Evaluation of unprocessed and cracked, soaked and cooked velvet beans (Mucuna pruriens) as feed ingredients for pigs

O O Emenalom, A B I Udedibie, B O Esonu, E B Etuk and H I Emenike

Department of Animal Science and Technology, Federal University of Technology, Owerri
PMB 1526, Owerri, Imo State, Nigeria
emenalom2000@yahoo.com

Abstract

Velvet bean (Mucuna pruriens) is a tropical legume, which has potential as an energy and protein supplement in livestock feeds. Unfortunately, the use of raw velvet bean in non-ruminant feeding is limited because of its content of anti-nutritional factors.

A 42-day feeding trial was conducted to determine the response of growing pigs to diets containing unprocessed, or processed (cracked, soaked and cooked) velvet beans. Unprocessed velvet bean seeds were dried and milled and incorporated at 15% dietary level, while another batch was cracked, soaked in water for 48 hours and cooked for 60 minutes, dried, ground and incorporated at 20%, 30% and 40% dietary levels. The control (0%) diet contained no velvet bean. Each diet was fed to four growing pigs. At the end of the 42^nd day, two pigs per treatment were fattened for 7 days, fasted for 18 hours, slaughtered and eviscerated for organ weight determination. Unprocessed velvet bean at 15% dietary level significantly depressed the general performance of the pigs when compared with other groups. The groups on cracked, soaked and cooked velvet bean diets performed significantly better in growth rate and feed conversion than the group on unprocessed velvet bean and compared favourably with the group on the control diet. Unprocesed velvet bean significantly decreased the organ weights of the pigs. Mortalities recorded among the group on velvet bean were attributed to the treatments.

It is suggested that 15% dietary level of unprocessed velvet bean is toxic to pigs and that cracking prior to soaking in water and cooking allows for a successful use of the bean, up to 40% in the diets of growing pigs.

Key words: Pigs, processing, toxicity, velvet bean

Introduction

Many indigenous tropical legumes can be said to be "under utilized" because little has been done to explore ways to stimulate their production, processing, marketing or use. However, with the ever increasing demand for energy and protein feedstuffs and the subsequent competition between humans and livestock for the few available grains, there is need to explore ways to exploit these indigenous legumes, one of which is velvet bean (Mucuna pruriens) which is widely used as a cover crop (Berhe 2001).

Velvet bean is high in protein (Emenalom and Udedibie 1998) but contains toxic substances (Siddhuraju Vijayakumari and Janardhanan1996) that can be destroyed by heating (Udedibie and Carlini 1998). Few data are available on the use of velvet bean in pig nutrition. David (1986) reported that the raw seeds are not utilized by poultry but can comprise up to 25% of a ration for pigs. EDN (1997), in contrast, observed that while the seeds usually give good results with cattle and sheep even when fed up to 70% of the diet, they are generally unsatisfactory for pigs when forming up to 5% of the ration and may even cause severe vomiting and diarrhoea at 25% dietary level. Studies with poultry have shown that the raw bean is toxic to broilers (Emenalom and Udedibie 1998; Carmen et al 1999; Esonu 2001) and that cooking the bean (Emenalom and Udedibie 1998) only gave indications of partial detoxification hence its dietary inclusions could not exceed 10%. Soaking the bean in water before cooking (Udedibie et al 2001) allowed for a successful use of the bean at 20% for broilers.

Recently, Emenalom et al (2002) observed that cracking the bean into 2 to 4 pieces before soaking in water and cooking was more effective in improving the performance of broilers. This procedure has not been used for pig rations. This study was therefore designed to evaluate the response of pigs to diets containing raw, and crack - soak - and - cook velvet bean.

Materials and methods

The velvet beans used were divided into two batches. The first batch of the seeds (VB) was air-dried, ground and incorporated into the diets of grower pigs at 0% (control) and 15% levels. The second batch was cracked into 2 to 4 pieces using an ASKO AII (manufactured by Nigerian electrical plants ltd) grinding machine. The cracked beans were soaked in water for 48 hours (after which the water was discarded), rinsed with fresh water, cooked for an hour (period of cooking was taken as starting from the point of boiling), sun dried and milled to produce cracked, soaked and cooked meal (PVB). This meal was incorporated in the diets of grower pigs at 20, 30 and 40% levels respectively (Table 1).

Table 1. Ingredient composition of the experimental diets
Ingredients	Control, 0%	VB 15%	PVB, 20%	PVB, 30%	PVB, 40%
Maize	55.00	47.00	44.00	38.00	30.00
Mucuna seed meal	0.00	15.00	20.00	30.00	40.00
Soybean meal	15.00	8.00	6.00	2.00	0.00
Brewers’ dried grains	5.00	5.00	5.00	5.00	5.00
Wheat offal	12.00	12.00	12.00	12.00	12.00
Palm kernel cake	5.00	5.00	5.00	5.00	5.00
Fish meal	2.00	2.00	2.00	2.00	2.00
Blood meal	2.00	2.00	2.00	2.00	2.00
Bone meal	3.00	3.00	3.00	3.00	3.00
L-lysine	0.25	0.25	0.25	0.25	0.25
L-methionine	0.25	0.25	0.25	0.25	0.25
Salt	0.25	0.25	0.25	0.25	0.25
Vit./TM premix*	0.25	0.25	0.25	0.25	0.25
Total	100.00	100.00	100.00	100.00	100.00
Calculated analysis
Crude protein (CP)	19.12	19.57	19.83	20.10	20.36
Crude fibre (CF)	4.85	4.51	4.41	4. 32	4.22
Ether extract (EE)	4.23	4.17	4.15	4.13	4.10
Calcium (Ca)	1.23	1.37	1.42	1.47	1.51
Phosphorus (P)	1.02	1.05	1.06	1.07	1.08
ME, Kcal/kg	2776	2817	2861	2904	2948
*To provide the following per kg of feed: Vit. A, 10,000iu; Vit D₃, 1500iu; Vit. E, 3iu, Vit K, 2mg; ribofl, 3mg; pantothenic acid, 6mg; niacin, 15mg; choline, 5mg; Vit. B₁₂, 0.08mg; folic acid, 4mg; Mn, 8mg; Zn, 0.5mg; Iodine, 1.0mg; Co, 1.2mg; Cu, 10mg; Fe, 20mg.

Twenty crossbred pigs (Large White x Land race) of mixed sexes having body weights of 17.0 to17.5 kg were divided into five groups of four pigs each and randomly assigned to the five experimental diets in a completely randomised design. Each treatment was replicated four times with the pigs housed individually, weighed at the beginning of the experiment and weekly thereafter. Rations were offered at four percent of body weight adjusted weekly, while water was provided ad libitum. At the end of the 42-day feeding period, 2 pigs from each group were fattened for another 7 days on their different diets, fasted for 18 hours, weighed, slaughtered and eviscerated. Weights of the liver, heart, kidney, lungs and carcass yield were recorded and expressed as percentage of live weights.

The data collected were subjected to analysis of variance (Snedecor and Cochran 1967). Where the analysis of variance indicated significant treatment effects, the means were compared using Duncan's New Multiple Range Test (DNMRT) as outlined by Obi (1990).

Results and discussion

The data on the performance and organ characteristics of the experimental pigs are shown in Tables 2 and 3.

Table 2: Mean values of performance data of pigs fed diets with raw (VB) and processed PVB) mucuna seed meal
Parameters	Control 0%	VB15%	PVB 20%	PVB 30%	PVB 40%	SEM
Initial live weight, kg	17.00	17.25	17.50	17.25	17.25	0.11
Final live weight, kg	32.50^a	28.50^b	31.83^a	31.83^a	32.00^a	0.72
Weight gain, kg	15.50^a	11.25^b	14.33^a	14.58^a	14.75^a	0.73
Growth rate, g/d	369^a	268^b	341^a	341^a	351^a	17.3
Feed intake, kg (dry weight.)	36.9	36.0	36.9	36.9	36.9	0.56
Feed conversion ratio	2.38^b	3.20^a	2.58^b	2.53^b	2.50^b	0.14
Mortality, %	0.00	50.00	0.00	0.00	0.00
ab: means within a row without superscript in common differ at P < 0.05

Table 3: Effect of dietary raw and processed mucuna seed meals on dressed/organ weights of pigs
Parameters	Control 0%	VB15%	PVB 20%	PVB 30%	PVB 40%	SEM
Live weight, kg	38.00^ab	40.00^a	38.00^ab	34.00^b	35.00^b	1.55
Carcass weight, kg	25.00^a	24.00^a	25.00^a	20.00^b	21.00^ab	1.54
Dressed percentage, %	65.79^a	60.00^b	65.79^a	58.82^b	60.00^b	2.16
Liver, %	5.55^b	5.75^b	5.68^b	6.50^a	5.71^b	0.17
Heart, %	1.87^a	0.95^c	1.74^ab	1.38^abc	1.23^bc	0.17
Kidney, %	1.18^ab	0.95^c	1.05^bc	1.29^a	0.97^c	0.07
Lungs, %	3.11^ab	2.20^b	3.82^a	4.32^a	2.46^b	0.40
abc: means within a row without superscript in common differ at P < 0.05

The deleterious effects of raw velvet bean on weekly weight gains are shown in Figure1. After 42 days feeding, pigs fed 15% velvet bean gained 56.8% of control as against 94.8% gained by pigs fed a ration containing 40% processed velvet bean. Pigs on 15% velvet bean diet recorded a slight decline in feed intake but a significantly poorer feed conversion ratio. The weights of heart, kidney and lungs were lowest for the15% dietary inclusion of unprocessed velvet bean. Fifty percent mortality was recorded in the 15% velvet bean group.

Figure 1: Effect of velvet bean meals on the growth of young pigs
(PVB is processed velvet beans and RVB is unprocessed beans)

The result was consistent with the findings of Khan et al (1979) who showed that heat treatment applied to legume foods improves their texture, palatability and nutritive value by destroying or inactivating heat-labile toxic compounds and other enzyme inhibitors. The increase in weekly weight gains in pigs fed 20, 30 and 40% velvet bean rations is particularly notable in view of the treatment applied to the seed. Josephine and Janardhanan (1992) and Ravindran and Ravindran (1998) reported that except for L. Dopa all anti-nutritional factors detected/quantified in Mucuna beans are heat-labile and could be eliminated by cooking. However, the denaturation of heat-labile inhibitors by thermal processing (Liener and Kakade 1969) is governed by temperature, duration of heating, particle size and moisture contents. Thus cracking the seeds prior to soaking and cooking reduced the particle size and increased the moisture contents of the seeds, and facilitated the cooking to softness at one hour contrary to 2.5 hours reported for whole soaked-seeds (Wanjekeche 2001). It appears that the practice of cracking prior to soaking and cooking improved the nutritive value of the bean for pigs. However, presence of L-Dopa and other anti-nutritional factors in Mucuna bean might have contributed to the decreased growth of pigs fed 15% velvet bean ration as against the processed velvet bean groups. This is in agreement with the reports of EDN (1997) that raw Mucuna bean is poisonous to pigs at any dietary level, but contradicted the findings of David (1986) that Mucuna bean would be tolerated by pigs up to 25% in the ration.

The slightly reduced feed intake of pigs fed 15% raw velvet bean could be attributed to the variations in the weekly weights of the pigs since they were fed 4% of their body weights adjusted weekly. It appeared therefore that inclusion of raw velvet bean at 15% and processed velvet bean at 20, 30 and 40% respectively did not affect feed intake of the pigs unlike raw or processed jackbean (Canavalia ensiformis) which was rejected by pigs when incorporated either raw or cooked in the rations (Emenike 1998) . The poor feed conversion ratio recorded in the 15% group was attributed to anti-nutritional factors present in the bean, which may have affected nutrient utilization and absorption. Generally pigs on processed velvet bean rations had good feed conversion ratios comparable to the control group.

The factors responsible for the high mortality and depressed organ weights of pigs fed 15% raw velvet bean were not clear and need further investigation. There were also observable changes in the colour of the lungs (from brick red to pale yellow) and accumulation of fluid in the bladder of the pigs fed 15% velvet bean rations. These observations showed that unprocessed seeds of velvet bean are not safe for use in pig rations (even at an inclusion level of 15%) but cracking the bean prior to soaking in water and cooking could allow for up to 40% inclusion in the rations of young grower pigs.

Acknowledgement

The authors are grateful to the International Foundation for Science (IFS), Sweden for financing the research.

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