Reference intervals for hematological and biochemical parameters, acute phase proteins and markers of oxidation in Holstein dairy cows around 3 and 30days after calving.

The establishment of specific reference intervals (RIs) is advisable when different metabolic conditions in the patient population are present or when existing RIs are not suitable. Holstein dairy cows, at the start of lactation, experience a negative energy balance and an altered immune function that can lead to different levels of blood parameters compared with cows at peak lactation. The aim of this study was the determination of RIs for Holstein cows at 3±1 and 30±3days in milk. To this aim, 145 cows, from 4 herds, were sampled. A wide panel of hematological and biochemical analytes was determined, as well as the measurement of markers of inflammation/oxidation. RIs were generated following the American Society of Veterinary Clinical Pathology (ASVCP) guidelines and the effects of lactation period, parity, herd and day of sampling were determined. Data from 39 out of 52 analytes were significantly different according to lactation period. Data of 13 out of 52 analytes were not significantly different between the two groups. Some differences were also recorded between herds and parity groups but the adoption of specific RIs for these subgroups, however, has practical limitations. In conclusion the use of RIs specific for the lactation period is highly justified from both a statistical and a biological point of view. Pre-analytical factors associated with parity or management need to be considered in the evaluation of results of some analytes.