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Duckweeds are fast-growing and nutritious plants, which are gaining increased attention in different fields of application. Especially for animal nutrition, alternative protein sources are needed to substitute soybean meal. The current bottleneck is the standardized production of biomass, which yields stable quantities of a defined product quality. To solve this problem, an indoor vertical farm (IVF) for duckweed biomass production was developed. It consists of nine vertically stacked basins with a total production area of 25.5 m2. The nutrient solution, a modified N-medium, re-circulated within the IVF with a maximum flow rate of 10 L min−1. Nutrients were automatically added based on electrical conductivity. In contrast, ammonium was continuously supplied. A water temperature of 23 °C and a light intensity of 105 μmol m−2 s−1 with a photoperiod of 12:12 h were applied. During a 40-day production phase, a total of 35.6 kg of fresh duckweed biomass (equals 2.1 kg of dried product) was harvested from the IVF. On average, 0.9 kg day−1 of fresh biomass was produced. The dried product contained 32% crude protein (CP) and high levels of proteinogenic amino acids (e.g. lysine: 5.42 g, threonine: 3.85 g and leucine: 7.59 g/100 g CP). Biomass of this quality could be used as a protein feed alternative to soybean meal. The described IVF represents a modular model system for duckweed biomass production in a controlled environment and further innovations and upscaling processes.
In a protein reduction feeding trial (Study 1) on a commercial broiler farm in northern Germany, it was attempted to be shown that research results from station tests on protein reduction can be transferred to agricultural practice. In a second study, the limits of the N reduction were tested in a research facility. In Study 1, commercial standard feeds were fed to the control group (variant 1:210,000 animals; n = 5 barns). In the test group (variant 2:210,000 animals; n = 5 barns), the weighted mean crude protein (CP) content was moderately reduced by 0.3%. The nitrogen reduction in the feed did not affect performance (feed intake (FA), daily gain (DG), feed conversion (FCR)), but nitrogen conversion rate increased from approx. 61% to approx. 63%. The solid litter weight was reduced by 12% and nitrogen excretion by 9% (p < 0.05). Significantly healthier footpads were due to lower water intake (−4%; p < 0.05) and a numerically drier bedding. In Study 2, responses of treatments (1250 broiler per variant; n = 5) showed that sharper N-lowering (−1.5% CP; weighted average) did not impair performance either, but N-conversion improved and N-excretions decreased significantly. Converted to a protein reduction of one percentage point, the N excretions were able to be reduced by 22% in Study 1 and 18% in Study 2. Feeding trials in the commercial sector, such as the present Study 1, should convince feed mills and farmers to allow the latest scientific results to be used directly and comprehensively in commercial ration design.