The production of ROS by spermatozoa is catalysed by certain metals which can further exacerbate oxidative stress by inhibiting DNA repair enzymes such as OGG-1 which is responsible for the repair of the DNA-base adduct, 8-hydroxy-2’deoxyguanosine (8OHdG). The aim of this study was to ascertain the relationship between systemic levels of metals in the blood and 8OHdG levels in the spermatozoa of Thoroughbred stallions (n = 39). ‘Dismount’ semen samples were collected by gentle milking of the urethra following breeding and diluted (1:2) with Kenney’s extender. Whole blood was collected using EDTA as an anticoagulant. Whole blood analysis for concentrations of Na, Mg, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Mo, Cd, Hg, Pb, Bi and U were performed using ICP-MS and 8OGdG levels in spermatozoa were ascertained by flow cytometry. Stepwise linear regression was performed (α to enter = 0.15) using the percentage of cells positive for 8OHdG as the response and blood metal concentrations (ppb) as predictors. The resulting regression equation selected blood Na, Sr, Cd and Mg as predictors for sperm 8OHdG levels, with an R² value of 0.63 between actual and predicted 8OHdG. The resulting equation is as follows:

8OGdG positive sperm (%) = -20.36 + (-0.343 × Sr) + (0.00003 × Na) + (11.8 × Cd) + (0.00096 × Mg)

While cadmium is known to exacerbate 8OHdG formation through inhibition of the DNA repair enzyme OGG-1, the strongest relationship observed was between Sr and 8OHdG levels (R² = 0.34, P <  0.0001). Additionally, Sr was the only metal that negatively influenced 8OHdG levels, potentially due to the suppression of ROS by Sr, a phenomenon which has previously been exploited for the treatment of oxidative stress associated with conditions such as osteoporosis and diabetes. These results indicate that oxidative damage in stallion spermatozoa may be ameliorated by manipulating dietary trace metals.