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Nannochloropsis oculata: a safe protein feed for growing rats and rabbits




Howe, Barbara, author
Archibeque, Shawn, advisor
Engle, Terry, committee member
Sampson, David, committee member
Roman-Muniz, Noa, committee member

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The challenge to replace fossil fuels as the primary source of energy has been a long and complicated task. In recent years, following a historic increase in crude oil (>$100/barrel in 2008) the focus has been shifted to the use of microalgae as a source of oil for biofuel. The utilization of algae over other biofuel sources is advantageous as algae require less water and land than traditional crops. Some microalgae species can produce upwards of 10,000 gallons of oil per acre and when compared to corn which can produce ~18 gallons of ethanol per acre, algae becomes quite interesting. The National Renewable Energy Lab (NREL) in Golden, Colorado has been working diligently on utilizing algae as an energy source. In 2010, NREL explained that replacing all the gasoline in the U.S.A. with corn ethanol would require a corn field 1600 km2, while replacing all the gasoline in the U.S.A. with algae oil would (theoretically) take an area only 176 km2. One of the algae species that is being closely investigated as a source of oil is Nannochloropsis oculata, from the phylum Heterokontophyta. This algal species has oil content greater than 20% (DM basis). A secondary benefit to utilizing algae as a source of biofuel is the high protein (>30% DM basis), mineral rich co-product that is produced after the oil is extracted. In order to further investigate the full potential of algae, a project was designed to determine the usability of the oil-free meal as a protein feed for animals. Within this project, two studies were done, one with 24 young, growing male Sprague-Dawley®™ rats, and one with 24 adolescent male New Zealand White rabbits. Both studies were conducted for 36 days, with 12 animals in each group. In each study, a diet was prepared with 10% Nannochloropsis oculata meal, and one without algal meal. The diets were formulated to be isocaloric and isonitrogenous. The study conducted with rats showed that the intake of DM, Crude Fat, ADF, NDF and ash was decreased in the algal fed rats (P≤0.05). The apparent digestibility of DM, Crude Fat and ADF was also decreased in the algal fed rats (P<0.05), while NDF apparent digestibility was increased (58.28% v. 51.60%) (P>0.05). More N was excreted in the feces (P>0.05) and urine of the algal group (P<0.05). The apparent digestibility of macro minerals was unaffected (P>0.10). Overall the rats fed the algal diet displayed no measureable nutritional deficiencies, and no toxic effects were noted. In comparison, the study conducted with rabbits resulted in the intake of DM, Crude Fat, NDF and ash being similar between the two groups of rabbits (P>0.05), while ADF intake was decreased in the algal fed rabbits (P<0.01). The apparent digestibility of DM, NDF and ash was increased for the animals fed the algal diet (P<0.05), while Crude Fat and ADF apparent digestibility was decreased (P<0.05). No difference was seen in the fecal or urinary excretion of N between the groups (P>0.10), while fecal P excretion was decreased in the algal fed rabbits (P<0.01). The apparent digestibility of Ca, Mg and P was increased in the rabbits fed the algal diet (P<0.05), while K and Na apparent digestibility was unaffected (P>0.10). Similar to the rat study, no toxic or diagnosed metabolic distress was noted. In both studies, the histology of the liver, spleen and kidneys (P>0.10) was not negatively affected by feeding a diet with 10% algal meal. The GE of the diets fed to the rats was similar (4.40 Mcal/kg v. 4.33 Mcal/kg) and the GE of the diets fed to the rabbits was also similar (4.33 Mcal/kg v. 4.37 Mcal/kg). The energy lost in the urine was greater in the algal fed rabbits (4.50 Mcal/kg v. 3.17 Mcal/kg) (P<0.05), while the overall effect on DE was negligible (P>0.10) between the groups. Utilizing the algal meal from Nannochloropsis oculata as a source of protein in growing livestock rations is a possibility when the algal meal is priced the same as DDGs. At the same market price, the cost per kilogram of protein is quite competitive ($0.66/kg v. $0.69/kg). The algal meal could also be considered a potentially competitive source of energy compared to DDGs ($0.15/Mcal NEg v. $0.14/Mcal NEg). In summary, the utilization of oil-free algal meal from Nannochloropsis oculata can be considered a safe and possibly economic protein source for growing animals. In order to fully understand the potential of algal meal in livestock rations, more research needs to be conducted in metabolically different animals.


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algal meal


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