[Blood urea concentration, a parameter for the assessment of protein metabolism in pregnant sows. 2. Relations between blood urea concentration and urine nitrogen excretion as well as estimation of urine nitrogen excretion from the blood urea concentration].
The influence of supplementing the ration with the limiting amino acid lysine on N-excretion in urine and the urea concentration in the blood (UCB) is investigated in an experiment with pregnant young sows. In contrast or the basic ration the most satisfactory N-utilisation reflects itself after a lysine intake of 8.2 g/animal and day during the early phase of gestation and 8.6 g during the last phase of gestation both in a diminished N-excretion in urine and a lower UCB. The following correlation coefficients were calculated for the relation between UCB an N-excretion in urine: early phase of gestation: 0.177 (n = 37); last phase of gestation. 0.431 (n = 30); gestation as a whole: 0.416 (n = 67). In a second experiment methionine supplementation in the feeding of a ration with a deficit of sulphur-containing amino acids led to a significant decrease of N-excretion in urine (alpha = 5%). While UCB also significantly decreased 5 hours after feeding, UCB virtually did not react to a changed level of amino acid intake when the blood sample was taken before feeding. In a third experiment, in which 49 g N/animal and day were taken in, differences regarding N-excretion in urine and UCB between pregnant and non-pregnant animals could not be established. When the results published in the first communication (Herrmann and Schneider, 1981) are included, the following correlation coefficients for the relation between N-excretion in urine and UCB are the result: 0.716 (n = 182) for sampling before feeding and 0.808 (n = 133) for sampling 5 hours after feeding. The confidence range of the estimated function y = -2.97 + 1.233 chi for the relation between N-excretion in urine (y; g/animal and day) and UCB 5 hours after feeding (chi; mg/100 ml serum) as well as the variability values do not make it possible to estimate N-excretion in urine from UCB with satisfactory accuracy.