The effect of corpus luteum on hormonal composition of follicular fluid from different sized follicles and their relationship to serum concentrations in dairy cows.

OBJECTIVE

To investigate the effect of the presence or absence of corpus luteum on hormonal composition of follicular fluid (FF) from different sized follicles and their relationship to serum concentrations in dairy cows.

METHODS

Ovaries were collected from 30 clinically healthy adult female cows (Holstein Friesian) 4-7 years of age with clinically normal reproductive tracts after slaughtering. Blood samples were collected from the jugular vein before slaughter from each cow. The stage of the cycle in the cows was determined postmortem. The ovaries collected from per cow were classified with corpus luteum (CL(+)) and without corpus luteum (CL(-)). FF was aspirated from small (3-5 mm), medium (6-9 mm), and large (10-20 mm) follicles in CL(+) and CL(-) ovaries. Serum and FF samples were analyzed for estradiol-17β, progesterone, testosterone, T3 and T4 concentrations.

RESULTS

Results demonstrated that the FF concentrations of estradiol-17β, progesterone and testosterone in different sized follicles categories (small, medium and large follicles in CL(+) and CL(-) ovaries) were significantly higher (P≤0.05) when compared with the serum. The FF concentrations of estradiol-17β and testosterone in same follicle size categories in CL(+) and CL(-) ovaries were also significant (P<0.05). Indeed, concentrations of these hormones in the CL(-) ovaries were higher than those of the CL(+) ovaries. However, there was a statistically significant difference between medium and large follicles for progesterone concentration in CL(+) and CL(-) ovaries (P<0.05). There was a significant correlation between concentration of hormones in serum and FF with increased follicular diameter.

CONCLUSIONS

These results indicated that the levels of hormonal composition in the FF were related to follicular size and interestingly to the presence or absence of a corpus luteum. Indeed, the corpus luteum locally affects neighboring follicular compositions during the luteal phase of the estrous cycle in dairy cows.