Seasonality is a characteristic that influences forage availability and quality. Research has been conducted to correlate seasonal variations with the modification of metabolic parameters in horses. Despite the adaptive capacity of animals, extreme conditions affect animal health and well-being. Knowledge of such information contributes to greater creative efficiency. This study aimed to determine the concentration of hematological, biochemical, and mineral biomarkers in fillies over a period of 12 months. From a batch of 40 animals, 25 clinically healthy Mangalarga Marchador fillies were used. Colts were performed once a month for 12 months, with the animals fasted overnight but with free access to water. The results were analyzed using the SigmaPlot 13.0 program for Windows® (Systat Software, Inc.), using analysis of variance with two factors and Tukey's test. The significance level was set at 5%. Results are expressed as means ± standard error of the mean. Although no clinical changes were observed in the animals, the findings of this study may reflect their general health status. Several species, such as horses, are subject to variation in physiological processes without denoting pathological states. From the data obtained, it can be concluded that the animals in this study were clinically healthy, and these data can be used as parameters for the evaluation of animals of the Mangalarga Marchador breed.