Abstract
BackgroundIn humans, it is now well documented that rising paternal age is correlated with decreased sperm DNA integrity and embryonic developmental failures. On the other side of the coin, it is also reported that very young fathers such as teenagers carry an increased risk of adverse birth outcomes. These observations suggest that, at least in humans, there is an age window for optimal sperm DNA integrity. In bovine, little is known about sperm DNA quality in young bulls and how it evolves with age. This study aimed to fill in this gap as it may be of importance for the bovine industry to know when exactly a bull is an optimal performer for reproductive programs.MethodsForty Nellore bulls were divided into three age groups: 1.8 to 2 years – young bulls; 3.5 to 7 years – adult bulls; and 8 to 14.3 years – aged bulls. Three ejaculates were collected from each bull, cryopreserved and evaluated for various parameters including: computer-assisted sperm analysis (CASA), plasma membrane and acrosome integrity, mitochondrial potential, sperm nuclear protamination, DNA oxidative damage, and Sperm Chromatin Structure Assay (SCSA).ResultsWe report here that young bulls presented superior values for motility, plasma and acrosomal membrane integrity, and high mitochondrial potential. However, they also presented higher values for sperm morphological abnormalities compared to adult and aged animal groups (p < 0.05). In addition, young bulls exhibited more defective protamination than older animals did. The oldest bulls showed more nuclear oxidative damage than the younger groups of bulls while both the young and aged groups were found more susceptible to DNA denaturation as revealed with the SCSA test (p < 0.05).ConclusionThese results indicate that young bulls spermatozoa best survived the freezing procedure, followed by adult and aged bulls. However, young and aged bulls were found to be more susceptible to DNA damage, respectively caused by protamine deficiency and oxidation. Therefore, although young bulls have correct semen parameters according to classical evaluation, our results indicate that they may show some structural nuclear immaturity.
Highlights
In humans, it is well documented that rising paternal age is correlated with decreased sperm DNA integrity and embryonic developmental failures
The mean total (MOT) and progressive motility (PM) values ranged from 38.0 to 67.8% and 22.1 to 36.9%, respectively, and were significantly higher in young bulls when compared to the two other groups
Concerning sperm DNA oxidative damage as evidenced by using an anti-8-OHdG detection system (OXIDNA assay) we found that this parameter increased with the age groups reaching its maximum value in the aged animals (Table 4, column 8-OHdG)
Summary
It is well documented that rising paternal age is correlated with decreased sperm DNA integrity and embryonic developmental failures. On the other side of the coin, it is reported that very young fathers such as teenagers carry an increased risk of adverse birth outcomes These observations suggest that, at least in humans, there is an age window for optimal sperm DNA integrity. Mammalian species are not identical when it comes to sperm nucleus organization and susceptibility to damage This is rather well illustrated by the observation that mammalian sperm are not able to sustain the stress associated with cryopreservation. In this respect, bulls appear to have a rather solid sperm nucleus/chromatin showing a good capacity to sustain the freezing/thawing processes as well as low levels of DNA fragmentation [4,5,6,7,8]
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