Altough IATA-LAR states 4 heads a pallet, it would be too much of a squeeze in most cases. It's usually 3 heads a pallet and as said elsewhere even with that you will bump against the max payload (on 747F ) before you run out of pallet positions ( Don't even think of using super lightweight rickety pens - if 1500 pounds of steak-to-be toss a tantrum you'll appreciate a sturdy pen ). Also, most of the cattle that gets airlifted is epxensive breeding stock; packing them too closely will increase the risk of injuries if the flight gets bumpy. Delivering injured goods will have the vets, the customer and god knows who else climbing all over you - not worth the hassle...