## 5 Animal Nutrition  
The shortage of traditional feed ingredients is becoming an increasingly significant problem for developing countries worldwide. To bridge the gap between feed supply and demand, non-traditional feed sources are coming into focus. Due to their high yield, economic benefits, nutritional value, and positive public perception, duckweed species offer a promising source of protein [12; 103; 104; 105]. _Spirodela polyrhiza_ is of interest as a feed material/component for fish, poultry, and pigs because its lower fibre content makes it easily digestible [44]. Duckweed can be utilised for nitrogen and phosphorus recovery from animal slurry, while also producing high-quality protein feed [106]. A study by [PERSON] et al. (2023) [107] demonstrated that blanched and sun-dried duckweed meals can replace soybean meal in the diet of _Oreochromis niloticus_ without negatively affecting protein digestibility or carcass protein levels, with protein digestibility ranging from 75.9% to 79.9% and energy digestibility from 58.4% to 64.5% [108]. Similarly, research with sheep showed that soybean meal can be partially replaced (up to 50%) with duckweed, maintaining economical production while reducing forage costs [109]. While the nutritional value of duckweed-containing feeds varies, stabilisation and optimisation could make duckweed a viable protein source for broiler chickens [110], although [PERSON] and [PERSON] (2013) [111] caution against exceeding 6% inclusion without further studies. In dog diets, duckweed inclusion reduces dry matter, gross energy, and crude protein digestibility, but the addition of exogenous phytase can improve crude protein digestibility at 30% inclusion levels while also enhancing stool consistency [112]. These findings highlight duckweed's potential as a cost-effective and versatile feed ingredient across various species, provided its composition is carefully managed. The variability in digestibility underscores the importance of selecting the right duckweed species and optimising its composition through cultivation and processing for different animal diets. Despite these challenges, duckweed's rapid growth, high protein content, and sustainable production make it a promising feed ingredient, particularly for supporting protein requirements in livestock and aquaculture systems. Duckweed is a new type of animal feed ingredient, and the proportion of duckweed replacing traditional feed may affect the digestibility and absorption of nutrients by animals. For example, in a study on tilapia, when the substitution rate of duckweed was 20% and the feeding amount was 3%, the weight gain and specific growth rate of the fish increased significantly. Compared to regular feed, the weight gain increased by 57.5% and the specific growth rate increased by 30.3%. However, when the substitution rate exceeded 25%, these indicators began to decrease [113]. Factors Influencing the Protein Digestibility and Bioaccessibility of Bioactive Compounds in Duckweed  
Duckweed has garnered significant attention for its potential as a source of bioactive compounds with various health benefits [114]. However, the access of these compounds can pose challenges. Bioavailability and bioaccessibility are two closely related concepts that are often used in the assessment of the absorption and utilisation of nutrients, drugs, and other compounds within the human body. Bioavailability refers to the proportion of a substance that is able to enter the systemic circulation and reach the site of action, whereas bioaccessibility describes the amount of a substance that is available for absorption by the body. _In vitro_ and _in vivo_ digestion models can be used to provide answers as to whether these degraded components retain their biological activity during their passage through the gastrointestinal tract, and if so, how this bioactive form is utilised: is it absorbed, or can it be utilised in an active form? [115]. One key factor that affects the bioavailability of bioactive compounds in duckweed is the intricate food matrix.