Meeting livestock nutritional requirements is extremely important in maintaining acceptable performance of neonatal, growing, finishing and breeding animals. From a practical standpoint, an optimal nutritional program should ensure adequate intakes of amino acids (both traditionally classified essential and nonessential), carbohydrates, fatty acids, minerals,Meeting livestock nutritional requirements is extremely important in maintaining acceptable performance of neonatal, growing, finishing and breeding animals. From a practical standpoint, an optimal nutritional program should ensure adequate intakes of amino acids (both traditionally classified essential and nonessential), carbohydrates, fatty acids, minerals, and vitamins by animals through a supplementation program that corrects deficiencies in basal diets (e.g., corn- and soybean meal-based diets for swine; milk replacers for calves and lambs; and available forage for ruminants). Additionally, dietary supplementation with certain nutrients (e.g., arginine, glutamine, zinc, and conjugated linoleic acid) can regulate gene expression and key metabolic pathways to improve fertility, pregnancy outcome, immune function, neonatal survival and growth, feed efficiency, and meat quality