Meta-analysis of in vitro studies on the effects of rumen-protected oils on rumen fermentation products, methane mitigation, microbial populations, and feed digestibility

Abstract

Oil is commonly supplemented in livestock diets to increase energy intake and fat consumption. Protected oils are designed to bypass rumen fermentation, reducing biohydrogenation and providing fatty acids that livestock can efficiently utilize. To date, no meta-analyses have been conducted to assess the effects of protected oil on rumen fermentation in vitro. This study investigated the influence of protected oil on rumen fermentation products, microbial populations, and digestibility through in vitro experiments. Research problem formulation in this meta-analysis study uses the PICO method. Meta-analysis was conducted using the PRISMA method for the selection of database development. Data collection was collected using the data tabulation process, and obtained the range of levels of protected oil used was between 1 % and 35 % of DM. The analysis process in this study used OpenMEE, Medcalc, and Microsoft excel applications. The meta-analysis revealed that protected oil significantly reduced (P < 0.05) methane (CH₄) production, total protozoa, and total bacterial counts. Protected oil was also associated with an increase (P < 0.05) in total volatile fatty acids (TVFA), although meta-regression indicated that this effect was not strongly correlated with dosage. Protected oil did not significantly affect (P > 0.05) pH and NH₃-N levels. It also significantly reduced (P < 0.05) in vitro dry matter digestibility (IVDMD), in vitro organic matter digestibility (IVOMD), and in vitro neutral detergent fiber digestibility (IVNDFD), while significantly increasing (P < 0.05) in vitro crude protein digestibility (IVCPD). Meta-regression revealed weak correlations between protected oil levels and IVDMD (R² = 0.19), CH₄ (R² = 0.02), and TVFA (R² = 0.01), indicating that factors beyond dosage likely influenced these outcomes. In the subgroup meta-analysis of IVDMD, TVFA, and CH₄ across oil types, protection methods, and control groups, varying results were observed. In conclusion, protected oil supplementation may enhance in vitro VFA production and help mitigate CH₄ emissions, although its effects are not clearly dose-dependent. This study highlights the potential of protected oils for nutritional and environmental benefits in ruminant diets, while underscoring the need for further standardized research.