Zinc oxide nanoparticles influence methane production and endoparasitic infection in lambs with minimal changes in key bacterial taxa

Zinc oxide nanoparticles (ZnO-NPs) represent a sustainable feed additive with potential anthelmintic effects and the ability to mitigate enteric methane (CH₄) emissions. This study evaluated the effects of ZnO-NPs as a commercial product (SkySpring Nanomaterials, Inc., Houston, USA) on dry matter digestibility (DMD), body weight, parasitological status, ruminal fermentation, enteric carbon dioxide (CO₂) and CH₄ emissions in lambs infected with the gastrointestinal nematode Haemonchus contortus . Twenty-four lambs were assigned to four groups (n = 6): control fed a basal diet (CON), control supplemented with ZnO-NPs (CON-ZnO-NP), infected fed a basal diet (INF), and infected supplemented with ZnO-NPs (INF-ZnO-NP). Infected groups received approximately 5000 third-stage larvae on day 0, while ZnO-NP supplementation started on day 1 and continued for 39 days. Enteric gas emissions were measured during the final nine days using open-circuit respiratory chambers. DMD was 6% lower in INF compared to CON, whereas supplementation increased DMD by 8% in INF-ZnO-NP relative to INF. Ruminal pH and ammonia nitrogen concentrations were significantly higher in infected groups than in uninfected groups. Faecal egg counts were reduced by 39.9–52.9% in INF-ZnO-NP compared with INF during the final week. ZnO-NP supplementation reduced CO₂ emissions by 12% and CH₄ emissions by 20% in infected lambs. Overall, ZnO-NPs reduced parasitic burden and enteric gas emissions while improving digestibility, demonstrating their potential as a functional feed additive under diverse farming conditions.