Czech J. Anim. Sci., 2026, 71(9):406-416 | DOI: 10.17221/48/2026-CJAS

Effects of fresh olive cake inclusion in ensiledtotal mixed rations on in vitro rumen fermentation kinetics and methane productionOriginal Paper

Murat Er ORCID...¹, Kanber Kara ORCID...², Eren Kuter ORCID...³, Hulusi Akçay ORCID...⁴, Sena Yılmaz Öztaş ORCID...²

¹ Department of Veterinary Medicine, Karşıyaka Vocational School, Izmir Bakircay University, Izmir, Türkiye

² Department of Animal Nutrition and Nutritional Diseases, Faculty of Veterinary Medicine, Erciyes University, Kayseri, Türkiye

³ Department of Animal Nutrition and Nutritional Diseases, Faculty of Veterinary Medicine, Burdur Mehmet Akif Ersoy University, Burdur, Türkiye

⁴ Department of Animal Science, Faculty of Agriculture, Aydin Adnan Menderes University, Aydin, Türkiye

This study evaluated the effects of replacing maize silage with increasing levels of olive cake (OC) in ensiled total mixed rations (ETMR) on microbial quality, in vitro rumen fermentation kinetics, methane production, and estimated energy parameters. Three experimental diets were formulated to contain 0% (Control), 10% (OC10), and 20% (OC20) olive cake on a dry matter basis and were ensiled for 60 days. On day 60, ETMRs were opened, microbial composition was assessed, and in vitro ruminal fermentation was conducted for 24 h using the gas production technique. No significant differences were observed among treatments in bacterial counts (P > 0.05), and coliforms and enterobacteria were below detectable limits in all groups. Increasing OC inclusion showed a trend toward reducing butyric acid concentration (P = 0.055) and significantly reduced propionic acid concentration (P < 0.05), whereas acetic acid concentration remained unaffected. Total short-chain fatty acids (TSCFA, mmol/l) concentration tended to decrease with increasing OC inclusion (P = 0.060). Furthermore, OC inclusion significantly reduced total gas production, metabolisable energy (ME), organic matter digestibility (OMD), and net energy for lactation (NE_L) (P < 0.001). Methane production (ml/0.2 g DM) decreased numerically by approximately 14%, although this reduction was not statistically significant. Methane as a proportion of total gas was also unaffected. Ammonia-N concentrations did not differ among treatments. The reduction in methane output appeared to be associated with a general suppression of fermentative activity rather than a shift toward propionate-driven hydrogen utilisation. The lipid-rich and phenolic composition of OC may have contributed to reduced microbial fermentation intensity and hydrogen availability. Although higher inclusion levels negatively affected digestibility and energy values, moderate inclusion may offer a balance between environmental benefits and nutritional efficiency.

Keywords: agro-industrial by-products; enteric methane mitigation; gas production technique; silage microbiology; ruminal fermentation profile

Received: April 1, 2026; Accepted: August 10, 2026; Published: September 29, 2026  Show citation