I am in the midst of reading "Devil in the Milk." This is a book that is all about the A1 and A2 milk debate.
From what I have read, the study that you are referring to was flawed. Some of the rodents were fed a diet that contained BCM7, the molecule that is formed in A1 milk. The peptide that forms when A1 Beta-casein is digested is an opioid. The data in the study showed that the rodents that did not receive the BCM7 tainted food did indeed have a higher % of diabetes (19% vs. 47% - and please realize that the rodents they used were bred to have a higher probability to get diabetes when fed cereal grains).
"Diabetologia", the journal that published the study, was informed, BY ONE OF THE AUTHORS OF THE STUDY, Bob Elliott, that the study was flawed. The journal said that it was not their responsibility to disprove the study and that it would cost too much money in any case.
There is plenty of proof, without that flawed study, of not only other studies of rodents AND humans, but also just by showing the increase in incidence of those diseases in countries with A1 cows. It looks to me that A1 milk does indeed increase the likelihood of heart disease, Type 1 Diabetes, autism, and other mental disorders, as well as a number of auto-immune diseases. I could name you study after study quoted in this book but it would be best if you read the book yourself.
The author of the book, Keith Woodford, is not affiliated with the A2 corporation. He is a professor of Farm Management and Agribusiness at Lincoln University. He was formerly 20 years at the University of Queensland in Australia. He is a founding member of the Weston A. Price Foundation. Although he admits that prior to writing his book there were people in his family who owned A2 stock, he himself did not personally own any. Because the ownership of that stock could possibly lead to the belief that he was writing articles for his own gain all the members in his family sold their shares. You can't keep everyone happy because I am sure some people would now say he won't put his money where his mouth is. However, to avoid a conflict of interest that is the path he took.