New Directions and Technologies in AA Research for Livestock

The world currently faces one of its greatest challenges, that of feeding in a sustainable manner, nine billion people by the year 2050. It is estimated by the FAO that meat consumption alone will double by 2050. There will be an important role for the pig and poultry industries in meeting this challenge. Considerable progress has been made over the last several decades in the improvement of the average daily gain and feed conversion efficiency in pigs and poultry and much of this improvement can be ascribed to gains from genetic selection and to advances in dietary formulation practice. Although genetic selection has led to animals with higher potential rates of whole-body protein deposition, lower body lipid to protein ratios and altered rates of food intake, the underlying efficiency of dietary protein utilization has remained consistently low. There is thus considerable scope for the further improvement of productive efficiency. Simulated values for the efficiency of utilization of dietary lysine for six commercial pig grower diets given at two levels of intake to a 50-kg female pig ranged from 35% to 59%. Generally over 50% of dietary lysine was not used for body protein deposition. Such inefficiencies highlight the importance of understanding the physiological processes leading to losses of amino acids (AA) from the body. The absorption and metabolism of AA is complex and highly integrated, with continuous flux within and between cells. It is useful, however, to visualise AA metabolism as a framework of discrete physiological processes. The integumental AA losses are quantitatively minor, as are losses from the use of AA to synthesise ‘other’ compounds, irreversible AA modifications and urinary AA losses. Supplying balanced dietary protein in excess of the requirement for maximal rates of body protein deposition (set by the genotype, breed and strain) can under some dietary conditions lead to considerable inefficiency of utilization. Losses due to preferential AA catabolism, inevitable AA catabolism, gut endogenous AA excretion, and structurally altered (damaged) AA and faecal AA excretion are less easily avoided and are critical causes of inefficiency in the utilization of the first-limiting AA. These losses and novel ‘omic’ approaches to studying them will be addressed.