Urinary dynamics and analytical composition of neonatal Brown Swiss calves' urine during the first week postpartum, fed either dam's milk or milk replacer

Monitoring urine composition is a valuable method for identifying metabolic disorders and diseases noninvasively. This study analyzed urination events, urine amounts, and urine composition in dairy calves during their first week of life, comparing calves fed dam's milk to calves fed milk replacer. Calves (n = 18) were housed individually in calf hutches and fed twice daily in unlimited amounts their dams' milk for the first 6 feedings, then switched to milk replacer or continued receiving dam's milk. Urine events were recorded by weight difference every 10 s and urine samples were collected quantitatively between feedings and analyzed for various parameters. Calves began urinating on average 10.5 h after birth. Time significantly influenced urine amounts and urination events, increasing from birth to d 7. Treatment did not affect urine excretion or urination events, but sex did, with females excreting less urine due to less feed consumption. Urine constituents were most concentrated immediately after birth, decreasing with increasing feed consumption. Proteinuria was identified in all calves immediately after birth, lasting 48.5 h. High urinary concentrations of purine derivatives indicated high nucleic acid turnover. Significant differences between treatments were absent for most parameters in urine except DM, crude ash, electrical conductivity, salinity, density, and xanthine concentration in calves fed milk replacer. These findings highlight the dynamic nature of calves' urine composition postnatally and its sensitivity to dietary variations. Understanding these changes is crucial for optimizing feeding strategies to ensure the health and growth of neonatal calves.