ABSTRACT
Domesticated livestock have been an essential integrated component of agriculture and human food systems for thousands of years (Bradford, 1999). Ecosystems of both arable and non-arable lands have developed in the presence of animals and consequently ecological succession is clearly shaped by the plant-animal interface. Sustainable coexistence of plant and animal agriculture is underpinned by the health and well-being of each component. This is well illustrated by the “Ancient Cow Contract,” which simply states that the herdsman contracts with his animals to provide housing, feed, safety, and care in exchange for milk, meat, ”ber, and other products (Anderson, 2000). Ruminant animals have and will continue to play a unique and essential role in the human-animalplant interface because of their diversity, adaptability, and ability to consume feedstuffs that are inedible by humans. These types of feedstuffs are abundant and include forages, crop residues, native grasslands, food-processing by-products, and other feed resources. A commonality shared by these feedstuffs is that the microorganisms in the ruminant foregut can utilize them and the microorganisms subsequently provide the animal with a source of nutrition. This unique symbiotic relationship, which is, in fact, analogous to the Ancient Cow Contract, has played a pivotal and sustainable role in providing food, ”ber, and clothing for almost every civilization in recorded history. The world population is expected to reach 7.7 billion by 2020 and nearly 9.2 billion by 2050 (United Nations, 2008; medium variant). The majority of the projected population growth is expected to occur in developing countries where the recent trends include increased per capita consumption of animal products (CAST, 1999). Consequently, the demand for more ef”cient and effective production of high-quality animal products will increase. Because of their unique ability to convert
Introduction .................................................................................................................................... 263 Historical Perspective ....................................................................................................................264 Ecological Balance and Sustainability ...........................................................................................264 Ruminant Animals .........................................................................................................................265 Feed Resources: Inedible for Humans, but Valuable for Animals ................................................. 267
Non-Arable Lands ..................................................................................................................... 267 Crop Residues and Food-Processing By-Products ....................................................................268
