67 Relationships of circulating and preovulatory follicular fluid hydrogen peroxide level with body condition score and metabolome profiles in lactating beef cows

Nutrient requirements of lactation often lead to negative energy balance accompanied by reduced body condition and fertility in cattle. A previous study identified increased abundance of serum metabolites associated with tissue mobilization and reactive oxygen species (ROS) generation in postpartum beef cows of thin versus moderate body condition. No studies, however, have measured ROS in serum and follicular fluid of postpartum beef cows for comparison with body condition. We hypothesized that beef cows of thin body condition would have elevated ROS, as indicated by hydrogen peroxide (H₂O₂), in serum and preovulatory follicular fluid. Preovulatory follicular fluid was collected using transvaginal aspiration of the largest follicle of each cow on Days 51–66 postpartum. Briefly, an ultrasound-guided aspiration device containing a CF4-9 convex ultrasound probe attached to a Samsung HM70A ultrasound, an 18 G needle, and a series of plastic tubing was positioned in the anterior vagina. The needle was pushed through the vaginal wall, ovarian cortex, and antrum of the preovulatory follicle. Serum and follicular fluid samples from thin (n = 12), moderate (n = 11), and obese (n = 16) cows underwent H₂O₂ bioluminescence assay using a commercially available H₂O₂ luminescent assay (ROS-Glo H₂O₂ Assay; Promega Corporation). Serum samples underwent 10× dilution in Ultra-Pure water before assay. The level of H₂O₂ from each biofluid was then assessed to determine relationships with cow body condition and 50 serum or 38 follicular fluid metabolites previously identified in the samples. All statistical procedures were preformed using R Studio (version 4.3.2; RStudio Team 2023). Best fit linear models utilizing cow parameters, estradiol and progesterone concentrations, and follicle size as covariates were used to determine relationships between H₂O₂ level (luminescence) in serum or follicular fluid among body conditions and with serum or follicular fluid metabolite abundances. Significance in all analyses was determined at P < 0.05. Level of H₂O₂ did not differ among body condition categories (P > 0.20). In thin cows, serum H₂O₂ was positively related to abundance of three metabolites with antioxidant activity (succinate/methylmalonate, taurine, and methyl succinic acid; P ≤ 0.0009). Among all animals, regardless of body condition score, follicular fluid H₂O₂ was positively associated with the abundance of 13 metabolites (aspartate, 2-oxoisovalerate, valine/betaine, leucine/isoleucine, phenylalanine, methionine, 3-methylphenylacetic acid, uric acid, citrulline, ornithine, creatine, glutamine, and alanine/sarcosine; P ≤ 0.049), many of which have antioxidant roles. Results suggest that postpartum beef cow metabolism has an impact on ROS in preovulatory follicular fluid or serum and highlight the need for additional studies to further investigate this potential factor influencing reproductive efficiency and sustainable beef production.

This research was funded by the USDA NIFA MultiState project NE 2227 and the University of Tennessee Department of Animal Science and AgResearch.