Studies on selected browses of southeastern Nigeria with particular reference to their proximate and some endogenous anti - nutritional constituents

I C Okoli, Maureen O Anunobi, B E Obua*,  and V Enemuo

Tropical animal health and production research laboratory, Department of Animal Science and Technology, Federal University of Technology, Owerri, Nigeria
icokoli@futo.edu.ng
* Department of Animal Science, Michael Okpara University of Agriculture, Umudike, Nigeria

Abstract

Seven Commonly utilized browse plants (Diodiascandens, Microdesmis puberula, Nuaclea popegnine, Palisota hirsute, Ricinodendron heudelotti, Urena lobata and Vernonia amygdalina) were collected from Ihiagwa in Imo State, Nigeria and analysed for proximate chemical composition and some anti-nutritive components of their leaves.

A high variability was recorded in values of percentage crude protein in DM (CP) (13.3 to 25.9), Ash (4.80 to 12.8), crude fiber (7.50 to 19.9), ether extract (7.50 to 19.9) and nitrogen free extract (40.1 to 57.6). The concentrations of anti-nutritional factors were generally low. Tannin content ranged from 0.38 in V. amygdalina to 1.97 in P. hirsuta, while phytin and hydrocyanic acid levels ranged from 13.8 mg/kg to 25.2 mg/kg and 1.52 mg/kg to 6.40 mg/kg, respectively.

The results show that the browse plants studied have good levels of nutrients, low and safe levels of anti-nutritional factors, and may therefore form good feed resources for modern intensive animal production.

Key words: Anti-nutritional factors, browses, leaf meal, proximate composition, southeastern Nigeria.

 

Introduction

Increasing demand and subsequent high cost of conventional animal feed ingredients in the tropics has created the need for sustainable alternatives, particularlynatural feed resources  indigenous to the region (Onwuka et al 1989; Abubakar and Mohamed 1992; Osagie 1998; Tian et al 1998). This search for alternative feed resources has over the past few decades rekindled research interest in the use of tropical browse plants as sources of nutrients for ruminants as well as non-ruminants (Mecha and Adegbola 1980; D'Mello 1992; Aletor and Omodara 1994).

Browses constitute an abundant biomass in farmlands, bush fallows and forests in the humid tropical environment of southeastern Nigeria. They are commonly utilized in the wild by small-holder livestock farmers for feeding small ruminants (Uwechue1990; Okoli et al 2002). The potential of leaf meals from these tropical trees and shrubs to yield relatively higher levels of crude protein and minerals and lower crude fiber levels than tropical grasses has also been recognized (Le Houerou 1980; Mecha and Adegbola 1980; Onwuka et al 1989; D'Mello 1992).

Of the over 5000 trees and shrubs listed as being suitable for feeding livestock in Africa (Le Houerou 1980; Brewbaker  1986; Okoli et al  2002), it has been suggested that only 80 are of real fodder value while 5 may be recorded as good (Brewbaker  1986). This probably underscores the lack of information on the values of many of these plants and the need to scientifically evaluate their nutritive importance.

Mecha and Adegbola (1980), Wahua and Oji (1987), Aletor and Omodara (1994), and more recently Oji and Isilebo (2000) and Okoli et al  (2001) among others, have characterized the nutrient composition of some indigenous browse plants of southern Nigeria. These studies showed that crude protein and crude fibre contents of such plants range from 15.3% to 33.3% and 2.7% to 15.6%, respectively. However, tropical browses have been shown to contain varying quantities of condensed tannin and other anti-nutritional substances in their biomass that affect their optional utilization by animals (Aletor and Omodara  1994; Onwuka  1994; Onwuka  1996; Osagie  1998).

The present study examines the proximate and some endogenous anti-nutritional constituents of seven commonly utilized browse plants of southeastern Nigeria in order to underscore their suitability for intensive livestock projection.

Materials and Methods

Botanical identification

Fresh leaves from the apical portions of the branches of seven selected browse plants were collected from secondary forests and bush fallows at Ihiagwa, Imo State, Nigeria. The plants: Diodia scandens, Microdesmis puberula, Nuaclea popegnine, Palisota hirsuta, Ricinodendron heudelotti, Urena lobata and Vernonia amygdaline were identified at the Forestry Department, Ministry of Agriculture and Environment, Imo State.

Chemical analysis

Fresh foliage of the selected browse plants was sun-dried for 3 days, cut into pieces (2 to 5cm), oven-dried at 60 to 70^oC for 24 hours and ground through 1mm screen for subsequent analysis. Proximate composition was determined for percentage of dry matter (DM), crude protein (CP), crude fibre (CF), ether extract (EE), ash and nitrogen free extract (NFE) according to the methods of AOAC  (1990). The fiber fractions, acid detergent fibre (ADF) and neutral detergent fiber (NDF) where determined according to the method described by Goering and van Soest (1970). Percentage hemi-cellulose content was obtained by finding the difference between NDF and ADF values (Church  1975).

Tannin content was determined with the Folin-Denis reagent method of Pearson (1976). Phytin in the plant samples was estimated as phytic acid using the method of Maga (1982), while hydrocyanic acid (HCN) was determined by the Knowels and Watkins distillation method as described by Pearson (1976).

Statistical analysis

The means and standard error of means were calculated for the proximate and anti-nutritional factor values. Means were subsequently separated using the least significant difference (LSD) method. (Steel and Torrie  1980).

Results

Proximate composition

Mean values for proximate composition and the fibre fraction are in Tables 1 and 2.

Anti-nutritional substances

Concentrations of tannin, phytin and hydro cyanic acid in the browse plants are shown in Table 3. Tannin levels in the plants were generally low and ranged from 0.38% in V. amygdalina to 1.91% in P. hirsuta.  Mean phytin content of all the plants was 19.28 mg/g ranging from 25.2 mg/g to 13.2 mg/g. Hydrogen cyanide (HCN) content of the browses ranged from 1.52 mg/g  to 6.40 mg/g.

Discussion

Results of proximate analysis are extensively employed in research and industry for quick estimation of nutrient potentials of feedstuffs. Although such results may not give a true indication of the nutritive value of a feed, they supply clues in research, to plants of potential value for further in vitro or in vivo studies (Mecha and Adegbola  1980; D'Mello and Fraser  1981; D'Mello  1992). Proximate analysis is specifically useful in screening the potentials of the array of tropical browse plants utilized by indigenous farmers for ruminant feeding.

The values for crude protein showed that the mean value of the seven plants analysed (17.9% in DM) is high compared to that of tropical grass species, which seldom exceed a level of 15% (Reynolds et al  1992). It compares favorably with that of cassava leaf meal (Mecha and Adegbola  1980;) and far exceeds the minimum protein requirements of ruminants (10 to 12%) estimated by ARC (1985). At 25.9% CP, M. puberula compares favorably with leucaena spp. and gliricidia spp. (22.2% and 22.5% ,respectively) (Tian et al  1985). Indigenous plants have however been shown to perform better than these exotic species in the acid soils of the region (Ndon and Essien  1987). Variations were observed between the CP values obtained in the present study and other reported values. For example, Okoli et al (2001) and Onwuka (1996) reported 33.3% and 23.4% respectively for M. puberula,  while in the present study it was 25.9%. Similarly, the CP value obtained for P. hirsuta (15.3%) is lower than the 20.9% reported by Oji and Isilebo (2000), while the 15.32% CP reported by Mecha and Adegbola (1980) for U. lobata is lower than the 18.17% obtained for the same plant in this study. This variability in the nutrient content of browses has been attributed to within species differences, plant parts, season, harvesting regimen, location, soil type and age (Norton  1994).

The mean crude fiber (CF) content of the seven plants (11.6%) is low when compared with that of tropical grass species, which may be as high as 45to 50% at more mature stages of growth (Uwechue  1990). It is also lower although comparable with the CF levels of cassava leaf meal (15.6%) guava leaves (16.1%) and poultry deep litter manure (16.60%) (Aduku  1999). Mean ether extract (EE) content was low at 5.07%. However, R. heudelotti value (7.00%) is comparable to the 8.32% and 7.5% obtained from palm kernel cake and rice bran respectively (Aduku  1999). Ash contents of V. amygdaline (12.80%), P. hirsuta (10.80%) and R. heudelotti (9.80%) were relatively high and comparable to the 11.0% reported for leucaena spp. by Alekan (1989), but lower than the 16.07% reported for cassava leaf by Oyenuga (1955).

The mean ADF and NDF fractions obtained in the present study compare favorably with those reported by Oduguwa et al  (1999) and Oji and Isilebo  (2000) for selected browses of southern Nigerian. The mean ADF and NDF values of 38.5% and 55.5% reported here were low to moderate when compared with low quality roughages, which ruminants can effectively degrade (Arigbede and Tarawali  1997). Mean hemi-cellulose fraction of the browses at 13.04% was low. However, D. scandens and M. puberula had values that compare favorably with the 30.3g/100g and 21.6g/100g reported for wheat offal and cassava root chaff (Aderemi et al  1999).

Mean tannin content of the browses was considerably lower than the 2.05% reported in Gliricida sepium (Ahn et al  1989) as well as the 3 to 14% reported in Leucaena leucocephala (D'Mello and Fraser  1981). A threshold concentration of tannin of 5% has been reported beyond which there may be rejection of browses by goats and wild browsers (Cooper and Owen-Smith  1985). In sheep and cattle, dietary tannin levels of 2 and 5% respectively have also been reported to have adverse effects on digestibility (Mcleod  1974).

The phytin levels reported in the present study (13.8mg/g to 25.2mg/g) were similar to those reported by Onwuka (1996)  and Aletor and Omodara (1994) but higher observed by Oduguwa et al  (1999). These levels are unlikely to have any adverse consequence in ruminants although they could be of dietary importance to monogastric animals since they lack the phytase needed to break down the phytin to release phosphorus.

The HCN contents of the browses were equally low. Siegler et al  (1989) reported that most commonly consumed browses are cyanogenic. However, the quantity of HCN produced by most of these species is too low to pose major animal health problems (Kumar and D'Mello  1996). Generally, only plants that produce more than 20mg HCN/100g fresh weight are considered deleterious (Everist  1981).

Conclusion

The browses analyzed in the present study have good levels of nutrients particularly protein and contained low levels of toxic constituents such as tannin, phytin and hydro cyanic acid. There is the need to expand the study to other nutrients and anti-nutritional factors such as oxalate, nitrite saponins and alkaloids. Feeding trails using ruminants and monogastric animals are recommended in order to fully ascertain the nutritional values of these browses.

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Received 10 December 2002; Accepted August 12 2003

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