Effect of different forages on feed intake, digestibility and growth performance of rabbits
 

Table 5. Effects of foliages and breed on the digestibility coefficient (%) in rabbits (Digestibility trial)
	DM	OM	GE	CP	EE	CF	NDF	ADF
Foliage (F)
RG	48.7a	52.4a	45.6a	52.4a	51.7a	30.7a	40.3a	41.9a
HL	79.3b	81.6b	74.3b	80.0b	64.0b	59.4b	57.8b	63.6b
MP	57.6c	61.0c	60.7c	50.6a	38.2c	45.7c	42.6a	39.3a
WS	72.6d	75.4d	65.8c	76.7b	36.8c	55.8b	67.1c	67.8b
SE	1.3	1.2	1.5	1.2	2.2	1.8	1.6	1.8
Breed (B)
NZW	64.4	67.8	60.9	64.3	46.8	47.2	51.0	53.3
NN	64.7	67.5	62.3	65.5	48.5	48.5	52.9	53.0
SE	0.9	0.9	1.0	0.9	1.5	1.3	1.1	1.3
Foliage * Breed
RG*NZW	49.9	51.4	43.7	52.0	51.6	30.6a	41.6ad	42.9a
RG*NN	47.5	53.3	47.2	52.9	51.8	30.8a	39.0a	41.0a
HL*NZW	77.0	83.8	71.3	77.6	61.7	53.6bcde	50.0d	56.1be
HL*NN	81.6	79.3	77.4	82.4	66.4	65.1bd	65.7bc	71.0cde
MP*NZW	57.2	61.4	63.1	50.2	37.3	45.2ce	42.3ad	41.6a
MP*NN	58.1	60.7	58.4	51.0	39.2	46.1ce	42.9ad	37.0a
WS*NZW	73.6	74.4	65.3	77.6	36.8	59.4de	70.2c	72.4de
WS*NN	71.5	76.5	66.3	75.9	36.8	52.2e	64.1c	63.1e
SE	1.9	1.7	2.1	1.8	3.1	2.6	2.3	2.5
Significance level
F	***	***	***	***	***	***	***	***
B	NS	NS	NS	NS	NS	NS	NS	NS
F*B	NS	NS	NS	NS	NS	**	***	***
a,b,c Means within foliage, sex or breed in a column with different superscripts are significantly different (P<0.05) *P<0.05; ** P<0.01; *** P<0.001; NS: Non-significant.

Growth and feed conversion ratio

The rabbits consuming Mimosa pigra, water spinach and head lettuce residue had significantly higher final weight and daily gain than the rabbits fed Ruzi grass (Table 6). The daily weight gain was highest in the group fed Mimosa pigra followed by water spinach and head lettuce residue, 18.5 g, 18.4 g and 17.6 g/day, respectively, but there was no significant difference between these three diets. The lowest FCR was found in the group fed water spinach, 3.6 g DM/g LWG, and the highest in the group fed Mimosa pigra, 5.2 g DM/g LWG (P<0.001). The NZW breed had higher final weight and daily gain than the NN breed (P<0.05). There was an interaction between foliages, breed and sex for FCR (P<0.05). Sex had no significant effect on growth rate and FCR.

Table 6. Effect of foliages, breed and sex on growth performance
	Live weight, g			FCR, g DM/g LWG
	Initial weight	Final weight	Daily gain
Foliage (F)
RG	652	2103a	14.8a	4.8ab
HL	689	2418b	17.6b	4.6a
MP	671	2488b	18.5b	5.2b
WS	659	2465b	18.4b	3.6c
Sex (S)
Female	679	2379	17.4	4.7
Male	660	2357	17.4	4.4
Breed (B)
NZW	663	2425	18.0	4.4
NN	673	2312	16.7	4.7
SE	25.4	91.7	1.0	0.3
Significance level
F	NS	***	***	***
B	NS	*	*	NS
F*S*B	NS	NS	NS	*
a,b,c Means within foliage, sex or breed in a column with different superscripts are significantly different (P<0.05) *P<0.05; ** P<0.01; *** P<0.001; NS: Non-significant RG=Ruzi grass; HL= Head lettuce residue; MP=Mimosa pigra; WS=Water spinach; NZW=New Zealand White; NN=Crossbred between New Zealand White and Native breed; FCR=Feed conversion ratio= g feed per g live weight gain.

 

Discussion

Nutrient content of the foliages

Head lettuce residue and water spinach, both also used as vegetables for human consumption, had a very high water content, and DM content was only about 40 g and 62 g/kg, respectively. Many different vegetables or vegetables residues have been shown to have low DM content e.g. cabbage residues (37 g to 102 g DM/kg), as reported by Ngu (2001) and sweet potato vines (119 g DM/kg), according to Vo Lam and Ledin (2005). Also the fiber content of head lettuce residue and water spinach was low, 127 g and 126 g/kg DM, respectively, compared to some other vegetable varieties such as cabbage and cauliflower, 186 g and 119 g/kg DM, respectively (Gupta et al 1993). The CP content was high in the water spinach, 252 g/kg DM compared to 232 g and 256 g/kg DM, reported by Gang et al. (2006) and Chhay and Preston (2006), respectively. The CP concentration of head lettuce in the present study was similar to the data from Wikipedia Foundation (2007), reporting about 40 g CP/kg DM and 96% water content.

Low DM and poor fiber content in head lettuce residue and water spinach may be negative factors leading to a risk of fiber deficiency. It is not clear what the minimum fiber intake for prevention of diarrhoea in rabbits should be. Research reports from Blas et al. (1994) and Gidenne and Jehl (2000) examining the effect of low fiber diets to rabbits, showed that a sharp decrease in fiber level from 19% to 9% in the diet doubled the risk of digestive trouble. The population of cellulolytic bacteria decreased in the caecum, and the microbial ecology system in the caecum became unbalanced, which may cause death from diarrhoea. In this study the fiber intake was 8.0 g and 6.0 g/day compared to the fiber requirements in growing rabbits at 4 to 12 weeks of age of about 11.2 g/kg BW/day (the data adapted from Table 22 in Chapter 2, FAO 1997). The requirements were almost twice the fiber intake in this study, but all the experimental rabbits survived and there was no mortality during the experiment. Bennegadi et al. (2001) reported that the direct effect of a fiber reduction is a slowing down of digesta transit, corresponding mainly to a longer retention time in the caecum and an increased fermentation rate of feed particles. The digestibility coefficient of fiber in the vegetables was higher than for the other two foliages which can be a consequence of longer retention time of feed particles in the caecum, or that the fiber was of a different quality.

For Mimosa pigra the present results were similar to those of Nguyen Thi Thu Hong and  Vo Ai Quac  (2005) who reported that the DM, OM, CP, NDF and ADF content of Mimosa pigra was 360 g, 928 g, 207 g, 534 g and 379 g/kg DM, respectively. The nutritive value of Ruzi grass in this study was in agreement with Narmsilee et al. (2003) showing 75 g, 829 g, 308 g, 644 g and 463 g/kg DM for CP, OM, CF, NDF and ADF content, respectively.

Feed intake, digestibility and growth performance

There was a relationship between CP intake and daily weight gain (Figure 1) but the relation was not strong (R²=0.36, P<0.001).

Figure 1. The effect of protein intake on daily weight gain

Obviously there was an individual variation in response to CP intake and there were other factors, like foliage and breed, affecting growth. The rabbits fed the foliages with high protein content, water spinach, head lettuce residue and Mimosa pigra, had significantly higher weight gain than the rabbits fed Ruzi grass. The daily gain of the group offered water spinach was 18.4 g/d compared to 14.0 g/d for the rabbits fed water spinach ad libitum as a sole feed (Samkol 2005) in Cambodia, about 18.1 g/d without broken rice (Phimmasan et al 2004) in Lao, and 31.4 g/d when supplemented with molasses block and concentrate at 2% and 3 % (DM) of BW, respectively, in Vietnam (Tran Hoang Chat et al 2005).

The DM intake expressed as g/W^0.75 was lower than the values reported from Laos, 66.9 g, 83.3 g and 75.8 g/kg W^0.75 for Guinea grass, native grass and Stylo 184, respectively (Phimmasan 2005). Energy intake per day was similar to the values of 1 MJ and 0.8 MJ/day, respectively, for Guinea grass and Spilanthes acmella reported by Phimmasan (2005). However, it was lower than the energy requirement recommended for growing rabbits by NRC (1977) and FAO (1997), 2.5 MJ DE/day. The intakes of the legume foliage and both vegetables were significantly higher than of the Ruzi grass. Phimmasan (2005) reported that legume hay and foliages generally have higher CP content and higher intake than grasses.

The high water content in the vegetable foliages probably affected intake negatively. The DM content can be improved by air-drying the foliages before feeding. Arias et al. (2003) reported that the greatest disadvantage of vegetable wastes used as feeds is the low DM content, resulting in low DM intake. The DM intake can also be improved by offering high fiber feeds such as maize stubble or maize cobs at the same time as the vegetables. Ngu (2001), using vegetable wastes as feeds for goats, included natural grass in the experimental feed ration to improve DM intake and fiber balance in the rumen. The DM intake of rabbits increased significantly when water spinach or sweet potato wines was offered together with Guinea grass (Gang et al 2006).

In the present study there were no significant differences in digestibility due to breed, but there was a significant difference in intake of concentrate. The NZW rabbits consumed more concentrate and thereby more CP and fiber than the crossbred rabbits, and also had a higher intake of protein and fiber in foliages, but not significantly so. This resulted in a significantly higher daily gain for the NZW rabbits than for the crossbreds (Figure 2). The higher intakes may explain part of the difference in growth rate, but probably the NZW rabbits, being selected for meat production, are also more efficient in metabolising and using the nutrients for tissue growth. The digestibility of DM of the vegetable foliages was high and comparable to the 71.2 % and 99.1%, respectively, for DM and OM in vitro digestibility of lettuce reported by Arias et al. (2003). The digestibility of DM and CP of water spinach was lower than reported by Gang et al. (2006), 86.1% and 84.7%, respectively, and 80.5%, 80.8% and 80.1% for DM, OM and CP, respectively (Samkol 2005). The legume foliage had lower digestibility than the vegetable foliages but was similar to Ruzi grass. Narmsilee et al. (2003) reported that the digestibility of Ruzi grass for DM, OM and CP was 61%, 67.9% and 46.5%, respectively.

Figure 2.  Mean values for live weight gain of rabbits fed Ruzi grass, Head lettuce residue, Mimosa pigra or water spinach as supplements to concentrates (NZW = New Zealand White; NN = New Zealand White x native breed)

Conclusions

• Head lettuce residue, Mimosa pigra and water spinach can be fed to growing rabbits as a roughage and will result in a better growth performance as compared to feeding Ruzi grass. Head lettuce residue, Mimosa pigra and water spinach had high protein content but fiber content was low and water content high in head lettuce residue and water spinach. The nutrient digestibility of head lettuce residue and water spinach was higher than for Mimosa pigra and Ruzi grass.

• The New Zealand White breed had higher growth rate than the crossbreds, but breed had no effect on digestibility. There was no effect of sex on growth performance or feed intake.

Acknowledgements

The authors would like to thank the Swedish International Development Agency/Cooperation with Developing Countries (Sida/SAREC) for funding this thesis research. Special thanks are given to the Royal Project Foundation allowing the research to be conducted at the Demonstration Farm. Thanks are also due to the Department of Animal Sciences, Chiang Mai University, for the use of the laboratory to analyse the samples.
 

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