PS1-20. Effects of 5-HTP Supplementation on Follicular Dynamics and Corpus Luteum Area and Blood Perfusion in Beef Cattle.

Abstract Serotonin (5-HT) has major reproductive implications, having been shown to regulate oocyte maturation, fertilization competency, and early embryonic development and viability. These outcomes are facilitated by localized 5-HT oocyte synthesis and 5-HT receptor presence on the oocyte membrane across several mammalian species, but whether these serotonergic mechanisms occur in beef cattle remains unexplored. Therefore, the objective of this study is to evaluate the effects of increasing circulating 5-HT on follicular emergence, ovulatory follicle size, Corpus luteum size and blood perfusion in beef cows. Multiparous, nonlactating, open beef cows were stratified by body weight into two treatment groups: unsupplemented feed (0.91 kg soybean meal/d; CON, n = 10) or 5-hydroxy-L-tryptophan (5-HTP) supplemented feed (0.91 kg soybean meal/d,1.5 mg/kg BW 5-HTP; SERO, n = 11). Treatment began at the initiation of the 7-day Co-Synch + CIDR estrus synchronization protocol (d 0) and concluded after establishment of Corpus lutea (d 17). Transrectal ultrasonography was performed daily using a linear transducer to assess ovarian structures, sizes, and Corpus luteum blood perfusion. Follicular emergence was determined by logistic regression for fixed effects of treatment, day, and treatment by day from days 0 to 5 and 8 to 14. Ovulatory follicle diameter, Corpus luteum area, and blood perfusion were analyzed by ANOVA for fixed effect of treatment. There were no differences in follicle emergence from d 0 to 5. There was a treatment by day effect (P = 0.03) for emergence after CIDR removal and prostaglandin administration on d 8, whereby SERO had less cows with emergence on d 9 compared with CON on d 8 and SERO on d 8 and 10. There were no differences (P > 0.05) in ovulatory follicle size, Corpus luteum area, or blood perfusion. This pilot study suggests 5-HT may not affect ovarian structures at the same magnitude of other species, however continued research is needed.