Abstract

Growth regulation in animals involves complex interactions among several hormone and growth factor systems that are programmed genetically and modified by diet and the environment to determine rates of tissue and organ growth. Cell number, cell size and cell function are all influenced by these factors and result in significant variation in phenotypic characteristics of animals used for food production. Intervention strategies to enhance efficiency and composition of growth in meat animals were developed once control of metabolic processes was achieved. Four general classes of animal growth regulators have evolved. This article discusses chemical characteristics, mechanism of action and dose response relationships of representative products, and lists those approved by the Food and Drug Administration for growth intervention. Anabolic steroid implants are used in growing finishing cattle to enhance growth rate and efficiency. Ionophores are used in finishing cattle to enhance efficiency of gain. Subtherapeutic feeding of antibiotics to protect or improve animal health are declining in use. Two classes of metabolism modifiers, beta-agonists and somatotropin, regulate growth primarily by enhancing skeletal muscle growth and concurrently reducing the rate of adipose tissue growth, with species and compound specificity that are significant. Both result in improved efficiency of growth when composition of gain is improved.