Establishing a Sperm Quality Index for Frozen–Thawed Bovine Semen Based on Sperm Motility, Viability and Capacitation Traits

Different routine parameters are commonly used to evaluate frozen-thawed semen quality, but no single parameter is sufficient to predict fertility accurately. The combination of multiple parameters could enhance the reliability of fertilising potential assessments in bovine semen doses; however, the simultaneous use of individual indicators becomes cumbersome and difficult to apply. This research aimed to evaluate the calculation and use of seminal quality indexes based on a set of traits from frozen-thawed semen, as a way of integrating and expressing, in a single value, the seminal quality of bulls. Ten ejaculates from five healthy and sexually mature Nelore bulls were used. The semen was frozen using a conventional nitrogen vapour protocol. Post-thawing, sperm motility and kinetics, viability and capacitation were evaluated using computerised analysis, fluorescence microscopy and flow cytometry, respectively. Sperm quality indexes (SQi) were calculated using principal component analysis (PCA). Normalisation of the SQi on a scale between 0 and 1 (N-SQi) was performed. Data were analysed using an N-way ANOVA for each dependent variable, and the means were compared between bulls using Tukey's test. Most of the parameters were positively correlated, except for the majority of the STR, LIN and NC correlations with the other variables, which were negatively correlated. The mean results for SQi and N-SQi were 1.10 ± 0.04 and 0.64 ± 0.02, respectively. There were differences in the results per bull in both MP and RAP, as well as for SQi and N-SQi. It is concluded that using seminal quality indexes is a feasible way to integrate and consolidate multiple traits from computerised analysis, fluorescence microscopy and flow cytometry of frozen-thawed semen samples into a single value to facilitate their interpretation.