Sperm motility and quality decline with stallion age and sperm preservation, but the mechanisms of functional deficit have not been explained. We tested the hypothesis that mitochondrial deficits underlie age- and cryopreservation-related deficits in stallion fertility by measuring mitochondrial function, motility, and reactive oxygen species (ROS) in 88 frozen-thawed ejaculates from 19 stallions of varying ages. As expected with increasing age, total sperm motility, progressive motility, and average path velocity decreased, and ROS production increased. For every unit increase in oxygen consumption, there was a 77% increase in the odds of sperm movement (P < .05), confirming the link between mitochondrial functionality and motility. In addition, the rate of mitochondrial oxygen consumption increased from 4 years of age to a peak at 12 years of age and decreased steadily thereafter (P < .05). This confirms the importance of mitochondrial functionality for overall sperm health and motility, implicating mitochondrial dysfunction as a major contributor to sperm aging and cryopreservation damage.
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