Evaluating the follicular output rate, follicle-to-oocyte index, and ovarian sensitivity index for bovine application as key performance indicators of ovarian response to follicle-stimulating hormone superstimulation in Holstein cows.

Variability in ovarian-stimulation (OS) response limits the efficiency of ovum pick-up (OPU)-in vitro production programs, with a minority of donors often producing most embryos. Reliable indicators to predict OS response in individual cows remain limited. In this study, we evaluated and quantified the ability of 3 key performance indicators adapted for bovine application-follicular output rate (FORT_bov), follicle-to-oocyte index (FOI_bov), and ovarian sensitivity index (OSI_bov)-to classify ovarian response in dairy cows. Records from 1,090 follicle-stimulating hormone-stimulated OPU sessions in 481 Holstein cows were analyzed, accounting for repeated sessions within cow in inference. Using the joint distribution of aspirated follicles and recovered cumulus-oocyte complexes (COC), sessions were classified as poor, normal, or high responders (overall mean ± 1 SD), representing 15.6%, 62.8%, and 21.7% of sessions, respectively. The FOI_bov, FORT_bov, and OSI_bov increased progressively across response groups and were associated with OPU outcomes; OSI_bov showed the strongest correlations with aspirated follicles, total COC, and grade A+B COC. In receiver operating characteristic analyses, OSI_bov discriminated poor from normal + high responders (area under the receiver operating characteristic curve [AUC] = 0.974, 95% CI 0.962-0.983) and high from poor + normal responders (AUC = 0.951, 95% CI 0.934-0.966), exceeding the performance of FOI_bov and FORT_bov; the corresponding optimal OSI_bov cut-offs were 11 and 25, respectively. OSI_bov-based categories agreed well with the clinical classification (quadratic weighted κ_w = 0.777). In single-predictor ordinal logistic regression, OSI_bov yielded the lowest Akaike information criterion and the highest concordance index (C-index = 0.956). Across cows with repeated sessions, antral follicle count and yield traits were highly repeatable, whereas FOI_bov and FORT_bov showed greater within-cow variability. We conclude that OSI_bov is a practical indicator of bovine OS response and may support donor ranking and individualized stimulation to improve embryo-production efficiency.