The National Research Council has reviewed published research results and production experiences from scientists throughout the world to establish the nutrient requirements for different physiological stages and levels of production of sheep. These studies and experiences represent our current knowledge of needs for specific nutrients, such as energy, protein, minerals, and vitamins, to meet clearly defined production objectives. The goal of this chapter is to discuss how to most efficiently and economically meet the needs of specific production functions with available nutrient resources in various ecosystems in which sheep production is a viable enterprise.

The initial sections of this chapter will address digestive physiology, nutrient requirements for different physiological stages of production, and nutrient composition of feedstuffs. The remainder will relate how these principles may be applied to specific production systems. The challenge to the sheep producer is to clearly understand the nutrient resources available and how these may or may not meet the needs of their sheep production system.

If sheep are to compete for land, labor, and other resources, they must be able to efficiently convert feedstuffs into products of economic value (i.e., meat, wool, and milk). The economics of the production system for any livestock enterprise is, in part, a function of the efficiency of conversion of inputs into salable products. Then, the availability, market demand, or economic value of these products will determine profitability. Available feed resources may dictate production levels of these end products. For example, baseline production levels are a function of the ability of sheep to harvest forages from rangelands or pasture to support reproduction, lamb growth, and wool production. The producers’ options to increase production above baseline levels are determined by the costs of increased nutritional and management inputs relative to increases in returns from the expected higher outputs.

The majority of the world’s sheep are located in arid to semi-arid ecosystems, such as the southwestern and western rangelands in the United States. In these environments, seasonal fluctuation in nutrient availability may limit reproduction and lamb growth. Wool production is generally more important than lamb production in these limited feed resource environments. If higher quality nutrient resources are available, as with improved pastures and lower cost concentrate supplements, the systems should support higher levels of reproduction, lamb growth, and wool production.

A student of sheep production systems in the United States and throughout the world must be impressed with two observations: (1) the diversity of ecosystems and production systems in which sheep can profitably function; and (2) the diversity of genetic resources, or breeds of sheep, that have evolved to function in these diverse ecosystems. Adaptability to the environment in which the animal is expected to produce is probably the most important genetic characteristic required for economical sheep production. The breed selected must be able to thrive, reproduce, and yield salable products within the limits of the environment. This is the reason for the hardy Merino and Rambouillet breeds being the foundation stock in range production systems. On the other hand, the genetic potential for reproduction that has evolved in the adapted range Merino and Rambouillet ewes may become a limiting factor in higher input/output production systems. If resources are less limited, increased reproductive rate to maximize resource use should be a higher priority than in more limited resource environments.

Profitability must be the primary determinant in sheep-production decisions. Because almost 60 percent of the cost per pound of lamb produced is feed cost, nutritional-management decisions are critical to enterprise profitability and sustainability. The producer must have a clear understanding of sheep-nutrient needs at various stages of the production cycle, of the nutritive value of available forage and feed resources, and of management techniques to produce a consumer-preferred product at the least cost.