CC BY
17
АРИДНЫЕ ЭКОСИСТЕМЫ, 2003, том 9, № 18
============= СИСТЕМНОЕ ИЗУЧЕНИЕ АРИДНЫХ ТЕРРИТОРИЙ==========
УДК 581.526-53+633-2
ПОЕДАЕМОСТЬ ПУСТЫННЫХ КОРМОВЫХ РАСТЕНИЙ
© 2003 г. И. В. Спрингель1, А. Н. Гуссейн,2 М. Эль-Ашри,3 М. Бадри1, А. Хамед1
1Ассуан, Университет Южной долины, Египет 2Ассуанская государственная служба по окружающей среде, Египет 3Каир, Университет Айн-Шамс, Египет
Настоящая работа была проведена в южной части Восточной Пустыни в Египте. До сих пор популяция бедуинов, которые населяют эту пустыню, зависит от домашнего животноводства (овцы, козы и верблюды). Вади Алаки была выбрана для этого исследования по ряду причин: это крупнейшая вади (сухое речное русло) в этом регионе, которая поддерживает значительные популяции бедуинов. На нижнюю часть вади воздействует недавно сформированное водохранилище (озеро Насер), также эта вади является важнейшим компонентом биосферного заповедника, где интенсивная исследовательская деятельность ведется с 1984 года.
Задачей данной работы является выявление пастбищного потенциала аборигенных видов растений, произрастающих в нижней части русла вади и описание их кормовой ценности.
Пустынные пастбищные растения были разделены на три группы по длительности жизненного цикла, когда они доступны как корм.
1. Первая группа представлена многолетними деревьями и кустарниками, которые формируют постоянный, но ограниченный источник корма для домашнего скота.
2. Вторая группа представлена многолетними растениями, которые запасают воду в различных органах во время выпадения осадков.
3. Третья группа — однолетние и эфемерные растения, которые прорастают из семян только после дождей и не обязательно каждый год.
В первую группу включены пустынные деревья (Acacia tortilis, A. raddiana, А. ehrenbergiana и Balanites aegyptiaca), являющиеся обычным и важным источником корма в Вади Алаки.
Tamarix nilotica также является важным компонентом пастибщного корма, произрастает преимущественно в обнаженных частях нижнего течения Вади.
Листва Balanites богата питательными веществами, протеинами и карбогидратами. Молодые свежие побеги также ценны в этом отношении, но содержат меньше питательных веществ, чем листья. Листва и молодые побеги Balanites имеют высокую зольность, некоторые из веществ весьма полезны для животных (кальций, магний, сода, фосфор и др.) но есть и вредные. Семена этих растений очень богаты жирами и протеинами.
Деревья акаций являются важнейшим источником корма в пустыне. В засуху они являются резервом корма, тогда как другие источники для скота недоступны. Акация содержит высокое количество питательных веществ и протеинов, которое колеблется от 5 до 14% в молодых побегах и 21% — в плодах. Содержание протеинов значительно колеблется по сезонам.
Tamarix nilotica доминирует в сообществах нижнего течения Вади Алаки. Тамарикс является источником самого лучшего пастбищного корма когда молод и особенно, когда его вегетативные части находятся под водой, тогда в них наименьшее содержание соли. Однако животным трудно питаться в этом случае. Листья тамарикса имеют высокое содержание протеинов, которое варьирует от 14 до 18%. Протеины вместе с высоким процентом сухого органического вещества удобоваримы, питательно ценны, но высокое
содержание ионов: хлора, магния и натрия, вероятно, способствуют низкой поедаемости этого растения.
Во вторую группу включены многолетники Senna alexandrina, Aerva javanica, Pulicaria crispa и Citrullus, которые доступны в сухой период года. Эти растения не богаты протеинами в зимний период и их количество уменьшается в засуху. Psoralea plicata заслуживает особого внимания в этой группе растений. Это засухоустойчивое бобовое растение, обычно доступное как корм для скота в течение 2-х лет после обильных дождей. Питательная ценность — 17% белков и высокое содержание минералов.
Коротко живущие однолетники Eragrostis aegyptiaca, Fimbristylis bis-umbellata, Crypsis schoenoides, Clinus lotoides, Hyoscyamus muticus доминируют по берегам озер в нижнем течении Вади Алаки. Большинство из этих растений содержат: белка 18 — 21%, карбогидратов (8—12%) и древесного волокна (25 — 27%).
Astragalus vogelii и Euphorbia granulata — эфемеры с коротким жизненным циклом (3-5 месяцев), произрастающие в пустыне только после дождей. Оба растения обеспечивают временный подножный корм для скота и имеют высокое содержание протеинов.
PALATABILITY OF DESERT FODDER PLANTS © 2003. I. Springuel1, A. H. Hussein2, M. El-Ashri3 ?M. Badri1, A. Hamed1
'South Valley University, Aswan, Egypt 2Aswan Governorate Office for Environment, Aswan, Egypt 3Ain-Shams University, Cairo, Egypt Introduction
The specific focus of the present work is to elucidate the grazing potential of common indigenous species growing in the downstream part of Wadi Allaqi, and to describe their value as fodder. The previous research on pasture plants conducted in Wadi Allaqi gave the grazing score to each plant based on indigenous knowledge and field observations (Springuel, 1994; White, 1995; Briggs et al., 1999).
The present work is based on chemical analyses of the plants which dominate the plant communities on the shores of Lake Nasser and in surrounding desert in downstream part of Wadi Allaqi. This is the combined work of many researchers of the Allaqi team. Seasonal (monthly) variations in the chemical compounds that characterise palatability of 10 common plants growing in the downstream part of Wadi Allaqi were analysed by Hussein (1997). Results on the minerals and organic component of 10 plants published by M. A. Badri and A. J. Hamed (2000), as well as unpublished results of M. A. Badri and J. Springuel, are also used in the present work. The main reference to this work is the International Development Research Centre (IDRC) report (Belal et al. 1998). Plants identified as having high grazing value could be used to improve the desert pastures, taking the advantage of the newly available water of Lake Nasser.
Characteristics of Pasture Plants
Desert pasture plants can be characterised into three groups based on the length of time for which they are available for use as a fodder.
The first group comprises perennial trees and shrubs, which form a permanent, but limited, source of fodder for livestock. Such plants tend to be geographically scattered and isolated and so access may be a problem. The foliage may be too far from the ground for grazing animals to reach. On the other hand, these tend to be a large plants, which provide shade for animals thus reducing water loss and lowering respiratory energy consumption.
The second group comprises perennials which respond to the availability of water stored in the wadi-fill deposits following rainfall events. Their availability as fodder is therefore sporadic, but they are tend to be relatively small undershrubs, herb and grasses, which are easily accessible to animals.
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СПРИНГЕЛЬ, ГУССЕЙН, ЭЛЬ-АШРИ, БАДРИ, ХАМЕД
The third group is made up of annual and ephemeral plants, which emerge from seeds only after rainfall events, but not necessarily every year. When they do emerge, such plants provide abundant, nutritional fodder for animals for a period of a few months.
Group 1: Trees and shrubs
The indigenous desert trees, Acacia spp. (A. tortilis, A. raddiana, A. ehrenbergiana) and Balanites aegyptiaca), are the most common and important fodder plants in Wadi Allaqi. Tamarix nilotica is also an important pasture plant that provides permanent fodder; it grows in previously inundated parts of downstream Wadi Allaqi.
Balanites aegyptiaca
Balanites is the most widely distributed tree in Sudan from where it has spread to the Nubian Desert of Egypt. In Egypt it is confined to water-receiving sites such as wadis and river banks. Small populations of this tree are found in the wadis of the southern part of the Eastern Desert and in Red Sea wadis. Relatively larger undisturbed populations of Balanites occupy the upstream part of Wadi Allaqi. It also grows in Kharga Oasis in southern part of the Western Desert.
Balanites is a useful tree for livestock farmers, as a source of shelter, protection and fodder for their animals. It is especially good for providing shade for livestock because the trees have a dense cover of dark green leaves and often keep their leaves during the dry season when most other trees are bare. In places where there is an abundant mixture of different pasture plants, or in the rainy season when pasture is easily available, livestock will often feed on other plants in preference to Balanites. However, when other fodder sources are scarce, especially towards the end of the dry season, animals do not hesitate to feed on the tree.
The foliage of Balanites is nutritious (Suliman, Jackson, 1959; Dougall et al., 1964; Bille, 1978; Toutain, 1980; Burkhill, 1985). A high content of crude protein (11-27%, table 1) and carbohydrates (45-57%, table 1) have been reported by different authors. The fresh green young shoots are also palatable but have less nutrition value than the leaves; they are particularly poor in carbohydrates and fat (9% and 0.97% respectively, table 1). The leaves and young shoots of Balanites have a high mineral content; some of these may be beneficial (calcium, magnesium, sodium, potassium, phosphorus) to animals while others are harmful (e.g, chloride).
Table 1. Balanites aegyptiaca: Nutritional value of green leaves and young shoots, expressed as % w/w*. Таблица 1. Balanites aegyptiaca: Питательная ценность зеленых листьев и молодых
Component Green leaves* Shoots**
Crude protein 11.6-27.5 12.90
Crude fibber 13-31.9 31.08
Fat 2.1-6 0.97
Carbohydrate 45.5-57.9 9.33
Ash 9.6-16.7 9.60
Calcium 1.1-2.0 1.40
Potassium 2.34 1.75
Magnesium 0.52 0.54
Sodium 0.07 1.50
Phosphorus 0.10-0.23 0.12
Silicon 00.26 nd
Net energy 6.1 MJ kg DM nd
* Sources (источники). Bille (1978), Burkhill (1985), Dougall et al. (1964), Suliman and Jackson (1959) Toutain (1980). **Badri and Springuel — unpublished (не опубликовано); nd - not detected (не выявлено).
Table 2. Balanites aegyptiaca: Nutritional composition of fruits pulp and seed kernel, expressed as % w/w. Таблица 2. Balanites aegyptiaca: Питательный состав фруктовой мякоти и ядра семени,
Component Pulp* Kernel* Fruits**
Total carbohydrate content 88 20.8 26.64
Crude protein 1.2- 6.6 27.6 8.80
Fats 0.1 -0.4 48.3 5.10
Crude fibber 0.4 - 4.4 0.3 24.22
Vitamin С 0.9 - 1.6 - nd
Ash 2.4 - 6.9 3.0 7.59
* Sources (источники). Abu-Al-Futuh (1983), Booth and Wickens (1988), Gilford (1974), National Research Council (1983), Nour et al. (1985). ** Badri and Springuel unpublished (не опубликовано) nd = n< detected (не выявлено).
The seeds of Balanites, enclosed within the hard woody stones of the fruit, are also edible and nutritious. The fruits (mesocarp) are particularly rich in oil (5%) and carbohydrates (26%), but poor in
protein (8%) compared with other fodder plants given in table 4. These results are confirmed by Cook
et al. (1998) who recorded the total protein of 7% in mesocarp of Balanites fruits. The seed itself (kernel) is very rich in fats (48%) and crude protein (27%, table 2) The mineral contents of fruits are less than what are present in young shoots except for phosphorus (table 3).
Table 3. Mineral content of plant samples collected from Wadi Allaqi area, expressed in % dry weight, (Badri; Hamed, 2000; M. Badri and I. Springuel - unpublished). Plant samples were collected in May 1997, from different locations to cover all range of micro-habitats in sampled area. All collected plants samples ( not less than 10 samples) were mixed together and 4 plant samples were randomly taken from this mixture for chemical analyses. Таблица 3. Минеральный состав растительных образцов, собранных в долине Wadi Allaqi, выраженный в % сухого веса, (Badri, Hamed, 2000; М. Бадри и И. Спрингель — не публиковалось). Образцы растений были собраны в мае 1997 года на различных участках, с целью охватить все микро-ареалы на исследуемой территории. Все собранные образцы растений (не менее 10 образцов) были перемешаны, и из этой смеси случайно выбраны 4 образца для химического анализа.
Species P% K% Na% Ca% Mg% Cl%
Trees and shrubs
Acacia raddiana (shoot & leaves) 0.20±0.04 0.92±0.13 0.16+0.03 0.80±0.14 0.42±0.05 0.53±0.10
Acacia raddiana (Fruit) 0.15±0.03 0.92±0.16 0.13±0.02 1.00±0.13 0.48±0.08 0.71±0.10
Balanites aegyptiaca (shoot) 0.12±0.02 1.75±0.30 1.50±0.20 1.40±0.27 0.54±0.10 2.13±0.36
Balanites aegyptiaca (fruit) 0.13±0.02 1.41±10.18 0.18±0.03 0.10±0.02 0.24±0.04 0.71±0.09
Tamarix nilotica (shoot & leaves) 0.28±0.04 2.01±0.28 1.68±0.29 1.60±0.29 1.44±0.20 2.66±0.37
Perennial herbs
Psoralea plicata 0.26±0.03 2.50±0.43 0.19±0.03 0.60±0.08 0.42±0.05 0.53±0.09
Citrullus colocynthis 0.23±0.03 2.01±0.34 0.19±0.04 3.70±0.63 0.66±0.09 0.89±0.13
Annuals
Crypsis schoenoides 0.18±0.03 1.31±0.20 0.43±0.06 0.28±0.05 0.31±0.05 0.89±0.12
Fimbrystlisbisumbellata 0.18±0.03 1.41±0.24 0.27±0.05 0.60±0.10 0.54±0.09 1.07±0.15
Eragrostis aegyptiaca 0.21±0.03 1.12±0.20 0.37±0.07 0.70±0.10 0.54±0.10 0.36±0.06
Euphorbia granulata 0.20±0.03 1.51±0.29 0.21±0.04 0.50±0.09 0.42±0.07 0.53±0.10
Astragalus vogelii 0.27±0.05 1.81±0.27 0.18±0.03 1.00±0.15 0.84±0.14 0.53±0.08
Table 4. The nutritional composition of plant samples collected from Wadi Allaqi area, expressed in % dry weight, (Badri, Hamed, 2000; M. Badri and I. Springuel — unpublished). Plant samples were collected in May 1997, from different locations to cover all range of micro-habitats in sampled area. All collected plants samples ( not less than 10 samples) were mixed together and 4 plant samples were randomly taken from this mixture for chemical analyses. Таблица 4. Питательный состав растительных образцов, собранных в долине Wadi Allaqi (выраженный в % сухого веса), (Badri, Hamed, 2000; М. Бадри и И. Спрингель — не публиковалось). Образцы растений были собраны в мае 1997 года на различных участках, с целью охватить все микро-ареалы на исследуемой территории. Все собранные образцы растений (не менее 10 образцов) были перемешаны, и из этой смеси случайно выбраны 4 образца дтя химического анализа.
Species Moist % Ash % Protein % Carb. % Fibre % Fat %
Trees and Shrubs
Acacia raddiana (shoot & leaves) 58.44±9.9 9.09±1.3 14.20±2.1 6.69±0.9 46.49±7.9 1.23±0.21
Acacia raddiana (Fruit) 59.20±8.9 5.90±0.8 21.20±3.6 11.89±2.0 34.93±4.5 1.37±0.18
Balanites aegyptiaca (shoot) 65.78±8.6 9.60±1.6 12.90±1.9 9.33±1.7 31.08±5.3 0.97±0.13
Balanites aegyptiaca (fruit) 13.10±1.8 7.59±1.0 8.80±1.1 26.64±4.5 24.22±4.1 5.10±0.66
Tamarix nilotica (shoot & leaves) 78.29±13.3 23.13±3.2 18.4±3.1 6.75±1.0 10.07±1.8 1.50±0.21
Perennial herbs
Psoralea plicata 77.45±13.9 8.71 ±1.5 17.80±2.7 8.20±1.1 39.22±5.1 1.33±0.17
Citrullus colocynthis 78.74±15.0 22.30±3.4 10.70±1.8 8.59±1.2 18.88±3.2 1.13±0.19
Annuals
Crypsis schoenoides 70.13±9.8 11.53±1.5 9.4±1.4 8.62±1.1 25.76±3.4 1.73±0.29
Fimbrystlis bisumbellata 78.12±14.1 20.25±2.8 9.9±1.5 12.19±2.1 27.38±4.7 0.83±0.15
Eragrostis aegyptiaca 71.00±9.9 13.15±2.2 12.3±1.6 10.44±1.5 40.37±5.7 0.63±0.11
Euphorbia granulata 61.26±10.4 6.55±1.2 11.40±1.5 10.33±1.8 36.60±6.2 2.33±0.30
Astragalus vogelii 78.11 ± 11.7 18.72±3.2 19.80±3.0 7.45±1.3 33.31±4.3 0.83±0.15
Acacia spp.
34
CnPMHTE.nb, ryCCEMH, 3.b-AWPM, BAflPM, XAMEfl
Acacia trees. (A. raddiana, A. ehrenbergiana and A. tortilis) form a principal element of desert plant communities in Egypt's South Eastern Desert. They are widespread in remote desert areas but sparse near settlements and urban areas as a result of human impact. Acacia trees play an important role in the function of desert ecosystems by forming the permanent frame work of plant communities (Springuel et al„ 1991).
The scarcity of water in the hot desert encourages the young tree to grow a deep root system that is able to make the best use of the available moisture in the soil. The growth of branches above the ground is slow whilst this is happening, and the tree can remain in dwarf form for many years before growing on to reach maturity.
Because of its slow rate of growth, grazing adversely influences the seedlings more than the mature trees. Very often plants stay in dwarf form until water becomes available after rain. As soon as favourable conditions come, they grow quickly. Usually this happens when rain falls in two successive years. This also results in source of considerable alternative grazing for livestock on ephemeral pasture, hence the grazing pressure on Acacia will decrease, and, using the available moisture, trees will quickly establish themselves (Springuel et al., 1995).
Observations in Wadi Allaqi show that, with under sufficient water supply and protection from grazing, the trees can reach a mature stage and height of seven meters in less than 10 years, while in natural conditions it can take approximately 50 years (Springuel, Mekki, 1994).
Acacia trees are of considerable importance as fodder plants in the desert. They are the drought reserve fodder, which is eaten by stock at times when other food is very scarce. The importance of permanent trees, as a drought reserve and as the staple source of food upon which people can always rely, is also noted for peoples living north and southeast of Allaqi (Goodman, Hobbs, 1988; Scholte, 1992). The ripe pods of this species, called ollaaf, arc important fodder for domestic and wild animals, particularly during the dry summer months.
Acacia trees are nutritious and contain high values of protein, ranging between 5% and 14% in young shoots and 21% in fruits (table 4). Carlisle and Ghorbial (1968) noticed that pods and leaves of Acacia possess sufficient nutrition to satisfy all the water and food requirements for the Dorcas gazelle in Sudan. The protein content shows high variability according to the season. It is higher in the wet season and low in the dry season. In December 1994 (after the rain of November 1994) the protein content of forage (CP about 10% in A. raddiana and 12% in A. ehrenbergiana) was higher than in dry December 1995 (6% and 5% for A. raddiana and A. ehrenbergiana respectively) when the rains failed for the year. Accordingly, the dry matter and organic matter digestibility (DMD and OMD) decreased in dry season (December 1995) in both Acacia species. Tamarix nilotica.
Tamarix nilotica, known locally as "Aabal", is the dominant plant in the downstream flooded part of Wadi Allaqi where it grows in extensive monospecific stands. It is a multiform species, varying in size from three to eight metres height, to small shrubs, with very small scale-leaves and white or pink flowers. Its foliage is green or greyish, which sometimes is covered with salt crystals. Tamarix grows in dense thickets that can be impenetrable, which results in only its perimeter being used, particularly browsed by animals, and hence overused, while the interior remains under-utilized. This plant is specially adapted to dramatic fluctuations in water availability. In times of abundant water (flood or inundation) it becomes a water spender, losing water at a high rate. In very dry conditions, Tamarix nilotica reverses its strategy and becomes a water saver (Springuel, 1996).
Tamarix nilotica is a fodder plant but until recently was considered by the Bedouin inferior for this purpose. Nevertheless Tamarix is considered at its best as a grazing source when it is young and particularly when it is still under water as its leaves, twigs, and shoots are less salty at this time. Though grazing on very wet foliage presents another problem as the animals fill their stomachs with water and do not eat enough solid food.
Results of the chemical analyses of the leaves and branches show a high content of protein which varies from 14% to 18% (table 4), however, as in case with acacias, the contents of protein decreased in the dry period (CP = 8% in December 95, Annex 1). Protein, together with the high percentage of dry and organic matter digestibility, indicates relatively high nutrition value, but the high mineral content, especially CI, Mg and Na being 2.66%, 1.44% and 1.68% respectively (table 3), most probably contribute to low palatability of this plant. The high contents of Na (1.9%) and Mg (1.6%) and low
crude protein content (3.7%) in T. nilotica shoots had been reported by M.A.H. El-Beheiry and H.F. El-Kady (1998), with reference to high variations of these elements in different locations. Group 2: Perennial plants
Common perennial plants growing in the middle and downstream parts of the main wadi channel and its tributaries were selected to evaluate their nutritional status and to identify the potential suitability for grazing. Senna alexandrina, Aerva javanica and Pulicaria crispa are woody perennials that grow as under-shrubs. Citrullus colocyntus grows prostrate on the ground. These plants are available in dry periods, usually the second year after the, rain, but they dry out after extended rainless periods. Aerva javanica and Pulicaria crispa have a low score for grazing value (Springuel, 1994), while Citrullus colocyntus and Senna alexandrina were reported to have no grazing value; however we have often observed the partly eaten fruits of Citrullus in Wadi Allaqi.
Chemical analyses show that Senna alexandrina, Pulicaria crispa, and Aerva javanica have a relatively moderate protein content in the winter season ( 13% for all species, unpublished record) which decreases in the dry season (9%, 7% and 4% respectively, unpublished record), especially the sharp decrease was notes for Aerva javanica. Analyses of Citrullus samples taken in summer time (tables 3, 4), show a lower protein content (10% ) compared with other species, but a high amount of minerals, especially Ca (3%, table 3).
Psoralea plicata merits special attention in the group of perennial fodder plants. It is a drought resistant leguminous herb that is usually available as animal food for up to two years after a strong rain event. It can produce new off-springs even following a light shower. It has a high grazing score (Springuel 1994) because it is abundant with high biomass. Chemical analyses of Psoralea plicata forage (samples taken in May 1997) show a high nutrition values with 17% of protein (table 4) and considerable amount of minerals, especially К (2.5%, table 3). Hamed et al. (1997, 1999) reported that Psoralea plicata contains vitamin E, phenolic cinnamate compounds, flavenoids, benzofuran and its glycoseds.
Group 3: Annual plants
During the summer season, annual pasture is available on the exposed shore of Lake Nasser in the downstream part of Wadi Allaqi as a result of the annual water fluctuation of the lake. Short living annual plants Eragrostis aegyptiaca, Fimbristylis bis-umbellata, Crypsis schoenoides, and Glinus lotoides dominate the plant communities on the lake shores. Eragrostis aegyptiaca, Fimbristylis bis-umbellata and Crypsis schoenoides are the short grasses with high crude protein (18-21%), moderate carbohydrates (812%) and fibre contents (25-27%), except Eragrostis which has a high fiber content of 40% (table 4). Amongst these plants, Glinus lotoides is the most abundant with high biomass, however it has a low grazing score (Springuel, 1994) compared with most of other species. The protein content (8-13%) of Glinus and DMD and OMD is not less than in most palatable species (for example acacias) and decreases toward the end of growing season. Low palatability of Glinus could be attributed to other plant characteristics (for example, high contents of saponins and phenolic glycosides (Hamed et al., 1996; 1997; Hamed, El-Emary, 1999) which are not included in the present study.
Hyoscyamus muticus, which also appears on the shoreline, was previously reported to have no grazing value. However, our experiments reveal that Hyoscyamus muticus is rich in protein (about 17% in winter period, unpublished data) and have high DND (above 40% in winter time). Also we observed small amounts of this plant being given to young animals.
Astragalus vogelii and Euphorbia granulata are ephemerals with a short life cycle (3-5 months) that grow in the desert after a rain event. Both plants provide temporal pasture for livestock. Astragalus vogelii has a high grazing score, that is confirmed by high protein contents (10-19%, table 4 and unpublished data). It is highly valued as fodder by the Bedouin who claim it encourages fertility and milk production in their animals. Euphorbia granulata is the small plant prostrate on the ground and because of its small biomass it has little contribution to animal diet.
Special attention should be paid to the aquatic plant Najas sp that grows in shallow water close to the shores. This is frequently collected by the local population (mainly women) to feed livestock, especially young sheep. This plant has moderate nutritional content, but it is important because shortage of fodder is usual in winter, when the shoreline pasture inundated is by lake water. It is also valued by local Bedouin because it can stored and saved for a time when other fodder plants are scarce. Comparative analyses of pasture plants
36 СПРИНГЕЛЬ, ГУССЕЙН, ЭЛЬ-АШРИ, БАДРИ, ХАМЕД
Results of the forage analyses given in Table 5 showed the range (min and max values) of plant compounds during a one-year observation period (December 1994—December 1995). All terrestrial plants showed a wide range of each component, that indicate diverse nutrition value of these plants. In almost all terrestrial plants, the digestibility values and crude protein content decreased forward to the dry season at the end of the year, that accompanied with increasing ash and fibre content in the plants. No large temporal variability of studied components were observed in the plant tissues of aquatic plants. The effect of aridity on reducing the protein content in the plants is supported by Abdulrazak et al (2000), who reported a total of 17.2% of CP in leaves of Acacia tortilis, in semihumid lands in Kenya, that is higher than our maximum records of 14.2% (table 4) and 10% (table 5). R.E. Lucas and B.D. Knezek (1972) indicated the weather effect on nutrient contents of plants. During the wet season the CP content was higher than in the dry season, and the reverse for dry matter degradation of 18 native fodder plants in the Nigerian humid area (Larbi et al., 1998). Phenological stage of the plants also can affect their nutrient content, as was shown by Kallah et al. (2000) in studies of the nutrition composition of fodder plants in Nigerian savannas, where a range of up to 9% was observed for CP, and up to 12% in DMD in the period from bloom to pod dry stages. Accordingly, the preference of browsing plant species by feral goats varied across seasons (Aldezabal, Garin, 1999).
Results from the forage analyses, given in table 5, show that the temporal variability of the plant compounds made indefinite the variations between plant species. Though, in plant samples collected once (tables 3, 4) large variability between plant species were detected.
Table 5. Forage analyses often pasture species from the downstream part of Wadi Allaqi. Figure indicate the range of values for each species. DMD % - in vitro dry matter digestibility ; OMD % - in vitro organic matter digestibility CP% Crude protein; CF% Crude fibre; EE% Ether extract; Ash % Таблица 5. Кормовой анализ десяти пастбищных видов с участков в нижнем течении Wadi Allaqi. Цифры отражают амплитуду значений для каждого вида. DMD % - in vitro (в искусственных условиях) перевариваемость сухого вещества; OMD % - in vitro (в искусственных условиях) перевариваемость органического вещества. СР % Непереваренный протеин; CF % Непереваренная клетчатка; ЕЕ % Эфирный экстракт; Ash Зола, %.
Plant species DMD OMD CP CF ЕЕ Ash
Acacia raddiana 29-40 26-37 6-10 30-56 3.4-4.2 7.3-8.9
A. ehrenbergianna 37-41 33-39 5-12 27-51 2.7-3.2 17-18
Tamarix nilotica 37-43 33-38 8-13 26-36 2.5-3.1 14-15
Senna alexandrina 35-41 31-37 8-13 27-37 3.6-4.2 17-25
Aerva javanica 31-40 26-36 4-13 41-57 3.4-4.6 8.2-1.8
Pulicaria crispa 31-38 28-32 7-13 33-39 2.7-2.4 14-16
Uyoscyamus muticus 38-42 32-40 9-16 35-48 2.8-3.3 8.9-9.9
Astragalus vogelii 35-40 31-36 10-15 39-45 3.4-3.8 10-11
Glinns lotoides 35-42 34-38 7-13 31-39 2.6-3.2 7.0-9.1
Najas sp. 31-38 28-34 7.9-10 49-61 2.4-3.1 15-17
A question rises: what are the main criteria to be adapted for plant palatability? Among the most common parameters protein, digestibility and essential micro and macro elements in the plants determine the nutrition status of the fodder plants.
Regarding the protein content, all studied plants, at least at definite periods, fulfil the category above the critical minimum level of 7.7% CP requested for goats that was given by Sawe et al. (1998), with his reference to National Research Council NRC (1981). On another hand, an optimum CP concentration of 16% for best lamb production was given by S.G. Haddad et al. (2001).
Pods of Acacia raddiana are the superior fodder regarding the higher CP content of 21% that is similar to 20% of CP recorded in A. tortilis by J.J. Sawe et al. (1998). It has also the lowest ash content than in other species and relatively high carbohydrates. Astragalus vogelii is another plant with CP above 15% that is considered by Norton (1981) as a minimum requirement for lactation and animal growth. Amount of CP below 14.7% was valued by A.A. Al-Jaloud et al. (1994) as low in desert plants of Saudi Arabia. Among 61 plants examined by the same authors, only 11 had the CP values above the lowest level, among these are four species of Astragalus. In spite of high protein in Astragalus vogelii, its DMD and OMD arc lower and CF and ash are higher than in some other plants.
A relatively high protein content above 15% was recorded in Psoralea plicata, Tamarix nilotica and Hyoscyamus muticus. The last two plants are considered to be a low palatable (tamarisk) or not palatable (Hyosciamus), which was also reported by A.A. Al-Jaloud et al. (1994) as not palatable with high CP content. Accordingly, the CP value alone could not be an adequate criterion of forage palatability value. A good example is A. raddiana, which is highly valued by Bedouins as a fodder for livestock in spite of its lowest CP content compare with other less palatable species.
Among the investigated plants, there are no plants with a digestibility value of above 45%, which is considered by M.S. Kallah et al. (2000) to be adequate for high animal performance on pasture; nevertheless most of studied plants have digestibility value above 40% at least at certain seasons.
Tamarix has a high digestibility value while still being considered as low palatable forage because of its high salt content in the leaves. Less digestible fodder, such as Acacia raddiana and Najas spp. has an ability to fill animals in time of feed shortage.
Ether extract (ЕЕ) did not show a high variability between plant species, and it is in range given by N.M. Pasiecznik et al. (1996) for Atriplex species. The same authors mentioned that large variability of ЕЕ is spatial rather that between plant species.
Regarding the carbohydrates, among the studies plants only the fruits and young leaves of Balanites aegyptiaca, have high a carbohydrate content (tables 1 and 2) which eaten.by local people and their livestock, particularly by goats.
Crude fibre and ash content has large temporal and between species variability. CF is very high in Aerva javanica (47-57%) and Najas spp. (49-61%) throughout all the studied period. Ruminant livestock require fibre for normal rumen function, but fibre also limits feed intake and digestibility (Ramana et al., 2000). High ash content (above 20%) was recorded in Tamarix nilotica, Citrullus colocynthis, Fimbrystilis bisumbelata (table 4) and in Senna alexandrina (table 5).
Palatability could be restricted to a high salt content in grazing of plants. Pasiecznik et al. (1996) referred to NAS (1980) that 'intake of feed with salt levels of 5% and below will not adversely affect the feed intake and weight gain of sheep'. In the studied plants only three plants (shoots and leaves of Balanites aegyptiaca, Tamarix nilotica and Citrullus colocynthis) have a high salt content which exceeds 5%. The major factor influencing the salt toxicosis in all animals is the availability of drinking water (Pasiecznik et al., 1996). Similarly, Bedouins observed that Tamarix fodder make animals very thirsty and they drink lot of water.
Despite of high nutrition content of some plant species, they are not eaten by animals or eaten only when other plants are not available. These plants rather are known for their medicinal value {Senna alexandrina, Hyoscyamus muticus, Clinus lotoides and Citrullus colocynthis) or have strong odour (Pulicaria crispa). The presence of different toxic elements in plants, such as alkaloids, phenolic compounds and particularly tannins 1, have a negative effect on the fodder value (intake and digestibility) of plants (Kumar, D'Mello, 1995; Degen et al., 1998). Cutting the plants or its parts and drying them in direct sunlight causes decomposition and break down of these compounds and hence improves palatability (Pasiecznik et al., 1996). The common practise by Bedouins is to cut the annual plant Glinus lotoides, that abundantly grows on the shores of Lake Nasser, dry them in the direct sun and feed animals when the shortage of food available. Also, they collect fruits of Citrullus colocynthis which have a very bitter taste when fresh, dry them and give to livestock in small amounts. However, S.J.A. Adam et al. (2001) warned that daily use of 25g/kg shade dried fruits of Citrullus colocyntus for 42 days caused slight diarrhoea and other poor effects on sheep's health. Conclusion
Desert plants could be considered as valuable forage in term of their nutrition value for supporting the livestock production in the arid lands. Interspecies and temporal variability of major plant components support the opportunistic lifestyles of nomadic populations in the desert which follow the incidence of rainfall to take opportunity in the utilisation of ephemeral pasture. They bring livestock close to the water in the driest period, when shallow rooted herbivorous plants dry out and woody plants may be the only living fodder resources available. Among the studied plants the leguminous plant Astragalus is the superior fodder of ephemeral pastures, while pods of Acacia raddiana have a perfect contribution to animal diet during prolonged dry periods.
For Bedouins, semi-settled in downstream Wadi Allaqi in close proximity to Lake Nasser, new opportunities in the utilisation of shoreline plants are available. However, the plant communities on the shores of the lake are poor floristically and are dominated by species which mainly have a low
38
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palatability (e.g. Tamarix nilotica, Glinus lotoides), or are even non-palatable (eg. Hyoscyamus muticus, Aerva javanica) in spite of the presence of sufficient nutritional compounds for animal consumption. Simple technology could be used to improve the palatability of plants by cutting and drying them in the direct sun that will break down the toxic compounds of these plants. More studies could be recommended on the toxic components of the plants in order to design a simple methodology for the decomposition of these compounds to improve the palatability of plants. Acknowledgements
Tannins precipitate proteins by hydrogen bonding and hydrophobic interactions to form stable complexes at rumen pH, which adversely affect protein and fibre digestion in the rumen and thereby protein availability to the animal (Ramana et al, 2000).
Authors wish to thank the Unit of Environmental studies and Development and personally Professor Ahmed Belal, the Director of Unit, for providing facilities for research work. Financial support of International Development Research Center (IDRC, Ottawa, Canada) for chemical analyses of plants is greatly appreciated. The British Council and DFID support to Professor Springuel for visit Glasgow University for work in library and collecting the references is acknowledged.
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