Introduction

The livestock industry is an economic enterprise and can also be considered as a "survival enterprise" for millions of herdspeople throughout tropical Africa, especially in the arid, semi-arid, and subhumid areas. Among the multiple roles of the livestock industry, food production and gainful employment are the most important. Over 12 million people in West Africa, of whom over 3 million are in Nigeria, depend primarily on livestock for their survival, while over 70 million people in the same region depend on livestock and livestock-related enterprises for their livelihood (Nuru 1982, 1983; McDowell and DeHaan 1986). One-third of the African continent's livestock population is in West Africa.

How can the African continent, particularly the Sub-Saharan region, increase its livestock product production to meet the everincreasing demands of its people now and in the future, using all available natural resources, with no or minimum environmental degradation? Above all, how may the environment be preserved or sustained for future economic development when major environmental constraints such as drought and erosion could retard future progress in development?

Land degradation (soil erosion), drought, desert encroachment, etc. pose a significant threat to the use of land for crops and livestock production, especially in the arid and semi-arid zones where agricultural activities are the main occupation of the people of Sub-Saharan Africa. To prevent further deterioration and to increase the productivity of food animals, it is necessary to act now.

Because of its economic and social significance, the livestock enterprise must be considered or viewed holistically: the animal, its environment, and productivity. It is the interaction between the physical environment and the animal's genetic make-up that determines productivity and even the survival of both animal and plant species within a given ecosystem. In this holistic approach, human factors such as culture and social and economic status as related to other production factors are also important because they influence productivity. Most African cattle are still in the hands of pastoral livestock owners - the Fulanis, Shuwas, and Fulas in West Africa and the Masais in East Africa. Their husbandry methods are indigenous and based on lowinput systems. However, their survival strategy is influenced by seasonal migration to areas with optimum forage resources to feed their animals. This has an effect not only on animal productivity but also on the ecosystem.