Oral Presentation ESA-SRB 2023 in conjunction with ENSA

An investigation into the effect of aging on DNA integrity in stallion spermatozoa (#148)

Róisín Griffin 1 , Natasha Harrison 1 , Narantsatsral Sandagdorj 1 , Kaitlin Mcintosh 1 , Laura A Dennis 2 , Ceilidh Jenkins 1 , Aleona Swegen 1 , Zamira Gibb 1
  1. College of Engineering, Science and Environment, The University of Newcastle, Callaghan, NSW, Australia
  2. School of Agriculture, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia

The progeny of younger stallions record significantly higher racing speeds (Sharman et.al.,2022) and more race wins (Brazil et.al.,2016), compared those sired by older stallions. We hypothesize that this may be due to an age-associated increase in sperm harbouring DNA damage, as has been demonstrated in other species. This study aimed to investigate the relationship between stallion age and sperm DNA damage.

Post-breeding urethral semen samples were collected from commercial Thoroughbred stallions (n=219). Samples were diluted (2:1,Equiplus®:semen), and fractionated (using Equipure™) to isolate the high-quality sperm populations. Sperm concentration and motility were assessed on-site, before aliquots were fixed and snap-frozen for morphological and DNA damage assessments. Pregnancy scan results, pertaining to each breeding, were collated. For this study, stallions aged ≤9 years were categorised as “young”, while stallions aged ≥16 years were categorised as “aged”.

Sperm count and motility parameters did not differ significantly between age cohorts (P≥0.05). Spermatozoa from older stallions had higher levels of morphological abnormalities (37.9±2.65% vs 19.9±1.23% for aged and young stallions, respectively;P≤0.001)—the most prominent of which was head defects (12.7±1.50% for aged vs 6.5±0.84% for young stallions;P≤0.001). In line with these findings, DNA strand breaks were higher in spermatozoa from older stallions (sperm chromatin dispersion assay:15.4±2.08% vs 9.9±1.30% for aged and young stallions, respectively;P≤0.001). This may be attributed to poor chromatin packaging, as older stallions had a concurrent deficiency of sperm protamines compared to young stallions (7.7±1.36 vs 4.2±0.41 chromomycin A3 positive cells;P≤0.05). Interestingly, the increased DNA damage recorded by older stallions did not influence pregnancy outcomes (P≥0.05). In conclusion, we have confirmed our hypothesis that sperm DNA damage increases with age in stallions. Further research is required to determine whether age-related DNA damage compromises the genome of the resulting progeny, and how this might contribute to losses in racing performance and potentially, reduced offspring health.

  1. Sharman.et.al. Royal Society Open Science. 2022;9:220691
  2. Brazil.et.al. Honours Dissertation. University of Limerick. 2016