Feeding yeast – comparative properties of nutritive and biologic value

Podobed L.I., Doctor of Agricultural Sciences

Yeast has been known on the feeding additives market since a long time. However, owing to significant extension of the assortment of such feeding products, it has only now become necessary to compare their nutritive properties and ascertain the features of efficient use in animal and poultry feeding.

In the broad biological meaning, yeast refers to a group of several types of single-cell fungi of various classes (Sac Fungi, Basidiomycota, Deuteromycota).

In terms of the kind and purpose of cultivated organisms, yeasts are divided into baker’s yeast, brewer’s yeast, distillers yeast, wine yeast, feeding yeast, etc. Notwithstanding the high feeding value, all the mentioned yeast  groups, except for the feeding one, have a limited significance as sources of nutritive materials in animal feeding. Feeding yeasts are used as feeding means only in case of change in their properties related to noncompliance with either manufacturing technology or exceeding the storage period. At that, visual and biochemical properties of such yeasts should remain at the level of standards peculiar to feeding yeast.

Feeding yeast is a dry concentrated biomass of yeast cells, which is purposely grown for feeds of livestock, poultry, fur-bearing animals, and fish. The variety of yeasts is determined by the strain of a producing fungus and the medium where the yeasts of a particular strain are grown.
The microscopic fungi of the following genus are mostly used as producing strains: Candida, Saccharomyces, Hansenula, Torulopsis. However, for the purpose of practical use, somewhat different classification of feeding yeast is applied depending on the environment, where a yeast cell has been grown. Thus, one may distinguish hydrolytic yeast, classic feeding yeast and protein-vitamin concentrate yeast (PVC).

If hydrolysates of wood waste (would-flour, shavings, chips)  and agricultural waste (straw, chaff, sunflower husk, corn) are used for cultivating yeast fungi,  then hydrolytic yeast is the final product. The product of the same quality is obtained at growing yeasts at the sulphite lyes of paper and pulp production.

Classic feeding yeasts are obtained by growing fungi of Candida (more rarely Torulopsis) genus at the distillers grains obtained as waste from the  spirit production.

PVC yeast is a product of cultivating the yeast cells at the waste from processing the non-vegetative raw materials such as paraffins (paprin), minor organic spirits such as methanol (meprin), ethanol (eprin), and natural gas (gaprin).

Sometimes yeast production technology involves the operation of their enriching with vitamin D. For such purpose, after the yeasts are cultivated, a culture liquid fraction  is directed into a column for ultraviolet exposure, and after derivation and drying the yeasts, the augmentation in vitamin D concentration in the yeasts is detected to be more than 100 times as great as the non-exposed yeasts.
Particular technological and organoleptic properties of three of the abovementioned yeast groups are listed in table 1.

Table 1.

Specific technological properties of yeasts of different groups.

Feeding yeasts  type Mediums for yeast cell cultivation Structure of the ready feeding Color of the ready feeding product Yeast yield  per 1000 kg dry raw material
Hydrolytic Wood and agricultural waste Powder, granules Yellow, dark yellow 240-450
Feeding classic Distillers grains Flaky powder, granules Bright brown – brown 260-400
PVC Oil paraffines, minor spirits, natural gas Powder , granules Bright yellow – bright-brown 600-800

Table 1 data shows that yeasts of all three groups are organoleptically different as for structure and color. Feeding classic yeasts produced at the distillers  grains have darker color and  flaky structure. These yeasts are distinguished by a relatively low yield of the ready product per  consumed raw material unit. However, that does not necessarily mean that the referred group of yeasts is surpassed by other varieties of the given feed additive as for nutritive value.

Owing the certain specialties of technology, various synthetic properties of the producer , unequal yield of the ready product per initial raw material unit, the yeasts supplied to the consumer have serious differences both in terms of cost and chemical composition of the ready product.

Comparison of chemical composition of yeasts from the observed groups ( Table 2) shows that the nutritive value and biological properties of these protein additives have significant differences.

Indicators Yeasts
Feeding yeasts, at distillers grains Hydrolytic yeasts , at wood waste PVC, at oil paraffines, spirits and gas
Crude protein, % 38-51 40-56 42-60,5
Protein according to Barstein, %

in % of crude protein







Digestible protein, %:

for swine

for poultry

for cattle












Purine bases concentration, %

2-6 8-13 8-10


Pyrimidine bases concentration, %

0-3 2-4 0-5
Probability of  RNA excess accumulation Irrelevant. Relevant. Relevant.
Probability of producer’s live cells accumulation Irrelevant. Irrelevant. Relevant.
Exchange energy, MJ/kg:

for swine

for poultry

for cattle










Crude fiber, % 1,2-2,9 1,3-2,7 1,5-1,9
Crude nitrogen-free extractive substances,% 33-35 31-34 25,9-33
Crude ash, % 3,9-7,1 4,4-7,7 5,9-7,8
Crude fat, % 2,2-3,1 2,7-3,3 7,2-7,6
Mono and disaccharides, g/kg 3,9-8,8 3,2-5,1 8-8,5
Organic acids, g/kg 23 18 21
Unsaturated fatty acids, mg/kg 540 590 500
Cholesterine, mg/kg 260
Dietary fiber, g/kg 1,8 2,9 2,1

The first distinctive feature of yeasts of various groups is significant fluctuations as for concentration of protein according to Barnstein and non-protein nitrogen. From the prospective of the protein maximum, one should point out PVC.  However, classic feeding yeasts feature a more stable content, although they have the same level of crude protein. Beside the protein content stability, classic feeding yeasts are distinguished by the highest percentage of true protein and the lowest concentration of non-protein nitrogen, which guarantees safe use at feeding young swine, poultry, and cattle.

One should hardly rely on the yeasts, the manufacturer of which conceals the indicator of true protein and non-protein nitrogen. High indicators of non-protein nitrogen presence evidence the entry of nitrogen-containing nutritive mediums into a ready product. Non-protein nitrogen of the yeasts causes digestive disorders (diarrhea) in young animals, decrease in productivity of animals, sharp deterioration in the quality of products obtained.
The second positive difference of classic feeding yeasts from the products grown at hydrolysates and PVC should be considered lower concentration of purine and pyrimidine residues of nucleic acids in them. This significant positive property is a guarantee of feeding security of classic yeasts as a factor that predetermines progression of urine acid diathesis in poultry and guanine podagra in piglings.

It is known (I.V. Petrukhin, 1989) that accumulation of nucleoproteids in yeasts becomes a cause for the increase in concentration of the referred nitrogenous bases in blood and intercellular substance of the animal and poultry organism.  The final product of purines and pyrmidines exchange is the uric acid. Balance disruption of its synthesis and disposal from the organism leads to blood acidification, occurrence of uroliths in kidneys,  and  deposition of uric acid salts. In case of excess of uric acid in the blood of birds, water exchange in cloaca is disrupted. There appears pain, maceration, cloacitis progresses, productivity decreases and progression of cannibalism is triggered. A bird that has received rations with the recommended yeast rates included, yet containing purines and pyrimidines  in excess,  quickly ages, the joints thicken, feathers quickly wear out, cloacitis progresses, and cannibalism frequently occurs. In this regard, feeding classic yeasts may be considered the safest among the reviewed group of feeding additives. At any rate, they  have 2-3.5 times lower concentration of purines and pyrimidines than such of hydrolytic yeasts  and PVC. The complexity of identifying the concentration of protein in conditions of compound feed factories’ laboratories does not allow the consumer to control the concentration of these substances on their own, and yeast manufacturers feel “shy” of regulating the concentration of the referred substances in their products.  There have been no cases in the feeding additives preparation practice when yeasts were absolutely devoid of purine and pyrimidine bases as well as RNA. It is all about concentration of these substances per mass unit of a ready feeding additive and the rate of yeast inclusion into the animals’ ration. The inclusion rate of yeasts for young animals and birds is restricted to the level of 3-5% of the mass due to the precaution concerned with existence of nucleotide residues in them.

It should be noted that yeasts accumulate mono and disaccharides (oligosaccharides), organic acids, and PVC, moreover, include  cholesterine. From the prospective of feeding properties, this fact may be treated ambiguously.

Oligosaccharides is an inevitable part of a yeast wall that is based on the known MOC group. Therefore, existence of such saccharides attaches sorptive properties to a yeast wall, which are quite beneficial for animal and poultry digestion in terms of sorption of mycotoxins. That means that the oligosaccharides should not be considered as their negative property. Organic acids of yeasts are stomach digestion stimulators, facilitating the increase in digestibility of protein of the animal and poultry ration. These acids stimulate the appetite and growth of useful microflora in the  bowel.

For more detailed review of protein nutrition value of  yeasts from various groups, one should analyze the amino acid content of these products (Table 3).

Table 3.  Comparative amino acid content of yeasts of various groups Amino acid content of yeasts %

Indicators Yeasts
FeedingCandida Feeding Hydrolyticin average PVC
in average on molasses
utilis fragleis
Crude protein 43,7 48,5 48,3 44,9 51,8 57,1
Lysine 6,7 8,8 6,8 7,5 3,47 4,2
Methionine 1,2 1,5 1,7 2,0 0,31 0,6
Cystine 1,0 0,47 0,3
Tryptophan 1,2 1,5 1,3 0,41 0,4 0,6
Arginine 5,4 4,9 5,6 4,3 3,16 2,5
Histidine 1,9 2,5 2,7 2,8 0,93 1,8
Threonine 5,5 5,5 4,2 5,5 2,5 2,8
Phenylalanin 4,3 3,9 4,2 2,3 2,9
Leucine 7,0 9,9 7,6 7,3 8,6 7,0
Isoleucine 5,3 5,5 5,5 6,0 3,5 4,8
Valine 6,3 6,6 5,9 5,3 3,63 3,0
Amount of indispensible amino acids, in % from  the total number 44,8 50,6 46,5 41,1 31,3 30,5

Arginine : Lysine

0,81:1 0,56:1 0,82:1 0,57:1 0,91:1 0,59:1

Methionine : Cystine

1,7:1 0,66:1 0,2:1
Biological protein value (BPV), % 86,1 87,3 86,5 85,2 82,8 82,4

* amino acids are presented in % оf crude protein

Table 3 data shows that feeding yeasts produced under classic technology  are richer than the  hydrolytic yeasts and PVC as for concentration of indispensible amino acids. Regardless of the substrate and variety of microscopic fungi, feeding yeasts are characterized by increased concentration of Lysine and Methionine compared to the hydrolytic yeasts and PVC. That, certainly, facilitates the growth of biological value of the mentioned feeding product in relation to  analogs. In classic yeasts, the content of Arginine in relation to Lysine is reduced, and the Methionine – Cystine proportion is more appropriate for balancing these amino acids in poultry. Increase in concentration of Lysine and Methionine as well as the increase in the amount of indispensible amino acids provides higher BVP indicator for the feeding yeasts of classic production.

The mineral content of feeding yeasts of various groups  varies to a lesser extent than their nutritive value (Table 4).

Table 4. Comparative mineral content of yeasts of various groups.

Name of element, g/kg Yeasts
Feeding, on distillers grains Hydrolytic, on wood waste BVP, on oil paraffines
Calcium, % 0,6-0,8 0,40 0,57
Phosphorus, % 0,9-1,4 0,95-1,33 0,9-1,34
Sodium, % 0,16 0,18 0,18
Potassium, % 0,5 0,67 0,62
Magnesium, % 0,032 0,038 0,041
Chlorine, % 0,005 0,008 0,011
Iron, mg/kg 32 39 35
Zinc, mg/kg 12,3-60 21,6-90 23,4-70
Copper, mg/kg 3,2-68 3,8-50 3,8-61
Manganese, mg/kg 45-100 55-60 67-90
Cobalt, mg/kg 0,5-0,9 0,78-0,88 0,54-0,78
Iodine, mg/kg 0,04 0,05 0,04
Molybdenum, mg/kg 0,08 0,11 0,14

It should be noted that the yeasts of all groups contain more phosphorus  than calcium, they have a quite high level of potassium and low concentration of magnesium and chlorine. It should be noted with regard to microelements that the yeasts are reach of magnesium and contain little cobalt and Iodine. There is a great hazard of accumulation of molybdenum within the content of yeasts,  which penetrates therein along with the nutrients.

Classic type feeding yeasts feature low concentration of heavy metals and harmful substances, provided that they are prepared on distillers grains or molasses. In case of using other substrates applied to cultivation of feeding yeasts, the environmental issues become relevant, and it is necessary to perform compulsory testing of such yeasts as for the concentration of lead, cadmium and other substances that cause animal poisoning and sharply reduce the quality of obtained animal breeding products.

The  value of feeding yeasts is frequently determined not only by the level of protein and amino acids within their content but also concentration of vitamins for which these products constitute a valuable source, in fact.

Group B vitamins are of a special value, they are accumulated by yeast cells in the process of their synthesis. Owing the fact that vitamins are active areas of the ferments of the yeast cell synthesis, accumulation of its concentration proceeds proportionally to the growth of yeast cells. A cuticle,  yeast membrane, reliably protects the vitamins from destruction in the process of product drying and, at the same time, protects these substances from oxidation at storing the yeasts.

One may estimate the vitamin nutritive value of yeasts of various kinds by analyzing Table 5.

Table 5. Comparative vitamin content of yeasts of various groups, mg/kg

Name of vitamin, g/kg Yeasts
Feeding, on distillers grains Hydrolytic, on wood waste BVP, on oil paraffines
Thiamine (В1) 11,4 9,9 10,2
Riboflavin (В2) 75,9 106 103
Pantothenic acid ( В3) 86 110 106
Choline (В4) 3200 2500 2560
Pyridoxine (В6) 26 31 30
Nicotinic acid 350 234 190
Biotin (Н) 3,8 2,9 3,0
Folic acid (Вс) 20 45 33
Cyanocobalamin (В12) 0,08 0,06 0,03
Tocopherol (Е) 5 5 3

Table 5 data shows that classic feeding yeast are richer than the hydrolytic ones and BVP as for the concentration of thiamine, choline, nicotinic acid, biotin and cyanocobalamin.  In turn, BVP  and products obtained of on the basis of hydrolysates are better provided with riboflavin and folic acid. That means that it is possible to regulate the vitamin provision of the ration  according to available B group vitamins,  Consequently, we may assume that the classic feeding yeasts are a verified and very efficient option  of enriching the rations with the yeast protein in relation to hydrolytic yeasts and BVP.

However, one should note that the classic feeding yeasts may greatly vary as for their feeding benefits within the same group.  It is more frequently related to adjustment of manufacture, raw materials base stability and the culture of microbiological process. Feeding yeasts are obtained in high-quality when the technologic process is not interrupted, and the volume of production exceeds 40-50 t of the end product per shift. Generally, major plants have a proper control of end product quality instituted, and there are no fluctuations in the nutritive value of yeasts from one lot to another.

In contrast to other types of yeast products, feeding yeasts grown on spirit waste under classic technology appeared to be more efficient in experiments with poultry  and piglings as for the productive effect. It has been established for sure that  the application of yeasts in optimal doses enables to obtain 0.5 t of  pork in addition, 1.5-2.0 t of poultry or 25-30 thousand units of  eggs per each fed ton of protein product.

Observations that we conducted at Odesa and Poltava poultry plants have shown that it is efficient to use the classic type yeasts  for chicken of the age starting from 2 weeks, and proceed the entire growing period of young chicken and  hens’ egg-laying after growing such young chicken. Fluctuations of doses of yeast inclusion into the compound feed content lay within the range of 2-5%. Application of yeasts results into saving the active homeostasis of poultry,  signs of uric acid diathesis are not detected, the terms of the economic use of poultry are extended for 2-4 weeks. In case of broilers, classic yeasts cause the effect of enhancing the taste qualities of meat, facilitate accumulation of protein in muscles, and provide quick maturation of muscles at intensive growth.

The equally important effect has been observed at feeding the yeasts to the piglings, lactating sows and rearing stock. In swine breeding, there has been formed a firm opinion on the yeasts as a factor of obtaining the high quality of pork and lowering the body fattening. Classic yeasts are characterized by a special impact on growing the swine of intense hybrids that require high-quality protein at the initial growth stages (up to 4 months of age). In this period, the yeasts stimulate the deposition of proteins in the body and growth of the internal organs of the animal.

Consequently, application of classic feeding yeasts within the content of the livestock’s ration is the best option for using the yeast additives. This option ensures the increased growth of animals, productivity enhancement and, mainly, is not coupled with deterioration of the physical condition that may be detected at feeding with the yeasts of other types.