## 1 Introduction  
The practice of feeding livestock with by-products from food processing industries dates back to the earliest days of animal domestication. This approach provides two key benefits: reducing livestock dependency on grains that could be used for human consumption and addressing the growing need to reduce the carbon footprint and increase sustainability in the food industry. The latter has become increasingly important due to population growth and the rising volume of crop and food by-products, especially in developed nations [1; 2; 3]. Additionally, the valorisation of agro-industrial by-products is necessary for global sustainability, as their traditional disposal in landfills presents significant environmental, social, and economic challenges. By-products such as peels, seeds, and husks hold high nutritional and functional value, making them valuable resources instead of waste. Biotechnological processes can transform these materials into new food ingredients, contributing to a circular bioeconomy that reduces waste, creates economic opportunities, and enhances human nutrition. Reinforcing their integration into the food supply chain promotes sustainable resource management while minimizing environmental impact [4; 5]. Finally, the use of agricultural by-products, offers a potential way to lower feeding costs while maintaining feed efficiency [6; 7]. Citrus fruit by-products, including sweet oranges, tangerines, lemons, and grapefruits, are well-suited for inclusion in ruminant diets due to the ability of ruminants to ferment high-fibre feed in their rumen. After juice extraction, the remaining residues consist of peel (flavedo and albedo), pulp (juice sac residue), rag (membranes and cores), and seeds [8; 9]. Sweet oranges (Citrus sinensis Osbeck) constitute one of the world's most popular fruit crops that, nowadays, are primarily used fresh or prepared as frozen juice concentrate [10]. In this context, orange peels represent a valuable by-product with significant potential for use in animal feed. As the primary by-product of the orange juice industry, they hold great promise as a secondary feed source. An orange consists of about 43% juice and 57% peel and pulp. For every litte of single-strength juice, 1.33 kg of peels are generated, while concentrated juice production yields more than 2.85 kg of peels per litte. Globally, orange peel production exceeds 8 million tonnes annually, with Europe contributing nearly 600,000 tonnes [3]. Various methods have been employed to improve the nutritional value of citrus by-products for animal feed. For example, fermenting citrus pulp, with or without molasses, has been effective in increasing its nitrogen content and buffering capacity. Similarly, ammoniation treatments, such as using urea or ammonium hydroxide, have significantly boosted the nitrogen content of dried citrus pulp. Other studies have explored supplementing non-protein nitrogen sources, such as urea or faba beans, to improve nitrogen utilisation and digestion. Among these, diets supplemented with faba beans demonstrated superior feeding value and animal performance compared to those supplemented with non-protein nitrogen alone. These techniques collectively enhance the nutrient profile of citrus by-products, making them a valuable resource for livestock nutrition [1]. In relation to orange peels, new methods are being developed to produce an improved feed ingredient by reducing pectin and free sugar content while increasing protein levels, resulting in a more balanced nutrient profile, as detailed in the recent study by [PERSON] et al. [3]. The effect of feed composition on milk yield and composition has been widely studied [11; 12; 13]. Alternative feed can significantly impact the technological and coagulation properties of sheep and goat milk, which are influenced by milk fat and protein composition, as well as somatic cell count. Furthermore, incorporating alternative feeds into the animals' diets can introduce nutraceutical or flavour-enhancing compounds into milk and dairy products [14].