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Regional papers

  The role of browse plants in animal production in the Sudanian zone of West Africa**

Bernard Toutain

Range scientist at the Institut d'Elevage et de Médecine Vétérinaire des Pays Tropicaux


Foreword

The Sudanian environment

2: the main browse species

2.1 Species present in rural areas

2.2 Species present in the bush but also found in rural or village environments

2.3 common browse species of the savanna

2.4 Species which are much browsed but scarce or only locally common

2.5 Common species which are unpalatable

3. Feed value of browse

4. Utilization prospects for browse plants

5. Conclusion

References


Foreword

Only the feed aspects of browse plants used in animal production will be discussed here. There are other highly important types of utilization of trees and shrubs, whether for animal health involving the use of traditional cures, or more usually as aids to livestock management involving live hedges or the use of branches to protect fields and compounds, or to restrain animals (zeribas, vaccination enclosures) and provide shade, etc. These aspects will not be dealt with here.

The Sudanian environment

The Sudanian climate of West Africa in characterized by a summer rainfall regime and dry winter season, with annual rainfall between 600 and 1200 mm or over. A further distinction is normally made between the northern Sudanian sector, where the active growth period for vegetation lasts under five months, and the southern Sudanian sector, with a five to seven-month active growth period.

The commonest type of vegetation is savanna. This primarily consists of a continuous grass cover composed mainly of Gramineae. There are many trees and shrubs, but these are scattered and the cover they provide does not normally exceed 30%. In the northern Sudanian sector, the vegetation approaches shrub savanna, with many annual grasses. In the southern Sudanian sector the savanna is wooded and the grasses are mostly perennial.

Ligneous plants are a basic component of savanna. The regular occurrence of bush fires maintains a kind of equilibrium between the grass and ligneous strata, favouring the dominance of grasses. Where competition from fires diminishes, the density of ligneous plants usually increases. In places where water conditions are favourable, the tree cover can be a very important factor. Savanna browse species are many and differ widely in height, habit and plant cycle. Height varies from 2 to 30 m.

Animal production has always been present in the Sudanian zone, particularly the traditional village system, with herds owned by peasant smallholders. It is of growing importance in the village environment, where there have been recent successes against epizootic disease or with the introduction of animal traction, and where growing numbers of transhumant pastoralists arrive from the Sahel zones in which they have become too numerous. The new settlers adapt their production methods to Sudanian conditions, with short periods of migration combined with cereal cropping, leading to a semi sedentary existence.

The grass feed available for animals in the savanna zone has its own cycle which differs from that of more arid areas. In the Sahel most grass is palatable throughout the year at all stages of the plant cycle. In the savanna, however, the availability of palatable species varies far more in accordance with the season. Annual and perennial grasses may be consumed in their entirety during the vegetative period, but during stem elongation parts of the plant become hard and are less willingly consumed or left untouched. After the rains the animals are surrounded by large quantities of vegetation, only a small proportion of which is really palatable. They select the greenest and most tender parts of the plant. After the harvest, the crop residues and many post-harvest plants represent highly palatable feed sources at a time when natural feed supplies begin to lose their attraction. Once dry most kinds of grass are in practice refused, or browsed only in small quantities. During this time, the same species which provide optimum dry season feed supplies in the Sahel are left untouched in the Sudanian zone where, having grown far larger, they have become much coarser.

Green feed is everywhere available to livestock from April–June to October–November depending on the area, i.e. for twice as long in the Sudanian zone as in the Sahel. After this period the animals move into the lower-lying areas, where green feed can still be found for several weeks or even months, and into dry areas where grassland recovers in the wake of bush fires. Not until late in the dry season, before the intertropical front returns and fresh rainfall precipitates new recovery, is there any shortage of green grass. This is the bridging period, lasting two to four months.

During this period feeding becomes increasingly problematic on account of the frequent bush fires, which burn off a large part of the grass cover from November onwards.

The foliage of Sudanian trees and shrubs is deciduous or persistent according to the species. For deciduous plants foliation occurs at the end of the dry season or at the beginning of the rains. The leaves fall during the first part of the dry season which often coincides with the occurrence of bush fires. For plants with persistent foliage the young leaves usually emerge during the cold dry season, between December and February, or at the end of this period. Faidherbia albida has a peculiar cycle, being devoid of leaves in the wet season. Flowering and fruiting periods vary greatly from one species to another, sometimes occurring during the rains and sometimes in the dry season. In some species they last only a short time, while in others they extend over a long period.

From the above analysis it may be seen that grassland and browse plants are complementary for feed purpose. At a time when grazing offers animals only dried grass at its least palatable, of poor feed value and often present in inadequate quantities, browse plants provide the following resources: a fresh green stage during the dry season, new shoots and buds and/or flowers and fruit.

Observations on animals at pasture, examination of plants in grazing areas and investigations with herdsmen show that, in the Sudanian zone, animal feed is largely drawn from the grass cover and primarily from Gramineae, which offer green parts for a large proportion of the year, especially in the wetter areas. As long as the grass cover provides sufficient feed supplies, utilization of browse species is only intermittent. On the other hand, during the bridging period ligneous plants constitute a real and highly nutritious feed resource and are sometimes intensively utilized. If foliage is out of reach of the animals the herdsmen bend or cut branches.

2  The main browse species

Amongst the many ligneous plants growing in the savanna only a small number have a real forage value. Palatability assessment for the plant parts consumed and utilization methods vary according to the area, and the authors are not always in agreement. The information which follows concerns only species where the feed value is more universally acknowledged. Human occupation has greatly altered the plant environment and the presence or distribution of species varies between villages or cropping areas and bushlands.

2.1 Species present in rural areas

Only one common species has any real forage value: Faidherbia albida. Two further species are sometimes introduced, Prosopis chilensis and Leucaena leucocephala. The other plants cited are very common in villages owing to their human food value, and their role in animal feeds is subsidiary.

Faidherbia albida (Del.) A. Chev. (Mimosaceae) 
Synonym: Acacia albida Del.; common names: cade, gao This large tree typifies the browse species of the Sudanian zone and especially its northern sector. The literature on this species, which was probably introduced to West Africa in ancient times and is now present exclusively in rural areas, is plentiful. Faidherbia sums up the Sudanian agropastoral system. "Its inversed cycle creates a micro-climate which favours crops. Its fallen leaves enrich the soil, giving rise to more frequent yields of millet and sorghum by avoiding the need for fallow periods. The nutritive value of the foliage and especially the pods is by no means insignificant, since these occur at a critical period for livestock. In addition, the tree tolerates trimming well". (Seignobos). Sedentary cattle production has a role of capital importance to play in the development of Faidherbia parkland (Pelissier).

It should be pointed out that the pods are consumed by all types of animal, but especially by small ruminants. They are gathered by hand for household animals and are bought and sold. The branches are cut for their leaves, which small ruminants find delicious. The leaves and pods both have an excellent feed value.

Table 1

 

FU

DCP6

Whole pods (March)

0.67

  70 g

Green leaves

0.88

103 g

aFU: Feed units/kg of DM

bDCP: Digestible protein, in G/kg of DM.

Prosopis chilensis (Molina) Stuntz (Mimosaceae)
Uncertain nomenclature (Burkart, Ormonde); Common names: prosopis, mesquite (amer). This tree was introduced from tropical America and is usually planted in hedges. It is especially suitable for dry regions. The pods are highly palatable but production is often irregular or low. The leaves are not greatly appreciated and are primarily consumed by sheep and goats. They provide 40–70 g of DCP/kg of DM.

Leucaena leucocephala (Lam.) de Wit (Mimosaceae)

Synonymus: Leucaena glauca (L.) Benth., Mimosa leucocephala Lam.
This shrub originally comes from tropical America. It is an excellent browse plant, suitable for improving existing pastures in areas with more favourable water supplies. It can be maintained in a bushy state for easy access by livestock. The literature on its establishment, utilization and toxicity to monograstics is plentiful.

Albizia lebbeck (L.) Benth. (Mimosaceae)

This introduced tree species is sometimes cultivated in towns and villages.

Adansonia digitata L. (Bombacaceae)
Common name: baobab
This species is virtually only found in villages, except in the Sahelo-Sudanian zone, where it is common in the bush. The foliage is cropped for human consumption. At the beginning of the dry season livestock consume the fallen leaves. Beneath the baobab, as beneath Balanites trees, dead leaves are never found. Baobab leaves have an excellent feed value which is greatly appreciated (1 FU/kg of DM and 110 g of DCP/kg). Small ruminants also eat the fruit pulp.

Mangifera indica L. (Anacardiaceae)
Mangoes are frequently found in Sudanian villages. The animals browse accessible foliage, necessitating the protection of young plants. During the productive period animals sometimes eat large quantities of the fallen fruit. However mango trees are not really a feed resource.

Ficus gnaphalocarpa (Mig.) Steud. (Moraceae)
Some species of wild fig bear foliage which can be consumed by animals. F. gnaphalocarpa is often protected in village environments, on account of its fruit production. Sometimes it is heavily lopped by nomads during the dry season. The fallen fruits are eaten by small ruminants.

2.2 Species present in the bush but also found in rural or village environments

Khaya senegalensis (C. Desr.) A. Juss. (Meliaceae) 
Common name: cailcedrat, acajou de Sénégal. This is a very common tree in the Sudanian zone, especially in the savanna of the humid zones, in valleys and land subject to flooding. It is frequently planted and protected in villages and along roads as a means of providing shade. It provides excellent timber. In some areas individual trees are very intensively utilized for their feed value and are lopped every year. Although less palatable than the foliage of Pterocarpus erinaceus, the young leaves during the dry season provide excellent feed.

Table 2

 

Cellulose

FU

DCP

Young leaves

27%

0.75

50g

Sclerocarya birrea (A. Rich) Hochst (Anacardiaceae)
This savanna tree prefers sandy soils. During bush clearance it is protected and is often left standing in fields and villages. The animals consume the leaves and fruit intermittently.

Acacia sieberiana DC. (Mimosaceae)
This is a thorny species found on bottom land and near areas subject to flooding in the Sudanian or Sahelo-Sudanian zone. It sometimes forms sizeable populations near villages. The young leaves have an excellent feed value at the end of the dry season. The pods are fed to sheep early in the dry season. The foliage is utilized by lopping.

Tamarindus indica L. (Caesalpiniaceae)
The tamarind tree is common near villages where it is protected for its edible fruit. In the bush it prefers to grow on disused termite mounds. The foliage is sometimes cut and fed to grazing animals. It is an excellent feed, but is only moderately palatable (0.87 FU and 69 g of DCP).

2.3 common browse species of the savanna

Pterocarpus erinaceus Poir. (Fabaceae), Common name: vene, Senegal jacaranda.
This is one of the best browse trees of the Sudanian and Sudano-Guinean zones. It is common in the West African savanna specially near valleys or on scree, but it is rarely abundant except in the wettest areas. It is well known to foresters owing to the high quality of its wood. Foliation occurs at the height of the dry season. The foliage, especially when young, is very palatable to cattle. As the trunk is erect the herdsmen have to climb up it and cut the branches to feed their herds. Cut branches are sometimes bundled for sale at market. Pods which fall to the ground are probably also consumed. The leaves have an excellent feed value.

Table 3

 

DM

FU

DCP

Young leaves (February)

28%

0.65

135 g

Afielia africana Sm. ex Pers. (Caesalpiniaceae)
Common name: Lingue
This species is found in most woodland savannas and is locally common, especially on gravelly soils. It may grow to a large size and is known by foresters for the quality of its wood. Foliation occurs around February. The young leaves are enjoyed by cattle, although they are less appreciated than those of Pterocarpus erinaceus. Herdsman utilize the browse potential by cutting the branches for their animals. Chemical analysis shows the browse to have an excellent feed value.

Table 4

 

DM

Cellulose

FU

DCP

Young leaves (February)

30%

31%

0.42

95 kg.

Acacia seyal (Mimosaceae)
This is a small prickly species of the Sahel, found only in the Sudanian zone and in the driest areas, on clayey soils. Its foliage and pods are much sought after by small ruminants. It is the favourite tree of herdsmen, and specially goatherds, who cannot resist lopping its branches, sometimes excessively, at the beginning or end of the dry season when the new leaves emerge. There is no stump growth and the tree withstands poorly lopping of over a third of the crown. The feed value of the leaves and pods is excellent.

Table 5

 

FU

DCP

Green leaves

0.85

120

Pods

0,64

140

Balanites aegyptiaca (L.) Del. (Zygophyllaceae)

This Sahel species is occasionally common in the northern Sudanian zone, on dry sites, but does not penetrate into the wooded savanna. It has considerable feed value on account of the browse quality of its leaves, its persistent foliage and its resistance to lopping and cutting. Animals are conducive to the dissemination of this species, the abundance of which is often an indication of intensive grazing. Its thorns make it more suitable for small ruminants than for cattle.

2.4 Species which are much browsed but scarce or only locally common

Feretia apodanthera Del. (Rubiaceae)
This small tree is found in Sudanian and Sahelo-Sudanian savanna areas, where it prefers disused termite mounds or the edge of swampland. The leaves and young branches are highly palatable for all species of animal.

Combretum aculeatum Vent. (Combretaceae)

This Sahelian and Sahelo-Sudanian variety is highly sought after by animals, which consume the leaves, flowers and young shoots. The browse provided is very rich in protein. Stocks withstand repeated browsing.

Oxytenanthera abyssinica (A. Rich.) Munro (Peaceae)
This member of the bamboo family has green leaves and produces young shoots which are highly palatable, but are left untouched when dry. Overutilization tends to eliminate it.

Lonchocarpus laxiflorus Guill. and Perr. (Fabaceae)
This small tree is not common in the savanna, but its foliage is greatly appreciated by animals and its feed value approaches that of Pterocarpus erinaceus.

Ossenia kirkii
Seeman, or C. harteri Seem. (Araliaceae) 
The leaves of this shrub are very palatable in some areas.

Bombax costatum Pell. and Vuill. (Bombacaceae)
This northern Sudanian tree flowers in January, when its leaves have fallen. The flowers fall to the ground and are eaten by animals, but the quantity of flowers produced is not high and they are poor in nitrogen.

Hymenocardia acida Tul. (Euphorbiaceae)
This small tree found in humid savanna provides a palatable foliage with good feed value.

Stereospermum kunthianum Cham. (Bignoniaceae)
This Sudanian species is found on bottom land in the Sahel, but it is rarely abundant. The palatability of the foliage is differently assessed by different authors. The browse is not very rich in nitrogen.

Celtis integrifolia Lam. (Ulmaceae)
This tree, found in damp sites, grows as far north as the Sahel. It is protected on account of its feed value. Its foliage is consumed by animals.

2.5 Common species which are unpalatable

Anogeissus leiocarpus (DC.) Guil.. and Perr. (Combretaceae) 
This large tree is frequent in Sudano-Sahelian savanna and on lateritic soils of the southern Sudanian zone. It is without leaves for most of the dry season. The young leaves, which appear before the rains, are often distributed to sheep and goats, especially in dry areas.

Prosopis africana (Guill. and Perr.) Taub. (Mimosaceae)
This is common in some Sudanian savanna areas, where it is protected by the local inhabitants on account of its hard wood. It is not found anywhere else. Its young leaves and pods may occasionally appeal to livestock.

Piliostigma reticulatum (DC.) Hochst. and Piliostigma thonningii (Sch.) Milne Redhead (Caesalpiniaceae)
These two shrubs, one Sahelian and Sahelo-Sudanian and the other Sudanian, produce large pods which are consumed in small quantities by livestock. Crushing the pods is thought to facilitate ingestion.

Table 6

P. reticulatum

Whole pod

FU/kg of DM     0.72

   

DCP

55-67g/kg

P. thonningii

Pods (March)

UF/kg de DM     0.56

   

MAD

30 g/kg

The leaves are also browsed, but in small quantities.

Gardenia erubescens, Stapf and Hutc., G. aqualla, Stapf and Hutch., G. ternifolia, Sch. and Thorn. (Rubiaceae)
These shrubs are very common in savanna or in low-lying areas. The fruit of G. eruvescens is often consumed, but is poor in feed value. The leaves, which are present for part of the dry season, are palatable in small quantities. It has a mediocre feed value (0.56 FU and 35 g of DCP), but it is rich in phosphorus.

Daniellia oliveri, Hutch. and Dalz. (Caesalpiniaceae)
This tree is very frequent in savanna areas, especially after fallow periods. The young shoots are common in fields and on fallow land. Only the young shoots are occasionally found to be palatable, and they represent an excellent feed (0.80 FU and 100 g of DCP).

Strychnos spinosa, Lam. (Leganiaceae)
This shrub, frequent even on unfertile savanna, sheds its leaves after bush fires. Its young leaves emerge during the hot dry season and are highly palatable. The dry leaves are eaten on the ground by goats. The feed value of the young leaves is excellent (0.70 FU and 80 g of DCP).

Acacia dudgeoni, Craib. ex Hall (Mimosaceae)
This Sudanian shrub has a botanic resemblance to A. Senegal, a strictly Sahelian tree. The pods and young leaves are consumed by small ruminants, but do not represent a very large feed resource as they occur in natural formations.

Mitragyna inermis, (Willd.) O. Ktze (Rubiaceae)
This small tree is present in the Sahelian and Sudanian zones, but is found only in bottom land subject to temporary flooding. The foliage is consumed by small ruminants, especially in dry areas, and very infrequently by cattle.

Butyrospermum paradexum, (Gaertn. F.) Hepper (Sapotaceae) 
The shea butter tree is protected by Sudanian crop farmers and sometimes forms parkland. However, its presence is not linked with animal production, owing to competition between plant and animal butter production. The leaves, whether green or dry, and the young shoots are sometimes consumed and have a good feed value.

Acacia nilotica, (L.) Willd. ex DC. var. adansonii (Guill. and Pen.) O. Ktze (Mimosaceae)
This tree is scarce in the savanna, since it is more usually a Sahelian variety. It is planted in villages for its pods, which are utilized in tanning. Leaves and pods are both palatable to goats.

Dichrostachys cinerea, (L.) Wight and Ann. (Mimosaceae)
This thorny shrub is not uncommon near villages in the Sudanian zone, or on the site of former villages where it can form dense thickets. The flowers and pods are palatable.

Guiera senegalensis, Gmel. (Combretaceae)
This shrub is rare in humid savannas, but is frequently found in the Sahelo-Sudanian area, especially on sandy soils. Its foliage is palatable in small quantities, especially for cattle.

The list given above is not exhaustive and many other ligneous species could also be cited having a local interest or browsed intermittently. Other varieties deserve to be introduced and investigated owing to the feed value which they possess in other countries (e.g. Morus alba, Gleditschia triacanthos).

3. Feed value of browse

As far as the ecology of the Sudanian zone is concerned, little is known about the deciduous biomass produced each year by browse species. To give some indication of scale, the annual leaf production measured was around 0.7 t/ha of DM in open shrub savanna on the southern Ivory Coast (Bamto), while it was 1.7t/ in dense shrub savanna (César and Menaut).

The part of this biomass which is actually consumed is low because the number of feed species represents only a small fraction of the ligneous flora and only a small amount is within reach of animals: utilization is usually direct, with the animals browsing the lower leaves and shoots in addition to the fallen leaves and fruit. Sometimes the herdsman may intervene by cutting branches or beating down the pods. In high-altitude savanna in the Cameroon, Piot estimated the quantity of leaves open to utilization by livestock during the dry season at 30 to 120 kg/ha, and approximately double that amount wherever there is supplementary utilization by man.

The main utilization period is the dry season when the need for browse feed is especially felt in areas where the grass cover is rich in annual Gramineae or too dry to produce regrowth, and where the bottom land which normally provides green grazing is absent or insufficiently productive.

The feed value, calculated from the results of chemical analysis, has been given for some species. It should be pointed out that the maintenance requirements of a head of cattle weighing 250 kg in the dry season are around 2.3 FU and 150 g of DCP. A kilo of dry feed consumed ad libitum has to provide 0.5 FU and 28 g of DCP merely in order to cover the maintenance needs of the animal. Dry grasses provide an energy ration which is hardly adequate and they are practically devoid of DCP. Browse plants provide a feed in which the chief quality is the high protein content.

Calculating from Piot's example, the energy content of browse per hectare would amount to 10 to 150 FU, while the protein value would be 2,500 to 20,000 g of DCP. Mineral and vitamin contents are other qualities which are very important in browse shrubs and trees, since they are imperative for balanced feeding.

4. Utilization prospects for browse plants

In the Sudanian zone the main constituent of livestock feeds is grass, which offers green matter over a long period. Supplementary feeding derived from browse plants is therefore subsidiary, but at certain seasons it becomes essential, especially in the driest areas or if production is to be maintained throughout the year (meat, milk and work).

Transhumance is practised by ethnic groups of nomadic herdsmen and it involves large herds. Transhumant migration patterns follow the season, leading the animals first out into the bush, remote from areas of human occupation, and then into areas close to arable farmland and even on to the fields themselves after the harvest. The herdsmen also have to take into account local health conditions, including the presence of tsetse fly and ticks, and the duration of water availability at water points.

Table 7:Foliage with a high mineral content

Calcium over 1%

Phosphphorus (over 0.3)%

Magnesium (over 0.5)%

Acacia spp

Combretum aculeatum

Balanites aegyptiaca

Adansonia digitata

Gardenia embescens

Daniellia oliveri

Anogeissus leiocarpus

Guiera senegalensis

Gardenia erubescens

Balanites aegptiaca

 

Prosopis chilensis

Khaya senegalensis

   

Prosopis chilenis

   

Stereospermum kunthianum

   

This production method will continue to utilize natural resources at minimum cost. Livestock development schemes aim to improve nomadic utilization of non-cultivated species by introducing water points, intensifying veterinary support and by introducing, or where possible, improving, grazing management. Rangeland planners are prevented from planting trees in the bush owing to the cost and they have to rely on existing resources.

Bush clearance in humid zone savanna encourages the recovery of grassland and increases herbage production. It will tend to eliminate species which are thought to be aggressive invaders on account of their considerable dissemination and encroachment capacities. It will also preserve browse species.

In drier areas, the rangeland will be protected from bush clearance for cultivation purposes, in order to preserve the rich variety of flora found on natural savannas. Fallow land is characterized by impoverished ligneous flora and is often of little interest to herdsmen. Bush clearance eliminated most browse species without discriminating in favour of animal production and reduces foliage and fruit production for a numer of years. Herdsmen must learn to utilize browse plants by practising lopping in moderation, in most cases not exceeding one quarter or one third of the crown.

Smallholder production, primarily based on animal traction, is carried out around villages and on cultivated land (from crop residues and fallow). Supplementary feed purchases are sometimes distributed to the animals.

Browse must be considered one of the most important and cheap feed resources. The combination of crop and animal production is likely to resuscitate the traditional African system of parkland in a new form. A few stocks of the most useful species for livestock production are now protected from bush clearance. The planting of browse trees in villages, beside fields, in compounds, along tracks and paths will be made easier. Former parkland will be restored, while more parkland might also be established. The most promising local or exotic species will be drilled or planted.

On Sudanian finishing ranches browse plants will provide a supplementary source of protein. Although grazing land is cleared of some ligneous plants, the browse species will preferably be preserved and utilized for lopping. The grassland can be enriched by introducing bushy varieties such as Leucaena leucocephala, from which the animals will browse the leaves directly.

5. Conclusion

Throughout the Sudanian climate zone where, for several weeks, the grass cover is completely dry and unproductive, including forage legumes, many browse plants are in full leaf and remain the only green vegetation. It is wholly logical to think in terms of utilizing the species with the best feed value from amongst these browse plants.

The main local species useful for animal production have been listed. For many of these plants forestry experts have already assembled detailed knowledge on their ecological requirements, possible propagation methods and growth. However, until now the efficient utilization of these feed resources, the utilization method which takes best account of the biology of the species concerned, the annual biomass available for use and the quantities ingested by animals, are all factors which have been little understood. The gaps in existing knowledge limit the promotion of browse plants.

Organizations involved in research on animal production in the tropics should plan research programmes on these questions. They should augment the volume of work already carried out by forestry experts in the search for exotic species with a high forage value for introduction.

However, for the time being those involved in livestock production or working on development schemes, as well as the villagers themselves, should become aware of the fact that animal production in the Sudanian zone can make good use of trees.

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