Simple SummaryReproductive failures in dairy farms are extremely costly for breeders; however, the cause of loss is often very hard to determine. The environment may reflect an influence on the quality of the oocyte follicular fluid (FF). It was suggested that FF can be used as an indicator for the functional status of the ovarian follicle in bovine species, however, the topic is still not well known. This study aimed to investigate the variations in FF parameters connected with acid–base balance, ions, and glucose analysis. It was proven that changes in the FF formula were associated with the follicle size.AbstractThe lack of fertilization and early pregnancy loss is seen in the quality and maturation of the oocytes. The environment of the first divisions and maturation of the oogonia, which is also a reflection of the quality of the oocyte, is the follicular fluid (FF). Thus, the purpose of this study was to investigate the variations in parameters such as pH, pCO2, pO2, standard HCO3−, actual HCO3−, base excess (BE), base excess of extracellular fluid (BE ecf), ctCO2, ions: Na+, K+, actual ionized calcium Ca2+, adjusted ionized calcium (at pH 7.4) Ca2+(7.4), Cl−, anion gap (AnGap), and glucose in FF collected from different size follicles in dairy cattle. The most apparent differences were related to pH, K+, and Ca2+7.4 concentration in comparison to changes in follicle size (p< 0.05). Several trends were also evaluated as an increase in follicular size was followed by an increase in pH, BE, and Ca2+7.4 value and a decrease in the K+concentration (p< 0.05). In conclusion, there are changes in FF formularies associated with the size of follicles. However, more research is necessary to establish the reference value, which then could be one of the factors describing the quality of the follicle and the developmental potential of the associated oocyte.