Abstract
Simple Summary
The rising costs and limited availability of traditional animal feeds have driven the search for alternative options. Olive leaves, an abundant agricultural byproduct, were studied after being treated with sodium hydroxide, urea, or polyethylene glycol to enhance their nutritional value and assess their environmental impact. Sodium hydroxide treatment effectively reduced fiber content and methane emissions, making it a sustainable choice for reducing greenhouse gases. Urea treatment improved protein content, energy availability, and gas production, offering nutritional benefits but with increased methane and carbon dioxide emissions. Polyethylene glycol proved the most effective for breaking down fiber and boosting microbial protein production, optimizing nutrient utilization. These findings demonstrate the potential of treated olive leaves as a sustainable livestock feed that supports agricultural recycling while mitigating environmental concerns.
Abstract
The purpose of this study was to investigate the effects of treating olive (Olea europaea) leaves with sodium hydroxide (NaOH) or urea (both at 4% for 40 d) or supplementing with polyethylene glycol (PEG) at 100 mg/g DM on their nutrient composition, gas production, methane (CH4) and carbon dioxide (CO2) productions, and fermentation profile. The results showed that NaOH-treated leaves had the lowest organic matter and fiber fractions, while urea-treated olive leaves exhibited the highest crude protein content (p < 0.001). Asymptotic gas production was significantly higher (p = 0.015) in urea-treated olive leaves compared to NaOH-treated leaves. Methane production was highest (p < 0.05) in urea-treated leaves and lowest in NaOH-treated leaves. During incubation, urea-treated leaves produced the highest CO2 per gram of degradable neutral detergent fiber (p = 0.015). Degradability parameters indicated that PEG supplementation led to the highest DM, neutral detergent fiber, and acid detergent fiber degradability (p < 0.05) compared to the untreated and NaOH-treated leaves. Urea-treated leaves produced the highest acetic acid (p = 0.016) compared to PEG-supplemented and NaOH-treated leaves, showing no significant difference from the control. Butyric acid levels were higher (p = 0.011) in NaOH-treated and PEG-supplemented leaves than in the control and urea-treated leaves. Metabolizable energy (ME) was significantly higher (p = 0.013) in urea-treated leaves than in untreated and NaOH-treated leaves, with the latter producing the lowest ME. PEG supplementation resulted in significantly higher microbial protein (MCP) production (p = 0.023) compared to NaOH-treated and untreated leaves, while the MCP level in the urea-treated group was comparable to all other treatments. In conclusion, PEG supplementation was the most effective treatment for olive leaves’ degradability and MCP, with urea treatment being the second option. From an environmental perspective, NaOH treatment was the most effective for reducing CH4 and CO2 productions during the fermentation of olive leaves.