[The problem of the use of urea in feeding swine]

For a period of 9 days growing fattening pigs (with liveweights ranging from 40 to 50 kgs were fed a ration of autumn barley, dried skim mild and wheat gluten supplemented with 0.5% of 15N labelled urea (12.5% of the total N). The N balance and the rate of 15N protein retention as well as the rates of protein and amino acid synthesis in the different organs and tissues of the carcasses were estimated by emission spectrometry after amino acid fractionation. On an average, 19.3% of the ingested urea were retained, while only 4% N were retained in the essential amino acids found in the carcasses. This proportion will, to a large extent, result from transamination processes and, to a lesser extent, from microbia synthesis. From this it may be concluded that urea N does not induce any appreciable synthesis of amino acids in pigs so that urea cannot be regarded as a suitable substitute for protein feeds in the feeding of monogastric animals.