Only once, to get a cell line, which you can then use indefinitely. That's the neat thing about stem cells: they make more of themselves, over and over, endlessly. You also don't have to kill the animal to get some cells out of it.
Unsurprising! So I guess meet and dairy products are going to become astronomically expensive?
Alternative milks are currently more expensive than cow milk (by a long way). If that changes, I can see the dairy industry crashing.
The one thing that I can’t find is a palatable alternative to cheese. Are there any yet?
To be honest I haven't tried any. But I know lab-grown "milk" is becoming a thing, if you're after the same taste I'd guess that would be your best bet. Not sure if there are any yet.
Lab produced dairy will basically eliminate the dairy farm, once perfected the change will be swift and catastrophic.
2 to 3 years to design and build a plant, one reasonable sized facility will replace 60k cows, that is 20 big farms, 1000 hectares replaced by 4-10 hectares.
I think you need to make it cheaper than cow milk and taste pretty much the same, with a similar nutrient profile. There will still be holdouts but I think the cost thing will be the tipping point. Up until it's the cheapest option, it's still a premium product for a niche market. Once that tipping point is reached, I'd hate to be a dairy farmer.
Different labs around the world are trialing different things. Drinkable milk is definitely on the cards, but in NZ it seems the focus is on getting casein protein for making better vegan cheese and ice cream. There's an article talking with one NZ company here.
The milk, cheese, and ice cream is already being created and taste tested. The problem is the scale, it needs to be scaled up significantly from current quantities and this may be a challenge. But there are many places working on it, so it's likely just a matter of time.