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.

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.

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.

The aim of the study was to examine different pH parameters, such as variations throughout the day, depending on differing concentrate feed proportions. Moreover, special attention was payed to individual variation in microbial efficiencies (microbial crude protein/fermented organic matter) and their relation to ruminal pH, nutrient flows and digestibilities. For this, cows were grouped according to microbial efficiency (more, n = 5, vs. less efficient cows, n = 4). After calving, thirteen ruminally cannulated pluriparous cows, including nine duodenally cannulated animals, were divided into groups offered rations with a lower (35% on dry matter basis, n = 7) or a higher (60% on dry matter basis, n = 6) concentrate feed proportion. Ruminal pH parameters were assessed continuously by using intraruminal probes. Nutrient flows, nutrient digestibility and microbial efficiency were determined for duodenally cannulated cows. For most ruminal pH parameters it seemed that individual variability was higher than the treatment effect. However, a positive relationship between actual concentrate intake and diurnal pH fluctuations was found. Besides, the effect of individually different microbial efficiencies was assessed. Again, there were no group differences for pH parameters. However, nutrient flows were significantly higher in more efficient cows, whereas digestibilities were lower in in more efficient cows.

To investigate the influence of two dietary sources of vitamin D on the vitamin D status, bone metabolism, welfare and birth progress of gestating and lactating sows, forty-nine multiparous sows were randomly assigned to one of two diets: “CON” (n = 25; 50 μg vitamin D₃/kg feed) and “HYD” (n = 24; 50 μg 25-hydroxycholecalciferol/kg feed). The basal diets were protein- and phosphorus-reduced. The trial started on day 3 ante insemination of the sows and ended with weaning of the piglets on day 28 postpartum. Dietary supplementation of 25-hydroxycholecalciferol resulted in improved maternal vitamin D status (p < 0.001), fewer gait changes (p < 0.01) and longer standing time after feeding (day 5 ante partum; p < 0.05) compared to vitamin D₃. However, the bone markers CrossLaps and osteocalcin were not affected. Overall, the present results suggest that sows fed 25-hydroxycholecalciferol instead of vitamin D₃ showed improved locomotion and stance strength. However, this outcome is probably not related to altered bone metabolism. The underlying mechanisms must be investigated in further studies.

Complete diets for laying hens are usually offered in meal form. This form initially promotes the laying hens’ natural feed intake behavior and allows them to satisfy their pecking behavior. At the same time, it can also cause difficulties, because it consists of different particles and is not a homogeneous unit. A homogeneous mixture is essential to ensure that each laying hen in the flock can meet its nutritional needs. If feed exhibits a wide particle size distribution, this can promote feed segregation during transport and selective feed intake behavior of laying hens. These two processes sometimes lead to significant differences between the composition of the feed produced and the composition of the feed that is finally ingested by the laying hens. Multi-stage sampling can be used to investigate progressing differences in feed composition. In this study, samples of different complete diets for laying hens (n = 76) were collected from ten organic farms in Germany to examine their particle size distributions (dry sieve analysis). Samples were taken at four different locations (V1 = loading, V2 = silo, V3 = at the beginning of the feed chain, V4 = at the end of the feed chain) in each farm. There was a tendency for V1 and V2 to be characterized by high proportions of particles between 1400 and 3150 µm (V1 = 61.2%, V2 = 43.5%). V3 and V4 consisted mainly of particles of size 500–800 µm and 200–400 µm, respectively. The lowest proportions across all variants were in the range above 3150 µm (V1 = 2.20%, V2 = 1.30%, V3 = 1.00%, V4 = 0.400%) and between 400 and 500 µm (V1 = 2.50%, V2 = 4.50%, V3 = 5.70%, V4 = 6.60%). The mean value comparison of the proportions of sieve mesh sizes from 200 to 1000 µm resulted in: V1 < V2 < V3 < V4; and of sieve mesh sizes between 1400 and 2000 µm in: V1 > V2 > V3 > V4. This observation can be explained by segregation of the feed during transport and a selective feeding behavior of the laying hens. However, trends were discontinuous and varied between the farms. Deviations from the guideline values were found in particular for particle sizes in the range of 1000 to 1400 µm.