7.1 Modelling and hypothesis
7.2 Component research
7.3 Field methods
7.4 Conclusion
Successful livestock management in a pastoral production system is the art of balancing production objectives against highly unpredictable and variable forage and water resources. Such a scenario is difficult to recreate on a research station and the scientist must be prepared to extend his experiments into the herds and flocks of the pastoralists.
The value of a modelling approach is that it disciplines the scientist to piece together scattered facts from isolated experiments and ideas into a coherent form (Figure 19). It may be difficult to define the units of a model. For example, there was a strong case for adding considerations of protein and mineral metabolism, but this has been excluded.
The consideration of an overall model also has the benefit of indicating factors in need of investigation (Van Soest, 1982). Simple models are the first step in providing scenarios for a range of conditions in applied situations (for example, Table 32 on daily, 2-day and 3-day watering), enabling better management decisions to be made (Christian, 1981). Governments and aid agencies need the most sophisticated projections they can get, if for no other reason than an insurance against expensive failures.
A study of almost any section of this report reveals opportunities for component research, either in the field, the research station or the laboratory. The research priorities outlined below are based on the most important topics and species and are biased towards the pastoral situation rather than the laboratory.
There is a need to improve the precision of the estimates in the following components of energy production, heat exchange and water turnover.
The most important and yet weakest link in the research chain of energy production is the measurement of forage intake. The fibre component of the diet may prove to be a more useful predictor of intake (e. g. Thornton and Minson, 1972; Van Soest, 1982) than digestibility and crude protein which are more frequently used at present (Konandreas and Anderson, 1982). The fasting metabolism or at least the maintenance requirements of the wide variety of breeds of African livestock need to be measured. The biggest drain on the pastoral cow is probably lactation, not walking, despite the cow's small milk yield. The energy expended (MJ ME) in producing 1 kg of milk was estimated to be the same as walking 14 km (section 5.1.3).
More work on heat exchange between the animal and its environment needs to be done in the field. Up to now much of it has been done in the laboratory and the calorimeter. The value of the work is unquestioned but it still has to be translated into the field or pastoral situation. The main difference between the two environments is of course the sun, but solarimeter readings are probably of less general value than temperature recordings in sub-Saharan Africa. The reason is that the heat load on the animal decreases with increasing altitude whereas solar radiation may increase. The overall vertical decrease in temperature (lapse rate) is between 0.5°C and 1.1°C per 100 m of altitude in the tropics, depending on the season, with a relatively constant rate of 0.6°C per 100 m in the highlands of eastern Africa (Barry and Chorley, 1971; Brown and Cochemé, 1973). Measurements of environmental heat load can be obtained from standard meteorological sites, but a more accurate picture of the microclimate affecting the animal is required.
A number of different indices of the thermal environment are discussed in the textbooks, each requiring different recording instruments (Kerslake, 1972; McDowell, 1972; Mount, 1979). Ideally these should integrate solar radiation, ambient temperature, wind velocity and air water vapour pressure. A simple index which has proved useful for reducing heat casualties in man during army training is the wet bulb: globe temperature index' (WBG Tg). If the normal wet bulb temperature (Twb) is used, from a forcibly ventilated wet bulb not exposed to radiation:
WBG Tg = 0.7 Twb + 0.3 Tg (6.02)
Tritiated water studies of TBW have increased our understanding of animal water transactions under field conditions. The most important intake is drink but water intake from forage requires further study. The separation of evaporative water loss (Maloiy, 1973) from that required for intermediary metabolism might be the next requirement of the model, if, indeed, the extra precision justifies the effort.
Work on nutrition heat load and body water turnover should proceed in parallel, otherwise it is very difficult to integrate the three components.
The zebu cow remains the most important animal in the pastoral system (Table 2), but priorities for research may be modified slightly towards other species for a number of reasons. There is a trend towards pastoralists keeping more smallstock, at least in certain areas such as Maasailand. The value of camels is becoming increasingly apparent, notably because more areas are being made available for them by the desertification process and also because their exploitation of fragile habitats is less destructive than that of goats, cattle and sheep. The donkey may thrive on neglect, but that does not mean that a small research input would not improve the lot of this much abused animal.
Field work on the priority topics already discussed (section 7.3.1) is not as difficult as it used to be; technical equipment is becoming increasingly compact and rugged so that samples can be collected, processed, preserved or even measured in the field. Communications by 4 wheel drive vehicles, light aircraft and scheduled air services provide ready access to advanced laboratory facilities.
Studies of the nutritional value of the diet are complicated by the difficulties of herding fistulated animals in a pastoral environment. Fortunately, where the preponderance of shrubs threatens to dislodge the fistula plug, the herbivore changes from a grazer to a browser and simulation of the diet by hand-plucking becomes more realistic. Similarly, while bagging techniques may be applied to free-ranging cattle (Dicko, 1981), the faeces produced by herbivores in dry, thorn scrub are often pelleted and easy to collect. One advantage of the nutritionist in Africa compared with colleagues in some other parts of the world, is that labour-intensive methods can be employed. The high ratio of good herdsmen to livestock also means that the animals are easy to catch and handle. There remains the problem of obtaining a representative sample of the herbage on offer from natural grassland.
Measurements of energy balance are frequently done using a portable weighscale. Such scales may not be accurate to more than 2% of bodyweight (e.g. 5 kg on a cattle weighbridge), which may mean that 20% of the body fat reserves may be missed. Similarly, it is easy to obtain a rough measure of milk yield and distance walked (e.g. Semenye, 1982) but difficult to get an accurate one.
Measurement of heat exchange in the animal in the field is the province of the specialist, but the general animal scientist should at least understand the principles involved and be able to describe the microclimate of the free-ranging herbivore. Whether or not an index such as WBG Tg is applied, two of the most useful portable instruments are: the whirling hygrometer which can measure shaded dry bulb temperature as well as wet bulb depression for calculations of total heat of evaporation, and the globe thermometer which measures the combined effect of radiation and convection.
Much useful information can be obtained from field observations of drinking, such as the physical limits to the volume that can be drunk and the time taken to completely replace lost body fluid. Is water intoxication really a problem in indigenous ruminants adapted to semi-arid environments, or are the symptoms caused by distension of the rumen, discomfort and weakness? What is the level of dehydration which will depress appetite and lactation in each breed and species under field conditions? The forage moisture content of the diet must be estimated as accurately as possible using hand-grab samples of the observed diet. Accuracy is most important when forage moisture is above about 35% when its contribution to total water intake starts to increase rapidly (Figure 4). Tritiated water studies should be continued, provided the potential size of the discrepancies between predicted and actual water input under intermittent watering regimes are recognized and precautions taken to minimise them (King and Finch, 1982).
An important contribution that the developer, and hence the scientist, can make to the productivity of pastoral systems will be to increase the efficiency with which scarce water and energy resources are used. As much as possible of the research should be undertaken in the environment in which the pastoralist is living so precariously, in order to understand the realistic possibilities for improvements in livestock production in pastoral systems.
