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The cow favours natural over synthetic vitamin E for the cow milk

When the cow is fed grass with a naturally high vitamin E content, the milk’s content of vitamin E is higher than when the cow is primarily fed feed containing synthetic vitamin E. The explanation is that the cow favours natural vitamin E over synthetic vitamin E. This is what studies conducted by researchers at AU Foulum show. The results have recently been published in the recognised journal FOOD Chemistry.

[Translate to English:] Køer på græs. Foto: Linda S. Sørnensen.
[Translate to English:] Det er den naturlige form for E-vitamin i foderet, der fortrinsvis udskilles til mælken hos køer, viser undersøgelser foretaget af Institut for Husdyrvidenskab, Aarhus Universitet. Foto: Linda S. Sørensen.

Vitamin E is a very important antioxidant, which among others prevents oxidation of food like milk and meat. Vitamin E is also of importance to the immune response system and may improve the immune response in animals deficient in vitamin E.

Over time, much debate has focused on the relative biological value of providing cows with natural vitamin E (RRR-a-tocopherol) and synthetic vitamin E (all-rac-a-tocopherol). Today, it is generally accepted that the biological activity of synthetic vitamin E is overestimated compared to natural vitamin E in many species. Experiments with rats have shown that the natural form of vitamin E has an activity of 1.36 times higher than the synthetic form, which has been a well-known fact since the 1940s. However, doubt has been raised about whether these results can be transferred to other species. American, Canadian and Danish studies in human, cattle/sheep and pigs have thus shown a higher exploitation of the natural vitamin E than the official values have shown.

The difference between synthetic and natural vitamin E


Synthetic vitamin E, chemically named all-rac-a-tocopherol acetate, consists of eight different forms of a-tocopherol of which only one (RRR-a-tocopherol) is the natural form. The fact that vitamin E appears in various forms must be understood in the way that the forms differ from one another in the same way that the left hand differs from the right hand. For synthetic vitamin E, 2×2×2=8 different reflections exist, making each occur with 12.5% in the synthetic vitamin E. If one imagines that vitamin E must fit like a glove in order to be transported in the body, it makes sense that the natural form is the better hand and thus has the highest vitamin value (biological activity).



Figure 1: Chemical structure of RRR-a-tocopherol – the natural form of vitamin E.

Experiments with natural and synthetic vitamin E for cows

Under practical farming conditions, the simple way has been to add more synthetic vitamin E to the feed; however, only very small amounts of this end up in the milk. “We started wondering about the difference in the milk’s content of vitamin E at different feeding strategies. When feeding the cows synthetic vitamin E, not much is transferred to the milk compared to when feeding them with grass (or grass silage rich on natural vitamin E). When feeding grass, the milk gets a substantially higher content of vitamin E”, says senior researcher Søren Krogh Jensen, Department of Animal Science, Aarhus University.

“In order to learn more about it, we conducted an experiment with cows receiving a single dose injection in the cervical muscle with 2.5 g of synthetic vitamin E containing all eight forms, including 12.5% of the natural form of vitamin E. Subsequently, we studied the individual forms’ secretion into the milk over the next 11 days”, continues Søren Krogh Jensen.

The cow distinguishes between synthetic and natural vitamin E and favours the natural form

The main result of the 11-day-long study is illustrated in Table 1. It shows that 16.3% of the natural form is secreted into the milk, 6.5% of the three synthetic dextrorotatory forms, but only 0.7% of the synthetic laevorotatory forms is secreted into the milk. In total, this means that 6–7% of the synthetic vitamin E is secreted into the milk.


Table 1. Segregation of synthetic and natural vitamin E in cow milk after injection of 50 ml Ido-E Vet.

Synthetic 'laevorotatory'   Synthetic 'dextrorotatory'   Natural 'dextrorotatory'  
Segregated in milk over 10 days 0,7%6,5%16,3%

”In this way, we have proved that mainly the natural form of vitamin E is secreted into the milk and that cows distinguish between natural and synthetic vitamin E. Thus, cows discriminate much more in favour of the natural vitamin E compared to for example rats. Therefore, the official conversion factor of 1.36 between synthetic and natural vitamin E does not fit very well with the cow’s biology”, explains Søren Krogh Jensen.

Thus, how much vitamin E the cow’s milk contains very much depends on how the farmer feeds his cows. “If you want to produce milk with a high content of vitamin E, it is important to choose cow feed with a naturally high content of vitamin E like for example fresh grass or grass silage rather than maize silage. However, you also need to know that the cow has an upper limit as to how much vitamin E it can secrete into the milk. The higher the milk yield, the thinner the milk will become in relation to the concentration of vitamins and microminerals”, concludes Søren Krogh Jensen. 

Facts about the project


The study was part of a business PhD project funded by the Ministry of Higher Education and Science, AgroTech, Aarhus University and Future Food Innovation Denmark.

Project partners

Aarhus University

More information

You can read the entire scientific article here: https://www.sciencedirect.com/science/article/pii/S0308814619320709?via%3Dihub


Senior researcher Søren Krogh Jensen, Department of Animal Science, Aarhus University.

Email: skj@anis.au.dk