Development of a Portable Device–Based Method for Predicting Follicle Number Using Vulvar Blood Flow Volume Measurement in Cows

Embryo recovery and transfer techniques efficiently assist superior cow selection for beef and milk production. In this study, we evaluated the use of vulvar blood flow volume (BFV) measurements obtained with a portable blood flow meter in predicting the follicle number. We explored the relationship between vulvar BFV and follicular hormone dynamics in cows. Eleven Japanese Black cows underwent superovulation treatment, after which vulvar BFV, serum estradiol (E₂) and progesterone levels, and follicle number were measured. All measurements were repeated in the luteal phase (7 days before estrus), 1 and 2 days before estrus, and 2 and 7 days after estrus. The vulvar BFV was significantly elevated 1 day before estrus compared with that during the luteal phase. Furthermore, the vulvar BFV dynamics mirrored the follicle number and serum E₂ level, both of which were significantly elevated 1 day before estrus compared with those during the luteal phase. In addition, positive correlations were observed between vulvar BFV and follicle number, between serum E₂ level and follicle number, and between vulvar BFV and E₂ level. Thus, vulvar BFV measurements could serve as a practical and non-invasive strategy for predicting follicle number and may provide a valuable tool for farmers.