Clinical physiological parameters of Holstein calves in the first month of life

In the postnatal period, neonatal adaptation in terms of cardiovascular, respiratory, metabolic, thermoregulatory, and immunological functions is required, thus demanding the establishment of baseline parameters for research on neonatal calves. Few longitudinal studies have presented a set of physiological reference values for neonatal calves. The objective of this study was to evaluate physical, haematological, and biochemical parameters in young Holstein heifers in order to obtain useful information on their neonatal adaptation. Twenty-eight healthy young Holstein heifers were assessed for the collection of blood samples by jugular venipuncture at the following time points: immediately after birth, and before colostrum intake (first day of life is D1), and D2, D7, D14 and D28 days of life. Two hours prior to morning milk feed, calves were sampled, after being physically examined to establish reference values for heart rate (HR), respiratory rate (RR), and rectal temperature (RT). Several changes in physical, haematological, and biochemical parameters, secondary to neonatal adaptation, were detected. The reduction in HR and RR over time represented the maturation of the cardiovascular and respiratory systems, respectively, and the increase in RT represented the development of thermoregulatory mechanisms. Colostrum intake was reflected in several parameters, including immunoglobulin absorption and alteration of the serum protein profile. In addition, changes in glucose and cholesterol concentrations reflected the activation of the calf’s metabolism. Changes in white blood cell parameters, such as an increase in lymphocyte count and decrease in neutrophil count, were associated with maturation of the immune system and the influence of cortisol levels at parturition, respectively. Changes in the red blood cell count parameters could be attributed to the replacement of erythrocytes from the foetal circulation. Variations in the physiological parameters of calves were observed during the first month of life; it is necessary to compare them with established age-specific reference ranges for a better clinical interpretation.