Advanced periovulatory follicle progression in beef heifers: association with higher estrous-associated temperatures and estrous activity on intrafollicular levels of estradiol and metabolites.

Female cattle engaging in estrous activity exhibit varying levels of higher estrous-associated temperatures (H.E.A.T.) that are functionally impactful on fertility important components in the periovulatory follicle. To test this hypothesis, estrus was synchronized in virgin Angus heifers. Follicular fluid hormones and metabolites impacted by estrous activity (categorized as Estrous Active or Inactive), alone or in combination with H.E.A.T. were evaluated. Estrus was defined as the first time a heifer stood to be mounted; treatment was assigned alternately at first mount (comingled with others to remain Estrous Active, n = 13) or prevented from engaging in estrous active behaviors (Estrous Inactive, n = 12) by moving to an individual open rail pen, in sight of others and allowing nose-to-nose contact. Vaginal temperature was recorded using a Thermochron iButton. Periovulatory follicular fluid was aspirated ∼11.9 ± 0.1 h after first standing mount. Multiple linear regression was performed. Metabolite pathway enrichment analysis was conducted using Metaboanalyst 6.0. Estradiol levels (intrafollicular and serum) were negatively related to H.E.A.T. (P < 0.001). Intrafollicular estradiol was lower in Estrous Active heifers (P < 0.0001). Twelve follicular fluid metabolites were positively related to H.E.A.T. (P < 0.05). Pathways enriched with H.E.A.T.-related metabolites (FDR < 0.1) included "Pyrimidine metabolism." Abundance of 25 other metabolites was lower in the periovulatory follicular fluid of Estrous Active versus Estrous Inactive heifers (P < 0.05). Pathways enriched with metabolites affected by estrous activity included "Arginine biosynthesis" and "Phenylalanine, tyrosine, and tryptophan biosynthesis." Six out of 12 other metabolites interactively influenced by H.E.A.T. and estrous activity are known for their antioxidant properties. In summary, periovulatory follicle progression is more advanced in Estrous Active heifers and in those exhibiting higher levels of H.E.A.T. Intrafollicular metabolites in the more advanced periovulatory follicles are linked to thermoregulation, steroidogenesis, antioxidant defense, and energy metabolism. Results provide new insight into pivotal changes in the periovulatory follicle when estrogen dominance is coming to an end, the initial differentiative shift in granulosa cells is occurring, along with other preparatory changes that may be important for eventual ovulation and meiotic progression of the oocyte contained within.