Abstract
Background: During the transition period in dairy cows, metabolic changes occur, many of them related to energy metabolism, which causes metabolic diseases or productive alterations. Aim: The objective of the present work was to evaluate two mineral and vitamin supplementation related to metabolic regulation mechanisms associated with insulin during the transition period and the first phase of lactation in grazing cows under tropical conditions, through metabolic indicators and insulin resistance indexes. Methods: Twenty-one animals were distributed in three groups, control (CTR), iodine supplementation (SUPP-1), and mixed mineral and vitamin supplementation (SUPP-2). The experimental period was from day 30 pre-partum to day 45 postpartum. It was carried out the evaluation of body condition score and blood samples collection by coccygeal venipuncture for serum analysis of metabolites beta-hydroxybutyrate (BHB), glucose and Non Esterified Fatty Acids (NEFA) and the hormones insulin, thyroxine, triiodothyronine, and cortisol. Variables related to energy and hormone metabolism were analyzed. Four proposed indices were calculated to identify insulin resistance: HOMA, QUICKI, RQUICKI, and QUICKI-BHB. Through linear regression, the effect of metabolites and hormones on the indices of insulin resistance studied was estimated. Results: The groups with supplementation did not show significant changes in mobilization of body reserves, NEFA, nor triiodothyronine for interaction between treatments and periods. HOMA and QUICKI indices used to estimate insulin resistance showed an inverse correlation (-0.97; p<0.001), and a greater capacity of linear adjustment for the estimation of the evaluated metabolites. Conclusions: The indexes values of insulin sensitivity in the present work constitute a starting point in tropical dairy cows to characterize insulin resistance and metabolic alterations. Vitamins and mineral supplementation did not show a positive effect on the metabolism of dairy cows during the transition period and the first phase of lactation in the study.

Key words: insulin resistance; transition period; dairy cows; metabolism, nutrition factors