Working backwards using the formula's loftar talked about on the irc a couple weeks ago I have been able to find an approximate value for the maneuver weight of a level 10 deer (I can use the same method on any animal just don't really feel like it).
The formula's loftar gave us were to calculate maximum damage (Base damage(sqrt(sqrt(quality*str)/10))) and how to calculate defense consumed by an attack (he gave us the formula sqrt(AW/BW)/2, (AW=Attack weight and BW=Maneuver's weight) I did some testing and found it to be wrong and PMed him about it and he clarified that it is really just AW/BW/2).
I calculated my max damage to be 1215.045 (don't know how rounding is handled). I then used valorous strike (with a full attack meter and neither I nor the deer had advantage) on a level 10 deer while I had 176 str and 158 melee combat and did 91 damage.
91 divided by 1215.045 is approximately .075 which is 7.5% of my max damage. That means that I took down 107.5% of its defense meter with my attack.
I used the defense consumed by an attack formula to solve for the deer's maneuver's weight. 1.075=(158*1.75(since valorous strike's weight is 1.75 melee combat))/x/2. By solving for x you find that the deer's approximate maneuver weight is 128.6 (I'd assume there was some rounding and stuff I did wrong so I'd bet its really 130).
This method can be used to find the maneuver weight of any animal (aslong as you don't 1 hit it).