OPTIMIZING THE PROTEIN NUTRITION OF GROWING-FINISHING PIGS

Growing-finishing pigs should consume each day the minimum amounts of energy and amino acids needed for maximum lean deposition. This should optimize performance traits, carcass leanness, and N excretion. These ideal conditions are difficult to achieve under experimental or farm conditions due to the factors affecting amino acid requirements and fe ed intake on a daily basis. Lean deposition rate and sex are two of th e major factors affecting amino acid needs. If possible, maximum lean deposition rates should be determined for each herd in order to custom ize feeding programs, and split-sex feeding will improve N utilization . Amino acid requirements have been determined empirically and by the factorial method. The latter is preferred if the efficiency of use of absorbed amino acids can be accurately determined. Development of comp uter models will likely be needed to accomplish this. Apparent ileal d igestibility of amino acids is the most practical means of estimating amino acid absorption at present, although it likely overestimates ami no acid availability for some amino acids. Crystalline amino acids can be used to improve amino acid balance and reduce excessive intake of protein which should improve feed efficiency. A portion of the high-qu ality protein feeds in pig diets can be replaced by synthetic amino ac ids without sacrificing performance, but the effects of these substitu tions on carcass merit is uncertain. Excretion of N, and the concomita nt reduction of N in manure that has to be disposed of, can be manipul ated nutritionally by increased use of crystalline amino acids to lowe r dietary protein, by use of highly digestible feedstuffs and by preci se matching of amino acid needs to amino acid supply. Use of these fac tors could lead to a reduction in total N wastes of 20-30%.