Effect of foliage of Mucuna pruriens as replacement for Para grass (Brachiaria mutica) on growth rate, digestibility and N retention in growing crossbred rabbits
 

Nguyen Van Thu and Lam Phuoc Thanh

Cantho University, Cantho City, Vietnam
nvthu@ctu.edu.vn

Abstract

Two experiments were conducted at the experimental farm of  Cantho University. In Experiment 1, sixty crossbred rabbits (local x improved breed) at 50 days of age, arranged in a Complete Randomized Design with 5 treatments and 3 replications, were offered levels of Mucuna pruriens forage corresponding to 0, 20, 40, 60 and 80% (DM basis) of the observed intake of para grass on the control (no Mucuna) treatment. Para grass was fed ad libitum and supplements of soybean waste and commercial concentrate were given at levels of 200 and 15 g/day, respectively, in all treatments. In Experiment 2, the experimental design was similar to that of the feeding trial; however, 12-week old rabbits were used. The animals had one week for adaptation and 6 days for recording quantities and taking samples of feces and urine

DM and crude protein (CP) intake increased with increasing ratio of Mucuna to Para grass in the forage fraction of the diet. Growth rate increased with increasing ratio of Mucuna as replacement for Para grass until a substitution level of about 0.50 after which it appeared to decrease. Feed conversion became worse as the proportion of Mucuna increased beyond 0.2. The ratio of Mucuna to Para grass did not affect the apparent digestibility coefficients of DM, OM and CP; however, the coefficients for the NDF and ADF fractions increased up to the 0.50 ratio of Mucuna followed by a decline at the higher level. Intake and retention of N increased with increasing ratios of Mucuna in the forage fraction of the diet.

It is concluded that Mucuna pruriens appears to have a high nutritive value for growing rabbits at ratios of up to 0.50 of the forage component of the diet. Subsequent research is needed to confirm this finding in all-forage diets without the confounding effects of high protein supplements such as soybean waste and commercial concentrates

Key words: Anti-nutritional compounds, cell wall fractions, crude protein, feed intake, forages

Introduction

In recent years, rabbit production based on low cost forages has increased considerably in Vietnam in order to meet the increasing demand for human food. However, studies on forage feeding and diet digestibility in growing rabbits are still limited.  Mucuna pruriens (MP) is widely grown in the tropics mainly because of the medicinal properties that appear to be found in all fractions of the plant (Sridhar and Bhat 2007). These authors reviewed the use of seeds and leaves of Mucuna as animal feed but rabbits were not mentioned. Mucuna is widely available in the Mekong Delta. The foliage has a higher crude protein content and less fibre than Para grass (Brachiaria mutica). Thus the combination between Mucuna and para grasss in diets for growing rabbits could be efficient in terms of increased nutrient intake. This study aimed to determine the optimum level of Mucuna pruriens as a replacement for Para grass in the diets of growing rabbits.

Materials and methods

Experimental design

Experiment 1: Feeding trial

The experiment was conducted at the experimental farm of Cantho University. Sixty crossbred rabbits (local x improved breed) at 50 days of age (average live weight of 615g) were arranged in a Complete Randomized Design with 5 treatments and 3 replications. Four rabbits (balanced for sex) in one cage was the experimental unit. The treatments were offer levels of Mucuna pruriens corresponding to 0, 20, 40, 60 and 80% (DM basis) (MP0, MP20, MP40, MP60 and MP80) of the observed intake of para grass on the control (MP0) treatment. Para grass was fed ad libitum. Supplements of soybean waste and commercial concentrate were given at levels of 200 and 15 g/day, respectively, in all treatments.

Experiment 2: Digestibility trial

The experimental design was similar to that of the feeding trial; however, 12-week old rabbits were used. The animals had one week for adaptation and 6 days for recording quantities and taking samples of feces and urine. 

Feeds, feeding and management

Para grass and Mucuna pruriens were collected daily in the areas surrounding Cantho city. These feeds were given in fresh form and were offered three times a day at 7:00h, 15:00h and 19:00h. Quantities offered and refusals were recorded daily for each forage. Fresh water was freely available. The rabbits were vaccinated to prevent hemorrhagic and parasite diseases.

Measurements

Feeds and refusals were analysed for DM, organic matter (OM), crude protein (CP) and ash according to AOAC (1990) procedures. NDF and ADF were determined following procedures of Van Soest et al (1991). Rabbits were weighed weekly.

Statistical analysis

The data from both experiments were analyzed using the General Linear Model option in the ANOVA of Minitab (Minitab 2000).

 

Results and discussion

Experiment 1: Growth trial

Mucuna pruriens was considerably higher in crude protein, lower in NDF and with similar  levels of ADF, compared with para grass (Table 1). Soybean waste and the concentrate had higher levels of crude protein than the forages.

Overall intakes of DM, OM, CP and ADF increased with increasing offer level of Mucuna (Table 1). NDF intakes were similar on all treatments. The planned ratios of Mucuna and Para grass were achieved for offer levels up to 40% replacement (M40) of Para grass but at the highest levels the observed replacement values of Mucuna were some 20% lower than planned (Figure 1; Table 3).

Growth rate increased with increasing ratio of Mucuna as replacement for Para grass until a substitution level of about 0.50 (Table 4; Figure 2) after which it appeared to decrease. Feed conversion became worse as the proportion of Mucuna increased beyond 0.2 (Figure 3).

Growth rates were high on all treatments which may partly have been a reflection of the supplementation with soybean waste and concentrates that together accounted for about one third of the total DM intake. There is no obvious explanation for the decline in growth rate with more than 50% replacement of the Para grass by Mucuna. However, the marked decrease in Mucuna intake (relative to Para grass) and the deterioration in feed conversion when Mucuna represented more than 50% of the forage DM intake, indicate that there may be some anti-nutritional factor in the Mucuna, the effects of which would be more apparent at the increased offer levels. Ravindran and Ravindran (1988) reported that the seeds of Mucuna contain a wide range of anti-nutritional factors which coiled be deactivated by heating. According to Ghosal et al (1971), hallucinogenic indoles (eg:  N-N-dimethyltryptamine, bufotenine, serotonin) are present in all parts of Mucuna pruriens (pods, seeds, leaves and roots).

Experiment 2: Digestibility and N retention

The feeds used in Experiment 2 (Table 5) were similar in composition to those used in Experiment 1.

DM feed intake tended to show a similar pattern to what was observed in Experiment 1, with a progressive increase until the ratio of Mucuna to Para grass reached 0.5. However, in contrast to what was observed in Experiment 1, intake appeared to decrease when the offer level of Mucuna exceeded 0.5 of the forage fraction (Table 6; Figure 4).

The ratio of Mucuna to Para Grass did not affect the apparent digestibility coefficients of DM, OM and CP (Table 7); however, the coefficients for the NDF and ADF fractions followed the same trend as for intake with increases up to 0.50 Mucuna followed by a decline at the higher level (Figures 5 and 6).

Intake and retention of N increased with increasing ratios of Mucuna (Table 7; Figures 7 and 8). Probably the higher intakes of digestible crude protein and the higher digestibility of the cell wall fractions in the Mucuna contributed to the improvement in N retention which, except at the highest Mucuna ratio, mirrored effects of the Mucuna ratio on growth rate.

Conclusions

·         Mucuna prupuriens appears to have a high nutritive value for growing rabbits at ratios of up to 0.50 of the forage component of the diet.

·         Subsequent research is needed to confirm this finding in all-forage diets without the confounding effects of high protein supplements such as soybean waste and commercial concentrates

Acknowledgements

The authors would like to thank the Department of Animal Science, Faculty of Agriculture and Applied Biology of Cantho University.

References

AOAC 1990: Official methods of analysis (15^th edition). Washington. DC, Volume 1: 69-90.

Ghosal S, Singh S and Bhattacharya S K 1971 Alkaloids of Mucuna pruriens: Chemistry and pharmacology. Planta Medica 19: 279-284.

Minitab 2000: Minitab reference manual release 13.20. Minitab Inc.

Ravindran V and Ravindran G 1988: Nutritional and anti-nutritional characteristics of Mucuna (Mucuna utilis) bean seeds. Journal Science of Food and Agriculture 46: 71-79.

Sridhar K R and Bhat R 2007: Agrobotanical, nutritional and bioactive potential of unconventional legume - Mucuna. Livestock Research for Rural Development. Volume 19, Article #126. Retrieved April 19, 2009, from http://www.cipav.org.co/lrrd/lrrd19/9/srid19126.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 Dairy Science. 74: 3585-3597.

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