Short communication
Nutrient composition of native forbs of semi-arid
and dry sub-humid savannas of Nigeria
Muh.S. Kallah
a,*, J.O. Bale
a, U.S. Abdullahi
b,
I.R. Muhammad
a, R. Lawal
aaNational Animal Production Research Institute, Ahmadu Bello University, PMB 1096, Shika-Zaria, Nigeria
bVeterinary Teaching Hospital, Faculty of Veterinary Medicine, Ahmadu Bello University, Samaru, Zaria, Nigeria
Received 20 January 1999; received in revised form 13 July 1999; accepted 3 November 1999
Abstract
A preliminary investigation was carried out to evaluate the nutritive value of six forb species widely used as feedstuffs in West Africa. The study examined four legumes (Crotalaria senegalensis,C. goreensis,Alysicarpus glumaceousandA. rugosus) and two non-legumes (Cassia mimosoidesandIpomea eriocarpa).
Field observations on gross phenology of these forbs illustrate their potentials in increasing the range of native forages for use in pasture development or improvement. All species sustained growth on residual soil moisture into the dry season providing green forage when most associated forages had dried up. Results of chemical analysis reveal that the species have properties in terms of contents of protein and some mineral elements that could be advantageously employed to balance animal ration or improve the quality of standing hay of tropical pastures. The species had mean values of 14±18% CP, 3.5±7.0% Ca and 40±58% DMD. Levels of Ca was high and more than 10 times the standard requirements for ruminant production in the tropics. While levels of P, K, Mg and Fe were suf®cient, Mn and Na were low, and apparently de®cient. The high levels of Ca resulted in unusually wide Ca : P ratios of 16 : 1±33 : 1 among the species. The implications of these ®ndings on uses of the forages in ruminant nutrition and the need for intensive studies on the observed results are discussed.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Crotalaria senegalensis;C. goreensis;Alysicarpus glumaceous;A. rugosus;Cassia mimosoidesand Ipomea eriocarpa; Forbs; Forage; Legumes; Herbaceous dicots; Nutrient composition; Digestibility; Ca: P ratio; Semi-arid; Dry sub-humid; Savanna; Nigeria
84 (2000) 137±145
*Corresponding author. Tel.:234-6950596; fax:234-6951272. E-mail address: lukman@abu.edu.ng (M.S. Kallah)
1. Introduction
The broad objective of this investigation was to explore the potentials of forbs (herbaceous dicotyledonous plant species) commonly described as `weeds' in arable crop systems for possible integration into livestock feeding systems. In the semi-arid and dry sub-humid savannas of West Africa, numerous species of herbaceous dicots especially from the generaCrotalaria,Alysicarpus,CassiaandIpomeaare known to be widely used in livestock production. Quite often they are plucked or cut, and fed either as fresh or conserved fodders. The utilisation of these and many other herbs growing naturally within the farm environment is rather opportunistic. Although there has been some interest among farmers of including `herbaceous dicotyledonous plants' in diets of animals, so far no deliberate attempt has been made to cultivate them to evaluate their agronomic requirements or nutritional value. A close examination of the possible roles of the palatable species in livestock production systems is quite desirable.
The data reported in this study arose as a result of preliminary observations made on feeding systems of peri-urban livestock production. While smallholder animal production around periphery of urban centres is becoming increasingly important as source of food and income supplement, availability of forage constitutes a major constraint. The paper presents nutritional information on the palatable species commonly observed being used in feeding systems of peri-urban livestock production.
2. Materials and methods
Four legume and two non-legume herbaceous dicots were examined during the study. The legume species were:Crotalaria senegalensis,C. goreensis,Alysicarpus glumaceus
andA.rugosus, while the non-legumes were Cassia mimosoidesandIpomea eriocarpa.
2.1. Plant materials
Plants populations growing naturally in grain sorghum (Sorghum bicolorL.) ®eld were sampled for chemical analysis. Whole plant cut at the base 10 cm above ground constituted a sample. The plants were harvested from Kallah-Sanawa Farms, Dutsin-ma Local Government Area in Katsina State at end of rainy season for a period encompassing bloom, pod-soft, pod-ripe and pod-dry stages of plant development. Harvesting was done at weekly intervals from 20 October to 15 December. The study site falls within the semi-arid zone at an altitude of 500 m (Latitude N 128270, Longitude E 078240). Soils within the area are sandy loams laden over sandy clay loams which according to FPDD (1989) are generally low in organic matter, available phosphate and cation exchange capacity. The annual rainfall is 870 mm in a discrete rainy season beginning early May and lasting until mid-October.
2.2. Chemical analysis
The forages were dried in a forced draught oven at 608C and the samples were ground to pass through 1.0 mm screen using a Christy & Norris Laboratory Mill. The ground
whole plant samples that included stems, leaves, ¯owers and pods/capsules were analysed for crude protein (CP), acid detergent ®bre (ADF), and lignin (AOAC, 1984; Procedures No. 7.003±7.37, 7.074±7.076) and neutral detergent ®bre (NDF) (Van Soest et al., 1991). Apparent dry matter digestibility (DMD) was calculated using the Van Soest (1967) summative equation as follows:
DMD0:98CCNDF 1:473ÿ0:789 log ADF ÿ12:9;
where CC is cell contents, NDF the neutral detergent ®bre and ADF the acid detergent ®bre.
The samples were analysed for the mineral elements according to procedures described by Faithfull (Faithfull, 1971; 1974). Calcium, Mg, Mn and Fe were read using atomic absorption spectrophotometer (Shimadzu AA Ð 650 model) while K and Na were determined by ¯ame photometry (FP 410 Corning). Phosphorus levels were estimated using Spectronic 20 Baush & Lomb.
2.3. Statistical analysis
The data were analysed using General Linear Models Procedure of Statistical Analysis System Computer Package (SAS, 1985). As there was no signi®cant interaction between species and period of sampling, data were pooled among sampling dates and least square means are given with their standard errors.
3. Results
3.1. General observations
Phenologically, seedlings of these plants emerge in mid-season, grow rapidly and produce numerous branches. Characteristically the Crotalaria and Cassia species are erect growing plants (up to 2.5 m). Both Alysicarpus species have basal rosettes with erect stems bearing long linear leaves.I. eriocarpa, on the other hand, is a trailing plant with bulbous meristematic bases that send out numerous stolons with tendrils which may spread horizontally or clasp to adjacent vertical object and grow spirally upwards. Development of organs in the six species was indeterminate with branches, ¯ower and pod/capsule production occurring simultaneously and continuously until moisture stress causes the plants to die off.
The last rain showers during the study year were received on 11 October. Thereafter, while associated grasses dried up, the species evaluated sustained growth under residual soil moisture with appreciable production of green forage material. At ®nal harvesting date (15 December) A. glumaceus and C. mimosoides had dried up. The other four species (i.e. Crotalaria senegalensis, C. goreensis, A. rugosus and Ipomea
eriocarpa) had vegetative green matter of leaf and herbaceous stems which were
3.2. Nutrient composition
Composition of nutrients in the species evaluated are presented in Table 1. Mean organic matter content vary from 83.4% for Ipomea eriocarpa to 89.4% for Cassia mimosoides. Crude protein content is fairly high in all species with a range of between 14.3% in C. mimosoides and 18.4% in Alysicarpus glumaceus. Cell wall constituents
Table 1
Nutrient composition of native forbs (herbaceous dicotyledonous plants) of semi-arid savanna of Nigeria
Component (% DM) Mean SEM Range
Crotalaria senegalensis OM 87.4 0.25 82.8±90.3
CP 17.3 0.34 13.8±19.3
NDF 50.0 0.54 47.5±52.8
ADF 34.4 0.20 32.6±39.5
LIGNIN 5.4 0.25 3.8±8.4
DMDa 49.0 0.32 44.6±51.1
Crotalaria goreensis OM 86.8 0.37 80.1±90.5
CP 17.3 0.33 13.5±20.5
NDF 55.6 0.52 46.7±61.9
ADF 40.4 0.20 32.1±47.6
LIGNIN 7.4 0.24 5.5±9.6
DMD 42.0 0.32 35.3±46.4
Alysicarpus glumaceus OM 84.5 0.28 80.0±87.7
CP 18.4 0.33 16.0±21.2
NDF 49.6 0.52 46.4±52.1
ADF 37.2 0.20 33.2±40.1
LIGNIN 7.3 0.24 6.5±7.9
DMD 48.1 0.32 45.0±51.2
Alysicarpus rugosus OM 85.7 0.35 81.3±89.1
CP 16.9 0.34 13.8±22.0
NDF 57.1 0.54 53.8±60.8
ADF 42.0 0.43 38.2±48.8
LIGNIN 9.2 0.25 7.2±11.3
DMD 39.7 0.20 34.8±43.8
Cassia mimosoides OM 89.4 0.29 85.0±92.0
CP 14.3 0.35 12.5±19.8
NDF 51.4 0.48 46.3±55.1
ADF 35.9 0.20 30.2±43.1
LIGNIN 8.9 0.17 6.9±9.6
DMD 47.5 0.32 42.0±53.9
Ipomea eriocarpa OM 83.4 0.33 80.6±82.2
CP 17.2 0.37 15.0±20.8
NDF 42.8 0.59 39.3±45.8
ADF 27.7 0.20 19.6±38.8
LIGNIN 5.4 0.28 3.2±7.4
DMD 57.5 0.32 54.5±64.4
aDMD calculated using Van Soest (1967) summative equation as follows: DMD0.98 cell contentsNDF (1.473ÿ0.789 log ADF)ÿ12.9.
Table 2
Mineral levels in native forbs (herbaceous dicotyledonous plants) of semi-arid savanna of Nigeria
Component (g/kg DM) Mean SEM Range
Crotalaria senegalensis Ca 48.2 1.44 41.92±56.37
P 1.9 0.06 1.60±2.20
Crotalaria goreensis Ca 48.9 1.44 40.11±61.18
P 1.7 0.06 1.20±2.10
Alysicarpus glumaceus Ca 48.0 1.44 40.98±53.03
P 2.0 0.06 1.70±2.30
Alysicarpus rugosus Ca 42.4 1.44 35.63±47.42
P 1.6 0.06 1.20±2.20
Cassia mimosoides Ca 35.3 1.40 33.31±39.38
P 1.9 0.19 1.60±2.40
Ipomea eriocarpa Ca 69.9 1.44 61.02±77.92
(NDF, ADF, Lignin) were lowest in the non-legume I. eriocarpa and highest in the legumeA. rugosus.TheCrotalariaandCassiawere intermediate. Reverse ranking order was found in terms of dry matter digestibility, with low of 39.7% forA. rugosusand high of 57.5% forI. eriocarpa.
The concentration of mineral elements in the six forb species is given in Table 2. With exception of Mn,I. eriocarparanks highest among the species in mean concentration of Ca, P, K, Mg and Na whileC. mimosoideshas the lowest contents of these elements. The
Crotalariaspecies had the lowest values of Mn and Fe, and intermediate in contents of
the other mineral elements.
3.3. Calcium to phosphorus ratio
Unusually wide ratios were found for the forbs irrespective of the grouping as legume or non-legume. Mean ratios vary between 19 : 1 for C. mimosoides and 29 : 1 for I.
eriocarpa. Calcium was as high as 7.8% (78 g/kg) inI. eriocarpa while the P content
varied from 0.12% (1.2 g/kg) in C. goreensis and A. rugosus to 0.26% (2.6 g/kg) in
I. eriocarpa.
4. Discussion
Observations on patterns of phenological development of the plants relative to the life cycles of associated forages in pasture ecosystems within the study area suggest the potentials of the species in increasing the range of forages available for sown pasture improvement. Besides extending the supply of green forage into the dry season, the levels of nutrient constituents were promising and could be of advantage in balancing diets or pasture stand quality. All species evaluated sustained growth producing fresh fodder and seeds for up to two months into the dry season when almost all associated grasses had dried up. The use of these species in pasture plant associations could be strategically employed to develop pasture system that would supply green forage for a signi®cant portion of the dry season.
The potential advantages of using dicotyledonous species to enhance the concentration of mineral elements (e.g. N, Ca, Mg) in the diet of grazing animal had been suggested by Wilman and Derrick (1994). Multi-species pasture containing the selected forb in a desired proportion may be developed and sustained. An option was to include in diet a proportion of species which are inherently high in concentration of particular elements. The species in this study are particularly high in Ca and K.
Relative to native grasses and other conventional fodder plants (e.g. Haggar, 1970; Kapu, 1975; Minson, 1990), the species analysed had nutrient levels indicative of forages of good quality. Crude protein range of 14.3 and 18.4% is more than that found in several tropical grasses (Minson, 1990). It is comparable to content in the introduced legumes tested in the coastal grasslands of West Africa (Adjei and Fianu, 1985; Ikhimioya and Olagunju, 1996). Earlier studies on a wide variety of naturally growing native herbaceous dicots in East Africa (Dougall and Bogdan, 1966; Gihad, 1976) indicated crude protein content in the range of 9.5±35.9%. The six species in the present report were within this
range. Ten species ofCrotalariain the report of Dougall and Bogdan (1966) had higher mean CP (25%) and P (0.3%) but considerably lower Ca (0.8%) than concentrations found in our study.
The forages appear promising in terms of their energy content for supporting production. Judging from the calculated coef®cients of dry matter digestibility, four of the species have digestibility values above 45% which is considered adequate for high animal performance on pastures (McDowell, 1972; Holt, 1977). Relative to most tropical forages the mean values of DMD found in this study are more than encouraging. The forages grown in combination with grass or included in ration formulation could enhance balance of nutrient elements that may be lacking in grasses at advanced stages of maturity.
Mineral composition of forages varies with soil fertility, plant specie and stage of maturity. In the present study, soil fertility status was not examined while interaction between composition and maturity was not found signi®cant for the stages examined. Relative to animal requirements for production in tropical grassland ecosystems (McDowell, 1997) all species appeared quite suitable for animal nutrition in terms of contents of Ca, P, K, Mg, and Fe, although rather low in Mn for production. They appear de®cient in Mn and Na compared to animal requirements from the feeding standards ARC (1980) and McDowell (1997). The levels of P in this study contrast to the sub-optimal levels of P commonly reported in grasses, legumes and browses of the savannas of Nigeria (Kapu, 1975; Adamu et al., 1993; Kallah et al., 1995; Campbell et al., 1996; Kallah et al., 1997, 1999).
The Ca : P ratio in feeds is an important consideration in the nutrition of the animal Ð with tolerable limits being in the range of 1 : 1 and 7 : 1 for ruminants. Wide ratios found in this study is attributable to high Ca content of the forages. Relative to the suggested range of 0.19±0.77% Ca requirements in diets of ruminants grazing native tropical pastures (McDowell, 1997) the forages recorded more than 10 times the levels of Ca. Although the levels of P in forages had been found to fall within the required range, the gross excess of Ca is likely to aggravate aphosphorosis in unsupplemented animals.
5. Conclusion
Forbs (herbaceous dicotyledonous plants) are important components of grassland ecosystem of the semi-arid and dry sub-humid savannas of West Africa. In arable crop systems, they are commonly referred to as `weeds'. Four legumes (Crotalaria
senegalensis, C. goreensis, Alysicarpus glumaceus, A. rugosus) and two non-legumes
(Cassia mimosoides and Ipomea eriocarpa) evaluated are potential useful forages for
Acknowledgements
The authors are grateful to the Director, National Animal Production Research Institute, Ahmadu Bello University, Shika-Zaria for permission to publish the work.
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