Weight
From MHWiki
The weight of a mouse used to be involved in determining the specific amount of points and gold earned for catching it.
A heavier mouse used to be considered easier to catch because of its girth. As a result, heavier mice were worth fewer points and more gold. Now the amount of points and gold is simple determined by the breed of mouse, irrespective of weight.
Statistics on the average weight and heaviest weight of each breed of mouse can be found on a Hunter's Profile under the "Mice" tab.