How much soya is needed to produce a glass of cow's milk?

Question

Producing soya beans is responsible for some significant amounts of deforestation in tropical areas and relying on soya introduces a demand for transportation in countries where soya is not grown.

I know that soya is used as a feed for livestock. I don't know the statistics for dairy livestock, but an advantage of cows is that they can produce food from local land which is only able to support grass but not crops, and they produce manure.

Question is how much soya, if any, is typically used in developed countries to produce a glass of ordinary full-fat/semi-skimmed milk? How do more developed compare with less?

Answer 1

To summarise @EnergyNumbers's response which applies for UK milk, I will quote a section from the report he linked:

"Between 60 and 112 litres of milk produced for each kilo of soya meal fed to cows, 7.5 litres of milk produced from each kilo of soya beans turned into soya milk"

The report points out that the UK has a better climate for grass (read rainy), and that there are some farmers who produce pasture-only or avoid use of soya in their feeds. Other reasons to avoid soya are the use of Roundup which is a listed carcinogen, the use of nickel and hexane as solvents in the production of soya oil for livestock feeds.