Potential relationships between apelin and metabolic-associated indices in transition dairy cows

Metabolic disorders pose significant challenges in transition dairy cows. Numerous parameters have been investigated in this context, and apelin has recently emerged as a potential metabolic indicator. Accordingly, this study aimed to assess the associations between this hormone and other metabolic parameters. Twenty-two adult Holstein-Friesian dairy cows, 21 days before their expected calving date, were selected for blood sampling and serum separation at four time points: 21 and 10 days before calving and 10 and 21 days after parturition. Serum concentrations of apelin, leptin, insulin, cortisol, T3, T4, non-esterified fatty acids, glucose, total protein, albumin, globulin, aspartate aminotransferase, alanine transaminase, triglycerides, cholesterol, high, low and very low-density lipoproteins, total, direct and indirect bilirubin were measured in these samples. Surrogate indices for insulin resistance, body condition score, and milk production were also evaluated. Throughout the transition period, a significant increase in apelin levels was observed. Various models were employed to identify associations between apelin and the studied metabolic parameters. Notably, significant correlations between apelin and Leptin, Insulin, Cortisol, T3, T4, NEFA, Cholesterol, LDL, VLDL, Total Protein, Albumin, Globulin, Total Bilirubin, Direct Bilirubin and Indirect Bilirubin were observed, with some being immediate while others developed over time. These findings indicate a mutual influence between apelin and specific metabolic indices. Changes in any component of the metabolic profile at one stage can lead to alterations in apelin levels in subsequent stages. The correlations uncovered between apelin and other components of the metabolic profile in transitioning dairy cows offer valuable insights, contributing to a better understanding of the potential effects of apelin on the studied indicators and vice versa.