I assume virtually everyone knows but I'll be pedantic anyway: if one wants to reduce the number of animals killed, the milk industry not immune. A cow's natural lifespan is 18-22 years (according to google). The average lifespan of a dairy cow is 4-6 years. A dairy cow has between 2-4 calves in that time. Only 1 is needed for replacement, meaning that for each dairy cow in the herd, you kill a calf every second year. Unfortunately it is not economically viable to slaughter dairy cows for meat (the meat is distributed in a non-efficient fashion on dairy cows). A cow produces about 8,800 litres of milk in a year (which is unbelievable to me), though only when calving. So the number of litres of milk per dead calf is about 5-7,000 (give or take -- it's the middle of the night so someone should better check my math ;-) ). It's surprisingly efficient, but not free.

If it's a male calf, it's almost always castrated and raised for meat (there's no difference in the "distribution of meat" on a dairy cow, simply that others are bred to make more), if it's a female it's normally raised to put into the milking herd. The cows that become too old to milk effectively are sold for slaughter as well, the new females are their replacements.

You only need one girl to replace the previous one. If you keep more than one, then your herd size increases (which you usually don't want).

Well I guess if you're at maximum capacity you wouldn't want additional female calves, but I would imagine some of those could be sold.

I have a friend who had a beef cow farm (which is slightly different, but close enough). Basically, you goal in building a herd is to strategically breed the best cows that you can. When you start, you buy some cows. Depending on what you are doing, you may or may not keep a bull yourself (you might artificially inseminate the cows, or pay for the services of a bull). Generally speaking you inbreed the cows, looking to develop specific traits that you want and occasionally breed your cows with a bull that you don't own for specific purposes (essentially improving the blood line). Once you have your initial cows, you almost never buy another one -- you just pay to breed with a higher quality bull. There are obvious exceptions, but that's the general rule.

It takes time to breed a herd of cattle. My friend had an outbreak of foot and mouth and he lost his whole herd one time. It took years and years and years to build it back up. At best you can double your herd size every year. In practice, though, some cows don't produce a calf every year. Also, there are cows that you don't want because they don't have the traits you want. But once you have the herd size you want, it is a steady state thing.

I tried to find some place to find the volume of cattle traded that's not destined for slaughter, but the data doesn't exist. It seems that dairy cows are traded mostly via want ads on the internet these days. Here's a typical site that specializes in it: https://www.dairylivestockservices.com.au/stock-for-sale/ Notice how all of the livestock is fully grown. That's because these are livestock from failed farms. I don't think anybody sells calves because there just isn't a market for it. You can't sell calves for meat either, because as I mentioned earlier, it's not economical (the price for a meat calf going to slaughter is only $125!)

It is sad to think about it, but the reality is that milk production necessarily relies on the death of cows to stay economical. If we drank a lot less milk and were willing to pay maybe 10x the price for it, then you could change that fairly easily. However, it's just not possible at anywhere near the price point we have for food right now.

there's nut milks and faux leather. nearly everything has a plant-based alternative and if something doesn't, it will have one soon.

Nut milks are nowhere near the same as animal milk. I have tried all sorts of alternate milks, and none of them come close to the flavor or texture of good whole milk from cows. So I'd say there are many things we really haven't figured out how to replicate without animals yet.

We do have faux leather. I have yet to find one that behaves like leather for footwear, however: Faux leather causes me to develop foot fungus. I can wear cloth, but by the time it gets treated as necessary, I'm not sure we are improving over the leather. But hey, it can improve.

Nut milks are an odd thing. They aren't really nutritionally the same nor do they behave similarly while cooking. The taste is lacking and I highly doubt they can make cheese. And if I remember correctly, many nuts milks are also bad for the environment - much better to just eat the nuts. I don't know if this is the same for oat milks. Soy milk is simply not edible. (I don't personally drink milk, but do cook with it).

Milk is truly one of those things that has to replace all functions for it to be a viable switch. The same goes for eggs.

All this basically to say that just because there is an alternative doesn't really mean it is viable. Cotton doesn't replace wools and neither do synthetic fabrics, for example. Not to mention that at least some synthetics are made with petroleum products. I always hope they are otherwise waste products from producing fuel (like many other plastics), but I'm not sure.

> many nuts milks are also bad for the environment - much better to just eat the nuts

I'm don't disagree with the rest of your comment, but I think the better comparison here would be to compare nut milk to what it's substituting for, which in this case is regular milk.