Livestock Research for Rural Development 20 (9) 2008 Guide for preparation of papers LRRD News

Citation of this paper

Effect of supplementation level of water spinach (Ipomoea aquatica) leaves in diets based on para grass (Brachiaria mutica) on intake, nutrient utilization, growth rate and economic returns of crossbred rabbits in the Mekong Delta of Vietnam

Nguyen Thi Kim Dong, Nguyen Van Thu, Brian Ogle* and T R Preston** 

Cantho University, Vietnam

ntkdong@ctu.edu.vn

* Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden

** UTA, TOSOLY, AA #48, Socorro, Santander, Colombia


 

Abstract

 

In the Mekong Delta water spinach (Ipomoea aquatica) stems are used for making pickles for human consumption, while the leaves (WSL) are normally discarded. This study was carried out to evaluate WSL as a potential feed for rabbits. Two experiments were carried out in the experimental farm of Cantho University to evaluate the effects of offering WSL at levels of 25 (WSL25), 50 (WSL50) and 75% (WSL75) of the intakes of  a control diet (WSL0) (DM basis). Both experiments were complete randomized designs with four treatments, three replicates and two female rabbits per experimental unit.

 

The first trial (Experiment 1) was done on growing crossbred rabbits at 8 weeks of age to evaluate feed utilization, growth rate and economic returns. In the second experiment (Experiment 2) feed digestibility and nitrogen retention was determined in twelve week old rabbits. In Experiment 1, the dry matter (DM) intake was highest (P<0.001) on the diet with para grass only (WSL0). Crude protein (CP) intake was significantly higher (P<0.01) in the WSL50 and WSL75 diets. Organic matte (OM), NDF and ADF intakes significantly decreased (P<0.01) with increasing levels of WSL in the diet. The highest daily gain was found in WSL75 (P<0.01). Lower feed cost and higher income per rabbit, resulting in higher net benefit, were found for the WSL50 and WSL75 diets. In Experiment  2 the apparent digestibility (%) of DM was significantly higher (P<0.05) in all the diets that included WSL compared with WSL0, with the highest value in the WSL75 diet.  The nitrogen retention tended to increase with increasing levels of WSL (P>0.05), and the highest value was found in the WSL75 diet.

 

It is concluded that the inclusion of WSL at levels of 50 and 75%in para grass based diets gave better daily gains and economic returns. 

Key words: Digestibility, economic return, growing rabbits, para grass, water spinach, weight gain


Introduction

In recent years, rabbit production in Vietnam has developed rapidly to meet an increased demand for fresh meat for human consumption to replace the shortfall in supplies of meat of chickens and ducks as a result of Avian Influenza.  The rabbit (Orytotagus cuniculus) is a non-ruminant, plant eating animal that has the ability to consume many kinds of natural grasses, vegetables, leaves from trees, fruits and by-products from kitchens or markets. It is also a meat-producing animal which is especially well adapted to utilization of protein-rich foliages due to the nature of its digestive system in which enzymatic digestion precedes microbial fermentation in the caecum.

 

Water spinach (Ipomoea aquatica) is a vegetable with high potential to efficiently convert nitrogen from biodigester effluent into edible biomass with a high protein content (Sophea and Preston 2001). It is a valuable forage resource for rabbits, according to the reports of Phimmasan et al (2004) and Chat et al (2005).  In The Mekong Delta, water spinach is widely used as a human food, particularly the stems, which are pickled for home consumption. This results in large amounts of water spinach leaves (WSL), which are cheap and high in protein being available for animals.  Para grass (Brachiaria mutica) has a high fibre content, and the correct combination between WSL and para grass could be ideal for feeding rabbits. However, optimum levels of WSL in roughage-based diets have not yet been determined.

 

This study aims to determine the optimum level of water spinach leaves as replacement for para grass in the diet on the feed utilization, growth rate and economic benefits of growing crossbred rabbits.

 

Materials and methods 

Experiment 1. Effect of different levels of water spinach leaf supplementation on the growth rate and economic benefits of growing crossbred rabbits

 

Animals and experimental design

 

The experiment was conducted at the Experimental Farm of Cantho University, Vietnam. Twenty-four crossbred female rabbits at two months of age were arranged in a complete randomized design with 4 treatments and 3 replications. Two females were housed in a wire mesh and wood cage, as an experimental unit. The dietary treatments were water spinach leaf supplementation to the diets at levels of 0 (WSL0), 25 (WSL25), 50 (WSL50) and 75% (WSL75) (DM basis) of the intake of para grass recorded on the control diet in which para grass was fed ad libitum. The diets were adjusted every week by increasing the allowance by 5% (DM basis). Paddy rice was supplied at the same level of 30g per day per rabbit for all treatments to provide energy. The experimental period lasted 8 weeks.

 

Feeds, feeding and management

 

Para grass was collected daily in the areas surrounding Cantho University. WSL were bought from farmers who plant and sell only WS stems for human consumption. The animals were fed three times a day at 8:00h, 15:00h and 19:00h. Para grass was offered ad libitum for all dietary treatments, and WSL was given at levels of zero (WSL0; control diet), 25 (WSL25), 50 (WSL50) and 75% (WSL75) of the amount of the paracontrol diet consumed (ad libitum), and adjusted daily. Paddy rice was supplied once per day at 11:00h with the amount of 30g / rabbit / day. Fresh water was available at all times. The refusals and spillage were collected and weighed daily in the morning to calculate the feed intake. The animals were vaccinated to prevent some diseases, especially rabbit hemorrhagic diarrhea and parasite diseases.

 

Measurements

 

The feeds and refusals were taken for analyses of DM, OM, CP, EE, NDF, ADF, and Ash following the procedures of AOAC (1990) and Van Soest et al (1991). At the beginning of the experiment two rabbits per experimental unit were weighed individually and thereafter weekly. Daily feed intakes, growth rate, and feed conversion ratios were measured and calculated. An economic analysis was also done for each treatment.

 

Experiment 2. Effect of different levels of water spinach leaf supplementation on nutrient digestibility and nitrogen retention

 

Animals and experimental design

 

The experimental design was similar to Experiment  1, except that 12-week old rabbits were used. One week was allowed for adaptation and then faeces and urine were collected for 6 days. Feeds and refusals were measured daily. Dry matter, CP, EE, NDF and ADF digestibility were calculated according Mc Donald et al (2002).  

 

Statistical analysis

 

The data from both experiments were analyzed by analysis of variance using the ANOVA of General Linear Model of Minitab Reference Manual Release 13.20 (Minitab 2000). Economic analyses were done using current prices in Vietnamese Dong (VND) to compare net incomes and feeds cost in the different treatments.

 

Results and discussion 

Experiment 1: Feeding trial

 

Feed characteristics

 

The chemical composition of the diet ingredients is presented in Table 1.


Table 1. Chemical composition of feed ingredients (% in DM)

Ingredient

Dry matter

Organic matter

Crude protein

Ether extract

Nitrogen free extract

Neutral detergent fiber

Ash

Metabolisable Energy, MJ/kg*

Para grass

16.6

87.6

12.9

6.00

76.7

36.9

12.4

9.23

Water spinach leaves

10.8

90.6

36.3

7.60

40.2

24.2

9.40

10.2

Paddy rice

87.1

95.6

6.74

1.40

25.1

13.8

4.40

11.8

 Source: NIAH 2002


WSL was considerably higher in crude protein compared to para grass and paddy rice, while NDF and ADF contents of para grass were higher than those of WSL. Therefore increasing the supply of WSL increased the overall protein content of the diet. The metabolizable energy content of the para grass was lower than of WSL. The DM content of WSL used in our experiment was slightly lower, and CP content higher than the values reported by Hue and Preston (2006) and Samkol et al (2006ab), possibly due to different ecological conditions, for example with respect to nutrient concentrations in the water. 

 

Feed and nutrient intakes

 

Daily intakes of the dietary ingredients and nutrients are shown in Table 2. 


Table 2.  Effect of level of offer of water spinach leaves (WSL) on feed and nutrient intakes (DM basis) of growing rabbits

Item

WSL0

WSL25

WSL50

WSL75

SE/P*

Daily intake, g / rabbit

 

 

 

 

 

    Para grass (PG)

73.8a

37.3b

28.9bc

19.6c

2.41/0.001

    Water spinach leaves

0.00

11.2a

19.2b

30.3c

1.29/0.001

WS/total forage          

0

0.231

0.399

0.607

 

WS/total DM

0

0.150

0.238

0.399

 

    Paddy rice

26.1

26.1

26.1

26.1

 

    Dry matter

99.9a

74.6b

80.8b

76.0b

1.58/0.001

    Organic matter

89.6a

67.8b

73.5b

69.6b

1.39/0.001

    Crude protein

11.3a

10.6a

13.9b

15.3c

0.24/0.001

    Neutral Detergent Fiber

63.2a

39.6b

40.5b

33.8c

1.17/0.001

    Acid Detergent Fiber

30.8a

20.1b

21.0b

18.2b

0.56/0.001

ME, MJ / day / rabbit

0.99a

0.76b

0.83b

0.79b

0.02/0.001

* WSL0: no WSL supplemented, WSL25, WSL50 and WSL75: WSL supplemented at levels of 25, 50, 75% of the amount of the control diet consumed, respectively

Means with different letters within the same row are significantly different at the 5% level.


Daily intake of para grass (PG) decreased significantly as the WSL supply increased (P<0.001). However, the total DM intake in rabbits fed PG only (control diet, WSL0) was significantly higher (P< 0.001) than for those fed the diets that included WSL, possibly due to the low DM content in WSL, although total DM intake was unaffected by the inclusion level of WSL in the offered feed, and was similar for WSL25, WSL50 and WSL75. The DM intakes were higher than the values of 49.7- 74.6g DM/day and 65-75.5g DM /day reported in previous studies in which rabbits were fed water spinach-based diets (Hue and Preston 2006 and Samkol et al 2006b).  CP intake was least on the PG only (WSL0) and WSL25 diets, and increased with increasing WSL intakes, being highest on the WSL75 diet, as a result of high CP content in WSL.  The CP intakes in the current study are considerably higher than those reported by Phimmasan et al (2004) (8.8 - 11.3g/day). The intakes of OM, NDF, ADF and ME in the WSL supplemented diets were lower than those in the control diet.

 

Growth rate, feed conversion ratio and economic analysis

 

Daily weight gain, feed conversion ratio and economic returns are presented in Table 3.


Table 3.  Effect of level of offer of water spinach leaves (WSL) on live weight and daily gains of growing rabbits

Item

WSL0

WSL25

WSL50

WSL75

SE/P*

Initial weight, g

870

800

892

788

57.4/0.53

Final weight, g

1,508ab

1,432a

1,738ab

1,820b

77.4/0.03

Daily gain, g/day

13.0a

12.9a

17.3b

19.0b

0.60/0.01

FCR, kg feed DM/kg gain

7.67a

5.85b

4.71c

4.03c

0.15/0.01

Feed cost, VND/rabbit

20,826

17,596

17,152

18,333

 

Income, VND/rabbit)

45,255

42,945

52,125

54,600

 

Difference, VND/rabbit

24,429

25,349

34,973

36,267

 

* WSL0: no WSL supplemented, WSL25, WSL50 and WSL75: WSL supplemented at levels of 25, 50, 75% of the amount of the control diet consumed

Means with different letters within the same row are significantly different at the 5% leve


Significantly higher final live weight and daily gains were found for rabbits in the WSL50 and WSL75 treatments as compared to those fed PG only and 25% WSL, with the highest values (P<0.05 and P< 0.01, respectively) for rabbits supplemented with 75% WSL. The difference was probably due to the higher CP intakes from WSL, as intakes of ME were higher for the WSL0 treatment. The performance results in the present study are similar to those in a study by Ha et al (1996), who reported that the weight gains of pure New Zealand rabbits fed grasses, concentrate and legume leaves were 15.5g and 20.6g per day.  The performance of the rabbits supplemented with WSL in this study were also within the range reported by Samkol et al (2006b), and were slightly lower than those found by Phimmasan et al (2004) and Hue and Preston (2006). Feed conversion ratio was poorest for animals fed PG alone (WSL0), and improved (P<0.01) with inclusion level of WSL, as a result of better daily gain and lower DM intakes compared to the control treatment. Feed conversion ratios were acceptable and similar to the values of 4.9 - 6.0, and 7.0, reported by Akinfala et al (2003) and Suc et al (2000), respectively.

 

The economic analysis was done for 8 weeks, and showed that the cost of feeds decreased with increasing levels of WSL. Furthermore, due to the increased growth rates with increasing supply of WSL the net benefit (feed costs minus income) were highest for the WSL50 and WSL75 treatments.

 

Experiment 2: Digestibility trial

 

The composition of the feedstuffs offered and the effects of level of offer of water spinach leaves (WSL) on diet DM and nutrient digestibility are shown in Table 4 and 5.


Table 4.  Chemical composition of diet ingredients (% in DM)

Diet ingredients

Dry matter

Organic
matter

Crude
protein

Ether
extract

Neutral
detergent fiber

Acid
detergent fiber

Ash

Para grass

16.6

88.5

11.7

5.62

67.8

35.7

11.5

Water spinach leaves

10.7

90.3

32.2

6.41

40.2

24.2

9.7

Paddy rice

87.1

96.8

6.69

3.37

25.1

15.4

3.2


The chemical composition of the feedstuffs used were similar to those in Experiment 1, except for a slightly lower CP content. Feed intakes ranged from 67 to 88g DM / day, and were lower for the diets including WSL, due to the lower DM content, although the differences were not significant.


Table 5.  Effect of level of offer of water spinach leaves (WSL) on digestibility of nutrients and nitrogen retention

Item

WSL0

WSL25

WSL50

WSL75

SE/P

Feed intake, g DM/day

88.0

67.0

73.5

74.5

12.1/0.18

Apparent digestibility, %

 

 

 

 

 

Dry matter

62.7a

70.5b

71.7b

73.0b

2.29/0.05

Organic matter

62.4a

70.1b

74.9bc

76.0c

1.14/0.001

Crude protein

82.0

84.5

83.5

83.0

2.24/0.90

Ether extract

72.7a

78.5b

80.0b

81.0b

0.86/0.01

Neutral Detergent Fiber

42.7

52.0

53.3

57.5

4.53/0.25

Acid Detergent Fiber

33.0

40.0

46.7

51.1

3.76/0.08

 Nitrogen balance, g/kgW0.75

 

 

 

 Nitrogen intake

1.21a

1.28a

1.48b

1.60b

0.04/0.001

 Nitrogen retention

0.76

0.84

0.88

1.07

0.09/0.15

Means with different letters within the same row are significantly different at the 5% level.


The apparent DM digestibility coefficients were significantly higher (P<0.05) in the diets with inclusion of WSL than that in the control diet. However, no significant difference in CP digestibility was found among the treatments. Digestibility of OM and EE was lower in the control diet (WSL0) than in the diets with WSL (P<0.05). The probable explanation is the high fibre content in PG, and Gidenne et al (1998) and Perez et al (1996) stated that a high level of fibre in the diet 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 diet digestibility (De Blas and Gidenne 1998). The DM and NDF digestibilities are similar to those in a study with rabbits reported by Samkol et al (2006a) in which water spinach based diets had a DM digestibility of 73.5 -78.3% and NDF a digestibility of 48.2- 56.3%. However, the CP digestibility values in the present study are superior to the values of 59.9 -70.9%  reported by Samkol et al 2006a). Our results are also in agreement with the lower digestibility indices of DM, CP and CF that were found in diets including high fibre supplements (Hue and Preston 2006).

 

Both the nitrogen intake and nitrogen retention increased corresponding with increasing levels of WSL in the diet, but differences were significant only for the nitrogen intake (P<0.001). The values in the present study are superior to those of Samkol et al (2006a).

 

Conclusions and implications  

    

Acknowledgements 

Financial support of this work from SIDA-SAREC is gratefully acknowledged. The authors would like to thank the Department of Animal Science, Faculty of Agriculture and Applied Biology of Cantho University for use of their favilities..

 

References 

Akinfala E O, Matanmi O and Aderibigbe A O 2003  Preliminary studies on the response of weaned rabbits to whole cassava plant meal basal diets in the humid tropics. Livestock Research for Rural Development, Volume 15 (4) http://www.lrrd.org/lrrd15/4/akin154.htm

 

AOAC 1990 Official Methods of Analysis (15th edition). Association of Offical Analytical Chemists. Washington, DC. Volume 1: 69-90

 

Chat T H, Dung N T, Binh D V and Preston T R 2005 Water spinach (Ipomoea aquatica) as replacement for guinea grass for growing and lactating rabbits. Livestock Research for Rural Development, Volume17, Article # 109. Retrieved November 23, 2005, from http://www.lrrd.org/lrrd17/10/chat17109.htm

 

De Blas E and Gidenne T 1998 Digestion of starch and sugars. In: The Nutrition of the Rabbit (Editors: C De Blas and J Wiseman). CABI Publishing. Wallingford. Pp: 17-38

 

Gidenne T, Pinheiro V, Facao E et Cunha L 1998 Conséquences d'une déficience en fibres alimentaires sur la digestion et le transit; premiers résultats chez le lapin adulte.7èmes Journées de la Recherche Cunicole, Lyon, France 147-150

 

Ha L T, Suc N Q, Binh D V, Bien L T and Preston T R 1996 Replacing concentrates with molasses blocks and protein rich tree leaves for production and growth of rabbits. Livestock Research for Rural Development. Volume 8 (3): 39-43 http://www.lrrd.org/lrrd8/3/ha83.htm

 

Hue K T and Preston T R 2006 Effect of different sources of supplementary fibre on growth of rabbits fed a basal diet of fresh water spinach (Ipomoea aquatica). Livestock Research for Rural Development. Volume 18. Article # 58. Retrieved September 18. 2006, from  http://www.lrrd.org/lrrd18/4/hue18058.htm

 

McDonald P, Edwards R A, Greenhalgh J F D and Morgan C A 2002  Digestibility evaluation of foods.  In Animal Nutrition, 6th Edition. Longman Scientific and Technical. New York. Pp: 245-255

 

Minitab  2000 Minitab reference manual release 13.20. Minitab Inc.

 

Perez J M, Gidenne T, Bouvarel I, Arveux P, Bourdillon A, Briens C, Le Naour J, Messager B et Mirabito L 1996  Apports de cellulose dans l'alimentation du lapin en croissance. Conséquences sur les performances et la mortalité. Annales de Zootechnie 45 (4): 299-309 http://animres.edpsciences.org/index.php?option=article&access=standard&Itemid=129&url=/articles/animres/pdf/1996/04/Ann.Zootech._0003-424X_1996_45_4_ART0002.pdf

 

Phimmasan H, Kongvongxay S, Chhay T and Preston T R 2004 Water spinach (Ipomoea aquatica) and Stylo 184 (Stylosanthes guianensis CIAT 184) as basal diets for growing rabbits. Livestock Research for Rural Development. Volume 16. Article # 34. Retrieved,  http://www.lrrd.org/lrrd16/5/hong16034.htm

 

Samkol P, Preston T R and Ly J 2006a Digestibility indices and N balance in growing rabbitfed basal diet of water spinach (Ipomoea aquatica) supplemented with broken rice. Livestock Research for Rural Development. Volume 18. Article #22. , from http://www.lrrd.org/lrrd18/2/samk18022.htm

 

Samkol P, Preston T R and Ly J 2006b 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.lrrd.org/lrrd18/2/samk18025.htm

 

Sophea K and Preston T R 2001 Comparison of biodigester effluent and urea as fertilizer for water spinach. Livestock Research for Rural Development Volume 13.  http://www.lrrd.org/lrrd13/6/kean136.htm

 

Suc N Q, Luyen L T and Binh D V 2000  Feeding systems for tropical rabbit production emphasizing root and bananas. Proceedings National Workshop-Seminar Sustainable Livestock Production on Local Feed Resources (Editors: T R Preston and B Ogle). Ho Chi Minh City, Vietnam. http://www.mekarn.org/sarpro/suctuber.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:  3583-3597 http://jds.fass.org/cgi/reprint/74/10/3583.pdf



Received 2 November 2006; Accepted 23 July 2008; Published 4 September 2008

Go to top