In order to produce protein-rich duckweed for human and animal consumption, a stable cultivation process, including an optimal nutrient supply for each species, must be implemented. Modified nutrient media, based on the N-medium for duckweed cultivation, were tested on the relative growth rate (RGR) and crude protein content (CPC) of Lemna minor and Wolffiella hyalina, as well as the decrease of nitrate-N and ammonium-N in the media. Five different nitrate-N to ammonium-N molar ratios were diluted to 10% and 50% of the original N-medium concentration. The media mainly consisted of agricultural fertilizers. A ratio of 75% nitrate-N and 25% ammonium-N, with a dilution of 50%, yielded the best results for both species. Based on the dry weight (DW), L. minor achieved a RGR of 0.23 ± 0.009 d−1 and a CPC of 37.8 ± 0.42%, while W. hyalina’s maximum RGR was 0.22 ± 0.017 d−1, with a CPC of 43.9 ± 0.34%. The relative protein yield per week and m2 was highest at this ratio and dilution, as well as the ammonium-N decrease in the corresponding medium. These results could be implemented in duckweed research and applications if a high protein content or protein yield is the aim.

Duckweeds can be potentially used in human and animal nutrition, biotechnology or wastewater treatment. To cultivate large quantities of a defined product quality, a standardized production process is needed. A small-scale, re-circulating indoor vertical farm (IVF) with artificial lighting and a nutrient control and dosing system was used for this purpose. The influence of different light intensities (50, 100 and 150 µmol m−2 s−1) and spectral distributions (red/blue ratios: 70/30, 50/50 and 30/70%) on relative growth rate (RGR), crude protein content (CPC), relative protein yield (RPY) and chlorophyll a of the duckweed species Lemna minor and Wolffiella hyalina were investigated. Increasing light intensity increased RGR (by 67% and 76%) and RPY (by 50% and 89%) and decreased chlorophyll a (by 27% and 32%) for L. minor and W. hyalina, respectively. The spectral distributions had no significant impact on any investigated parameter. Wolffiella hyalina achieved higher values in all investigated parameters compared to L. minor. This investigation proved the successful cultivation of duckweed in a small-scale, re-circulating IVF with artificial lighting.

The present feeding study was carried out to examine the effects of Fusarium toxin-contaminated diets on performance and slaughtering characteristics and on the transfer of the Fusarium toxins zearalenone (ZEN), deoxynivalenol (DON) and their metabolites into physiological matrices. A total of 61 bulls (483 ± 46 kg) were fed with graded proportions of Fusarium toxin-contaminated feed over a period of 10 weeks. The total mixed rations (TMR) consisted of 47 % grass silage, 20 % press pulp silage, and 33 % concentrate on dry matter (DM) basis. Increasing toxin concentrations were achieved by the exchange of control maize with Fusarium toxin-contaminated maize in the concentrates. Thus, dietary toxin concentrations between 0.08 and 0.69 mg ZEN and 0.36 and 8.31 mg DON per kg DM were covered by the four feeding groups. Based on increasing DM intake with increasing mycotoxin contaminations of the diet, the live weight gain and energy intake differed significantly between the groups. No effects were observed on slaughtering characteristics and organ weights. ZEN, α-zeralenol, β-zeralenol (β-ZEL), zeralanone, α-zearalanol, β-zearalanol, DON, and de-deepoxy-DON (de-DON) were simultaneously determined in urine, plasma, and liquor whereby quantifiable concentrations of ZEN, β-ZEL, DON, and de-DON were found in urine, of DON and de-DON in plasma, and solely of de-DON in liquor. Based on overall results it can be concluded that current EU-guidance values for critical concentrations of DON and ZEN can be regarded as safe levels also for growing bulls. Urine and blood toxin residue levels can be used to assess exposure of bulls.

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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.