Growth performance, meat quality, rumen morphometrics and microbiota of finishing bulls fed diets supplemented with oregano essential oils

The aim was to investigate the effects of microencapsulated oregano essential oil (OEO) dietary supplementation on growth performance, meat quality, rumen morphometrics and microbiota, in finishing bulls. Sixty-eight Limousin bulls were randomly allocated into 2 groups (CON: offered basal diet and OREG: basal diet supplemented with 50 mg OEO in microencapsulated form/kg dry matter). The trial lasted 90 days. Thereafter all bulls were slaughtered. At slaughter samples of Longissimus dorsi muscle (13 th rib steak) were collected to evaluate meat pH, color, fatty acids profile and oxidation status. Rumen tissue samples were collected to assess histomorphology. Additionally, rumen fluid samples were collected to examine bacterial diversity, through 16S rRNA sequencing. One of the key findings was that DMI was influenced by OEO dietary inclusion, with OEO supplemented bulls consuming less feed (P<0.01), without negatively affecting average daily gain and final body weight. In terms of meat quality OEO supplementation improved antioxidant status and caused a 47.31% reduction in Elaidic acid (P<0.05). Rumen papillae length and width remained similar between groups (P>0.05), while a 32% reduction in keratinized layer thickness (P=0.034) was observed in OEO supplemented bulls. However, no differences were observed in meat pH and color (P>0.05). The analysis of rumen fluid samples revealed that beta-diversity was significantly altered (P=0.009) and the abundance of Succinivibrionaceae family was higher (P<0.05) in OEO supplemented bulls, while Rikenellaceae RC9 gut group population decreased (P<0.05). Finally, glutathione peroxidase metabolic pathway, which is involved in protecting cells from oxidative damage, was upregulated by OEO supplementation. These findings suggest that microencapsulated OEO supplementation favorably modified rumen microbiome, contributing to reduced feed intake without compromising performance and meat quality in finishing bulls. Additionally, OEO supplementation in this study was associated with improvement in meat preservation. • Oregano essential oil (OEO) enhanced the productivity of finishing bulls • OEO supplementation improved beef oxidative stability and reduced elaidic acid • OEO altered rumen bacterial community, increasing Succinivibrionaceae abundance • OEO upregulated glutathione peroxidase promoting oxidative stress resilience.