Dose-dependent effects of selenium (Se)-enriched yeast containing nano-scale Se particles on Se bioavailability, rumen fermentation, hematological profile, and growth performance in female Thin-Tail sheep

Background and Aim: Selenium (Se) deficiency remains a significant nutritional challenge in sheep production due to the limited bioavailability of inorganic Se sources and the low Se availability in many soils and forages. Se-enriched yeast containing nano-scale Se particles may provide a more bioavailable organic Se source while also influencing rumen fermentation and animal physiology. This study evaluated the dose-dependent effects of Se-enriched yeast containing nano-scale Se particles on Se bioavailability, rumen fermentation, hematological profile, and growth performance in female Thin-Tail sheep. Materials and Methods: Fifteen clinically healthy female Thin-Tail sheep (8 months old; 17 ± 3 kg) were randomly assigned to three dietary treatments in a completely randomized design (n = 5/group): basal diet without supplementation (P1), basal diet supplemented with 0.35 g Se-enriched yeast/head/day (P2), and basal diet supplemented with 0.70 g Se-enriched yeast/head/day (P3). The Se-enriched yeast contained 410 ppm Se and was characterized by nano-scale Se-associated particles. Feed intake, body weight, blood Se concentration, hematological variables, and rumen volatile fatty acid (VFA) profiles were evaluated. Data were analyzed using one-way analysis of variance, followed by Tukey’s multiple comparison test, with statistical significance set at p < 0.05. Results: Particle size analysis confirmed Se-associated particles within the nano-scale range (149.2–191.1 nm). Se-enriched yeast supplementation significantly increased blood Se concentration in a dose-dependent manner (p = 0.001), with mean concentrations increasing from 98.70 ppb in P1 to 156.50 ppb and 206.56 ppb in P2 and P3, respectively. Iso-valerate and total branched-chain iso-acids in rumen fluid also increased significantly in supplemented sheep (p < 0.05), indicating enhanced ruminal nitrogen metabolism and microbial activity. However, total VFA concentration, major VFA proportions, body weight gain, and most hematological variables were not significantly affected (p > 0.05). Feed intake differed only during the first experimental week and remained comparable thereafter. Conclusion: Dietary supplementation with Se-enriched yeast containing nano-scale Se particles effectively improved systemic Se status in a dose-dependent manner and selectively enhanced ruminal branched-chain VFA production without adversely affecting hematological homeostasis or growth performance. Supplementation at 0.35–0.70 g/head/day appears to be a safe and highly bioavailable strategy for improving Se nutrition in female Thin-Tail sheep and may contribute to improved rumen microbial function under tropical production conditions.