Assessment of nutritive value of four dominant weed species in north central Nigeria

A Akinfemi and A A Mako*

Nasarawa State University, Keffi, Faculty of Agriculture, Department of Animal Science, Shabu-Lafia, Nigeria
akinfemiabayomi2003@yahoo.com
* Department of Agricultural Production and Management Sciences, Tai
Solarin University of Education, Ijagun. Ijebu Ode, Ogun State. Nigeria

Abstract

Four selected tropical weeds: Cleome viscosa, Cyperus esculentus, Diodia scandens and Eurphorbia hirta were evaluated for their nutritive value by proximate composition, mineral composition, anti-nutritional factor and in vitro gas production method.

Proximate composition showed that all the weeds were quite high in crude protein (7.67-16.74%), crude fiber (19.21-26.89%), ash (9.38-12.67%) and low in ether extract (2.36-5.61%). The weeds had sufficient composition of calcium, magnesium, potassium, sodium and phosphorus to meet the requirement for ruminants. The constituent of iron, copper, zinc and manganese were far less than recommended levels required for growth, reproduction and milk. The net gas volume (mL) at 48h, metabolisable energy (MJ/Kg DM), short chain fatty acid (µmol) and organic matter digestibility (%) ranged from 77-86, 11.0-13.6, 1.40-1.78 and 80.3-97.3 respectively. The studies showed that Cleome viscosa had the best nutritive value followed by Eurphorbia hirta with the least from Diodia scandens and Eurphorbia hirta. All the selected weeds may serve as potential supplements for ruminants in north central Nigeria.

Key words: in vitro, organic matter digestibility, ruminants, tropical weeds

Introduction

Weed forages are very important non conventional feed resources for ruminants in north central Nigeria especially when grass forages are limiting in the dry season. However, the utilization of tropical weed is limited by the high lignin content and the presence of anti-nutritional factors which apart from being toxic may depress digestibility in ruminants, the most implicated being tannin. Feed shortages which are identified as the major constraint affecting the livestock industry in Nigeria has necessitated the need for cheap alternative feed resources. The appellation, alternative feed resources has become commonly used to design those local feeds, which could replace partially or totally conventional feedstuffs either grass forages or concentrate feeds without reducing livestock performance but should decrease the feeding cost (Sallam 2005).

Cleome viscose, Cyperus esculentus, Diodia scandens and Eurphorbia hirta are four common typical weeds that grow in the beginning of the raining season and continue into the early part of the dry season in the pasture of Nigeria. After most of the grasses are dried, Cleome viscosa and Eurphorbia hirta are still surviving among the dried grasses. But little is known about their nutrient potentials and values, and anti-nutritional contents thus making it very difficult to assess their potentials in sustaining ruminant production in the tropics. Additionally, the determination of intake and digestibility of feedstuffs using in vivo is time consuming, laborious, expensive, require large quantities of feed and is unsuitable for large scale feed evaluation (Coelho et al 1988). Therefore, in vitro gas production and in situ rumen degradability, both rapid and low-cost methods have been used to assess the degradation and nutritive value of feedstuffs (Sallam 2005). The present study attempts to determine the chemical composition, anti-nutritional factor and in vitro gas production of four common weeds in north central Nigeria.

Materials and methods

Sample collection 

Samples of Cleome viscose, Cyperus esculentus, Diodia scandens and Eurphorbia hirta were collected from the Teaching and Research Farm, Nasarawa State University, Keffi Shabu-Lafia Campus, Lafia, Nasarawa, Nigeria. The weeds were collected in late raining season (October) when they have attained full maturity. The materials were milled and oven-treated at 65⁰C until a constant weight was obtained for any dry matter determination. 

In vitro gas production 

Rumen fluid was obtained from three West African Dwarf female goat through suction tube before the morning feed. The animals were fed with 40% concentrate feed (40% corn, 10% wheat offal, 10% palm kernel cake 20% groundnut cake, 5% soybean meal, 10% brewers grain, 1% common salt, 3.75% oyster shell and 0.25% fishmeal) and 60% Guinea grass. Incubation was carried out according to (Menke and Steingass 1988) in 120ml calibrated syringes in three batches at 39⁰C. To 200mg sample in the syringe was added 30ml inoculum that contained cheese cloth strained rumen liquor and buffer (9.8g  NaHCO₃ + 2.77g Na₂HPO₄ + 0.57g KCL + 0.47g NaCL + 0.12g MgSO₄. 7H₂0 + 0.16g CaCI₂ . 2H₂0 in a ratio (1:4 v/v) under continuous flushing with CO_2.  The gas production was measured at 3, 6, 9, 12, 15, 18, 21 and 24h. The average volume of gas produced from the blanks was deducted from the volume of gas produced per sample. The volume of gas production characteristics were estimated using the equation Y = a + b (1 – e^ct) (Ǿrskov and McDonald 1979), where Y = volume of gas produced at time ‘t’, a = intercept (gas produced from the soluble fraction), b = gas production from the insoluble fraction, (a+b) = final gas produced, c = gas production rate constant for the insoluble fraction (b), t = incubation time. The post incubation parameters such as metabolizable energy (ME, MJ/Kg DM), organic matter digestibility (OMD %) and short chain fatty acids (SCFA) were estimated at 24h post gas collection (Menke and Steingas 19 88).

ME = 2.20 + 0.136* Gv + 0.057* CP + 0.0029*CF;

OMD = 14.88 + 0.88Gv + 0.45CP +0.651XA;

SCFA = 0.0239*Gv – 0.0601;

Where Gv, CP, CF and XA are net gas production (ml/200mg DM) at 24 h incubation time, crude protein, crude fibre and ash of the incubated sample respectively. 

Chemical composition 

DM was determined by oven drying the milled samples to a constant weight at 105⁰C for 8 hours. Crude protein was determined as Kjadhal nitrogen x 6.25. Ether extracts and ash were determined according to (AOAC 1995) method. Neutral detergent fibre (NDF), Acid detergent fibre (ADF) and Acid detergent lignin (ADL) was determined using the method described by Van Soest et al (1991).Hemicellulose was calculated as the difference between NDF and ADF while cellulose is the difference between ADF and ADL. Anti-nutritional properties like saponin were determined by gravimetric method, oxalate by permanganate titrimetric method, and tannins by Folin-Dewis spectophotometric method and cyanogens (Onwuka 2005).  

Statistical analysis  

Data obtained were subjected to analysis of variance (ANOVA) and means separation was by Duncan multiple range tests using Statistical Analysis System (SAS) 1999 package.  

Results and discussion

Chemical composition and mineral content of selected weeds

The chemical composition and mineral contents of the four selected weeds are presented in Tables 1 and 2. Generally wide variations were observed in the chemical composition of the investigated weeds. The crude protein content ranged from 7.69% in Diodia scandens to 16.74% in Eurphorbia hirta. The crude fiber content of weeds investigated was lowest in D. scandens and highest in Cyperus esculentus. Ash content ranged from 9.38% in Cleone viscose to 5.61% in E. hirta. The crude fiber fractions differ significantly among the weeds. The highest values for NDF, ADF and Cellulose were observed in C. esculentus while the highest values for ADF and hemicellulose were observed in C. viscose. E. hirta was generally low in NDF, ADF, ADL and cellulose compared with other weeds under investigation. D. scandens was observed to be high in major minerals compared with other weeds. The values obtained are adequate to meet the requirement for growth, reproduction and milk in West Africa dwarf sheep and goats (Babayemi 2006). The calcium and phosphorus ratio in C. esculentus were within the range approved 1:1 to 2:1 ranged recommended (McDowell 1985). Additionally, the values obtained in the study for the major mineral elements were higher than those obtained by Babayemi (2006) for Enterolobium cyclocarpum. Iron, copper, zinc and manganese in the present study were extremely deficient, and the reasons for this are unknown. This therefore implies, as suggested by Babayemi (2006) that the feed (weed) may be fortified with the minerals in form of either salt lick or diet inclusions.

There are many factors affecting chemical composition and mineral content of feedstuffs such as stage of growth, maturity species or variety (Von Keyserligh et al 1996; Agbagla Dohnani et al 1997) and soil types (Thu and Preston 1999).

Those factors may partially explain differences in chemical composition between our study and others. 

Anti-nutritional composition

The total condensed tannin ranged from 0.029 to 0.052mg/g DM (Table 3). The values were much lower than the 0.5mg/g DM reported by Okoli et al (2003) for south eastern browse species in Nigeria and also lower than those reported by Njidda et al (2010). The lower values obtained might be due to the effective drying which the weeds were subjected to. The concentration of tannin as obtained in this result were generally low and would not be life threatening to ruminants consuming these weeds. As a matter of fact a moderate level of tannin (2-4% of DM) in ruminant diet has been found to increase protein flow into duodenum (Barry 1989) which ultimately improves the protein fraction absorbed and consequently animal growth (Ahamefule and Azubike 2010). Other benefits of low tannin ingestion by ruminants include improved live-weight gain (Waghorn et al 1999), improved lambing percentage (Min et al 1999) and reduced parasite infection (Hoskin et al 2000). 

The saponins were also generally low in concentration in the weed samples. They are produced by a range of different plants and are plants defense mechanism against pathogens. Saponins have a bitter taste and so cause a reduction in feed intake. They can be tolerated by adult ruminant and can indeed increase the efficiency of rumen fermentation by reducing the amount of methane produced while increasing the amount of microbial protein to the animal (Babayemi et al 2004). At low levels, they are excellent foaming agents forming strong insoluble complexes with cholesterol (Ahmaefule and Azubike 2010) while high levels decreases apparent digestibility especially that of nitrogen (Abdu et al 2008). The levels obtained in this study are low to cause any problem. 

The phytate concentration reported in the present study ranged from 1.22 to 1.34 mg/gDM. These levels are unlikely to have adverse effect in ruminant diets. Ruminants readily utilize phytate because of phytase produced by rumen macro-organisms. Phytic acid is a strong chelator of important minerals such as calcium, magnesium, iron, zinc and can therefore contribute to mineral deficiencies.

The results for oxalate ranged from 2.36 to 3.24mg/g DM. The value was lower than the 20g/kg oxalate reported to be deleterious for pigs, poultry and rabbits (Acamovic 2004). Oxalate at higher levels binds to calcium in the gut and reduce the absorption and availability of calcium to animals. 

In vitro gas production

The gas volume and estimated parameters of four weed forages are shown in Table 4. The results obtained showed variations in the gas volume obtained at 24hr and 48hr. Since gas production on incubation of feeds in buffered rumen fluid is associated with feed fermentation and carbohydrate fractions (Sallam et al 2008). So the hither produced by Cyperus esculentus at GV48, and has lower gas produced by Eurphorbia hirta could be related to fibre fractions content. This is consistent with De Boever et al (2005) who reported that gas production was negatively related with NDF content and positively with starch. The negative effect of cell wall content with gas production in E. hirta could be due to reduction in microbial activity through increasing the adverse environmental conditions as incubation time progress. Sallam et al (2007) reported that cell wall content (NDF and ADF) were negatively correlated with gas production at all incubation times and estimated parameters. Despite the higher cell wall content obtained for E. esculentus in this study, the cumulative gas was high. Gas production is basically the result of fermentation of carbohydrate to acetate, propionate and butyrate (Wolin et al 1960) and substantial changes in carbohydrate fractions were reflected by total gas produced (Deavile and Givens 2001). 

The predicted ME, SCFA and OMD profile were widely varied in the four weed forages under investigation and were particularly high in E. hirta and Cleomen viscosa. Menke and Steingass (1988) reported a positive correlation between ME calculated from in vitro gas production together with CP and fat content with ME value of conventional feeds measured in vivo. Therefore, this result suggests that E. hirta and Cleomen viscose has a higher potential of being used in ruminant nutrition compared with other weeds under investigation. 

The OMD differed among the different weeds under investigation. Very high OMD were observed in C. viscosa and E. hirta followed by C. esculentus and D. scandens. This result implies that the microbe in the rumen and animal have high nutrient uptake (Chumpawadee  et al 2007). 

Gas production can be regarded as an indicator of carbohydrate degradation and low gas production obtained for E. hirta may also be explained by the presence of the condensed tannins. Although the condensed tannins obtained in E. hirta is within tolerable limit, one cannot eliminate the binding effects of tannin in the carbohydrate and then by inhibition of enzymes or microorganism (Griffiths 1986), complexing with lignocellulose and preventing the microbial digestion. 

The variations observed in the SCFA may be explained by the variation in the in vitro gas production on incubation of the different weed samples. The highest rate of gas production (C) observed with Cleomen viscosa followed by Diodia scandens, Cyperus esculentus and the least from Eurphorbia hirta. The show rate in E. hirta could be explained by the fact that protein in feeds has a depressing effect on gas production and that this could be due to a change in the partitioning of the fermented substrate between microbial cells (microbial biomass) and short chain fatty acids (SCFA) and gas (Osuga et al. 2006). 

The gas volume at asymptote (b) described the fermentation of the insoluble fractions. The fermentation of the insoluble fractions of the four selected weeds differed (P < 0.05) with the best value obtained in Cleomer viscose and the least value recorded for Diodia scandens. 

High fermentation of the insoluble but degradable fraction was observed in Cleomen viscosa and Eurphorbia hirta, possibly influenced by the carbohydrate fractions readily available to the microbial population (Chumpanadee et al 2007). 

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Received 14 March 2012; Accepted 22 October 2012; Published 6 November 2012

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