{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T21:28:59Z","timestamp":1791581339867,"version":"4.3.4"},"reference-count":57,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2025,2,28]],"date-time":"2025-02-28T00:00:00Z","timestamp":1740700800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Animals"],"abstract":"<jats:p>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 &lt; 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 &lt; 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 &lt; 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\u2019 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.<\/jats:p>","DOI":"10.3390\/ani15050705","type":"journal-article","created":{"date-parts":[[2025,2,28]],"date-time":"2025-02-28T10:12:33Z","timestamp":1740737553000},"page":"705","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Optimizing Olive (Olea europaea) Leaves as a Sustainable Ruminant Feed: Effects of Chemical Treatments on Nutritional Value and Greenhouse Gas Emissions"],"prefix":"10.3390","volume":"15","author":[{"given":"Hajer","family":"Ammar","sequence":"first","affiliation":[{"name":"Laboratoire SPADD, High Agriculture School of Mograne, 1121 Mograne, University of Carthage Tunisia, Zaghouan 1121, Tunisia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0472-4770","authenticated-orcid":false,"given":"Ahmed Eid","family":"Kholif","sequence":"additional","affiliation":[{"name":"Department of Animal Sciences, North Carolina Agricultural and Technical State University, Greensboro, NC 27411, USA"},{"name":"Dairy Science Department, National Research Centre, 33 Bohouth St. Dokki, Giza 12622, Egypt"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6485-2489","authenticated-orcid":false,"given":"Moy\u00f2sore J.","family":"Adegbeye","sequence":"additional","affiliation":[{"name":"Research Centre for Animal Husbandry, National Research and Innovation Agency, Cibinong Science Centre, Jl. Raya Jakarta-Bogor, Cibinong, Bogor 16915, Indonesia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6630-9292","authenticated-orcid":false,"given":"Uchenna Y.","family":"Anele","sequence":"additional","affiliation":[{"name":"Department of Animal Sciences, North Carolina Agricultural and Technical State University, Greensboro, NC 27411, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4909-4426","authenticated-orcid":false,"given":"Tarek A.","family":"Morsy","sequence":"additional","affiliation":[{"name":"Dairy Science Department, National Research Centre, 33 Bohouth St. Dokki, Giza 12622, Egypt"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mohamed M.","family":"Abdo","sequence":"additional","affiliation":[{"name":"Dairy Science Department, National Research Centre, 33 Bohouth St. Dokki, Giza 12622, Egypt"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7404-4263","authenticated-orcid":false,"given":"Gouda A.","family":"Gouda","sequence":"additional","affiliation":[{"name":"Dairy Science Department, National Research Centre, 33 Bohouth St. Dokki, Giza 12622, Egypt"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7620-2026","authenticated-orcid":false,"given":"Hossam H.","family":"Azzaz","sequence":"additional","affiliation":[{"name":"Dairy Science Department, National Research Centre, 33 Bohouth St. Dokki, Giza 12622, Egypt"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Soha","family":"Ghzayel","sequence":"additional","affiliation":[{"name":"High Agriculture School Le Kef 7119, University of Jendouba, Jendouba 8189, Tunisia"},{"name":"Laboratoire des Substances Naturelles, National Institute of Research and Physico-Chemical Analysis (INRAP), Sidi Thabet, Ariana 2020, Tunisia"},{"name":"Palestine National Agriculture Research Center Biotechnology Department, Higher Agriculture School of Le Kef, University of Jendouba, National Research Center, Beit Qad Agricultural Station, Jenin 206, Palestine"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Halimeh","family":"Zoabi","sequence":"additional","affiliation":[{"name":"High Agriculture School Le Kef 7119, University of Jendouba, Jendouba 8189, Tunisia"},{"name":"Laboratoire des Substances Naturelles, National Institute of Research and Physico-Chemical Analysis (INRAP), Sidi Thabet, Ariana 2020, Tunisia"},{"name":"Biotechnology Department, Ministry of Agriculture, National Agriculture Research Center, Jenin 227, Palestine"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bassam","family":"Abu Aziz","sequence":"additional","affiliation":[{"name":"High Agriculture School Le Kef 7119, University of Jendouba, Jendouba 8189, Tunisia"},{"name":"Laboratoire des Substances Naturelles, National Institute of Research and Physico-Chemical Analysis (INRAP), Sidi Thabet, Ariana 2020, Tunisia"},{"name":"Epidemiology Department, Ministry of Agriculture, Jenin 227, Palestine"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6267-683X","authenticated-orcid":false,"given":"Secundino","family":"L\u00f3pez","sequence":"additional","affiliation":[{"name":"Instituto de Ganader\u00eda de Monta\u00f1a (CSIC-Universidad de Le\u00f3n), Finca Marzanas, 24346 Grulleros, Spain"},{"name":"Departamento de Producci\u00f3n Animal, Universidad de Le\u00f3n, 24007 Le\u00f3n, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mario","family":"de Haro-Mart\u00ed","sequence":"additional","affiliation":[{"name":"Gooding County Extension, University of Idaho, 203 Lucy Lane, Gooding, ID 83330, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mireille","family":"Chahine","sequence":"additional","affiliation":[{"name":"Department of Animal, Veterinary and Food Sciences, University of Idaho, 315 Falls Ave, Twin Falls, ID 83301, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,2,28]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1246","DOI":"10.1080\/1828051X.2022.2105265","article-title":"Effect of Olive Leaf (Olea europaea L.) 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