This review explores the potential of Chlorella vulgaris (CLV) as an alternative supplement in animal feed. CLV is rich in essential nutrients including fatty acids, amino acids, vitamins, and minerals, as well as bioactive compounds such as antioxidants, which contribute to its health-promoting properties. The nutritional composition of CLV can vary depending on factors such as cultivation methods, nutrient availability, light intensity, temperature, water pH, strain, and processing techniques. The rigid cell wall of the microalga limits nutrient accessibility, particularly in monogastric animals. However, processing techniques such as enzymatic treatments can disrupt the cell wall, enhancing nutrient bioavailability and improving its utility as a feed ingredient. Research across livestock species has demonstrated the positive effects of CLV supplementation. For instance, CLV has improved milk production and composition in ruminants, modulated rumen microbiota, enhanced lamb growth, and elevated blood immunoglobulin levels. Moreover, the impact of CLV on ruminal fermentation is dose-dependent, with higher inclusion rates exhibiting more pronounced effects, and it may also play a role in mitigating methane emissions. In poultry, CLV supplementation leads to better growth, feed conversion ratios, immune responses, and meat and egg quality. Similarly, studies on pigs suggest that CLV can benefit immune response and fatty acid profiles, while in rabbits, CLV has been found to reduce oxidative stress and improve immune responses. Additionally, CLV has shown promise in aquaculture, improving feed utilization, immunity, and disease resistance in various fish species. While CLV shows considerable potential, the variability in animal responses and the need for optimized inclusion levels necessitate further species-specific research to elucidate the long-term implications of its inclusion in animal diets.

Intensive dairy farming, particularly enteric fermentation and manure management, is a major contributor to negative impacts on the local and global environment. A wide range of abatement measures has been proposed to reduce livestock-related emissions, yet the individual and combined effects of these innovations are often unknown. In this study, we performed an attributional life cycle assessment of three innovative measures modeled in two synthetic German dairy farm systems: Feeding of the seaweed Asparagopsis, installing an in-house cow toilet system, and performing on-field slurry acidification. These measures were modeled both individually and in combination to account for single and cumulative effects and compared to a reference scenario under current practices. Our results showed that feeding high levels of Asparagopsis and the combination of all three measures were most effective at reducing global warming potential (20–30 %), while only the latter mitigated eutrophication (6–9%) and acidification potential (14–17 %). The cow toilet required additional adapted manure management (separated storage and injection of urine) to effectively reduce eutrophication (8–10 %) and acidification potential (19–23 %) and to decrease global warming potential (3–4%) and abiotic depletion (4–5%). Slurry acidification slightly affected all considered environmental impact categories. All three measures involved trade-offs, either between LCA impact categories (global warming potential vs. abiotic depletion), the location of impacts (off- vs. on-farm), or the emission reduction in individual gases (ammonia vs. nitrous oxide). Measure combinations could compensate for the observed trade-offs. Our study highlights the potential of novel abatement measures but also shows the interdependencies of measures in different stages. This calls for a revisiting of current priorities in funding and legislation, which often focus on single objectives and measures (e.g. ammonia reduction) toward the preferential use of measures that are effective without driving trade-offs or improving resource efficiency.

Stricter nutrient surplus and lower emission targets are placing adaptation pressure on livestock farms in European countries, while the public debate on how farms should react upon this pressure is controversial. In this paper, we performed an integrative literature review on different farm adaptation options, including (i) structural adaptation, (ii) technological adaptation, (iii) manure redistribution, and (iv) farm system conversion. Our analysis showed that stricter environmental legislation, together with complementary supply- and demand-related drivers, induced various farm responses. These ranged from easy to implement solutions (e.g. moderate livestock destocking to the legal levels combined with the adoption of emission abatement technologies) to novel niche concepts (e.g. animal husbandry without slaughtering). Possible reactions of farmers differed in their complexity and feasibility across different farm types and involved different trade-offs between environmental and socioeconomic interests. Future livestock production is expected to be diverse with different coexisting models that combine features of different adaptation options. The private and public sustainability of these models depends on their ability to simultaneously address multiple emerging challenges (e.g. emission reduction, animal welfare, biosecurity, and circularity). Current technological solutions often focus on a single objective (e.g. emission reduction). Integrated and multifunctional solutions (e.g. low-emission animal welfare barns compatible with biosecurity measures) are not yet sufficiently adopted, which calls for a rethinking and shifting in priorities in legislation and funding schemes.

Intensive livestock farming in the European Union requires extensive feed imports, such as soybean meal (SBM), which is associated with negative environmental impacts. Black soldier fly larvae (BSFL) have been identified as an option to substitute SBM in pig diets and as bioconverters of pig manure, contributing to closing the loop between manure production and the provision of protein-rich pig feed (pig–insect–pig nutrient loop). This option is not legally permitted in the European Union (EU) but is practised on other continents and could contribute to closing the EU protein gap. However, its influence on the environmental impact of pig production, compared with permitted substrates such as pig feed used as feed for BSFL, is still unclear. In this study, we conducted an attributional life cycle assessment (LCA) to compare the environmental impacts of pig production using pig feed-fed and pig manure-fed BSFL meals at different SBM substitution levels. Our LCA revealed that pig manure-fed BSFL performed better in 4 out of the 7 selected impact categories, causing a slightly lower impact on GWP than pig feed-fed BSFL. Compared with using SBM, pig feed-fed or pig manure-fed BSFL meal could not improve the environmental impact of pig production, except for land use using pig manure. Considering manure as a burden-free resource or frass as an avoided process could not sufficiently improve the environmental performance of BSFL meal to make it more competitive with SBM in this study. BSFL meal production is a promising approach that utilises nonedible residual side streams, thereby contributing to reduced land use pressure and mitigating feed–food competition in the EU. Further research should focus on improving the BSFL conversion efficiency and protein yield to increase the substitution rate with SBM, which we identified as the key factors for improving the environmental impact of BSFL meal in pigs.