J G Raats
Department of Livestock and Pasture Science
University of Fort Hare
P/B X1314, Alice 5700, South Africa
Introduction
The diversity of veld types in Africa and the associated range in species composition, forage production and nutritive value present herbivores with a wide choice of food, which through mixing and matching can sustain an equally diverse herbivore population. On the other hand, however, due to seasonal changes in climate and growth stages of plants, herbivores are often unable to satisfy their nutritional requirements, especially during the reproductive phase. In most areas of Africa, these factors and processes culminate in an annual cycle of forage production that peaks during the wet period and is severely limited during the dry period in terms of the nutritional requirements of herbivores. Although exceptions do occur, a distinct pattern of limiting nutritional factors for free ranging animals emerge from a very generalised classification of dry (<650mm per annum) and moist climates (>650mm per annum) and leached and fertile soils in Africa.
Nutritional limitations during the dry period
Arid areas
Rainfall is highly variable and the average ranges from less than 100 to about 650 mm per year. Excluding true deserts, the vegetation types commonly found in these areas include the dry shrublands, -grasslands (steppe) and -savannahs. Dry shrublands include the Nama-Karroo and the Acacia semi-desert areas of the Kalahari and Sahel, the succulent Valley bushveld and the Karroo. Dry grasslands include the steppe grasslands of the Sahel and the Kalahari-sandveld and dry savannahs include the Mopane woodlands (sweet bushveld) and False Thornveld of the Eastern Cape.
Generally, the soils are fertile and the most important factor controlling plant composition and productivity of these areas is rainfall, or soil humidity. Exceptions are found in the leached sandy soils of the Kalahari and Sahel regions where both rainfall and soil fertility are limited. Seasonal dry periods vary between two and nine months, while periodic droughts are common and may last for one year or longer. Soil humidity, which is largely determined by the amount of rainfall that infiltrates the soil, is the main factor determining biomass in these areas. A minimum of 400 kg biomass per ha is required to protect the sensitive soils against erosion (Penning de Vries and Djitèye, 1991) and to ensure adequate infiltration of water. Due to the variation in annual precipitation and especially distribution of rainfall, forage production varies substantially from one year to the next, although it is generally accepted that the available forage remains palatable and nutritious when it is mature, hence the term “sweetveld” (Tainton, 1999).
Critical factors
The lack of food during the dry seasons and droughts are probably the most limiting factors in animal production in the dry shrublands and savannahs of Africa. In the dry shrublands, nutrient deficiencies in well conserved areas are unlikely and loss of weight and poor animal performance are mainly due to lack of food as a result of over grazing or droughts (van Niekerk, 1996). Over a 20 year period the grazing capacity of the False Thornveld of the Eastern Cape (av. rainfall: 570mm per annum) varied from 0.5 ha per animal unit (AU) to 12.5 ha per AU (Trollope, 1993). Supplementation trials consistently show animal production responses to energy only, suggesting that protein is not limiting in these areas (Van Niekerk and Louw, 1959; Van den Vyver and Van Niekerk, 1965). This has been substantiated by research over the past thirty years, which has failed to show any meaningful response to urea and phosphorus supplementation in the sweet Bushveld areas of Southern Africa (Skinner, 1964).
In the dry grasslands, energy can also be regarded as a limiting factor in animal nutrition, mainly due to seasonal and periodic droughts (Van Niekerk, 1996). In addition, critical phosphorus deficiencies on these sandy soils have been reported in South Africa, (Theiler, 1920; Theiler et al., 1927; Theiler et al., 1932; cited by Van Niekerk, 1996; Bisschop, 1964; De Waal and Koekemoer, 1993), Botswana (APRU, 1976), Sahel (Penning de Vries and Djitèye, 1991) and in Senegal (Friot and Calvet, 1971, cited by Butterworth, 1985).
Moist areas
Whereas the quantity of forage is the most limiting nutritional factor in the arid areas, quality of forage (notably low protein and digestibility values) is usually the factor limiting livestock production in the higher rainfall areas. Generally, rainfall is more reliable and the mean annual precipitation varies from about 600 mm to well above 1000 mm. Excluding tropical rain forests, grasslands and tropical savannahs are vegetation types commonly found in these areas. Grasslands are more usually found in temperate climates, though they occur at high altitudes (> 2000 m) as on the highveld plateaus of South Africa, Malawi and Uganda and also in badly drained areas such as the “vleis” of Southern Africa or “dambos” of Malawi. In South Africa, these areas are characterised by heavy thunderstorms during the wet season (summer) and frost in winter (dry season). The duration of the dry season is normally less than six months. This vegetation type has a high carrying capacity, which varies between one to five ha per animal unit (Tainton, 1999) and is relatively stable in terms of cover and soil erosion. Livestock production is excellent during the growing season, even under relatively high stocking rates. During the dormant period (autumn / winter), however, forage quality deteriorates to sub-maintenance levels, hence the term “sourveld” (Scott, 1947, cited by Tainton, 1999). The tropical or moist savannahs (excluding rain forest) are synonymous with the dry plainslands of Africa:- grasslands studded with flat-crowned acacias and carrying a profusion of wild ungulates (Huntly, 1982). In these areas the dry period is usually between two and six months and frost is absent.
Critical factors
The nutritional quality of the fast growing grass species that dominate these areas decreases substantially towards and during the dormant stage of the plant. In the absence of supplements, animals in these areas may lose 25 to 30 percent of their maximum summer body mass, culminating in low calving and lambing percentages (Van Niekerk, 1996). Protein has been repeatedly shown as the primary deficiency causing these losses. It is, however, possible to reduce the rate of weight loss or even prevent it in both cattle and sheep through the supplementation of protein or non-protein nitrogen (NPN). Such improvements are largely mediated directly through the supply of essential protein, with a secondary effect on improved appetite and thus energy intake. The mechanism for this higher intake does seem to be found in a higher digestibility and a faster through-flow of digesta as a result of a healthier rumen microbial population. Koster (1994) showed an improvement in digestibility in both the rumen and lower digestive tract when low quality roughage was supplemented with degradable intake protein (DIP). In the same study, it was estimated that approximately 4 g total DIP per kg BW75 or 11 percent of digestive organic matter (DOM) would be required to maximize total DOMI of low-quality hay in cattle.
Energy supplementation on mature (winter) grassveld in the absence of protein supplements, has either given no response in animal production or has ended up depressing animal performance (Hoflund et al., 1948; Clark and Quin, 1951; Rhodes, 1956; Von La Chevallerie, 1965 and Nel et al., 1970; cited by Van Niekerk, 1996). This lack of response to energy supplementation can be attributed to the negative or substitution effect of readily available carbohydrates on cellulose digestion with a consequent depression in pasture intake.
When phosphorus is given as the only dry-season supplement to animals in a state of weight loss, either no response (Bisschop and du Toit, 1929; Bisschop, 1964; Ward, 1968 and Van Schalkwyk and Lombard, 1969), or even a negative response has been observed (Van Niekerk, 1996).
Role-players confronted by nutritional limitations during the dry period
At least, during the larger part of their development, ruminants (10–15 million years; Van Soest, 1982) were confronted with this variation in forage quality and quantity and as a result, developed very efficient counter mechanisms. These include: nutrient recycling, energy / protein reserves, migration or low density stocking and in some cases, linking reproduction to seasonal changes in available forage. The annual migration of Blue Wildebeest in the Serengeti (Tanzania) and Maasai-Mara (Kenya) is one of the last remaining large-scale examples of the use of migration to counter nutritional limitations during the dry season.
For a large part of the history of domesticated livestock in Africa (earliest records of cattle in Africa: 4400 BC; de Lange, 1996), the practice of migration was very effectively copied by nomadic and later semi nomadic and transhumance livestock farmers (Okigbo, 1985). Due to its effectiveness, the practice of “migration” was also successfully adopted by the first European farmers who settled in Southern Africa about 300 years ago. Like the large herds of wild herbivores, livestock farmers moved their animals to the high lying, high rainfall sourveld areas during summer (wet period) where the young were born and reared and during autumn moved back to the more arid, sweetveld areas where they stayed during the dry winter period. Today, remnants of the traditional “trek routes” are still visible in some areas, eg. Eastern Cape. Due to social, economic and political reasons, migration and nomadic pastoralism have almost disappeared from the African scene. The result is that animals are restricted to relatively uniform vegetation types throughout the year and are unable to offset nutritional limitations (forage quality or quantity) during the dry period.
It is obvious that without migration or pastoralism, the only options left for “over-wintering” of livestock are supplementation and low stocking rates to allow for maximum selection. In response, a great deal of research has been devoted to supplementation throughout Africa. During the past 50 years substantial progress has been made in this field and has resulted in a wide range of energy, protein, mineral and vitamin supplements, administered in an equally wide range of methods and they have proven very popular and successful in the livestock industry of southern Africa. Unfortunately, the vast majority of these methods and techniques are exclusively used in the commercial livestock industry and little or no supplementation is used in the small scale or communal livestock sectors of Africa.
Potential for improved nutrition during the dry season
Arid areas
In the drier areas where energy is the most limiting nutritional factor in livestock production, rotational resting and realistic and flexible stocking rates are basically the only economically viable managerial tools available for the stabilisation of any livestock production system. Because soil moisture is the first limiting factor in forage production in the arid areas, the primary aim of any management programme should therefore be to maximise infiltration of rain water through sufficient cover. In this respect, Mr Matthews, a farmer in the Alice district, developed a very successfully veld resting programme, for the False Thornveld of the Eastern Cape (Matthews, 1956). The aims of this programme are: (i) to maximise cover, infiltration and hence forage production, (ii) establishing a seed bank and (iii) to provide a forage bank during the dry periods. This programme entails resting of one third of the total grazing area for a full year. An adapted form of this programme, i.e. the rest period is limited to the growing season only, was suggested for the communal grazing areas of the Eastern Cape by de Bruyn and Raats (1999). Due to the large variations in DM production in the arid areas (Trollope, 1993), the following management programmes were designed as early warning indicators in order to match stocking rate with optimum carrying capacity of the veld:
In addition, drought resistant crops to supplement the diet of pregnant or lactating animals during the dry season have been shown to be very effective. The use of energy supplements (fortified concentrates i.e. chocolate maize/wheat) is very effective, but due to high costs its use is normally limited to droughts only, or to supplement pregnant or lactating females. Crop residues are normally not available or too expensive to transport.
Moist areas
There is no doubt that the feeding of agro-industrial by-products to free ranging livestock during the dry period will increase animal production. The supply of sufficient amounts of this material to the extensive livestock farming areas, is however, a major problem. To date, this potential has only been exploited in the higher rainfall, mixed farming areas of Africa, and mainly in more intensive sectors e.g. dairy farming. The development of large-scale crop production units, spread amongst small scale farmers may provide a more stable flow of additional forage (crop waste) to large areas in Africa.
Various practical and safe methods for the treatment of low quality roughage are available, i.e. ammonia and urea treatment methods. Because of its simplicity, the cold-wet urea treatment of straw has a high potential for use in small-scale farming with plenty of crop residues. Urea is dissolved in water at a level of four to five percent (m/v), poured over the straw (1 lt of urea solution per 1 kg straw) and mixed thoroughly. The soaked straw is stored under air-tight conditions (covered with plastic) for at least seven to 10 days (Sasaki, 1992). The “knead cutter” and microbial treatment methods which were recently developed in China, offers great potential in the treatment of low quality crop residues for the small scale livestock farmer. For example, dry matter intake of maize stover increased from the normal 50 percent to 95 percent after being processed with the “knead cutter” (Peiyu, 1995).
Commercial lick blocks are excellent supplements and have been extensively used in beef, sheep, and goat farming systems. On-farm production of lick blocks provides a practical and cheap alternative to the more expensive commercial blocks. Another effective form of supplementation is the use of liquid supplements. This method of supplementation provides for the “safe” supply of large quantities of supplement that will last for long periods and is of particular interest in remote livestock production areas. The spraying of a mixture of molasses, urea and water on low quality veld grazing can be seen as a variation on the liquid supplementation method which was developed 40 years ago by Bishop (1957) in the Dohne sourveld of South Africa. This technique is only applicable in areas with dense stands of low quality standing hay. The molasses and urea mixture is sprayed directly on a strip of the veld, sufficient for one day's grazing. This method does not only provide the animal with much needed nutrients to stimulate the rumen micro-flora, but in addition, it improves the effectiveness of harvesting and utilisation of the available forage.
Supplementation during the dry season: Potential in Africa
In spite of the potential benefit from the use of supplementary feeds during the dry period, the majority of livestock farmers in Africa do not make full use of this knowledge and as a result suffer major losses in production. Reasons normally given for this situation range from lack of appropriate technology, education, extension, infra-structure, markets and differences in production methods and objectives. The lack of progress after decades of research and development makes it doubtful whether any of these reasons address the key issues in livestock supplementation. On the other hand and in spite of these limitations, small-scale dairy and poultry farmers in many parts of Africa have successfully adopted a wide range of supplementary feeding methods. From this, it seems that the root of the problem is “financial return” rather than factors concerning production. Based on current prices in South Africa, communal farmers earn about 40 percent less than the potential income from animals in good condition. Cattle in poor condition (end of dry season; 38 percent slaughter) fetch about R2.54/kg live weight compared to R4.26 (52 percent slaughter) for cattle in good condition. In most of the communal farming areas of Africa, this situation is even worse as little if any beef reaches the affluent markets (export, hotels and restaurants). Against this, the minimum cost of protein supplements (commercial lick blocks; South Africa) for a period of three months would amount to R54.00 per animal. It is therefore obvious that unless a strong marketing incentive exists, it does not make economical sense to invest additional funds on supplementation in the cash and infrastructure limited communal farming systems.
In order to address these problems, an “emphasis shift”, from production related issues to the quality of the product is required. Future research and development should therefore focus on quality and adding value to livestock products for which a niche market can be found. In this respect, indigenous livestock, raised under free ranging conditions have an advantage, which as yet, has not been utilised to it's full potential. Indications for this potential was shown by Kadzere et al., (1996, unpublished data) from a meat quality study in which Nguni meat was favoured by a “taste panel” and contained less fat than that from other beef breeds. Together with the limited use of chemical substances and feed additives in these production systems, local and international niche markets for “healthy” meat could be developed. As a first step, proper investigation of all aspects of meat quality and appropriate production systems, followed by a consumer awareness campaign are necessary to create sufficient demand and markets. With this in place, substantially higher financial returns on selected products (e.g. weaners) could be expected. This may provide the necessary incentive for the adoption of improved production methods, including supplementation in the communal livestock production systems of Africa. On the other hand, if these challenges are seen to be too difficult, the contribution from extensive livestock farming systems to the development, and wealth creation in Africa will be minimal and these farmers will continue to suffer major losses in production.
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