Vitamin A and beta-carotene levels in plasma, corpus luteum and follicular fluid of cyclic and pregnant cattle.

This study was carried out to examine the relationship between the corpus luteum (CL) weight, CL and follicle diameters and progesterone, beta-carotene and vitamin A levels in reproductive organs of cattle obtained from the slaughterhouse. The beta-carotene and vitamin A levels were determined in plasma, CL and follicular fluid (FF) using a spectrophotometric method at different stages of the oestrous cycle (n=40) and at 3-6 months of pregnancy (n=10). The diameters of the CL and follicle were measured using ultrasonography. Plasma progesterone concentrations were determined by an enzyme immunoassay method. The vitamin A levels of the plasma, CL and FF were not related to each other. The highest plasma vitamin A levels were observed in the proestrus and oestrus, at which periods follicular activity dominates. The vitamin A levels in the CL and FF were negatively related to the weight and diameter of the CL and the diameter of follicle, respectively. In contrast to vitamin A, beta-carotene concentrations of plasma, CL and FF were significantly correlated with each other. The highest beta-carotene levels in the plasma, CL and FF were found during pregnancy when there is maximal luteal function, and the beta-carotene level of the CL was significantly correlated with the weight and diameter of CL. Furthermore, the intrafollicular beta-carotene level was negatively correlated with the follicle diameter. There was a positive correlation between plasma progesterone level and the weight and diameter of the CL, but a negative correlation between plasma progesterone level and follicle diameter. Moreover, plasma, FF and CL beta-carotene levels were positively correlated with plasma progesterone levels. This study revealed that beta-carotene levels in the plasma, CL and FF were influenced by the stage of the oestrous cycle or the pregnancy and were related to bovine luteal function without depending on vitamin A.