In vitro fermentation of olive oil mill wastewaters using sheep rumen liquor as inoculum: Olive mill wastewaters an alternative for ruminant's nutrition

Olive oil mill wastewaters (OMWW) are the main liquid effluents generated by the olive oil production industry. This liquid, considered pollutant and toxic, is characterised by its high content of organic matter including mainly sugars and fats, and phenols compounds, which can be used in ruminants feeding. The purpose of this study is to valorise this agricultural by-product in ruminant feeding by estimation its in vitro degradability in presence of ovine ruminale microbiota comparatively to vetch-oat hay, using in vitro gas production technique coupled with NH3-N and protozoa measurements. Cumulative gas production was recorded at 3, 6, 9, 24, 48, 72 and 96 hours of incubation. The determination of gazes produced (carbon dioxide and methane) was recorded at 6, 9, 24, 48 and 96 hours. However, Ammonia and protozoa number were recorded after 24 hours of incubation. Fermentation profile was fitted to the exponential model y = a + b (1 – e-kt). The OMWW are characterized by their high sugars content (39.91%) and their low content in ash (1.99%) and crude protein (2.70%). This by-product is also characterized by its high concentration in total phenols (7.2%) and tannins (4.5%). However, they contain a very small amount of condensed tannins (0.89%). Comparatively to vetch-oat hay, OMWW produced low amount of gas (-23.6 units). Furthermore, its in vitro fermentation generates low volume of methane (9.83%, V/V), suggesting that the OMWW nature enhanced the efficiency of ruminale microbiota towards microbial biomass production and inhibition of ruminale methanogenesis pathway. This result is reinforced by the reduction of ammonia production (-0.35 units) and protozoa proliferation (-1 unit) comparatively to vetch-oat hay. The anaerobic biodegradation of OMWW reveal their significant use by the rumen microbiota, allowing us to strongly recommend its use as a supplement in feed ruminant. In addition, it allows considering using this residue as a feed additive in diets of ruminants for the reduction of ruminal methanogenesis.