The relationship of increased susceptibility of sperm DNA to denaturation and fertility in the stallion

Abstract

The relationship between fertility and susceptibility of sperm DNA to denaturation was determined in a group of 84 actively breeding, clinically fertile stallions. Susceptibility of DNA to denaturation was determined using the sperm chromatin structure assay (SCSA). The SCSA measures, mean of alpha-t (meanα t), standard deviation of alpha-t (SDα t), and the COMP of alpha-t (cells outside the main population)] were significantly correlated with the percentage seasonal pregnancy rate (SPR; meanα t, r = −0.24, P ≤ 0.05; % COMPα t, r = −0.27, P≤ 0.05); percentage pregnant per first cycle (FCP; SDα t, r = −0.30, P ≤ 0.01; % COMPα t, r = −0.42, P≤ 0.0001); and the percentage pregnant per cycle (PC; meanα t, r = −0.31, P≤ 0.01; SDα t, r = −0.32, P≤ 0.01; % COMPα t, r = −0.41, P≤0.0001). This study describes detectable intrinsic variation in sperm chromatin structure among fertile stallions (SPR, mean = 83%; FCP, mean = 58%; PC, mean = 57%) in an active breeding population (number of mares bred/stallion/year, mean = 37), in the absence of overt reproductive abnormalities and apparent diseases such that an increase in the susceptibility of sperm DNA to denaturation is associated with reduced fertility, both in terms of efficiency of reproduction (FCP and PC) and seasonal pregnancy rate (SPR). Both COMPα t and meanα t were useful indicators of fertility, with COMPα t being the only SCSA value able to identify mean differences between fertility groupings for SPR and FCP, and overall it was the most reliable indicator of fertility in this group of stallions. The SCSA is able to evaluate a compartment of the spermatozoa which is different from that of traditional tests for sperm quality such as motility and morphology.