Impact of Estrous Active Behavior and HEAT on Intrafollicular Hormone and Metabolite Levels in the Preovulatory Follicle in Beef Heifers

Estrual females exhibit estrous active behaviors and varying levels of higher estrous associated temperatures (HEAT). This hormonally induced, sexually related form of exercise, alone or in combination with elevated body temperature affects circulating metabolites. To evaluate the extent to which intrafollicular components are impacted, preovulatory follicular fluid hormones and metabolites were compared in heifers that were comingled with others or restricted from engaging in estrus active behaviors. Estrus was induced in Angus heifers using a seven-day controlled internal drug release (CIDR)-PGF_2α protocol. Vaginal temperature was recorded every 5 min using a Thermochron iButton. Estrus was defined as the first time a heifer stood to be mounted. Treatments were assigned alternately. Preovulatory follicle fluid was aspirated ~11.9 h after first mount and submitted for ultra-high-performance liquid chromatography-high resolution mass spectrometry metabolomic analysis (106 metabolites identified). Hierarchical linear regression models were performed using hormone and metabolite abundance (dependent variables) and total area under HEAT curve, treatment (estrous active or restricted) and respective interaction. Best fit models were determined using backwards manual selection. Intrafollicular and serum levels of estradiol ~11.9 ± 0.4 hours after 1^st mount were negatively related to HEAT. Restricted heifers had higher intrafollicular estradiol levels compared to those allowed to comingle with others after 1^st mount. Twelve follicular fluid metabolites were related to HEAT (P < 0.05). Significantly enriched pathways (FDR < 0.1) included ‘Pyrimidine metabolism’. Abundance of 25 other metabolites differed by treatment (P < 0.05); all were higher in the preovulatory follicular fluid of heifers restricted from engaging in estrous active behaviors. Significantly enriched pathways (FDR < 0.1) included ‘Arginine biosynthesis’ and ‘Phenylalanine, tyrosine and tryptophan biosynthesis’. Twelve other metabolites were interactively influenced by HEAT and estrous active behaviors. In summary, preovulatory follicle progression in estrual heifers is more advanced in females exhibiting estrous active behaviors and experiencing greater levels of HEAT. These initial, LH-induced changes are pivotal for granulosa cells to transition into lutein cells. Advanced follicle progression likely impacts the cumulus oocyte complex contained therein and other components that may be involved in events important for setting stage for ovulation later.