Schizochytrium limacinum SR-21 as a source of docosahexaenoic acid: optimal growth and use as a dietary supplement for laying hens

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Abstract
Culture conditions for the marine fungus Schizochytrium limacinum SR-21 (SR-21) to produce microbial docosahexaenoic acid (DHA) were evaluated, and the practicality of using this fungus product as a dietary supplement for laying Leghorn hens was investigated. The data showed that the cultured fungus produced high biomass and DHA. It generated 584 mg DHA/L of culture at the end of a 6-day culture. The fungus grew better at 25ºC than at 20ºC or 30ºC. With an increase in glucose concentration from 1% to 5% in the culture medium, biomass and DHA production were enhanced. A 6% glucose treatment reduced the biomass production compared with 5% glucose. A bioreactor was used to mass-produce SR-21. The biomass was increased from 1.12 g/L at Day 0 to 12 g/L at Day 4. We established optimal culture conditions of 5% glucose, 2% sea salt, and 1% yeast extract for SR-21. Three concentrations of dried fungal meal (0, 1, or 3% in the diet) were fed to birds over a 3-week period. There were no negative effects of 1 and 3% dietary SR-21 on egg production, egg weight, and egg yolk weight. The DHA content of yolk was increased by the dietary supplementation with the fungal meal both in the 1 and 3% treatments. Dietary fungal meal treatments increased the DHA concentrations of liver and plasma. However, dietary DHA enrichment had no effect on the expression of hepatic lipogenic genes in laying hens.

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