If the cause were beef and milk consumption as such, it seems unlikely that a severe shift like this would occur. To me, it's far more likely to be something like crop dessication for grains--they started soaking cereal crops in glyphosate prior to harvest and suddenly this category of food that sustained the planet for millennia suddenly starts causing broad spectrum inflammation that people blame on the crop and not the processes and adjuncts.
I smell a Bayer, Nestlé, DuPont, J&J, Pfizer, Monsanto, etc-style hidden externality at work rather than animal husbandry. Like, what are the colorectal cancer rates for those people that actively practice transhumance? Do they differ significantly despite predominantly animal-product and dairy-based diets?