Simple SummaryA valid strategy for increasing the sustainability of food production systems is the use of industrial by-products in livestock diets, which allows food processing industries to profitably mitigate the costs generated by waste disposal. The agro-industrial olive sector produces large quantities of olive by-products, considered extremely toxic, with a highly adverse environmental impact. Thus, to valorise a by-product of the oil industry, the aim of this study was to evaluate the inclusion of different levels of ensiled olive cake in the fattening diets of Apulo-Calabrese pigs as a strategy to partially replace the conventional cereal-based diet and improve animal performance and meat fatty acid profile. The results showed that the inclusion of ensiled olive cake in the diet improves the fatty acid composition of meat, improving health by increasing the oleic acid level (C8:1n-9,p< 0.001), decreasing the linoleic acid level (C18:2n-6,p< 0.001) and altering the polyunsaturated/saturated ratio (P/S,p< 0.001). In conclusion, ensiled olive cake is suitable for dietary supplementation at up to 40% for fattening pigs and could represent a valid strategy for naturally improving the nutritional value of meat and valorising a by-product of the olive industry.AbstractThe aim of this study was to evaluate the inclusion of different amounts of ensiled olive cake, a major pollutant from olive oil production, in the fattening diets of 30 Apulo-Calabrese pigs as a strategy to partially substitute the traditional cereal-based diet and improve animal performance and meat fatty acid composition. The animals, during a fattening period of 120 days, were fed with three dietary treatments containing increasing levels of ensiled olive cake: 0% (C), 20% (OC20) and 40% (OC40) on dry matter. No effect of the dietary treatment was found on the animal performance and proximate meat analysis results. The inclusion of ensiled olive cake in the diet led to differences in the fatty acid (FA) profile of intramuscular fat, with a higher proportion of monounsaturated fatty acid (MUFA;p< 0.001) and oleic acid (C8:1n-9,p< 0.001) and a lower concentration of polyunsaturated (PUFA,p< 0.001) and linoleic acid (C18:2n-6,p< 0.001). In conclusion, the supplementation of ensiled olive cake at up to 40% in the diets of fattening pigs could represent a useful strategy in Mediterranean areas to naturally improve the nutritional value of meat and valorise a by-product of the olive industry, reducing its environmental impact and promoting the exploitation of this local feed resource according to the principles of the circular economy.