2.1 The ecology of animal husbandry

Natural conditions are largely decisive for the development of domestic animals, ea. the camel in arid areas and the water buffalo in humid areas. Occurrences of diseases are another factor influencing the spreading of animal species. These are often transmitted by insects or in some other way. In Africa, large areas are unsuited for cattle production on account of the tsetse fly which transmits sleeping sickness. Some areas can be quite inaccessible to domestic animals because of the pressure of diseases. In other areas, however, local types of cattle have evolved a certain power of resistance against micro-organisms (trypanosomes), while imported animals may be more vulnerable. In East Africa, there are cattle that are resistant to the much dreaded East Coast Fever, and also partly to the cattle plague. In spite of this, large areas of many tropical countries can be said to have preserved rich ecosystems due to the fact that cattle husbandry has been difficult or impossible, thus preventing agricultural development.

Much is still unclear concerning the origins of domestic animals. Most investigations suggest that cattle, sheep, goats and pigs originally came from Central or West Asia. The llama, which belongs to the camel family, has its origins in North or South America. Ancestors of our single and double hump camels presumably immigrated to Asia across the Bering Strait. Various breeds have gradually evolved adapting themselves to varying climatic conditions. A typical example is cattle, of which there are two main types: Bos taurus without a hump and Bos indicus (zebu) with a hump. The zebu cattle, of which there are various types, are generally better adapted to tropical climates than European cattle. The camel is, of course, especially capable of sustaining arid conditions, since it can manage without water for several days. Besides, the camel generally takes nourishment from the leaves and twigs of shrubs and trees (browse) and only to a small extent from grass, which is scarce under extremely dry conditions.

For ages, grazing has generally provided the foundation of livestock production based on ruminants. Grazing land can be divided into natural pastures and cultivated pastures. According to the quality, natural pastures can in turn be divided into different types, such as:

Rain forests usually have low productivity as pastures. In Africa, elephant grass (Pennisetum) is a common grazing plant in the rain forest, whereas Imperata species are more common in Asia. Nitrogen-fixing grazing plants are uncommon in rain forests. Such pastures, therefore, can be improved by the introduction of leguminous plants, ea. Stylosanthes.

Dry forested land are areas with less rain than in rain forests. The largest areas are found in Central and East Asia, but they also occur in West Africa, Australia and in Central and South America. Production in these areas is moderate. Forest fires can convert dry forested land into savannas.

Savannas, steppes and semi-dry thorn-bush land constitute the largest ranges, in Africa as well as in Latin America. They can be described as open grassland with some scattered trees and shrubs. The quality of these pastures can be excellent, but variations can be considerable with precipitation ranging from 500 to 1200 mm annually.

Mountain grazing generally takes place at heights between 1100 and 3000 metres above sea level. There may be great amounts of precipitation, 1000 - 5000 mm per year, and in some years there are hardly any dry periods at all. The turf is usually short, with few leguminous plants, but with different types of herbs. Many species that are common in the temperate zone also thrive here.

Cultivated pastures are pastures that have been cleared and sown with more productive (improved) grasses and/or legumes. Cultivated pastures can be divided into different types:

Permanent or perennial pastures. These consist of mixtures of perennial grass species with or without leguminous plants and herbs. Those species that manage best tend to become dominant. Occasionally, such pastures are "freshened up" by means of sowing. They are characterized by great productivity and are therefore well suited for milk cows and fattening of feeders. Except for tropical America and Oceania, there are only small areas with permanent cultivated pastures in the tropics. In humid tropical areas, possibilities of establishing permanent pastures are fairly good.

Short-term pastures or fields consist of mixtures of grass and/or leguminous plants or other fodder plants to be cultivated in rotation with food crops. They are often grazed for periods of 2 to 5 years before the land is ploughedand used for crop plants, etc. The advantage of this system is that it improves the structure as well as the fertility of the soil.

Temporary or annual pastures are used in connection with the most intensive forms of grazing systems. This often includes pure stands of grasses, legumes or other fodder plants. Such pastures are characterized by large yields at a relatively high cost as compared with perennial pastures.

While grazing, especially two factors are decisive as to how much feed is available for the animals. One is the plant growth which to a great extent depends on the cover of plants, the nutritive state of the soil and precipitation. The other is the stocking rate (animal density). In many areas where the range is communal property, the users have tended to keep more animals than the pasture could sustain. As a consequence, the pastures have often suffered depletion, the result being little or no production (cf. paragraph 3.2).

Shrubs and trees as feed (browse) have recently become more widespread. This generally involves nitrogen-fixing plants with leafage that is especially rich in protein. They can therefore be used as a protein supplement to other kinds of feed which is low in protein. Deep roots make such plants keep green into the period of drought. Numerous such plants exist, but Leucacna leucocephala and Gliricidia septum are among the most common. These plants can either be grazed directly or harvested (stripped) manually and given to the animals. The latter will particularly be the case wherever the shrubs and trees are tall, or if the animals are kept in stalls (zero grazing) or in feedlots. A disadvantage of these plants is that some of them may be poisonous if large amounts are used as feed. The leafage can also be dried and used as a protein supplement for monogastrics.