66 RELATIONSHIP BETWEEN PLASMA CHLORIDE LEVELS AND FOLLICLE DIAMETER IN CYCLING SPANISH PUREBRED MARES

Abstract

Several studies in cows have shown that plasma levels of chloride are positively correlated with the diameter of the preovulatory follicle (FD), establishing at the same time a significant positive association between plasma levels and intraoviducal concentration of this electrolyte (Hugentobler et al. 2007). These relationships may reflect the influence of changes in systemic metabolic plasma on follicular fluid, physiological events that might be closely related to the quality of the oocyte and granulosa cells of the preovulatory follicle (LeRoy et al. 2004). However, these mechanisms remain unknown in the mare. The objective of this research was to investigate the relationship between plasma chloride concentrations and growth of FD during the ovulatory period in the Spanish purebred mares. This research was approved by the Animal Ethics Committee of the CEU-Cardenal Herrera University. A total of 30 reproductive cycling Spanish purebred mares, aged 4 to 17 years old, were studied. Plasma concentrations of chlorine and follicular growth (FD) were determined daily by extracting blood samples and monitoring of ovarian ultrasound all mares, from Day –5 to the day of ovulation. Plasma chloride concentrations were evaluated by an analyzer with selective electrodes Vetlyte^® (IDEXX, Hoofddorp, the Netherlands). To analyse the effect of cycle day on FD and concentrations of chloride, ANOVA was used. The interrelations between both parameters were expressed by Pearson correlation coefficient. The FD increased significantly, from 27.02 ± 2.113 to 40.23 ± 1.377 cm, during the 5 days prior to ovulation. Plasma chloride decreased from 105.6 ± 0.928 mmol L^–1 on Day –5 to 104.5 ± 0.128 mmol L^–1 on Day –1, and increased significantly, to 107.4 ± 1.442 mmol L^–1, on the day of ovulation. No significant correlations between FD and chloride concentrations (r = 0.21) were found. Unlike what happens in the cow, plasma chloride levels affect preovulatory follicle development in Spanish purebred mares to a lesser extent. Nevertheless, plasma chloride or any other electrolytes have some kind of involvement in the dynamics of growth and maturation of oocytes.