A recent study published in Animals evaluated onion peel, a by-product of onion processing, as a natural feed additive for dairy cows. Results suggest it may improve nutrient degradability and reduce methane emissions, particularly in high-forage (HF) diets.
Study Design and Diets
Researchers examined the effects of including onion peel at 2.5% (OP2.5), 5% (OP5), 7.5% (OP7.5), and 10% (OP10) in two diets: a high-concentrate total mixed ration (HC) and a high-forage corn silage diet (HF). They measured gas production, including methane (CH₄), carbon dioxide (CO₂), ammonia (NH₃), and hydrogen sulfide (H₂S), along with nutrient degradability.
Key Findings
The HC diet produced more total gas but lower CH₄, CO₂, NH₃, and H₂S than the HF diet. Adding onion peel to the HF diet increased gas emissions at all levels, though the OP5 treatment showed the lowest CH₄ production in the HF diet. In contrast, the OP7.5 treatment in the HC diet resulted in the highest gas and CH₄ production.
Degradable dry matter was highest with OP7.5 in the HC diet, while the lowest was seen with OP2.5. Onion peel also linearly increased degradable acid detergent fibre in both diets. The OP5 treatment reduced total volatile fatty acids (VFA) and acetate levels in the HC diet, with OP5–OP10 showing lower VFA concentrations overall.
Conclusion and Recommendations
The study concludes that onion peel is more effective in HF diets, where 5% inclusion appears optimal for reducing ruminal methane and enhancing nutrient degradability. While onion peel had mixed effects on HC diets, its benefits in HF diets support its use as a natural strategy to improve fermentation efficiency and reduce environmental impact.
Call for Further Research
Though promising, the exact optimal inclusion level remains unclear. Further in vitro and in vivo research is needed to confirm long-term effects, understand mechanisms of action, and assess practical applications in real-world dairy farming.
