Mitigating heat stress in rabbit bucks using carvacrol-loaded chitosan nanoparticles: improvements in health status, semen quality, testicular morphology, sperm ultrastructure, and fertility potential

Abstract

This study explored how carvacrol, both in its free form (CRV) and encapsulated in chitosan nanoparticles (CRV-CNPs), affects the health and reproductive performance of heat-stressed V-line rabbit bucks. Thirty mature bucks were divided into three groups: a control group fed a standard diet, a group receiving CRV, and a group receiving CRV-CNPs, both at 500 mg/kg diet. Rabbits exposed to high temperatures showed signs of stress, including elevated body temperature and faster breathing. Supplementing their diet with CRV and especially CRV-CNPs helped stabilise these physiological responses. The nanoparticle-treated bucks also showed stronger immune activity, with higher levels of blood cells, antibodies, and other immune markers. Antioxidant defences improved, liver enzymes decreased, and overall biochemical health markers were better preserved. Reproductive performance was clearly enhanced: semen quality, sperm structure, and testicular tissue were all improved, and bucks receiving CRV-CNPs fathered more successful pregnancies with larger litter sizes. However, the study has some limitations, including a relatively small sample size, the absence of a nanoparticle-only control, and no direct measurement of systemic bioavailability, which should be considered when interpreting these results. These findings suggest that encapsulating carvacrol in chitosan nanoparticles not only helps bucks cope with heat stress but also supports their reproductive health more effectively than the free compound. In summary, CRV-CNPs improved health and reproductive parameters in male rabbits under heat stress, suggesting potential benefits for mitigating the effects of challenging environmental conditions.