The horses that ship internationally like this are generally worth $1M+ so its not like this was the solution every settled on as "eh, good enough" and more like, even with all this time and effort, this is still the beat solution we can come up with. Also for what its worth, I don't know that this measure has ever been taken in my lifetime. The sedatives have always worked in every case I've know. Putting down a horse in international shipping for safety is an extreme edge case