[Concentration of urea in blood, a parameter for the assessment of protein metabolism of pregnant sows. 1. Development of the concentration of urea in blood after the intake of proteins and its relation to N-excretion in urine].
After feeding a ration rich in protein and subsequent N-free feeding of 6 served gilts provided with intravenous permanent catheters and bladder catheters, the change of the urea concentration in the blood (UCB) and the N-excretion in urine were investigated. UCB increased during the first few hours after the intake of the protein containing ration, reached its maximum after 4 hours an 38 minutes and then decreased continuously. The maximum of the hourly N-excretion in urine was ascertained after 9 hours and 46 minutes. 60 hours after the protein intake UCB as well as N-excretion in urine reached an average minimal level of 10.5 mg urea/100 ml blood serum resp. 0.57 g N/hour. In a further experiment with four served gilts the close correlation between UCB and N-excretion in urine was confirmed after feeding 4 different protein levels. Blood sampling at the moment of feeding resulted in lower UCB values and smaller dispersion (d% = 5.9) in comparison to blood sampling 6 hours after feeding (d% = 12.2). The relation between UCB and N-excretion in urine however was lower at the moment of feed intake (r = 0.949 in contrast to r = 0.987). Under consideration of the maximum UCB, blood sampling for the determination of the UCB for the purpose of characterising N-excretion in urine and protein utilisation between 4 and 5 hours after feeding is recommended.