[Methodical investigations on evaluation of lysine utilization in pigs after extreme changes of protein quantity and...

Aim of investigations was to measure lysine utilisation under dietary conditions which could have negative effects on well known relation between limiting amino acid and level of N-utilisation. Incorrect conclusions about level of lysine availability (efficiency) could be drawn under such conditions. Therefore N-balance trials were done with 32 female pigs (35-45 LW, fitted with urine bladder catheters), based on semisynthetic diets (wheatgluten / cornstarch) supplemented with glutamic acid as additional nitrogen source. Lysine concentration in the protein was further reduced by this way near to N-balance +/- 0. Data calculation followed a further developed N-utilisation model from Gebhardt (1966). Experimental conditions resulted in disturbed relationships between lysine concentration and protein utilisation and led to the conclusion, that N-balance trials related to estimation of amino acid efficiency in feed proteins resp. to amino acid requirements should be realised under conditions of > 500 mg / LWkg0.67 daily N-balance connected with > 2000 mg/LWkg0.67 daily N-intake.