ABSTRACT
Ruminant nutrition has been the subject of intense research for many years, primarily to determine the nutrient requirements for maximal growth and produc tion. In temperate, developed regions of the world, livestock production systems have evolved to become more intensive and, in some instances, dependent on diet formulations that are not consistent with the nutritional strategy that has evolved in ruminants. Feedlot cattle and high-producing dairy cows are now fed as little as 10 to 15% and 40 to 50% dry matter as forage, respectively, primarily to ensure proper ruminal function and digesta propulsion. This replacement of structural carbohydrates with rapidly degradable starch in ruminant diets has improved nitrogen retention in meat and milk (Huber and Herrera-Saldana, 1994), and, in feedlot cattle, the use of “protected” proteins and ionophores have also resulted in productive alterations of ruminal metabolism and animal performance. Today, the United States has a relatively cheap and abundant supply of beef, milk, and other dairy products as a result.
