Large dose of cobolt makes more unhealthy milk

Janne Karin Brodin

The saturated fatty acid content in milk increases when large doses of cobolt are used as markers in digestion experiments. This is counterproductive as far as the nutritional value of the milk is concerned

One cobolt compound in particular is in regular use as a marker in digestion experiments, because it is more or less indigestible. A small amount is, however, absorbed, and approximately 3 % is found in the urine. By adding a certain amount of the cobolt compound to the feed, scientists can measure the digestibility of the feed by analyzing the cobolt content in urine and faeces, and relate the concentration of other nutrients to the cobolt concentration.

A previous experiment using cobolt as a marker showed that the fatty acid profile of the milk was significantly altered. The scientists wanted to find out more about what was occurring and whether the amount of cobolt that is added to regular milk cow feeds is important to the fatty acid profile of milk.

Researcher Ole Taugbøl and PhD-student Inger Johanne Karlengen are taking bloodsamples Foto: Janne Brodin

One of the questions that PhD student Inger Johanne Karlengen at the University of Life Sciences asked herself was: how large cobolt doses does it take to affect the milk fat profile.

Takes high doses
The results showed that it takes very large doses of cobolt to achieve an alteration of the milk fat, and that the amounts used in regular feeds do not change the fatty acid profile.

Cobolt is added to feed concentrates and mineral compounds for ruminants because the cobolt content in the feed raw materials can be relatively low, and ruminants need sufficient amount of cobolt to produce a satisfactory level of vitamin B12.

The amounts that are normally used in concentrates and mineral compounds are far lower that the amount it takes to change the fatty acid profile, says Karlengen.

An enzyme produces the monounsaturated fatty acids in milk, and the experiments show that it is reasonable to assume that cobolt in some way affects the activity of this enzyme system in the udder.

To find out whether the change was unique to ruminants, corresponding experiments were conducted with lactating sows. The effects on the milk fatty acids in sows were mainly the same as seen in milk cows, although somewhat slighter.

Only relevant to feed experiments
The results from the experiments have helped clarify and establish that today’s recommendations for adding cobolt to milk cow feeds does not affect the composition of milk fats, says Karlengen.

Given that the amount of cobolt it took to achieve changes is so high, the results will not change the recommendations given to milk producers. On the other hand, they will affect the use of cobolt as a marker in experiments. Given that it affects an enzyme which is central to fat metabolism, it should not be used when parameters relating to fat metabolism are examined.

Publisert: 01.12.11
Oppdatert: 06.12.11
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