A report issued last month showing the results of a trial in USA proved a link between dairy and breast cancer. It is thought that natural growth factors in dairy closely resemble eostrogen which is known to promote breast cancer. This should not come as a surprise because it has been recognised for a long time that breast cancer is far less prevalent in China and Japan where less dairy is consumed. This anomoly cannot be explained by ethnicity since Chinese women in Hong Kong who have a more westernised diet develop higher rates of breast cancer than those in rural parts of China.
Unlike goats, cows have developed a defense mechanism which relies upon piling on weight in a short time to protect them against predators. On the other hand goats rely upon being 'fleet of foot' - so goat's milk has fewer bulk producing agents.
About a decade or so ago farmers were adding more artificial growth factors to cow's feed such that the milk yield of cows was growing year on year. Apparently the milk lake and butter mountain just wasn't big enough! These additional growth agents were subsequently banned by the EU and since then the incident of breast cancer in UK has reduced. Auntie NHS has told us that this is because more women are undergoing screening but did they say this because they just happened to be promoting screening at the time?
Many would argue that dairy has always been part of a healthy diet. This is true but today because lactose and whey are cheap and tasty they come top of every food technologists list of ingredients so we consume far more dairy than say the Victorians did. NB - even cows give up dairy once they pass puberty.