Many semiarid regions of Sub-Saharan Africa (SSA) are experiencing vast increases in human population pressure and urbanization. These augment the demand for agricultural products and have led to the expansion, intensification, and often closer integration of crop and livestock production systems. The transition of crop and livestock production from the current relatively extensive, low input/output modes of production to more intensive, higher input/output modes of production presents numerous challenges to the achievement of required long-term production increases from these farming systems. This paper provides an overview of the challenges facing agricultural production in semiarid SSA with a focus on West Africa. A description of mixed crop-livestock farming systems and their evolution is followed by an overview of the principal linkages between crops and livestock: income, animal power, feed, and manure. The most detailed discussions relate to nutrient cycling in these farming systems. Most livestock derive their feed almost exclusively from natural rangeland and crop residues, and livestock manure is a precious soil fertility amendment. However, most farmers have insufficient livestock and therefore manure to sustain food production. Nutrient harvests from cropland often exceed nutrient inputs, and soil nutrient depletion is a principal concern. The paper concludes with a discussion of strategies that may improve the productive capacity of these mixed farming systems.

Feeding is one of the major problems which farmers have in maintaining draught oxen in smallholder croplivestock system in Eastern and Southern Africa. This paper reviews some of the studies that have been carried out to improve the effectiveness of supplementary feeding of work cattle. Most studies have involved draught oxen, although supplementation clearly becomes more justifiable economically as more outputs are expected from the animals. While body condition and weight losses during work may not constrain the animal when it is used for a short period they take on greater significance when animals are used for longer periods or are required to provide a calf or milk in addition to work. Studies have shown the supplementation is most effective when it is given within the working period although some supplementation before the working period starts can also enhance performance. Crop residues on their own do not always provide sufficient supplement to meet requirements for work to animals maintained on dry-season grazing. Good quality feed supplements need to be provided if supplementation is to be of any value to the working animal. Various supplements can reduce weight loss and enhance performance of working oxen and can reduce the time the animals need to spend in feeding activities. The paper concluded with some examples of the development of improved feeding practices for draught animals in Zimbabwe, Niger, Bangladesh and Indonesia to illustrate the range of factors which need to be considered in improving the feed supply to draught cattle.

SUMMARY Chronic Fasciola gigantica infections were established in lambs maintained on diets differing in their protein and nitrogen content. The course of the disease and their production parameters were compared with that of similarly maintained uninfected controls. Parasitological, haematological, serological, biochemical and post-mortem data indicated light F. gigantica infections were successfully established in the experimentally infected sheep. Nutritional and production parameters indicated little difference in the growth rates of infected and control sheep maintained on medium (14%) protein diets and that a proportion of the dietary nitrogen (2.4%) could be derived from urea without detrimental effect on production parameters. In contrast infected sheep maintained on either high (> 19%) or low (7%) protein diets did not grow as well as their respective controls and the former group displayed a degree of inappetance. It is therefore suggested that a diet containing approximately 14% protein may help alleviate the negative production effects often associated with fasciolosis. This level is close to that generally recommended for ruminant diets but since many ruminants in Nepal are maintained on diets of a lower protein content, feed supplementation to increase the overall protein content of the diet may be a suitable option. Similarly diets with too high a protein content (> 19%) should be avoided in areas endemic for fasciolosis.

L'utilisation de l'énergie animale permet, le plus souvent, aux paysans d'Afrique sub-saharienne d'augmenter leur production agricole et d'améliorer leur qualité de vie. L'utilisation efficiente de l'animal de trait dépend d'une bonne maîtrise de ses capacités de travail, des conditions d'élevage et des facteurs qui peuvent influencer ses performances. Ces aspects sont passés en revue dans cet article dans le contexte de l'utilisation de l'énergie animale pour l'agriculture en Afrique sub-saharienne. L'espèce animale utilisée conditionne la quantité d'énergie disponible au niveau du paysan. Les performances des ânes, des chevaux et des boeufs de trait ont été comparées lors d'essais sur les capacités de travail. Les équidés sont plus adaptés à un travail rapide de faible intensité où leur plus grande vitesse de travail est mise à profit. A des intensités de travail plus fortes, où la vitesse est moins importante, le surplus pondéral des boeufs devient plus avantageux. La récupération du rythme cardiaque après le travail constitue une bonne indication de la fatigue et de l'état physique des équidés dans des conditions normalisées d'expérimentation. Bien que les dépenses énergétiques liées au travail soient généralement faibles, la qualité du fourrage peut être si indigente que les animaux se trouvent dans l'incapacité d'en ingérer en quantité suffisante pour couvrir leurs besoins énergétiques lors de travaux et perdent ainsi du poids pendant la saison des travaux.

Draught animal research carried out by scientists at the Centre for Topical Veterinary Medicine (CTVM) in Edinburgh and overseas is reviewed and the major findings are reported. The remit for the work has been to provide basic information on draught animals which can be applied by researchers and extension workers to their own geographic situations. Instrumentation is described which has been designed and manufactured to assist in the measurement of draught animal performance, particularly work output and energy consumption. Energy requirements of cattle, buffaloes and equids for work and ways in which these can be met from feed intake and body reserves reported. Studies on heat stress and diseases, 2 of the constraints to work performance, are also described.

Four donkeys and four ponies maintained in climate rooms, were provided with meadow hay or barley straw supplemented with minerals and vitamins ad libitum. Both diets were given to all animals for periods of 21 days. Measurements were made during the last seven days following single doses of two non-absorbable markers (Cr-fibre and Co-EDTA). After six weeks the donkeys repeated the trial, walking 14 km and ascending 260 m five days per week. At rest ponies ate more than donkeys, however the donkeys showed a higher digestibility of dry matter (DM), organic matter (OM) and acid detergent fibre (ADF) than the ponies. Both species lost weight, ate less and had a lower digestibility of DM, OM and energy on the straw than on the hay ration. Fibre digestibility (neutral detergent fibre [NDF] and ADF) was higher on the straw than the hay diet. Gastrointestinal transit time was slower in the donkeys than in the ponies on both diets. Both species showed a higher mean retention time of digesta on straw than on hay. Exercise had no significant effect on food intake and liveweight changes in the donkeys. Although digestibility coefficients were higher in exercised animals, the effect was not significant. We conclude that, although it is generally considered that donkeys can thrive better on poor feeds than ponies, when the animals are allowed ad libitum access to hay and straw better intakes by ponies may compensate for any differences in digestibility seen in donkeys. Intake of barley straw by both species was not sufficient to meet maintenance requirements.

The effect of controlled amounts of exercise on the outcome of Trypanosoma evansi infection was studied in groups of swamp buffaloes (Bubalus bubalis) experimentally infected with T evansi. Daily body temperature, packed cell volume (PCV) and parasitaemia measurements were obtained from each animal for up to 110 days after infection. Exercise did not appear to exacerbate the effect of T. evansi infection in that similar temperature, PCV and parasitaemia profiles were obtained with both exercised and rested animals. Trypanosoma evansi infection, however, had a marked effect on temperature and PCV profiles, both of which could adversely affect an infected animal's work output and work tolerance.

One group of five oxen in the Koshi hills of Nepal ate rice straw plus 4 kg fresh weight per day of the fodder tree Ficus auriculata. Another group of five oxen ate only rice straw. Calculations showed both diets were low in rumen degradable nitrogen (RDN). The animals which ate the tree fodder had a higher dry matter (DM) intake than those eating rice straw alone. Both groups consumed less food and lost weight in weeks when they worked for 5 to 6 h (walking 16 km, climbing 600 mlday) than in weeks when they were not walking. No significant differences in digestibility of food were seen. In the weeks after work the group receiving the tree fodder regained weight, while cattle eating only rice straw remained at a lower weight. Supplementation of rice straw with tree fodder rather than expensive concentrate may be acceptable when feeding working oxen although both diets are likely to be deficient in RDN.

Two pairs of cattle and two pairs of buffaloes carted loads, in wooden wheeled local carts, 16 to 17 km over the same flat route on village tracks. One team worked each day in temperatures of 24 to 37°C for a total of 6 days per team.Body temperature, respiration rate and stepping rate in one animal from each pair and work done and distance travelled were monitored.Buffaloes and cattle started work at speeds of 1 m/s or more. Cattle kept this up for most of the day whereas the buffaloes showed a steady decrease in speed over the day to speeds of less than 0·9 m/s in the last hour. Body temperature of the buffaloes increased during work. By 3-5 h, increases of up to 3·5°C in starting values could be seen. It was necessary to stop and let the buffaloes wallow for at least 20 min to allow them to cool off before they would continue to work. During wallowing body temperature decreased to or below values seen at the start of the day's work. Unlike the buffaloes, the cattle showed changes of less than 1°C in body temperature during work. Respiration rates of buffaloes increased at least two-fold as they began panting usually after 1·5 to 2·5 h. Respiration rates of the cattle could also increase up to three-fold during work. The results have shown that in well fed animals there is little to choose between buffaloes and oxen in daily work output. Estimated daily energy expenditures by the buffaloes and cattle on working days were similar, 1·75 to 1·79 and 1·74 to 1·78 × maintenance, respectively. However, buffaloes usually took longer to achieve the work, as time had to be allowed for wallowing. This is seen as the main disadvantage of using buffaloes for carting on longer routes.

The work done, distance travelled and body temperature of five teams of oxen ploughing land for winter crops was measured continuously over a 5-h working day. On terraces in East Nepal the cattle worked at slow speeds (about 0·3 m/s). Daily work output was variable and depended on ground and soil conditions and on the man working the team. Estimated daily energy expenditure on working days in October and November was 1·25 to 1·46 × maintenance. Differences between teams were small. No noticeable change in performance occurred over the 5-h work, with the exception of one team which usually worked erratically over the last 2 h. Only one animal showed signs of heat stress during work, when its body temperature increased by 1·8 to 2°C, otherwise body temperature varied little (< 1°C) during work.

crop production technologies. In many regions, live- stock are also a means of storing capital, of buffering Many semiarid regions of Sub-Saharan Africa (SSA) are experienc- food shortages in years of poor crop production, and of ing vast increases in human population pressure and urbanization. meeting social and religious obligations of farmers. These augment the demand for agricultural products and have led to In these systems, the productivities of livestock, range- the expansion, intensification, and often closer integration of crop and livestock production systems. The transition of crop and livestock lands, and croplands are inextricably linked. Although production from the current relatively extensive, low input/output most agricultural products are used for subsistence pur- modes of production to more intensive, higher input/output modes poses, some outputs of rangeland (wood, bush straw, of production presents numerous challenges to the achievement of and fruits), cropland (grains, crop residues, and legume required long-term production increases from these farming systems. hays), and livestock (animals, milk, meat, and skins) are This paper provides an overview of the challenges facing agricultural sold. Crop residues are vital livestock feeds during the production in semiarid SSA with a focus on West Africa. A description 6 to 8 mo dry season, and manure enhances soil fertility of mixed crop-livestock farming systems and their evolution is fol- for crop production. Natural forages from rangelands lowed by an overview of the principal linkages between crops and and fallow lands provide important livestock feeds and, livestock: income, animal power, feed, and manure. The most detailed through manure, nutrients for cropland. Manure is ob- discussions relate to nutrient cycling in these farming systems. Most livestock derive their feed almost exclusively from natural rangeland tained from either one's own livestock, from the live- and crop residues, and livestock manure is a precious soil fertility stock of other farmers, or through exchange relationships amendment. However, most farmers have insufficient livestock and with pastoralists. Manure contracts between farmers therefore manure to sustain food production. Nutrient harvests from and pastoralists are still important in many West African cropland often exceed nutrient inputs, and soil nutrient depletion is dryland areas, and farmers have developed a variety of a principal concern. The paper concludes with a discussion of strategies ways to combine their own smaller herds to manure that may improve the productive capacity of these mixed farming large cropland areas. systems. A principal challenge facing agriculture in many parts of SSA is how to achieve sustainable increases in crop and livestock production with limited use of fertilizers M ost dryland farmingsystems of SSA integrate and feed supplements. Farmers continue to rely princi- crop and livestock production. Pearl millet (Pen- pally on organic matter recycling to maintain soil fertil- nisetum glaucum (L.) R. Br.), sorghum (Sorghum bicolor ity. However, the harvest of N, P, and K exceeds the (L.) Moench), and maize (Zea mays L.) are the principal input of these nutrients, and yields appear to be declin- cereals, fonio (Digitaria exilis (Kippist) Stapf) is impor- ing. Low rural incomes and the high cost of fertilizer tant in some areas, and rice (Oryza spp.) is cultivated and feed supplements, among other factors, prevent the in delta areas and along river and stream borders. The widespread use of these external nutrient sources. The legumes cowpea (Vigna unguiculata (L.) Walp.) and use of fertilizer is limited to small land areas devoted groundnut (Arachis hypogaea L.) are both subsistence to cash crops, and diet supplements for livestock are and cash crops; grain and hay may be sold. Household used scantly in semi-intensive livestock-fattening opera- livestock holdings range from a few to hundreds of head tions around urban areas and for fattening animals be- per household with varying ratios of cattle, sheep, and fore religious and social festivals. Animal manure is goats (Wilson, 1986; Swinton, 1988). In some areas, es- currently perhaps the most important soil fertility amend- pecially associated with cash crop production, cattle, ment. As long as fertilizers and feed supplements are donkeys, horses, and camels provide draft power for unavailable, the fertility of cropland will continue to tillage, crop planting, weeding, crop harvest, processing, depend on the nutrients supplied from rangeland in the and transport. Livestock also provide meat and milk for form of manure. households and cash income that is often invested in The climatic and socioeconomic changes occurring in many parts of SSA are rapidly transforming traditional, extensive crop and livestock management practices,