> In 2014 the world wide Aquatic Plants (which include ALL Macro-Algae) production was around 27 Million tons.

I can add something about that.

Most algae production is Chinese and brown macroalgae.

Brown and red algae are really different creatures. It seems that brown are not even seen as plants currently and have moved to kingdom protista (something that could explain their strange flagellated spores), whereas reds are still plants, I think.

They are so far away phylogenetically, that is not reasonable to be interchangeable just because they are both "algae". Expecting a Phaeophycea having the same effect in cows as a Rhodophyta, would be like expecting Geraniums have the same chemical properties as tuberculosis.

We most probably would have: either none effect Y or a different effect X, still unknown

Second thing: Lets assume for a moment that the effect would be the same. Those 27 million tons do not exist. Of those 27 tons, around half are brown macroalgae, but -very important- this is probably fresh weight. Macroalgae are not sold fresh, they must be dried before to reach the market. Therefore we would't have a production of 15 million tons of brown algae. What we really would have is 4 million tons of dried brown algae to feed 1.5 billion of cows, that is a worse situation

Therefore we would need to start growing algae as crazy somewhere. We have three options.

1) At the sea

We would need to make room in extensive coastal areas, (some of those protected areas with a high biodiversity) to grow Asparagopsis.

Distroying valuable coastal areas that support coastal cities, to grow just sheeps would be increasing the risk and putting all of our eggs in the same basket economically. If the wool market sinks and the fisheries were turned into auxiliar activities around wool's industry, there are not other activities that could act as a buffer and save the day. Not to mention than extensive farmers employ much less workers than fisheries.

2) In tanks

As the ocean is a place with a million of unpredictable variables and trophic chains we probably would prefer to do it in laboratory. So we need to build many and learn how to do it. That is more easier to say than to do, because Asparagopsis is just one of two forms in a complex life cycle (the other was called Falkenbergia). So we need to learn how to grow two algae in one.

Can be done? Yes, but is several levels much more complicated that just trowing some seeds in a field and see fodder grow.

3) In other countries

We could also save ourselves all the headaches and left it to experts (i.e. import it). A few red algae are cultured in several Asian countries, specially Japan but they are seen as culinary delicacies and they control the amount of algae put in the market to keep prices high. So using it to make wool maybe would be like selling 100 dollar bills at 15 cents each. Not a really economically viable activity.

Is unclear how including cows in aquaculture would disturb the market or the geopolitics. I would expect an increase in the actual Chinese hunger of buying or silently grabbing as many sea bottom areas as they can.

https://en.wikipedia.org/wiki/Territorial_disputes_in_the_So...

All of that, without mention the carcinogen aspect, that is also very troubling.