An odd way to prune an Arborvitae unless you are a deer.  Here is a classic example of deer browsing on one of their favorite foods.  The eat off the fresh new foliage on the part of the plant they can easily reach, and continue to eat as new growth is formed. 

If you are not into hunting, what are some options? 

Fencing the plant itself in this case might be a simple option in this case since the Pyramidal Arborvitae stays quite narrow on its own so a small amount of fencing around the base of the plant up five feet or so would eliminate the browsing and the plant would be allowed to grow naturally. 

Another option would be to apply a spray deterrent or repellent of some type.  Deer repellents are basically something that tastes terrible to the deer once sprayed on the foliage without harming the plant.  The deer spray will need to be re-applied every couple of weeks or when the rains wash it off.  It is reasonable priced and economical to save your plant from deer browsing.

Another option is to plant plants that deer do not prefer.  Deer preferences change from one area to another so talk to your local landscape companies or talk with local gardeners to find out what works in your neck of the woods. 

An alternate option for most arborvitae that deer may not eat would be Green Giant or Spring Grove which are a different species that deer do not prefer.  Or perhaps you can select an upright Juniper like an Eastern Redcedar that you might have better luck with.

One other note in areas with high deep pressure when you plant new plants, deer will many times sample that new plant as it was just place before them.  Always be sure to always use a deer repellent on all new plants the very first night so that deer won’t have to damage your plant to find out they do not like that plant.