Purified diets containing 5 graded levels of threonine were fed to young, growing and finishing pigs to determine the threonine requirement for growth and maintenance. A model was developed to subdivide the threonine requirement for the maintenance from the requirement for growth. From this model, the threonine requirement for growth was 7.733, 10.968 and 11.235 g/kg live weight gain and the maintenance requirement was 0.118, 0.048 and 0.024 g per unit of metabolic body size at each stage of growth, respectively. In the young pigs, the threonine requirement for growth was 0.388 g/g N gain and the maintenance requirement was 0.122 g per unit of metabolic body size. The breakpoint of plasma threonine concentrations was 3.995, 7.933 and 7.738 g/d, respectively. Expected requirements obtained from these formulae were in general agreement with previous estimates. Based on the weight gain vs N gain equation, about 4.24% of the retained protein was comprised of threonine and compared to 3.81%, the mean threonine content of pig muscle CP.
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