The rise in global population has led to explorations of alternative sources of energy and food. Because corn and soybean are staple food crops for humans, their common use as the main source of dietary energy and protein for food-producing animals directly competes with their allocation for human consumption. Alternatively, de-fatted marine microalgal biomass generated from the potential biofuel production may be a viable replacement of corn and soybean meal due to their high levels of protein, relatively well-balanced amino acid profiles, and rich contents of minerals and vitamins, along with unique bioactive compounds. Although the full-fatted (intact) microalgae represent the main source of omega-3 (n-3) polyunsaturated fatty acids including docohexaenoic acid (DHA) and eicosapentaenoic acid (EPA), the de-fatted microalgal biomass may still contain good amounts of these components for enriching DHA/EPA in eggs, meats, and milk. This review is written to highlight the necessity and potential of using the de-fatted microalgal biomass as a new generation of animal feed in helping address the global energy, food, and environmental issues. Nutritional feasibility and limitation of the biomass as the new feed ingredient for simple-stomached species are elaborated. Potential applications of the biomass for generating value-added animal products are also explored.
While feeding food-producing animals with microalgae was investigated several decades ago, this research has been reactivated by the recent exploration of microalgae as the third generation of feedstocks for biofuel production. Because the resultant defatted biomass contains high levels of protein and other nutrients, it may replace a portion of corn and soybean meal in animal diets. Our laboratory has acquired 4 types of full-fat and defatted microalgal biomass from biofuel production research (Cellana, Kailua-Kona, HI) that contain 13.9 to 38.2% crude protein and 1.5 to 9.3% crude fat. This review summarizes the safety and efficacy of supplementing 2 types of the biomass at 7.5 to 15% in the diets of weanling pigs, broiler chicks, and laying hens. Based on their responses of growth performance, egg production and quality, plasma and tissue biochemical indicators, and/or fecal chemical composition, all 3 types of animals were able to tolerate the microalgal biomass incorporation into their diets at 7.5% (on as-fed basis). Holistic analysis is also provided to explore the global potential of using the defatted microalgal biomass as a new feed ingredient in offsetting the biofuel production cost, reducing the dependence on staple crops such as corn and soybeans, decreasing greenhouse gas production of animal agriculture, and developing health value-added animal products.
Two experiments were conducted to determine the nutritional and metabolic impacts of defatted green microalgal (Desmodesmus sp.) biomass (DGM), protease, and nonstarch polysaccharide degrading enzymes (NSPase) in diets for weanling pigs and broiler chicks. Pigs fed 10% DGM for 28 days had growth performance comparable to the controls, but 23-39% lower (P < 0.05) plasma urea nitrogen concentrations. Broilers fed 15% DGM had 16% greater (P < 0.05) gain/feed efficiency than the control (0.78 vs 0.67) over the 42 day period. Supplemental protease (0.06%) decreased (P < 0.03) plasma uric acid concentrations in pigs on day 14, whereas supplemental NSPase showed negative effects in broilers. Dietary inclusions of DGM or enzymes altered (P < 0.05-0.1) hepatic and muscle protein levels of key regulators in the mTOR pathway. In conclusion, weanling pigs and broiler chicks tolerated dietary inclusions of 10 and 15% DGM, respectively, and adding protease might help digestion.
Murine regenerating islet-derived 3β (Reg3β) represents a homologue of human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein and enhanced mouse susceptibility to the acetaminophen (APAP)-induced hepatotoxicity. Our objective was to determine if and how knockout of Reg3β (KO) affected the APAP (300 mg/kg, ip)-mediated protein nitration in mouse liver. The APAP injection produced greater levels of hepatic protein nitration in the KO than the wild-type mice. Their elevated protein nitration was alleviated by a prior injection of recombinant mouse Reg3β protein, and was associated with an accelerated depletion of the peroxynitrite (ONOO−) scavenger glutathione by an up-regulated hepatic glutathione peroxidase-1 (GPX1) activity. The enhanced GPX1 production in the KO mice was mediated by an 85% activity rise (p < 0.05) of selenocysteine lyase (Scly), a key enzyme to mobilize Se for selenoprotein biosynthesis. Knockout of Reg3β enhanced AP-1 protein and its binding activity to the gene promoter of Scly, up-regulating its gene transcription. However, knockout of Reg3β did not affect gene expression of other key factors for selenoprotein biosynthesis. In conclusion, our finding unveiled a new metabolic role of Reg3β in protein nitration and a new biosynthesis control of GPX1 by a completely “unrelated” regenerating protein Reg3β via transcriptional activation of Scly in coping with hepatic protein nitration. Linking selenoproteins to tissue regeneration will have profound implications in understanding mechanism for Se functions and physiological coordination of tissue regeneration with intracellular redox control.
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