rabbits at 30 days of age, and with body weights ranging from 0.7-1.0 kg, were placed in individual cages and randomly allocated to 6 treatments, according to a 3*2 factorial arrangement. The factors were:

Foliages:

Water spinach, Sweet potato vines, mixture of Water spinach and Sweet potato vines

Source of additional fibre:

Guinea grass or none

Individual treatments were:

• WS: Water spinach

• WSGG: Water spinach and guinea grass

• SP: Sweet potato vines

• SPGG: Sweet potato vines and guinea grass

• WSSP: Water spinach and sweet potato vines, hanging

• WSSPGG: Water spinach and sweet potato vines, and guinea grass

In addition all rabbits were offered a molasses block at 5% of live weight, consisting of: 15% soybean meal, 25% cassava root meal, 20% rice bran, 5% minerals and 35% molasses. Water spinach and sweet potato vines were harvested and chopped into 20-30 cm lengths before being put in the rack located in the roof of the cage. Feeds were offered 3 times per day at 08.00, 14.00 and 20.00h, and refusals were measured daily.

Measurements

Live weight was recorded every 7 days, and feed intake daily.  Samples of offer and refusal of sweet potato vine and water spinach were taken daily, pooled weekly and analyzed for DM and crude protein (AOAC 1990), and NDF and ADF (Van Soest et al 1991).

Statistical analysis

The data were analyzed by ANOVA using the General Linear Model (GLM) software of Minitab (Version release 13.31) (Minitab 2000). Sources of variation were: Source of foliage, guinea grass, interaction foliage*guinea grass and error.

Experiment 2: Effect of a supplementary fibre source (Guinea grass) on digestibility in rabbits fed water spinach or sweet potato vines or a mixture of the two

Design and treatments

Six weaned New Zealand White rabbits at 30 days of age were given the 6 treatments described in experiment 1, according to a 6*6 Latin Square arrangement (Table 1). The rabbits were kept in individual metal metabolism cages, allowing the collection of faeces. Experimental periods were of 14 days with collection of faeces during the last 7 days.

Table 1.  Experimental design
Animal /Period	1	2	3	4	5	6
Period 1	WS	WSGG	SP	SPGG	WSSP	WSSPGG
Period 2	WSSPGG	WS	WSGG	SP	SPGG	WSSP
Period 3	WSSP	WSSPGG	WS	WSGG	SP	SPGG
Period 4	SPGG	WSSP	WSSPGG	WS	WSGG	SP
Period 5	SP	SPGG	WSSP	WSSPGG	WS	WSGG
Period 6	WSGG	SP	SPGG	WSSP	WSSPGG	WS

Feeding system

The feeding procedure was similar to that in Experiment 1. The faeces were collected daily and put in a freezer until analysed for DM and crude protein. All rabbits were weighed for two consecutive days at the beginning and the end of each 7-day collection period.

Statistical analysis

The data were analyzed by ANOVA using the General Linear Model (GLM) software of Minitab (Version release 13.31) (Minitab 2000). Sources of variation were: Animals, diets, periods and error.
 

Results and discussion

Chemical composition

The water spinach and sweet potato vines had more than twice as much protein and less than half the cell wall components compared with the Guinea grass (Table 2).

^*

Feed intake, growth and digestibility

Giving the rabbits access to Guinea grass resulted in significant increases in total DM intake and growth rate (Tables 3 and 4; Figures 1 and 2) but decreases in the apparent digestibility of DM and crude protein (Table 5 and Figure 3). Similar findings were reported by Samkol et al (2006) when they offered a basal diet of water spinach at high levels which permitted selection of the leaf component at the expense of the stem. This resulted in higher digestibility but lower growth rates.

Figure 1: Effect of access to Guinea grass on feed intake of growing rabbits

Table 4. :Mean values for growth rate of rabbits fed a molasses block and either Sweet potato vines, Water spinach or a mixture of the two foliages, and access or not to Guinea grass on
	WS	WSGG	SP	SPGG	WSSP	WSSPGG	SEM
Live weight, g
Initial	980	940	925	970	930	950	0.04
Final	2700	2890	2530	2900	2760	3060	0.06
Daily gain, g	21.9	26.4	21.1	26.7	23.1	27.2	1.11
DM feed conversion	10.7	8.23	7.68	7.26	6.21	7.03	0.52

Figure 2: Effect of access to Guinea grass on growth rate of rabbits fed a molasses block and
either Sweet potato vines, Water spinach or a mixture of the two foliages

Table 5. Mean values for digestibility coefficients in rabbits fed a molasses block and either Sweet potato vines, Water spinach or a mixture of the two foliages, with or without access to Guinea grass
	WS	WSGG	SP	SPGG	WSSP	WSSPGG
Intake, g/day
DM	119	138	121	129	123	124
Crude protein	20.1	202	25.4	22.3	24.9	21.9
Digestibility, %
DM	86.1	79.3	84.5	71.3	84.9	77.1
Crude protein	84.7	75.6	85.1	73.3	85.7	77.5

 

Figure 3. Effect of access to Guinea grass on digestibility in rabbits fed a molasses block
and either Sweet potato vines, Water spinach or a mixture of the two foliages

The findings of these two experiments emphasise the important role played by fibre in the digestive processes in the rabbit as outlined by Leng (2006). The Guinea grass played this role in the present experiment. However, the positive effects of the Guinea grass on intake and growth rate were offset by the reduced DM and crude protein digestibility. Future research should aim to identify sources of fibre which are both highly digestible and at the same time support the process of caecotrophy, which gives an important comparative advantage to rabbits compared with most other herbivores (Leng 2006).

Conclusions

• When rabbits were fed a basal diet of concentrates (15% soybean meal, 25% cassava root meal, 20% rice bran, 5% minerals and 35% molasses) and highly digestible foliages (water spinach and / or sweet potato vines) there were beneficial effects on growth rate when they also had access to Guinea grass, even although this resulted in a decrease in digestibility of the overall diet.

References

AOAC 1990 Official Methods of Analysis: Association of Official Analytical Chemists. 15^th edition (K Helrick editor) Arlington pp 1230

HongthongPhimmmasan, Siton Kongvongxay, Chhay Ty and Preston T R 2004: Water spinach (Ipomoea aquatica) and Stylo 184 (Stylosanthesguianensis CIAT 184) as basal diets for growing rabbits. Livestock Research for Rural Development.Vol. 16, Art. #34. Retrieved, from http://www.cipav.org.co/lrrd/lrrd16/5/hong16034.htm

Kean Sophea and Preston T R 2001 Comparison of biodigester effluent and urea as fertilizer for water spinach vegetable. Livestock Research for Rural Development. Vol. 13, No 6.Retrieved , from http://www.cipav.org.co/lrrd/lrrd13/6/Kean136.htm

Le Van An, Lindberg B E F and Lindberg J E 2003 Effect of harvesting interval and defoliation on yield and chemical composition of leaves, stems and tubers of sweet potato (Ipomoea batatas L (Lam.)) plant parts. Field Crops Res. 82, 49-58.

MINITAB 2000 Minitab reference Manual release 13.31.

Pok Samkol, Preston T R and Ly J 2006 Effect of increasing offer level of water spinach (Ipomoea aquatica) on intake, growth and digestibility coefficients of rabbits. Livestock Research for Rural Development. Volume 18, Article #25. Retrieved March 7, 2006, from http://www.cipav.org.co/lrrd/lrrd18/2/samk18025.htm

Van Soest P J, Robertson J B and Lewis B A 1991:Symposium: Carbohydrate methodology, metabolism and nutritional implications in dairy cattle: methods for dietary fiber, and non-starch polysaccharides in relation to animal nutrition. Journal of Dairy Science. 74: 3585-3597.

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