It's all bullshit. Complete and utter lies to sell a product. There is plenty of calcium and protein in plants. Calcium deficiency comes from losing calcium through excess consumption of protein and phosphoric acid and lack of weight-bearing exercise. (More information, including references, can be found in these articles.)
And it's borderline racist. The majority of the world's people, especially those of African and Asian descent, cannot even digest lactose properly after infancy. And they are marketed pills and expensive lactose-free cow's milk so that they can be "normal" just like their white friends.
We don't need dairy products to be healthy. And there is no way to produce them ethically. The "happy cow" farms advertised are also bullshit. People see cows on such farms grazing on grass instead of crammed together in factories and figure that they're being treated nicely, so what's the harm?
First and foremost, virtually every single one of those cows is killed once they are no longer producing milk. A cow's normal lifespan is 20-25 years; on a farm, even a "humane" farm, they are spent after 4-6 years. It makes no economic sense to keep an animal around for years doing nothing but grazing on grass and not producing any product, so they are killed. There are virtually no exceptions to this. Anyone thinking otherwise, that the cows that produced the dairy they are personally consuming (not just gallons of milk, but ingredients like whey and casein that are added to many other foods) somehow escaped the slaughterhouse, ought to do the research and find out the truth for themselves.
I cannot emphasize this point enough. These animals are killed. They are made into fast-food hamburgers, cat food, or other "low-quality" meat. It doesn't matter whether they come from a factory farm or a family farm; they all end up in the slaughterhouse.
Second of all, in order to keep producing the milk, the animals must be repeatedly impregnated. This is often done by artificial insemination. i.e., the farmer inserts bull semen into the cow. They don't just wait until the cows and bulls decide to mate of their own accord. They are forcibly and continually impregnated. Most of the male calves are sent off to be made into veal. Again, even on "happy, humane" farms, there is no economic incentive to keep every calf born to every cow around until it dies of old age.
Third, the cows' babies are taken away from them, sometimes in as little as a day. On "happy" farms they might get to stay for another week or two, maybe even longer. But ultimately the milk intended for the calves is taken by the humans, because that's what dairy farming is. Because Americans have been brainwashed into thinking that it is perfectly normal and healthy for a human to drink the milk of another species.
The situation I have described above, if applied to humans, would be considered slavery, rape, theft, and murder. But since the victims are cows, these practices are considered "humane".
Cows are sentient beings. They have awareness, experience pain and suffering, and desire to live. Some have argued that they've been bred to be "too dumb to care". Is a cow too dumb to care when a rod is pushed into her vagina? Is she too dumb to care when her baby is taken away from her and a milking machine clamped onto her udder in its place? Is she too dumb to care if she lives or dies??
A life in captivity is not a "good life". There is no way to improve this system to make it humane. Treating a sentient being as property - as an economic commodity - is inherently inhumane.
All animal farming is exploitation. The only way to stop the exploitation is to stop participating in it, by not buying or consuming animal products. That is why I am vegan.