The objective of this study was to analyse the DNA Fragmentation Index (DFI) and spermatic viability in frozen-thawed seminal samples from fighting bulls.
The functional integrity of the spermatic membrane is essential to fertilization, but it does not contribute in further processes of embryo development, while DNA integrity is mainly involved in the initial stages of embryonic development. An adaptation of the sperm chromatin dispersion (SCD) test has been used to determine DNA fragmentation. This test is based on the differential response of sperm nucleus to a desproteinization treatment. Sperm cells containing fragmented DNA show a large peripheral halo of chromatin dispersion after staining with a fluorochrome. However, when DNA is not fragmented within the sperm nuclei, a restricted spreading of DNA close to the flagellum can be observed. The sample observations were performed by a fluorescence microscope. Moreover, sperm viability was assessed using a supravital stain based on the red/green emission of two fluorescent dyes, acridine orange (AO) and propidium iodide (PI), respectively.
We determined the basal DFI in 53 fighting bull semen samples, resulting in 7.88±6.27 and lower and upper limits 1-34 %, respectively. The vitality average was 23.09±15.80, the lower and upper limits being 1-60 %, respectively. A negative correlation between both parameters was observed when relating DNA fragmentation and vitality of bull sperm samples.
The results of the study are evidence of the high individual variability for both parameters, probably due to external individual factors that are being studied. We suggest that DFI should be introduced as a routine analytical parameter for semen analysis, as damaged DNA could contribute negatively to fertility.

* This work was funded by FEDER.