Dietary thymol supplementation improves growth performance and reproductive endocrine status in growing Texel × Kazakh rams and remodels the rumen microbiota and metabolome

Dietary thymol supplementation improved growth performance and reproductive hormone levels in growing rams, but the clinical relevance of these findings needs further investigation.

Summary and findings

This study evaluated the effects of dietary thymol supplementation on growth performance and serum reproductive hormone levels in growing Texel × Kazakh rams. The rams were supplemented with 30 mg/kg thymol for 72 days. Results indicated improved growth performance and changes in serum hormone levels.

Abstract

<title>Abstract</title> <p>Background Thymol is a natural monoterpene phenolic compound with antimicrobial, antioxidant, and anti-inflammatory activities and has been reported to modulate rumen fermentation and nutrient utilization in ruminants. However, its effects on growing rams, particularly on reproductive endocrine status and rumen microbiota–metabolome interactions, remain unclear. This study evaluated the effects of dietary thymol supplementation on growth performance and serum reproductive hormone levels in growing Texel × Kazakh rams and explored the associated changes in rumen fermentation, microbial community structure, and metabolite profiles. Results Thirty 13 ± 0.5-month-old Texel × Kazakh crossbred rams with similar body weight were randomly assigned to a control group fed a basal total mixed ration or a thymol group fed the basal diet supplemented with 30 mg/kg thymol on a dry matter basis, with 15 rams per group. The experiment lasted 72 days. Thymol supplementation increased total weight gain and average daily gain and decreased the feed-to-gain ratio (P < 0.01), without affecting average daily feed intake. Apparent digestibility of crude protein, ether extract, neutral detergent fiber, and acid detergent fiber, as well as nitrogen and phosphorus retention efficiency, was improved in the thymol group (P < 0.05). Serum total cholesterol and high-density lipoprotein cholesterol concentrations were decreased (P < 0.01), whereas testosterone and estrone concentrations were increased (P < 0.01), and estradiol and corticosterone concentrations were also increased (P < 0.05). Ruminal pH was elevated (P < 0.05), while ammonia nitrogen concentration was reduced (P < 0.01). 16S rRNA gene sequencing showed that thymol increased rumen microbial richness and evenness and altered microbial community structure. Several fibrolytic or carbohydrate-utilizing genera, including Rikenellaceae_RC9_gut_group, NK4A214_group, Christensenellaceae_R-7_group, and Treponema, were enriched in the thymol group, whereas Prevotella and Selenomonas were reduced or tended to be reduced. Untargeted metabolomics identified 569 differential metabolites, which were mainly enriched in the cAMP signaling pathway, purine metabolism, nucleotide metabolism, cGMP-PKG signaling pathway, and glutathione metabolism. Representative metabolites, including adenosine monophosphate, 3-hydroxybutyric acid, inosine, and adenosine, were significantly correlated with average daily gain, rumen fermentation parameters, and serum reproductive hormone levels. Conclusions Dietary supplementation with 30 mg/kg thymol improved growth performance, feed conversion efficiency, nutrient digestibility, nitrogen and phosphorus retention, and serum reproductive hormone levels in growing Texel × Kazakh rams. These effects were accompanied by increased rumen microbial diversity, enrichment of fibrolytic bacterial taxa, reduced ruminal ammonia nitrogen, and shifts in rumen metabolites related to purine metabolism, cAMP signaling, and glutathione metabolism. These findings suggest that thymol may serve as a natural feed additive for improving growth and reproductive endocrine status in growing rams, potentially through coordinated modulation of the rumen microbiota and metabolome.</p>

Limitations

Not reported in abstract.

Elsewhere in the Glutathione (GSH) corpus