Nutritional Value of Duckweed as Protein Feed for Broiler Chickens—Digestibility of Crude Protein, Amino Acids and Phosphorus

SIMPLE SUMMARY: An increasing global population will lead to an increased demand for protein and a protein deficit. The production of soy, the most common protein source in animal nutrition, is often associated with deforestation and long transport distances. In this context, duckweed can be considered an alternative protein source for animal nutrition. The term duckweed describes a group of small plants floating on the water surface with sizes up to 1.5 cm. Three different duckweed batches consisting of different species were tested as feed for broiler chickens. They showed different impacts on feed intake, animal growth, and digestibility. Digestibility describes the share of nutrients resorbed within the digestive system. Possible compounds that inhibited the digestibility were identified. The results suggest that the nutritional value of duckweed and its influence on animal performance are variable. Hence, a stable duckweed biomass quality adapted to the requirements of broilers is needed. ABSTRACT: Duckweed is gaining attention in animal nutrition and is considered as a potential alternative protein source for broiler chickens. In order to evaluate the nutritional value of duckweed, three individual batches were investigated. They consisted of a mixture of Lemna minuta and Lemna minor (A, 17.5% crude protein), Spirodela polyrhiza (B, 24.6% crude protein) and Lemna obscura (C, 37.0% crude protein). Treatment diets contained 50% batch A, 50% batch B, and 25, 50 and 75% of batch C. All diets were fed to broiler chickens (Ross 308) from an age of 21 to 27 days. Diets with a share of 50 and 75% of batch C led to decreased feed intake (109.3 and 74.9 g/day, respectively) compared to the control. Standardized ileal digestibility of crude protein and amino acids differed significantly between duckweed batches, at values for methionine between 49.9 and 90.4%. For all amino acids, batch A consistently had the lowest and batch C the highest digestibility. Batches had different tannin contents of 2943, 2890 and 303 mg/kg for batches A, B and C, respectively. The apparent ileal digestibility of phosphorus differed significantly between all batches (50.8–78.9%). Duckweed can be used as a protein feed for broiler chickens. However, a defined and stable biomass composition optimized for the requirements of broiler chickens is needed.