I work in a biomedical technology company, and we would easily hit 375 (1500 animals/4 years) animals in a year, mostly comprising of pigs. Our work is pretty regulated, requiring protocols that go into detailed justification of why a live animal is needed for your work, and how you are taking every measure possible to minimize the animal's suffering. I would imagine that Neuralink is required to follow something similar, but maybe their quality/audit reviews deemed their justifications (which may be in favor of balancing the risk of animal suffering/loss of life against the pie in the sky outcome for developing something that decreases human suffering) more leniently. It's not necessarily as evil as "we don't care about animal suffering, go torture and kill as many as you want". It could often be more like "This is study 2b that is evaluating this alternative pathway of prototype development, and we need 30 subjects that we have to follow over x days for the study to have statistical strength." So you can end up going through a lot of animals.