L. Reynolds
International Livestock Centre for Africa
Humid Zone Programme, P.M.B. 5320, Ibadan, Nigeria
Introduction
Conclusion
References
In tropical Africa there are estimated to be about 104 million sheep and 125 million goats (Jahnke, 1982) kept predominantly within the small-farming sector. It is only in highland regions that sheep outnumber goats (Table 1). Throughout the continent there are many different breeds, ranging from small trypano-tolerant animals found in the humid zone of West Africa to long-legged, rangy animals found in most arid regions. Day length in the tropics has little variation, females breed throughout the year, and variations in birth patterns from month to month are related to the plane of nutrition at the time of conception.
Table 1. Ruminant livestock population by species and ecological in tropical Africa
|
Ecological zone |
Cattle |
Sheep |
Goats |
Livestock units |
|
|
(x 106) |
(x 106) |
(x 106) |
(x 106) |
|
Arid |
31.5 |
37.1 |
48.3 |
41.7 |
|
Semi-arid |
45.5 |
23.1 |
33.2 |
37.5 |
|
Sub-humid |
32.8 |
14.2 |
20.3 |
26.4 |
|
Humid |
8.8 |
8.2 |
11.6 |
8.1 |
|
Highland |
29.0 |
21.4 |
11.9 |
23.6 |
Source: Jahnke, 1982.
Mortality rates are usually high (25-40% per annum), and young stock are particularly at risk in the first three months postpartum. Neonatal losses can be closely correlated with birth weight, which is in itself a reflection of maternal nutrition during the final two months of gestation. The disease pattern varies from area to area and season to season. At all times animals that are undernourished will be at high risk. Undernutrition also lengthens kidding interval and decreases kidding percentage and growth rates which, together with survival rate, are components of productivity index.
Productivity index = KP x 365/KI x S x BWWhere
KP = kidding percentage/100
KI = kidding interval (days)
S = survival rate to weaning expressed as a proportion
BW = body weight at weaning
Thus any strategy to improve productivity of small ruminants must look closely at nutrition.
Table 2. The effect of alley farming on the yield of maize (tons/ha in southern Nigeria)
|
|
1983 |
1984 |
1985 |
1985 |
|
Continuous cropping (control) |
2.19 |
2.55 |
1.16 |
2.49 |
|
Continuous alley cropping
|
2.54 |
3.75 |
1.45 |
2.83 |
|
(1.16)a |
(1.47) |
(1.25) |
(1.14) |
|
|
Alley grazing/cropping
|
- |
- |
- |
3.88 |
|
|
|
|
(1.56) |
|
|
Alley cropping/grazing
|
2.56 |
3.43 |
1.27 |
- |
|
(1.16) |
(1.35) |
(1.09) |
|
a Values in parentheses indicate yield expressed as proportion of control yield.
Source: Atta-Krah, Sumberg and Reynolds (1985)
Table 3. The effects of supplementary Leucaena and Gliricidia, with ad-libitum Panicum maximum, on the productivity of West African Dwarf sheep (mean ± SE)
|
Browse g/day |
0 |
400 |
800 |
|
Parturition interval (days) |
262 ± 13.5 |
226 ± 8.4 |
241 ± 8.9 |
|
Little size |
1.26 ± 0.087 |
1.19 ± 0.082 |
1.17 ± 0.078 |
|
Survival to 90 days |
0.65 |
0.65 |
0.82 |
|
Birth weight (kg) |
1.80 ± 0.069 |
1.52 ± 0.073 |
1.72 ± 0.067 |
|
Daily liveweight gain to 90 days (g) |
64.4 ± 2.98 |
73.4 ± 4.98 |
83.8 ± 3.69 |
|
Productivity indexa |
8.67 |
10.15 |
13.46 |
a Productivity index = kg of lamb weaned/dam/year.
Source: Reynolds and Adeoye, 1985.
The Current Situation
On the African continent food production for human consumption lags behind population growth and increased areas show a food deficit. Ruminants have a distinct advantage over simple-stomached animals, being capable of converting organic material unsuitable for human consumption into products of high nutritional value, while at the same time providing excellent fertilizer from undigested residues. Furthermore, in extensive farming systems, small ruminants, particularly goats, are complementary to cattle. Goats have catholic tastes and consume many more plant species than cattle. By preference goats are browsers rather than grazers while cattle take the opposite role. Provided an area is not overstocked, and in many areas of Africa that condition is Unlikely to be fulfilled, goats and cattle together ensure a carrying capacity higher than would be possible for either species on its own.
The myth of the destructive goat should have been finally demolished by Staples, Hornby and Hornby (1942) who described the comparative effects of goats and cattle on fenced plots of semi-arid wooded grassland in central Tanzania. After four years of the trial considerable modifications had been effected to the plots. Goats browsed all plants within reach, but did not browse any plant down to ground level, so that none were destroyed as a result. Little bark damage was caused to trees, and young trees large enough to produce branches out of reach of the goats continued to grow. Thus a good ground cover was maintained at a stocking rate of approximately 1.4 livestock units/ha/year. In contrast, cattle, at a slightly higher stocking rate, concentrated on the grasses and eventually produced open thicket with little ground cover. Carrying capacity was reduced and erosion accelerated. Environmental degradation was therefore more likely from cattle than from goats. It is realized, however, that when an area is overstocked with goats damage to vegetation will occur.
In areas of extensive farming where the soil is of low agricultural potential, animal productivity is also low. There is little competition for the land and extensive livestock systems are most appropriate to the conditions. In such areas, despite the fall in nutritional value of maturing grasses, small ruminants are frequently better nourished than cattle because of their preference for browse (Marais 1983 and Coetsee 1983, 1984). In east Africa many browse species start to produce new growth ahead of the onset of rains. This contributes to a rising plane of nutrition and is associated with a peak in conception rates (Walker 1980; Reynolds 1985). The flush of young grass that accompanies the early rains, although highly nutritious, does not result in the expected increase in production. A concurrent rise in levels of both internal and external parasites also occurs (Adeoye 1985).
Forage availability during the dry season determines the overall carrying capacity of the land. On more fertile land the perceived needs of pastoralists and arable farmers compete. Throughout Africa, with increasing population pressure, former grazing areas are being used for arable farming and the true pastoralist is restricted to a decreasing area. Although it may appear contradictory, this can be to the advantage of the pastoralist. In a symbiotic relationship pastoralists can graze animals on crop residues in the dry season, and the settled farmer benefits from deposited manure. It has been demonstrated that this can result in an increase in overall carrying capacity because the crop residues can support more animals than natural pasture during the critical dry period. In areas of higher soil fertility and cropping intensity, local communities view wandering animals with disfavour, and may demand that livestock be penned or tethered. Most localities, however, have areas unsuitable for cropping that can be set aside for communal grazing; but overstocking will be a hazard. Traditionally, herding of livestock has been performed by children, but with the spread of primary education, and in some places compulsory school attendance, this source of free labour is decreasing and herdsmen must be employed. One response to these combined pressures is stall- or pen-feeding where animals are not allowed out.
A continuum of management systems can be found between nomadic pastoralism and stall feeding. Where do small ruminants fit into these systems? In most parts of Africa they are merely adjuncts to the farming systems, albeit important ones. Attention is paid to cattle while sheep and goats continue as they have done for generations. It is only under special situations in moderate- to high-rainfall areas, for example, where tsetse flies combined with government directives exclude cattle, that small ruminants assume a dominant role. Where such situations exist infrastructural development is invariably poor. Farmers have difficulty marketing their animals because roads and transport to centres of population, and hence consumers, is lacking. Prices paid by itinerant buyers to farmers are low, and profits accrue to middlemen rather than to the farmer. In some African countries the demand for goat meat is high enough to favour the development of the goat industry. At the other extreme, where demand for land is intense, there may be moves to exclude livestock completely.
Scope for Improvement
Small ruminants are raised under a low-cost system and farmers are less likely to buy feedstuffs or provide veterinary care for sheep and goats than for cattle. Interventions that call for expenditure are unlikely to be adopted widely, while those that are simple adaptations of existing systems could be more acceptable.
Productivity can be improved by two major routes, with a degree of interdependence. The first involves improved health care, which reduces the mortality rate. ILCA (1985) have shown that prophylatic health measures in south-west Nigeria allowed goat numbers to rise over a two-year period by 118% compared with a 24% increase in control villages. The possibility of overstocking must always be borne in mind. However attractive increasing flock size appears in the short term, it is a long-term recipe for disaster unless forage availability is also increased. Are more animals needed or could higher productivity be achieved through better nutrition and health care while reducing the total population? If a reduction in numbers is to accompany health and nutrition interventions, this necessitates increased offtake. Are existing marketing arrangements adequate?
The second major route is through improved feeding. The form taken by any nutritional intervention will depend upon the overall farming system employed and environmental conditions. Certain questions must be asked whatever the farming system. What can be found on the uncultivated land? What is available from crop residues? Is the farmer aware of the nutritional value of the potential feed resources? Will using that material as animal feed fit into the existing farming system? If not, what changes will be necessary?
It can be argued that extensive systems, implying little competition for the land from arable farmers because of low soil fertility and lack of water, are the most difficult to assist given the necessity of minimal cost interventions. The major feed resource in extensive systems is uncultivated browse and grasses. Goats, in particular, are capable of selecting the most nutritious plants, and parts of plants, obtaining a reasonably balanced diet throughout the year. It is rare to see extensively raised goats in poor condition unless carrying capacity is exceeded. Farmers may assist by lopping branches that would otherwise be outside the reach of livestock, and by providing water to animals overnight. This latter intervention will be particularly beneficial to lactating females since 86% of milk is water. Shortage of water will inhibit milk production. Bush improvement may be suitable for selected areas within cattle ranches, but is generally uneconomic for small-ruminant farmers. Communal agreement to reserve an area for dry-season feeding can be beneficial and has been successfully adopted in some areas. On such example is in West Mzimba, Malawi (Dzowela 1980) where the reserved area was improved with Stylosanthes guianansis cv. Cook.
A cost-effective approach for research workers is to check on mineral nutrition. Tissue and feed samples will show whether supplementation is necessary, if so, they can easily be incorporated into salt-licks. Use must be made of whatever crop residues are available. Crop residues left in the field will help to maintain soil structure through the provision of organic matter. Is it more beneficial to allow incorporation of residues into the soil or to return manure from livestock as a by-product of crop residue feeding? The value of feedstuff from a particular residue will be related to the overall feed situation. Where there is a shortage of forage, a residue of low nutritional value will assume a greater importance than when adequate feed is available. Under the latter conditions quality rather than quantity becomes the major factor.
As human population density rises, the importance of crop-residue feeding increases relative to uncultivated forage. Livestock can have free access to arable fields after harvest in addition to whatever natural forage is available. Animals grazing maize stover always waste part of the feed by knocking it over. Contamination with soil, urine and faeces occurs, and the resultant mixture is unpalatable. A bimodal rainfall patter limits access to first-season crop residues in situ because second-crop cultivation closely follows the first harvest. Access to fields after the second harvest is less restricted and labour is more readily available for collection and transport of residues to animal pens.
In many areas, maintenance of soil fertility depends upon the inclusion of fallow periods in the farming system. Regrowth during these periods can be available to animals. ILCA in West Africa have shown that alley farming, the use of leguminous trees such as Leucaena leucocephala and Gliricidia sepium in rows, with food crops between the rows, provides mulch and browse to the advantages of both crops (Atta-Krah, Sunberg and Reynolds 1985, Table 2), and livestock (Reynolds and Adeoye 1985, Table 3). This provides high-quality feed on a cut-and-carry basis for confined animals. Emphasis is placed on managing the trees to ensure maximum forage availability for the dry season. In addition, mulch helps to maintain soil fertility (Kang, Grimme and Lawson 1985) and reduces the need for a fallow period so that a higher proportion of available land can remain under cultivation.
The resultant crop residues are important feed resources during the dry season. The same question that was raised earlier, whether the farmer is aware of the value of crop residues, must be asked here. In addition, household and small-scale food-processing wastes, such as maize bran and cassava peels, may also be available. Maximum use must be made of them since as energy sources they complement high-protein browse. Less wastage of feed occurs in cut-and-carry systems but the labour requirement is naturally, high. In the Oume Province of the Republic of Benin, with confined animals on a cut-and-carry system, forage is deliberately spread on the floor so that much of it becomes unpalatable. Food residues, mixed with urine and feaces, are composted in situ and the resultant manure is highly valued. Animals are kept, therefore, to provide manure, with meat as the by-product of the system (Atta-Krah, personal communication)-. Does the labour requirement for a cut-and-carry system conflict with other farm activities? Who owns the animals, and who looks after them during the owner's absence? The farmer puts a low cost-value on his labour, but in any economic analysis labour time will be charged at the market rate. What is the return that the farmer can expect for his extra labour and is this economic system?
Where there is only a limited amount of supplements available, preferential feeding of these to animals in late pregnancy and lactation is advisable. This will ensure that animals under the greatest nutritional stress will benefit. In intensive systems the provision of extra rations prior to malting (steaming-up) has been demonstrated to increase litter size, particularly when breeding females are in poor-to-moderate body condition initially. With an extensive system and year-round breeding it would be difficult to implement steaming-up, but where confinement is practiced implementation is quite feasible.
It is possible to select for twin-bearing females to increase the overall kidding percentage of the flock, but unless adequate nutrition is provided this may simply result in a higher mortality rate. A close inverse relationship exists with birth-type classes between birthweight and mortality rate. Single offspring are heavier at birth than twins, which in turn are heavier than triplets. Neonatal deaths amongst offspring from multiple births is higher than for singles. Undernutrition of the dam during the final two months of gestation, when foetal growth is greatest, will adversely affect birthweight. Improvement of the genetic base must, therefore, be accompanied by good nutrition, otherwise the additional potential, gained at such cost during selection over a number of years, cannot be realized.
Selection for improved growth rates to weaning, in part at least, is selection for higher milk production from the dam. Milk yield will depend on both condition, nutrient intake, and number of offspring being suckled, as well as on genetic potential. When the crude-protein level in natural grasses is low and lignin levels are high, as happens after flowering in maturing plants, digestibility will fall. At this stage the provision of additional nitrogen, whether from browse or from urea, will increase rumen microbial growth rates and improve digestibility. This, in turn, will be matched by a higher food intake because of a faster rate of passage of food through the gastro-intestinal tract. Thus the nutrient intake of lactating females on poor-quality forage can be greatly improved by the provision of browse.
Milk production from small ruminants kept for meat has received little attention in Africa, and it may be useful to extrapolate from cattle data, differences in response to supplementary feeding during lactation have been noticed between beef and dairy breeds. Incremental increases in feed intake of dairy cows have most effect on total milk production during the early lactation period and decline thereafter (Broster, Broster and Smith 1969). Hart et al (1975), in a matched-pair trial with beef and dairy cows, showed that beef cows gained weight but produced little milk, while dairy cows on the same level of feeding lost weight but had a high milk yield. Supplementary feeding of small African ruminants and Zebu cows at any stage of lactation produces a response comparable to that observed in temperate beef cattle. Genetic selection for high milk production has increased the importance of early-lactation feeding, but in meat animals the timing of supplementation during lactation is less critical. Nevertheless, milk production is important, ensuring as it does a high pre-weaning growth rate. Zebu cows are sometimes expected to provide milk for human as well as for calf, often to the detriment of calf growth. Lambs and kids are less likely to be affected since human consumption of sheep and goat milk is less widespread.
Small-ruminant production by small farmers is at present a low-cost enterprise. Development agencies must take this fundamental point into account, and look first for modifications of the existing farming systems before proposing drastic changes. Low-cost intervention might include pro of water in pens, maximum use of residues from small-scale food processing, household wastes, crop residue utilization and the reservation of areas of the bush for dry-season use. The use of leguminous trees for browse should be considered.
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