Testicular transcriptome analysis under the dietary inclusion of L-carnitine reveals potential key genes associated with oxidative defense and the semen quality factor (SQF) in aging roosters

Abstract L-carnitine (LC) has been widely studied as a natural antioxidant molecule for treating low-fertility gametes. However, the molecular mechanism of the effect of LC supplementation on the testes of aging cocks has not been evaluated. Therefore, the objective of this study was to reveal the mechanism of testicular oxidative defense induced by LC supplementation in relation to the semen quality factor (SQF) in the aging cock through a transcriptome study conducted from a new perspective. A total of 24 Jing Hong cocks at 55 weeks of age were randomly divided into two groups (n=12). All cocks were fed a standard isocaloric and isonitrogenic breeder diet (control, LC-0), and the other group was supplemented with LC at 150 mg/kg/day (treated, LC-150) for 12 weeks. Remarkably, seminal characteristics and enzymes, sex hormones, and cock fertility related to testicular oxidative defense were considerably improved by LC supplementation. LC-150 testes showed the differential up- and downregulation of 97 and 90 transcripts, respectively, compared to LC-0 testes. The majority of upregulated transcripts were involved in testicular oxidative defense as well as spermiogenesis optimization, whereas the downregulated genes were responsible for oxidative stress, in contrast to the SQF. Functional analysis of the transcriptionally altered genes indicated the testicular deregulation of long-chain fatty acid and lipid peroxidation, enhancing fatty acid breakdown to release ATP production via β-oxidation. These findings could lay the foundation for the discovery of new molecular markers of SQF-associated LC supplementation and potential targets for therapeutic intervention to optimize fertility in aging cocks.