NUTRITION ECOLOGY IN THE LIVESTOCK PRODUCTION SYSTEM - ALGAE POTENTIAL AS SUSTAINABLE FEED INGREDIENTS

The transition towards more sustainable livestock production systems represents one of the major challenges for contemporary animal production. The growing demand for animal-derived food, combined with the need to reduce environmental impact and limit antibiotic use, requires the development of innovative and circular nutritional strategies. In this scenario, algae emerge as a highly promising resource, due to their high productivity, ability to grow in marginal environments without competing with arable land used for human food production, and rich content of bioactive compounds with documented functional properties. This doctoral research aimed to provide a multidimensional assessment of the potential of algae as sustainable and functional feed ingredients, integrating in vitro, ex vivo, and in vivo approaches. In the first phase, several algal species were characterized from a chemical, nutritional, and functional perspective, with particular focus on the presence of bioactive compounds with antioxidant, antimicrobial, and immunomodulatory activities. In vitro studies investigated the stability and bioavailability of algal bioactive compounds during simulated digestion, highlighting the preservation of relevant biological activities. Subsequently, ex vivo studies explored the mechanisms of interaction between algal extracts and immune cells derived from mice and pigs models, demonstrating significant effects in modulating inflammatory responses and regulating macrophage functions under chemical stress conditions. These findings confirmed the potential of algae not only as alternative nutrient sources but also as genuine functional ingredients capable of supporting immune health. In vivo trials, carried out on weaned piglets and neonatal calves, evaluated the impact of algal supplementation under real farming conditions. The results showed positive effects on gut health, with a reduction in the incidence and severity of post-weaning and neonatal diarrhea, which represent a serious health and economic problem for farmers and are conditions in which antibiotics are often extensively used, though frequently with limited effectiveness, as well as improvements in growth parameters and overall health status. Moreover, the use of algae demonstrated potential in reducing antibiotic reliance, thereby promoting more sustainable farming practices. Overall, the outcomes of this project highlight the strategic role of algae in the future of animal nutrition, combining environmental sustainability, food security, animal welfare, and production resilience. This research contributes to strengthening the applicability of the nutritional ecology framework within modern livestock systems, outlining innovative scenarios in which algae can represent a cornerstone of functional and circular diets. However, their practical application is still limited by factors such as the relatively high production costs and the heterogeneity in composition among different algal species and cultivation systems, which may affect consistency, scalability, and economic feasibility.