Comparative intrafollicular and plasma iron, ferritin, and transferrin concentrations in cycling mares

In females of various species and experimental animals, iron (Fe) status in follicular fluid (FF) is associated with local physiological reproductive events related to follicle development, steroidogenesis, and oocyte maturation. However, these mechanisms remain unknown. This study aimed to determine and compare the intrafollicular and plasma concentrations of Fe, ferritin (Ferr), and transferrin (TRF) in cycling mares.

Sixty ovaries were collected during the breeding season from 30 clinically normal mares raised for slaughterhouse meat production. Blood samples were collected before slaughter. Follicles were classified into three categories according to size: Small (20-30 mm; n = 20), medium (≥31-40 mm; n = 20), and large (≥41 mm; n = 20). The FF samples, after collection, were immediately taken to the laboratory for processing and were centrifuged, and the Fe and Ferr concentrations in the supernatant and plasma were determined by spectrophotometry.

Although intrafollicular Fe and Ferr were similar to plasma, TRF was significantly higher in FF than in systemic circulation (p < 0.05). Follicular development does not modify the status of Fe in the mare.

Based on this evidence, it is possible that the acquisition of this molecule possibly originated from a local de novo source, whereas their diffusion through ultrafiltration does not play a relevant role. These results provide new scientific insights into the status of follicle Fe, suggesting its involvement in normal ovarian functions in mares.