Protein Supplementation of Grazing Livestock: A Review

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Abstract
Protein supplementation of grazing livestock has been studied for decades. However, despite theseefforts, supplementation remains highly empirical. Unfortunately, refinement of supplementation programs will necessarily remain empirical due to thelimited ability to quantify relationships among energy and nitrogen (N) in forages, nutrient yields to the grazing animal, and animal product yield thatare required in the more recent models of N requirements (83, 129). Development and application of programs based on ruminally degradable protein (RDP) and undegradable protein (UDP) will involve formulation based upon empirical knowledge of animal response to various supplements and observationsof forage nutrient composition. Monitoring livestock response to supplements with varied RDP/UDP profiles and corresponding forage conditions (chemical composition and digestibility, forage availability) should allow nutritionists to begin to develop a rational basis for formulating supplementsbased on easily measured forage characteristics. Additionally, development of methods to monitor the plane of nutrition of grazing livestockwould improve the application of supplementation programs. Supplementation can be one of the greater economic drains on production of livestockfrom range and pastures. This inefficiency can result from utilizing relatively poor feedstuffs, improper timing of feeding, and (or) incomplete understanding of supplement requirements of different livestock classes and physiological states. Areas that could improve economic efficiency are: 1) for mulations that reduce the quantity of supplement required to maintain a desired level of performance,2) tailored supplements for varied forage conditions and animal requirements, 3) more efficient delivery methods, and 4) improved monitoring of the nutritional status of grazing livestock.