Preliminary study on the effect of season on urinary analytes in healthy Italian dairy cows

Background: Season is known to affect serum analyte concentrations in dairy cows, and the same can be hypothesized for urinary analytes, but information in this regard is lacking. Objectives: The aim of the study was to assess the effect of seasonality on urinary variables in healthy dairy cows. Methods: Twelve Italian Holstein cows were randomly selected from a local herd, and urine specimens were collected once in each season of the year. For each cow, the lactation stage at each sampling time was also registered (lactation vs dry period), and physical examination and hematology and serum biochemistry measurements were used to assess health status. Three cows were voluntarily culled from the herd during the year; therefore, nine cows were included. Concentrations of urinary analytes recorded in each season for each cow were compared. Results: Seasonality affected urinary protein-to-creatinine ratios (P = 0.012) with lower median values in summer compared with spring (P = 0.020) and autumn (P = 0.004); differences were also found in urinary sodium-to-urinary creatinine ratio (P = 0.009), with lower medians in summer compared with spring (P = 0.003) and autumn (P = 0.020). The direct consequences of higher summer temperatures and the acclimation strategies needed to adapt to this environment could explain the changes in urinary analytes that were recorded in the current study; in fact, decreased food and water consumption tend to increase urinary creatinine concentrations and decrease renal excretion of proteins and electrolytes. Conclusions: The present results suggest that seasonality can affect urinary variables of healthy dairy cows.