Physiological responses of male dairy calves to long-distance transport during the unweaned period

This observational study characterised the responses of unweaned male dairy calves to a single 12 h (750 km) journey under routine commercial conditions. Sixty-six Montbéliarde calves (21 ± 7 days old) were sampled before loading at an assembly centre and upon arrival at the rearing farm. Calves received a glucose-electrolyte hydration solution 2 h before loading and had access to water during a rest stop. Blood biochemistry and haematology were analysed to characterise changes in energy metabolism, fluid and electrolyte balance, circulating proteins and haematological variables. Transport was associated with significant changes in several physiological parameters. Glucose decreased significantly, whereas non-esterified fatty acids and beta-hydroxybutyrate remained unchanged. Immunoglobulin G concentrations increased, while haptoglobin concentrations decreased between sampling points. Urea and sodium concentrations decreased, whereas potassium and haematocrit increased slightly. Mild increases were also observed in hepatic biomarkers, while creatine kinase and lactate dehydrogenase remained unchanged. Transport was further associated with reductions in platelet, leukocyte and neutrophil counts. However, several biomarkers were already outside reported reference ranges at the assembly centre sampling point, suggesting that calves may have entered transport in an altered physiological state. This highlights the importance of pre-transport management conditions when assessing calf physiological response during commercial transport.