It's not unusual to go through 30 mice in a two week trial, and euthanizing them after. If you do the math would be about 700 mice a year, but here's the thing, they don't immediately start another trial with 30 mice for another 2 weeks after. There is a long period between trials to work out the data, figure out what they learned, adjust the study, and then repeat.

Neuralink decided "adapting the study is inefficient, let's just repeat the experiment with the data we gathered from the dead animals 3 trials ago!" Which can be faster, since you are always gathering more data, but it's inefficient. You might kill 2-3 trials worth of animals before you realize you hit a dead end and need to completely rethink the approach.