I'm not sure that I understand why the number of lives lost is relevant in this context. Its obvious that more chickens will have to die than steers to produce 1,000 pounds of meat.
As for efficiency:
I think many Americans eat more meat than is necessary, or that is good for them, as mentioned above it would be better to directly consume many of the feeds we give animals.
Seems to me that ruminants should be grazed on rough land that is not suitable for other agricultural purposes and taken from grazing directly to slaughter.
Hogs and poultry should be raised as much as possible on by products of human food production and where possible by foraging for themselves. Particularly in the case of hogs, only where they can do so without causing excessive damage.
These are just thoughts on minimizing inputs of natural resources.
If looked at as producing food to put on the grocery store shelf, as cheaply as possible, I think the American farmers and manufacturers are doing a good job now.
I also believe that our food is generally safe but there have always been and there will continue to be food borne illness. We should strive to minimize this however possible.
Lastly, I think the biggest inefficiency in this country comes from waste.