The Australian chickenmeat industry is extremely interested in lowprotein diets which, axiomatically, contain high inclusions of an increasing range of synthetic amino acids. A fundamental issue to the development of lowprotein diets is how efficiently broiler chickens utilise synthetic amino acids. Ted Batterham demonstrated that synthetic lysine utilisation in pigs was influenced by feed access. Pigs fed on a continuous basis utilised synthetic lysine far more effectively than restrictedfed pigs. This was attributed to an imbalance of synthetic lysine versus proteinbound amino acids at sites of protein synthesis because the absorption of synthetic amino acids is more rapid than the prior digestion and absorption of proteinbound amino acids. Continuous access to feed dampens this potential imbalance. This outcome suggests that the utilisation of synthetic amino acids would be compromised in poultry by lighting regimes with relatively long ‘lightsoff’ phases. However, David Baker failed to replicate Batterham’s findings in poultry and suggested that free lysine may be conserved in tissue pools rather than undergoing deamination. Moreover, early work with rats on lysine free diets found that lysine was retained in tissue pools (plasma, liver, muscle) to substantially greater extents than threonine. Other relevant issues include synthetic amino acid requirements in lowprotein diets and catabolism of amino acids in the gut mucosa and their subsequent postenteral availability. Thus the core of this project is to determine the requirements for (synthetic) amino acids, impacts of feed access on their utilisation, their postenteral availability and retention in tissue pools.
The University of Sydney
One objective, which is essential, is to assess requirements for 12 synthetic amino acids in the context of lowprotein diets using the PlackettBurman design in the first study. A second objective is to determine the impact of feed access duration (lighting regimen) on synthetic amino acid utilisation. Therefore, the second study will almost repeat the Batterham (1974) study but include methionine and threonine plus lysine to determine if feed access (16 versus 24 hours) influences retention in tissue pools and utilisation of these critical synthetic amino acids. Either glucose or amino acids (predominantly glutamate) are catabolised in the gut mucosa for energy provision (Watford et al. 1979; Reeds et al., 2000). Synthetic amino acids may be less prone to catabolism than proteinbound amino acids because they are more rapidly absorbed, if so their postenteral availability is enhanced. Therefore, the third objective is to investigate the postenteral availability of synthetic amino acids in the final study. Both Baker and Izquierdo (1985) and Benevenga and Blemings (2007) sugggested that lysine is retained in tissue pools in rather than deaminated. Yamashita and Ashida (1969) found that lysine was retained in plasma by 37.5% (0.072 versus 0.192 mole/ml), in liver by 84.0% (0.168 versus 0.200 mole/ml) and in muscle by 76.5% (0.364 versus 0.476 mole/ml) in rats. In contrast, corresponding retentions of threonine were only 5.6%, 10.8% and 15.3%, respectively. Therefore, in the two final studies retention of amino acids in tissue pools at intervals following feed withdrawal will be determined.
Project Start Date
Wednesday, May 31, 2017
Project Completion Date
Friday, October 4, 2019
Journal Articles From Project
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