Effect of weaning on serum biochemistry and establishment of reference intervals for peri-weaning period of Holstein calves

Biochemical profiles help vet practitioners identify problems in the weaning process when major metabolical changes occur. Reference intervals (RI) are useful in this respect but have not been established for this period. The objective of this study was twofold a) to identify the effect of time relative to weaning, adjusted for age at weaning, on the biochemical profile and b) to establish relevant RIs and assess the necessity of using time-specific RIs for the pre- and post-weaning periods instead of a single RI for this time frame. Two-hundred and forty-one clinically healthy Holstein calves from 9 commercial dairy farms were blood-sampled, at -7d, 0d and +7d relative to the day of weaning (0d). Samples were analyzed to determine the concentration of serum total protein (TP), albumin (ALB), globulin (GLOB), blood urea nitrogen (BUN), cholesterol (CHOL), triglyceride (TRIG), total bilirubin (tBIL), aspartate aminotransferase (AST), gamma-glutamyl transferase (gamma-GT), ll-hydroxybutyrate (BHB) and non-esterified fatty acids (NEFA). The effect of time relative to weaning (TIME-W), adjusted for age at weaning and accounting for herd- and calf-level random variation, was assessed using linear mixed models. Reference intervals for total peri-weaning (PeriRI), pre-weaning (PreRI) and post-weaning (PostRI) periods were generated with the freeware Reference Value Advisor. Established RIs were visually compared with Adult cow RIs (AC). In order to test the agreement between PeriRI and PreRI/PostRI, the Cohen's kappa coefficient (lc) was used. The effect of TIME-W was significant for all parameters, except CHOL. Estimated marginal means for TP, ALB, GLOB, BUN, AST and BHB increased across TIME-W, while those of tBIL and NEFA decreased from 0d to +7d and of TRIG decreased from -7d to 0d. Total peri-weaning period RIs differ from AC for all parameters except gamma-GT; PeriRI should be used for all biochemical parameters except for BUN, AST and BHB for which, PreRI and PostRI are preferable. The latter three parameters are potential candidates for assessing weaning management.