• olive pomace
• olive polyphenols
• milk
• sheep

The estimated growing of world population coupled with the increase of food demand, especially of animal products, will lead to an increase in agro-industrial food waste. The food-processing industries generate several by-products and wastes that still contain valuable amounts of nutrients. In particular, in the Mediterranean area the production of olive oil is associated with high amounts of waste and by-products, liquid (wastewater) and solid (olive pomace), rich in nutrients such as fatty acids, pectins and bioactive molecules as polyphenols.
The present thesis focused on the use of different olive oil by-products in dairy ewes feeding as a sustainable way to improve milk fatty acid composition without affecting the overall feeding efficiency of the animals. In the first trial, an olive crude phenolic concentrate (OCPC), obtained by specific treatments of olive wastewater, was added to the diet of dairy ewes. In the second trial, two different kind of stoned olive pomaces (PSO2 from two-phase oil extraction and PSO3 from three-phase oil extraction) containing high amounts of polyphenols were adopted as feed ingredient. In order to amplify the effect of olive polyphenols on rumen biohydrogenation (BH) process of dietary polyunsaturated fatty acids (PUFA), the diets adopted in both trials were supplemented with extruded linseed.
In both trials, dietary treatments did not affect milk yield and gross composition (fat, protein, lactose and urea content). Regarding the milk fatty acid profile, in both trials, the amount of α-linolenic acid (C18:3n3) significantly increased in milk fat, especially at the highest dose of OCPC (first trial) and when ewes fed PSO2 die (second trial). In the second trial, the content of oleic acid in milk fat was significantly higher in milk samples of ewes supplemented with olive pomace, irrespective of the kind of olive pomace considered. Stearic acid content in milk fat, did not significantly vary in both trials, although in rumen liquor the content of stearic acid was lower from ewes supplemented with higher dose of OCPC or with PSO. In the first trial, OCPC linearly decreased the BH of C18:3n3. However, a significant accumulation of C18:3n3 in the rumen liquor was obtained only at the higher dose of OCPC in the concentrate (nearly 1.2 mg/ 100 g DM). Data about overall composition of rumen microbioma supported that the highest dose of OCPC could be effective in perturbing microbes. In the second trial, PSO2 diet resulted more effective than PSO3 in the perturbation of rumen BH of C18:3n3.
In rumen liquor, the pattern of correlation between the composition of dimethyl-acetals (DMA) and the presence of olive polyphenols in the diet was also investigated. DMA derive from fatty aldehydes released from plasmalogen lipids (a subclass of phospholipids), contained in the membranes of ruminal bacteria. The presence of olive polyphenols in the diet of dairy ewes did not lead to changes in total DMA content of rumen liquor. However, in both experiments, a significant difference in the relative proportion of individual DMA (i.e. DMA16:0) was observed, by comparing diet containing olive polyphenols and control diets. According to the discriminant analysis applied to data about DMA composition of rumen liquor, the canonical variables obtained allowed to correctly separate samples of different diets in both trials, suggesting that a few DMA have discriminant power in order to identify specific rumen environment related to feeding conditions.
In conclusion, the use of olive by-products in the diet of dairy ewes did not have any negative effects on milk yield and gross composition and on animal health. Moreover, at the highest dose, the olive polyphenols were able to reduce the rumen biohydrogenation of PUFA, resulting in a higher content of PUFA in milk fat. Moreover, since olive by-products are considered waste with high polluting power, their use in dairy ewe feeding may have beneficial environmental effects. At the same time, olive pomace may replace part of the daily ration, reducing the use of soil and water to produce other ingredients for the concentrate feed, and consequently reducing feeding costs.