The morphological characteristics and DNA integrity of spermatozoa have been linked to fertility in a range of species (1, 2). Spermatozoa which record high morphological abnormalities are thought to be less fertile due to their inability to navigate the tract, fertilise the oocyte and often result in pregnancy loss (3). Compared to humans and other livestock species, where these two parameters have been shown to be correlated, little focus has been given to the potential interplay between the DNA integrity and morphological abnormalities of ram spermatozoa post-thaw (4). As such, this study directly compares the DNA integrity and morphology of ram spermatozoa following cryopreservation to understand the relationship between semen quality traits.
Semen was collected from Merino rams (N=250) and frozen using industry-standard techniques. Each sample was assessed for the percentage of abnormal sperm using phase-contrast microscopy (x400 magnification, 200 cells) and DNA fragmentation using flow cytometry (Acridine Orange; Thermo Fisher Scientific, NSW) immediately after thawing (3) and following 6hr of incubation at 37⁰C to establish a DNA fragmentation index (DFI%).
Statistical modelling (R Studio) revealed DFI% at 0hr and 6hr post-thaw returned a positive correlation with morphological abnormalities (R2 = 0.53, 0.33, respectively). There was also a significant increase in DFI± SEM% from 0hr (3.97±0.24%) to 6hr (6.91±0.51%, p<0.001) post-thaw.
These findings demonstrate a positive correlation between DFI% and morphological abnormalities of frozen-thawed ram spermatozoa and an effect of incubation time on DFI% in ram spermatozoa. The results imply that the processes that cause abnormal sperm morphology negatively affect the DNA integrity of sperm. Further research is required to explore the collective impact of such traits on the fertility of semen following artificial insemination and the acceptable levels for processed semen.