Nucleotides in Brewer's Yeast: What They Do in Feed and How Much Whole Yeast Supplies

In short: Brewer's yeast is one of the richest natural sources of nucleic acids used in feed. Published work puts yeast nucleic acid at about 5 to 8% of dry matter, with 8.1% RNA reported for spent brewery yeast. At a 2 to 5% inclusion, whole dried brewer's yeast supplies roughly 1 to 4 g of nucleic acid per kg of feed. That is in the same range as, or above, the nucleotide doses tested in shrimp, piglet and kitten trials. Salmonids break down dietary purines with liver uricase, and trout trials report no adverse physiological effects from high dietary nucleic acid nitrogen.

What are nucleotides, and why is brewer's yeast rich in them?

A nucleotide is a small molecule made of a nitrogen base, a five-carbon sugar and one or more phosphate groups. The bases are the purines adenine and guanine and the pyrimidines cytosine, uracil and thymine. Cells link nucleotides into chains to build RNA and DNA. They also use free nucleotides as energy carriers and as signals.

Animals can make nucleotides themselves through de novo synthesis. They can also recover them from food and from broken-down cells through the salvage pathway. De novo synthesis uses energy and amino acids. Tissues that divide fast, such as gut lining and immune cells, rely heavily on salvage. This is why nutritionists treat nucleotides as conditionally essential during weaning, early life and periods of stress.

Yeast grows fast, and fast-growing cells carry a lot of ribosomal RNA. A review of yeast protein by Jach and co-workers (2022) reports that 70 to 80% of total yeast cell nitrogen comes from amino acids. The rest comes mainly from nucleic acids, especially RNA. The same review states that most yeasts contain 5 to 8% nucleic acids, and it cites 8.1% RNA for spent brewery Saccharomyces cerevisiae. It also notes that high RNA levels are usually harmless for animals.

Older trout work gives a useful cross-check. In Rumsey and co-workers (1992), a yeast nucleic acid extract was fed at 0.6 to 4.1% of the diet to match 7.5 to 50% dietary S. cerevisiae. That ratio implies a nucleic acid content of about 8% in the source yeast, close to the 8.1% figure above.

What do feeding trials show for shrimp and fish?

Shrimp have the most consistent dataset. Three recent Pacific white shrimp (Litopenaeus vannamei) studies are summarised below. For wider context on yeast in aquafeed, see our guide to brewer's yeast for aquaculture.

• Pond scale, 110 days. Novriadi and co-workers (2022) fed 22,500 shrimp in intensive outdoor ponds in Indonesia. Diets with 0.1% nucleotides (1 g/kg) and 6 to 10% fish meal gave better performance, healthier hepatopancreas histology and higher survival after a Vibrio harveyi challenge.
• Yeast RNA plus free nucleotides. Ratanaprapaporn and co-workers (2026) found 0.50 g/kg optimal for growth in juvenile shrimp. A dose of 0.75 g/kg gave the highest immune responses and the best tolerance of hypoxia and bacterial challenge.
• Winter conditions, 56 days. Abdel-Rahim and co-workers (2021) fed 500 ppm (0.5 g/kg) nucleotides. Survival, growth, feed utilisation and nonspecific immune indices improved over the basal diet.

The working dose range in these shrimp trials is therefore 0.5 to 1.0 g of nucleotide material per kg of feed.

What do trials show in weaned piglets and other young animals?

Weaning cuts off the nucleotide supply from milk at the moment the gut is under most stress. Li and co-workers (2015) fed 140 weanling pigs (28 days old, 8.3 kg) diets with 150, 220 or 275 mg/kg nucleotides for 42 days. Body weight, daily gain, gain to feed ratio and nutrient digestibility were higher than in the control. In a second experiment with an E. coli K88 oral challenge, pigs fed nucleotides had higher IgA, IgM and IGF-I. They also had lower cortisol and TNF-alpha, lower faecal E. coli counts and better faecal scores.

These doses are low, at 0.15 to 0.28 g/kg. Our article on brewer's yeast in weaned piglet diets covers protein, palatability and inclusion rates in more detail.

What evidence exists for dogs and cats?

Published dog work on dietary nucleotides centres on clinical settings rather than healthy-animal nutrition. We therefore do not draw dose conclusions for dogs here. The data for cats are clearer.

Zhang and co-workers (2026) fed 16 weaned kittens a dry diet with or without 0.03% yeast-derived nucleotides (0.3 g/kg) for 42 days. Supplemented kittens showed higher apparent digestibility of dry matter, organic matter and crude protein. Serum growth hormone, IGF-1, IgG, IgA and IgM were also higher. Atwal and co-workers (2023) fed kittens a diet with 0.33 g nucleotides per 100 g (3.3 g/kg) together with short-chain fructooligosaccharides, xylooligosaccharides, beta-carotene and vitamin E for 28 weeks. Kittens stayed healthy and produced stronger antibody responses to feline parvovirus and herpesvirus vaccination. Because that diet combined several ingredients, the effect cannot be assigned to nucleotides alone.

Processing matters for pet food. Russo and co-workers (2018) measured nucleotide recovery after manufacture and storage. Dry food kept 75% after processing and 74% after a 12-month shelf life. Canned food kept 43% and 41%. Extruded dry formats therefore retain most of what goes in. See our overview of brewer's yeast in pet food for formulation notes.

Which trials and doses should a nutritionist compare against?

The table lists the trials cited in this article with species, product form, dose and main outcome.

How much nucleic acid does a whole brewer's yeast inclusion supply?

A simple estimate uses the published range of 5 to 8% nucleic acid in yeast dry matter (Jach et al., 2022). Multiply the inclusion rate by the nucleic acid content:

• 1% inclusion: 0.5 to 0.8 g nucleic acid per kg feed.
• 2% inclusion: 1.0 to 1.6 g/kg.
• 5% inclusion: 2.5 to 4.0 g/kg.
• 10% inclusion: 5.0 to 8.0 g/kg.

Compare these numbers with the table. A 1 to 2% inclusion already matches the 0.5 to 1.0 g/kg used in shrimp work and sits well above the 0.15 to 0.28 g/kg used in piglets. Trout studies went much higher. Rumsey and co-workers (1992) fed up to 4.1% nucleic acid extract, and growth and nitrogen retention rose with each step.

Two cautions keep this estimate honest. First, most nucleic acid in whole yeast sits inside the cell as RNA polymer, not as free 5'-nucleotides. The animal's own pancreatic and intestinal nucleases must release the nucleotides. Purified products used in many trials are already in free form. Second, yeast nucleic acid content varies with growth phase, so a batch analysis is the right basis for a formulation. The difference between whole yeast and refined fractions is explained in brewer's yeast vs yeast extract.

Can salmon and trout handle the nucleic acids in yeast?

Yes. Salmonids keep active liver uricase (urate oxidase), the enzyme that converts uric acid from purine breakdown into allantoin. Rumsey and co-workers (1991) fed rainbow trout diets with 0, 25, 50 or 75% brewer's dried yeast. Nucleic acid nitrogen made up 20% of the yeast protein nitrogen. Uricase activity was present in all fish and rose in direct proportion to dietary nucleic acid. Trout fed 25% yeast grew faster and used feed more efficiently. The authors reported no adverse physiological effects from the high nucleic acid nitrogen intake.

Atlantic salmon show the same adaptive response. Andersen and co-workers (2006) found that juvenile salmon fed a nucleic acid-rich microbial protein meal increased liver urate oxidase activity. Plasma, muscle and liver urea also rose, which is the expected end product of purine breakdown in fish. For trout and salmon formulation details, read our guide to brewer's yeast in trout and salmonid feed.

What should a specification and label claim say?

TBESBY Inactive Dried Brewer's Yeast is a whole yeast, not a nucleotide concentrate or yeast extract. We make it from fresh brewer's yeast collected from international breweries in Vietnam. It is drum-dried at our own facilities in Vietnam. The process runs through receiving, drum drying, milling and sieving, packing and laboratory testing.

• Typical specification: 40 to 46% crude protein, moisture below 10%, ash below 6%, fat max 0.5%, fibre max 1.5%, lysine 30.5 g/kg.
• Shelf life and packing: 12 months; 25 kg bags or 600 to 1,200 kg jumbo bags.
• Status: U.S. FDA registered, ISO 22000:2018 certified, non-GMO.

For claims, describe nutrient supply. A defensible line is "contains naturally occurring yeast nucleic acids (RNA), a source of dietary nucleotides". Avoid claims about preventing or treating disease, which most feed regulations reserve for veterinary products. If a nucleic acid or RNA figure appears on a specification, request it as a measured value with the method named. The full product data are on our product page.

To discuss specifications, samples or a documentation pack for TBESBY Inactive Dried Brewer's Yeast, contact our team. Tell us your species, feed format and target inclusion rate, and we will send the data you need to run the calculation above.

Sources

• Jach M.E. et al. (2022). Yeast protein as an easily accessible food source. Metabolites 12(1):63. https://doi.org/10.3390/metabo12010063
• Novriadi R., Roigé O., Segarra S. (2022). Effects of dietary nucleotide supplementation on performance, profitability, and disease resistance of Litopenaeus vannamei. Animals 12(16):2036. https://doi.org/10.3390/ani12162036
• Ratanaprapaporn T. et al. (2026). Effects of dietary yeast nucleic acids and free nucleotides in juvenile Pacific white shrimp. Journal of Fish Diseases. https://doi.org/10.1111/jfd.70195
• Abdel-Rahim M. et al. (2021). Dietary supplementation of brown seaweed and/or nucleotides in juvenile whiteleg shrimp. Marine Drugs 19(3):175. https://doi.org/10.3390/md19030175
• Li H. et al. (2015). Response to an Escherichia coli K88 oral challenge and productivity of weanling pigs receiving a dietary nucleotides supplement. Journal of Animal Science and Biotechnology 6:49. https://doi.org/10.1186/s40104-015-0049-5
• Rumsey G.L., Kinsella J.E., Shetty K.J., Hughes S.G. (1991). Effect of high dietary concentrations of brewer's dried yeast on growth performance and liver uricase in rainbow trout. Animal Feed Science and Technology. https://doi.org/10.1016/0377-8401(91)90058-Z
• Rumsey G.L. et al. (1992). Nutritional value of dietary nucleic acids and purine bases to rainbow trout (Oncorhynchus mykiss). Aquaculture 108:97-110. https://doi.org/10.1016/0044-8486(92)90321-B
• Andersen Ø. et al. (2006). Purine-induced expression of urate oxidase and enzyme activity in Atlantic salmon (Salmo salar). FEBS Journal. https://doi.org/10.1111/j.1742-4658.2006.05288.x
• Zhang C. et al. (2026). Effects of dietary nucleotide supplementation on growth performance, immune function, and intestinal microbiota in weaned kittens. Frontiers in Veterinary Science. https://doi.org/10.3389/fvets.2026.1843322
• Atwal J. et al. (2023). Dietary supplementation with nucleotides, scFOS, XOS, beta-carotene and vitamin E influences immune function in kittens. Animals 13(23):3734. https://doi.org/10.3390/ani13233734
• Russo N., Candellone A., Galaverna D., Prola L. (2018). Nucleotides inclusion in pet food: effect of thermic treatment and shelf-life. bioRxiv. https://doi.org/10.1101/353813