Olive by-products as feed additives : in vitro evaluation on rumen fermentation parameters

The new technologies of olive fruits processing produce every year many tons of vegetable residues which must be disposed or recycled. Indeed, during the last decade, the use of olive by-products derived from the oil extractions has been intensively investigated in small ruminant feeding. However, these by-products have a low nutritional value by the presence of phenolics such as tannins, which may limit nutrient availability. Since numerous studies have highlight the beneficial effects of tannins at low levels of intake on efficiency of rumen microbial protein synthesis, the effects of olive fruits after oil extraction as feed additive on the in vitro rumen fermentation parameters were investigated. The batch culture incubation system was carried out with rumen fluid withdrawn from three rumen-fistulated not-lactating dairy cows. The rumen fluid was added to a mineral salt buffer, mixed in a bottle warmed at 39°C, purged whit anaerobic grade N2/CO2 (80/20, v/v) and standardized at pH 6.8  0.1. One hundred mL of solution were placed in glass bottles supplied whit a substrate for microbial growth (0.8 g/100ml alfalfa hay and 0.2 g/100ml corn meal). In this study, olive by-products were tested in duplicate at three different concentrations. The bottles were purged with anaerobic grade N2/CO2 (80/20, v/v), closed and incubated in a water shaking bath at 39°C for 9h. pH, VFA, ammonia N and Total Bacterial Count (TBC) were determined at 0 and 9h of incubation. Statistical analysis was performed using SAS. We tested olive fruits after oil extraction at low level of inclusion, as feed additive. Although, the NH3-N concentrations was not affected by this rich tannins waste, we evidenced a decreased in the total VFA concentration, significantly at the tested doses (P<0.001), showing a detrimental effect on rumen fermentation parameters. The hypothesis of their use as additives to modulate rumen fermentation was rejected. If they will be used for other purposes, these negative properties must be taken in account.This study was performed under European Community 6th Framework Program: EU Project SAFEWASTES n.513949.