143 Impact of higher estrus-associated temperatures and mounting activity on the periovulatory follicular fluid metabolome in beef heifers

Estrual females exhibit varying levels of activity and higher estrus-associated temperatures (HEAT). Each, alone or in combination, affects circulating metabolites. To determine if HEAT, estrus activity, or both are impactful, the periovulatory follicular fluid metabolome in estrus active (comingled with others; engaged in mounting) was compared with estrus nonactive (after first mount, restricted from mounting activities by placing in an individual pen adjacent to others). Estrus was induced in Angus heifers using a 7-day controlled internal drug release (CIDR)-PGF_2α protocol. Vaginal temperature was recorded every 5 min using a Thermochron iButton affixed to a blank CIDR. Onsite ambient temperature and relative humidity were recorded hourly. Heifers were visually monitored for estrus continuously. Estrus was defined as the time when a heifer first stood to be mounted. Treatment assignment alternated (comingled, n = 13; restricted, n = 12). Periovulatory follicle fluid was aspirated 11.9 ± 0.4 h after the first standing mount and submitted for ultra-high-performance liquid chromatography–high resolution mass spectrometry metabolomic analysis (116 metabolites identified). Hierarchical linear regression models were performed using metabolite abundance (dependent variable) and total area under HEAT curve (AUCtotal), treatment (estrus active or nonactive), and respective interaction. Best fit models were determined using backward manual selection after ensuring lack of collinearity among other heifer covariates (e.g. follicular fluid and serum hormone levels, follicle sizes) and data normality. Enrichment analysis was conducted using Metaboanalyst 6.0. Eleven follicular fluid metabolites were positively related to HEAT (P ≤ 0.05). Significantly enriched pathways (FDR < 0.1) included “Pyrimidine metabolism.” Four of the associated metabolites (i.e. cytidine, orotate, uracil, and uridine) are known to play a role in increasing body temperature. The abundance of 33 metabolites differed by treatment (P ≤ 0.05); all were higher in the follicular fluid from restricted heifers. Significantly enriched pathways (FDR < 0.1) included “Arginine biosynthesis” and “Phenylalanine, tyrosine, and tryptophan biosynthesis.” Adenosine may aid in regulating body temperature. Citrulline and glycine of “Arginine biosynthesis” are noted to be involved in response mechanisms associated with increased body temperature. Six other metabolites were interactively influenced by HEAT and estrus activity. For example, taurine abundance was not related to HEAT in estrus active heifers but increased as HEAT increased in estrus heifers restricted from engaging in mounting activity (HEAT × treatment interaction; P = 0.0038). In summary, both HEAT and estrus mounting activity were related to marked changes in the periovulatory follicular fluid metabolome involved in thermoregulation, energy metabolism, and oxidative stress management.

This study was supported by Agriculture and Food Research Initiative Competitive Grant no. 2022-67015-36374 from the USDA National Institute of Food and Agriculture, UT Institute of Agriculture, and Animal Science Department.