The standard human cortical screw is suitable for very large dogs and equines. Because it is a human product made in large numbers, 4.5mm screws are relatively inexpensive.
Use of Self Tapping Screws can save considerable time and trauma. Reducing surgery time will reduce morbidity. Pull out strength is not affected provided the self tapping flutes lie outside of the cortex. Self Tapping Screws are less effective in dense cortical bone. e.g. calcaneus. It is advised that an appropriate tap be available should the need arise.
Drill data: Pilot Drill 3.2mm Clearance Drill 4.5mm