When I took my butchery class in culinary school we received a whole lot more information on cows than I knew even existed. We were required to learn all the top breeds of both cows that are raised to sell their meat and cows that are used to sell their milk. The milk cows were Holsteins, Guernsey, Jersey, Brown Swiss and HoJo (a cross breed of Holstein and Jersey). Holsteins supply the majority of milk consumed, with Guernsey coming in second. Guernsey has lower output and richer milk. Of course, since the production output of Holsteins is higher, it lowers the cost of the milk.
But we never touched on the controversy regarding the A1 type milk associated with the Holsteins and the A2 milk associated with Guernsey cows. It wasn’t until I started making cheese and talking directly to organic cow farmers that I became aware of the scientific debate surrounding these milk categories. To keep it simple, A1 milk is a variant that was created in European cows many years ago. This variant has a protein in it that when digested creates a substance called BCM-7. BCM-7 is an opioid that can attach itself to receptors in the brain. Researchers around the world have been aggressively debating the effect of this substance for the last 2 decades. Some researchers believe there is a direct link between this substance and Type 1 diabetes, autism, and schitzophrenia. Others researchers are disagreeing with this claim. I never knew such a controversy with the milk we drink even existed. If you are interested, there is a bunch of detailed research you can read at http://www.betacasein.net/BCM7.html .
Here is my take on this from a cook’s perspective. Guernsey cow milk is associated with A2 milk. This is the type that is considered safe from these effects along with Jersey cow milk. Guernsey cows also don’t have the ability to digest beta carotene, and thus pass the nutrient into their milk (that is what gives it a light golden hue). Along with the richer energy density (remember that energy density is calories and must be managed appropriately), it seems the Guernsey cow milk will produce better tasting and more nutritious dishes. After reading a dozen or so scientific abstracts I can tell you I am not trying to be an expert. But who knew the ‘moo’ could be so controversial?