Chemical composition and in vitro dry matter
digestibility of four parasitic plants (
Tapinanthus
lugardii
,
Erianthenum ngamicum
,
Viscum
rotundifolium
and
Viscum verrucosum
) in Botswana
O.R. Madibela
a, W.S. Boitumelo
a,*, M. Letso
b aSebele Station, Department of Agricultural Research, P/bag 0033, Gaborone, BotswanabBotswana College of Agriculture, P/bag 0027, Gaborone, Botswana
Received 18 May 1999; received in revised form 8 September 1999; accepted 16 December 1999
Abstract
Parasitic plants, Tapinanthus lugardii, Erianthenum ngamicum, Viscum rotundifolium and V. verrucosumwere harvested during months (January, March, May and June) in 1998 at the Sebele Research Station. The samples were separated into leaves and stems, (®rst 15±20 cm of shoots) or used as whole plants and analysed for crude protein (CP), acid detergent ®bre (ADF), acid detergent lignin (ADL) and minerals. In vitro dry matter digestibility (IVDMD) was determined. There was a signi®cant (p<0.05) month and species effect on CP. The month effect assumed a linear (p<0.01) response. The CP increased from the ®rst month (January) of sampling to a maximum at the last month (June) of sampling and ranged from 104 to 206 g/kg DM. Although the month effect was not signi®cant (p>0.05) on minerals, Cu increased in a linear (p<0.05) fashion from the ®rst month to the last month of sampling, while the reverse was true for Ca. The speciesV. rotundifoliumhad signi®cantly (p<0.01) higher CP thanE. ngamicum(163 vs. 125 g/kg DM). There were signi®cant species in¯uences on Cu (p<0.05) and Zn (p<0.01).V. rotundifoliumhad higher Cu and Zn than the other species. Crude protein (182, 125, and 98 g/kg DM), ADF (208, 332 and 402 g/kg DM), IVDMD (59.1, 41.3 and 33.8% DM), Fe (205, 112 and 95 ppm) differed signi®cantly (p<0.01) between leaves, whole plant and stems of E. ngamicum. There were also signi®cant (p<0.05) differences between leaves, whole plant and stems ofE. ngamicumfor Ca, Mn, Zn and ADL, except Cu and P. Higher levels of Ca, Mn and Zn were found in the leaves than in the stems, while the converse was true for ADL. Plant fractions ofT. lugardiidiffered signi®cantly for ADF (219, 265 and 357 g/kg DM;p<0.01), ADL (91, 107 and 150 g/kg DM;p<0.05), IVDMD (48.8, 46.7 and 34.6%;p<0.01), and Zn (20, 21.8 and 30.3 ppm;p<0.05) in the leaves, whole plant and stems
84 (2000) 97±106
*Corresponding author. Tel.:267-328780; fax:267-328965.
E-mail address: dar@info.bw (W.S. Boitumelo)
respectively. Crude protein, Ca, P, Cu, Fe and Mn were not signi®cantly (p>0.05) different among the plant fractions of.T. lugardii.For the speciesT. lugardiiandE. ngamicum, the stems had high content of ®bre and lignin but low IVDMD. Although there was variation in chemical composition among the species and months, the levels of nutrients were constantly higher than what is expected in natural grasses, especially during the dry season. This suggests that these parasitic plants can be effectively used as nutrient supplements.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Parasitic plants; Chemical composition; In vitro dry matter digestibility
1. Introduction
Traditionally, livestock in Botswana rely on natural vegetation to meet their nutrient requirements. However, with the advent of increased land use and recurrent droughts, shortage of feed supply has become a major constraint to increased animal production. During the dry season, natural pasture has low nitrogen, sulphur and other mineral contents while the ®bre content is high (Bonsi et al., 1994). In drier environments, like Botswana, shrubs and tree foliage play an important role in providing fodder of better quality to ruminants (Givens et al., 1989; Kibon and Orskov, 1993; Baloyi et al., 1997; Tolera et al., 1997) and, particularly, to goats.
As the environment is drastically changing, resulting in less feed from the range, there is a need to exploit all potential locally available feed resources that can be used by livestock, especially in the poor smallholdings. Smallholder farmers are increasingly using leaves and pods of indigenous trees, such asAcacia tortilis, for livestock feeding (APRRD, 2000). During the dry season, when natural pastures have deteriorated, both in quantity and quality, some trees and shrubs provide the only quality feed resource to livestock (Givens et al., 1989; Kibon and Orskov, 1993; Bintende and Ledin, 1996; Tolera et al., 1997). According to Sidahmed et al. (1981) browse plants, shrubs and tree leaves should be given more attention in the feeding management of goats.
Common parasitic plants are mistletoes that attach themselves to branches ofAcacia
species, Boscia albitrunca, Ziziphus mucronata and other trees found in the semi-arid conditions of Botswana. These parasitic plants are sometimes speci®c to a host plant and/ or to a locality. Their ultimate goal is to develop under conditions, where they stand the best chance of establishment and survival (Visser, 1981). Due to long root system of host plants and adequate nutrients and water supply, some parasitic plants may maintain high nutritive value during the dry season.
and to harness this indigenous knowledge, a catalogue of non-conventional feed resource is being evaluated by researchers. The nutritional signi®cance of these feed resources will then be assessed so that better strategies of using them can be established. The aim of this study was to determine the chemical composition and in vitro dry matter digestibility of four parasitic plants from January (wet season) to June (dry season). Data presented herein reports a preliminary study on chemical attributes of these plants in Botswana.
2. Materials and methods
2.1. Location of study
Samples ofTapinanthus lugardii,Erianthenum ngamicum,Viscum rotundifoliumandV.
verrucosumwere collected in January, March, May and June in 1998 from the Sebele
Research Station farm. The Station is situated at latitude 248330
S and longitude 258570 E, at an altitude of 994 m a.s.l. The vegetation type is a mixture ofAcacia savanna with broad-leaved middle layer trees, likeCombretum apiculatum,Burkea africanaetc. Grass consists of species of intermediate forage value, such as Eragrostis rigidior, and E.
lehmanmiana. Species, rated good in forage value, includePanicum maximum,Digitaria
milanjiana,Urochloa masambicensiandU. trichopus. Grasses of poor nutritional value
are Aristida congesta and Melinis repens. The soil type of the area is classi®ed as
moderately deep-to-very deep, imperfectly-to-moderately well drained, dark brown-to-red, sandy clay loams-to-clays (De Wit and Nachtergaele, 1990). Data for rainfall and temperature for the Sebele Station over the past twenty years were collected from Botswana Meteorology Services weather station, located 0.5 km from the study site. Mean rainfall for the area is about 500 mm. Monthly average minimum and maximum temperature is 12.8 and 28.68C, respectively.
2.2. Sampling and chemical analysis
2.3. Statistical analysis
Analysis of variance (ANOVA) procedure (SAS Institute Inc., 1990) was used to determine the effects of months and species of whole plants or plant parts on chemical composition and IVDMD. Differences between species, and between plant parts were separated by using Duncan's multiple range test. General linear models (GLM) procedure (SAS Institute Inc., 1990) was used to test the effects of month of sampling on chemical composition of the four species.
3. Results
3.1. Effects of month and species on chemical composition and IVDMD
Tables 1±3, and Figs. 1 and 2 show the effect of month, species and plant fractions on chemical composition and IVDMD. Among all plants, there were signi®cant (p<0.05) species effects on CP (Table 1). The species V. rotundifolium and V. verrucosum had signi®cantly (p<0.01) higher CP thanE. ngamicumandT. lugardii. There were signi®cant (p<0.05) species effects on Cu and Zn.V. rotundifoliumhad signi®cantly (p<0.05) higher Cu and Zn and tended to have (p0.07) higher Mn than the rest. There were signi®cant (p<0.05) month effects on CP. The month effect assumed a linear (p<0.01) response where CP increased from the ®rst month of sampling (January), reaching a maximum
Table 1
Nutrient and mineral contents and in vitro dry matter digestibilityaof the whole plants
CPb ADFc ADLd IVDMDe Caf Pg Cuh Fei Mnj Znk T. lugardii 132 265 107 46.7 12 2 4.8 108.5 32.5 21.8 E. ngamicum 125 332 162 41.3 9 2 4.8 111.8 24.5 19.8 V .verrucosum 158 277 141 52.9 11 2 4.3 77.0 24.5 25.8 V. rotundifolium 163 241 121 52.8 9 2 8.8 74.0 45.8 48.5
Mean 145 279 133 48.4 10 2 5.6 92.8 31.8 28.9
SED 1.2 2.8 2.4 5.3 0.23 0.03 1.4 17.0 7.8 6.1
Level of significancel * NS NS NS NS NS * NS NS *
aThe units are in g/kg DM, except for IVDMD (%) and Cu, Fe, Mn and Zn which are in ppm. bCrude protein.
cAcid detergent ®bre. dAcid detergent lignin. eIn vitro dry matter digestibility. fCalcium.
gPhosphorus. hCopper. iIron. jManganese. kZinc.
lLevel of signi®cance: NSp>0.05; *p<0.05; **p<0.01; and ***p<0.001.
Table 2
Mean crude protein , ®bre content, in vitro dry matter digestibility and mineral of the leaf, stem and whole plant (WP) fractions ofT. lugardiiandE. ngamicum
Parametersa T. lugardii E. ngamicum Main effects
Leaves Stems WP Mean SEDb SLc Leaves Stems WP Mean SEDb SLc Mean SED Species Fractions
CP (g/kg) 135 104 132 124 1.4 NS 182 98 125 135 1.3 ** 129 1.3 NS **
ADF (g/kg) 219 357 265 281 1.6 ** 208 402 332 314 2.5 ** 297 1.9 * ***
ADL (g/kg) 91 150 107 116 2.1 * 107 188 162 152 2.5 * 134 1.6 * **
IVDMD (%) 48.8 34.6 46.7 43.4 3.7 ** 59.1 33.8 41.3 44.7 4.5 ** 44.1 4.4 NS **
Ca (g/kg) 15 10 12 13 0.2 NS 10 8 9 9 0.08 * 11 0.2 ** NS
P (g/kg) 2 2 2 2 0.2 NS 2 2 2 2 0.03 NS 2 0.02 NS NS
Cu (ppm) 4.0 4.3 4.8 4.3 1.2 NS 6.3 5.8 4.8 5.6 0.98 NS 5.0 0.72 * NS
Fe (ppm) 108 72.3 109 96.3 27 NS 205 91.5 112 136 19.4 ** 116.1 19.0 * **
Mn (ppm) 34.3 33 32.5 33.3 2.0 NS 42.8 19.8 24.5 29 5.2 * 31.1 4.4 NS *
Zn (ppm) 20 30.3 21.8 24 3.0 * 15.5 21.5 19.8 18.9 1.5 * 21.5 2.1 ** **
aCP, crude protein, ADF, acid detergent ®bre, ADL, acid detergent lignin, IVDMD, in vitro dry matter digestibility. bStandard error of difference.
cSigni®cance level: NSp>0.05; *p<0.05; **p<0.01; and ***p<0.001.
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value at the last month of sampling (June) (Fig. 1). Although there was no signi®cant (p>0.05) month effect on most minerals, there was a signi®cant (p<0.05) linear effect on Ca and Cu (Fig. 2). Ca decreased linearly from January to June.
Between T. lugardii and E. ngamicum there was no signi®cant (p>0.05) species difference in CP, but there were signi®cant (p<0.01) fraction effects (Table 2). E. ngamicumleaves had signi®cantly (p<0.05) higher CP than stems and whole plant. There were signi®cant (p<0.05) differences in ADF among species (E. ngamicum vs. T. lugardii) and fractions (p<0.001). ADF was signi®cantly (p<0.001) higher in the stems than in leaves and whole plants of the two species. Species (p<0.05) and plant fractions (p<0.01) also signi®cantly in¯uenced ADL.E. ngamicumhad higher ADL values thanT.
lugardii, while stems had higher values than the leaves and whole plant. Leaves had
higher IVDMD than stems and whole plant for eitherT. lugardii(p<0.01) orE. ngamicum
(p<0.05). Although there was no signi®cant (p>0.05) fraction effect, leaves ofT. lugardii
Table 3
Correlations among the chemical attributes and in vitro dry matter digestibility (IVDMD)
CP ADF ADL IVDMD
Crude protein (CP) ÿ0.48 NSa ÿ0.09 NS 0.47 NS
Acid detergent ®bre (ADF) 0.65** ÿ0.77**
Acid detergent lignin (ADL) ÿ0.39 NS
aSigni®cance level: NSp>0.05; *p<0.05; **p<0.01; and ***p<0.001.
Fig. 1. Effect of month on crude protein, acid detergent ®bre (ADF), acid detergent lignin (ADL) and in vitro dry matter digestibility (IVDMD) of four parasitic plants.
had higher (p<0.05) Ca content than stems and whole plant. Iron was higher (p<0.05) in
E. ngamicumthan inT. lugardiiand differed signi®cantly in the fractions ofE. ngamicum
only, the leaves having the highest (p<0.01) levels of iron. Mn was not different between the two species but was higher (p<0.05) in the leaves of E. ngamicumthan in the stems and whole plant. Species and fractions signi®cantly (p<0.01) in¯uenced Zn content, with stems having higher (p<0.05) Zn content than leaves, while T. lugardii had higher (p<0.05) Zn content in stems thanE. ngamicum.
Among the chemical attributes and between chemical attributes and IVDMD, ADF was negatively (rÿ0.77,p<0.001) correlated to IVDMD, while CP tended to be (p0.06) correlated to ADF and positively (r0.47,p0.06) correlated to IVDMD (Table 3).
4. Discussion
Tree foliage is a common feedstuff for animals, particularly for browsing species like goats (Sidahmed et al., 1981) and wildlife. Crude protein among the four parasitic plants was different and high inViscumspecies. Crude protein ranged from 104 to 206 g/kg DM and was higher than in natural grass (70 and 40 g/kg DM) for the wet and dry seasons, respectively (APRU, 1975). Acid detergent ®bre (ADF) differed between the four species, but was lower than in browse Brachystegia spiciformis in Zimbabwe as reported by Baloyi et al. (1997). In the present study, differences in CP and ®bre did not affect the in vitro dry matter digestibility. The mean IVDMD of 48.4%, was about 3 percentage units above 45% which, according to Youngquist et al. (1990), is the level needed for maintenance of cattle in the tropics. Because of the high nutrient content of these plants, it can be safely inferred that they can be used as feed by ruminants.
Minerals were also higher than in natural pastures, especially P which is usually the main mineral limiting livestock productivity in Botswana (APRU, 1980). Soils in Botswana are low in P, hence it is also low in natural pasture. The results from pasture clippings over several years have shown that phosphorus rarely reaches 1.0 g/kg DM at any time of the year to satisfy the minimum levels required by livestock (APRU, 1980). A common feeding management in Botswana involves offering a mineral lick containing dicalcium phosphate which is usually not easily accessible to resource-poor farmers. Therefore, because these plants are endowed with ample Ca and P, they can be good alternative mineral supplements for the livestock. Copper levels were also higher than in natural grass and were well below the levels that can cause toxicity in ruminants (10±20 mg/kg DM) as reported by McDonald et al. (1988). Manganese levels were also within the recommended levels for ruminants. One conspicuous observation about these plants is that three of them remain green throughout the year. According to McDonald et al. (1988), most green foods contain suf®cient amounts of Mn. Although animal by-products are known to be richer in Zn than plant protein supplements, the three parasitic plants contain substantial amounts of Zn, thus making them potential Zn supplements.
The setback is likely to be the unavailability of some minerals due to low digestibility and possibly complexing with the phenolic and/or other compounds in the plants. Complex phenolic compounds (tannins and ¯avanols) are widespread, abundant and appear to be the major constraint of some leguminous plants, because of their effect on intake, digestibility and animal metabolism (Kumar and Singh, 1994). Free, condensed tannins may bind protein and make it less soluble in neutral detergent and increase the content of NDF (Reed et al., 1987). It has been noted that the large faecal-N excretion in ruminants on multipurpose trees are invariably associated with consumption of high amounts of anti-nutritional factors in the diets (Powell et al., 1994).
The time of harvesting as indexed by sampling month had signi®cant effect on nutritive value of the plants. The nutritive value as indexed by increase in CP increased linearly as the season progressed from wet to dry. It is of particular interest that May and June are times when natural pasture is dry with low CP content, the use of these plants at this time could, therefore, be expected to improve the nutritive quality of livestock feeds. This indicates that, during the dry season, parasitic plants may provide a more nutritious diet or supplement to livestock. Since during the wet season (January to March), the nutritive quality of these plants is low, it offers an advantage because during that time there is alternative nutritious resources available and they can be reserved to be used during the time when they are required.
5. Conclusion
Farmers use parasitic plants as feed supplements, especially for their small ruminant livestock. The nutritive value, as indexed by increase in CP, increased as the season progressed from wet to dry, thus offering nutritious diet to animals during the dry period season. The four parasitic plants, T. lugardii, E. ngamicum, V. verrucosum and V.
rotundifoliumshould be included in an inventory of useful and nutritious feedstuff for
livestock. It is thus recommended that alternative feeds like parasitic plants should be evaluated further and that indigenous knowledge in livestock feeding be documented to increase the source of local information. There is a need to investigate the presence of anti-nutritional factors, degradability and correlation of nutritive value with that of host plants. A study is already on ground assessing animal response to feeding of these plants. Biological studies may include growing behaviour and response to harvesting of the plants, since the plants are above the browse line of most farm animals.
Acknowledgements
recognised for critiquing the manuscript. The study was supported by Botswana Government.
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