Urine testing is a convenient, non-invasive method of obtaining information about body functions. Depending on the intended purpose, urine testing may be qualitative and/or quantitative. Urine analysis can also include
proteins. There are no data in the literature on the occurrence of
proteinuria in healthy neonatal calves. The present study was the first that aimed to quantify the hypothesis of
proteinuria occurrence in these animals in the first week of life, to assess its intensity and dynamics and to understand the underlying causes of
proteinuria in healthy calves. The research was carried out on 15 healthy calves in the first seven days of life. Calves were catheterized to determine minute diuresis. Total
protein concentration was determined in blood plasma and urine. Urine
proteins were separated by electrophoresis (SDSPAGE) and their concentration and percentage were determined by densitometry using an image archiving and analysis software. The separated
proteins were divided into three groups according to molecular weight for
albumin, LMW and HMW
proteins. The results were standardized per 1 m2 of body surface area and statistically analyzed. Neonatal
proteinuria was demonstrated in healthy calves, mainly resulting from the high concentration of LMW
proteins in the urine. Their percentages decreased significantly from 84.46% on the first day of calves' life to 64.02% on day 7. At the same time, a statistically significant increase was observed in the proportion of
albumin and high molecular weight
proteins in urine total
protein.
Albumin percentage increased from 9.54% (on day 1) to almost 20% (on day 7), while the proportion of HMW
proteins increased from 6.68% to 18.13%, respectively. The concentration of total
protein in the urine of newborn calves amounted to 14.64 g/L and decreased statistically significantly during the first 72 h of postnatal life, stabilizing at the level of 3-4 g/L. The mean value of total
protein excretion in the first week of life was 4.81 mg/min/m2 (i.e., 6.93 g/24 h/m2). The analysis of
protein concentration in the urine and its excretion, as well as changes in urinary excretion of the tested
protein fractions, indicated that neonatal
proteinuria in healthy neonatal calves was tubular (i.e., main reason is the reduced absorption of
proteins in nephrons). In addition, research showed that there was a rapid improvement in resorptive mechanisms in tubular cells. It should be assumed that the filtration barrier in the kidneys of these animals after birth is morphologically prepared to retain high molecular weight
proteins. It seems that the increased permeability of the filtration barrier in the glomeruli does not necessarily indicate the immaturity of the kidneys, but may indicate the kidneys' adaptation to excess
protein removal from the body during feeding with high-
protein food (colostrum), with an open intestinal barrier enabling
protein absorption from the gastrointestinal tract to the blood.