Determination of reference intervals for selected liver biomarkers with focus on pre- and postanalytical factors in lactating dairy cattle

Background: Measurement of liver enzymes and metabolites for both clinically healthy and sick cattle is a routine part of dairy herd management. Reference intervals (RIs) are influenced by many variables, including pregnancy, breeding, and geographical variables, and can shift over time. Few previous studies have addressed the specific RIs of dairy cows, and none have specifically addressed the RIs of German Holstein Friesian cows.

Objective: The aim was to determine the RIs of German Holstein Friesian cows considering variables such as age, parity, milk yield, body condition score, days in milk, and pregnancy. Additionally, this study aimed to evaluate the effects of anticoagulant use on the RIs.

Methods: Serum, lithium heparin, and EDTA plasma samples from 131 lactating, apparently healthy Holstein Friesian cows from 10 dairy farms were collected. The levels of glutamate dehydrogenase (GLDH), γ-glutamyltransferase (GGT), aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), creatine kinase (CK), cholesterol, nonesterified fatty acids (NEFAs), and total bilirubin were measured, and new RIs were determined.

Results: The following RIs were determined: beta-hydroxybutyrate (BHB): 0.25-1.00 mmol/L; ALP: 71.1-258.9 U/L; GLDH: 9.1-121.0 U/L; CK: 65.4-257.2 U/L; GGT_pregnant: 8.7-65.3 U/L; GGT_{not pregnant}: 12.3-48.6 U/L; NEFAs_{> 42 Day in Milk}: 65.4-308.7 μmol/L; ALT: 14.0-34.5 U/L; cholesterol: 2.7-7.5 mmol/L; AST_pregnant: 76.6-279.7 U/L; AST_{not pregnant}: 67.1-187.1 U/L; total bilirubin: 0.9-5.2 μmol/L.

Conclusion: New and more precise RIs for cattle could help veterinarians detect hepatocyte damage with minor enzyme leakage and liver stress at an early stage.