Persistent directional selection on body size and the paradox of stasis

"Given that investment in offspring affects size in general, we expect selection against investment per offspring to balance upward selection on size."

This approach could be effective if the juvenile's growth curve was perfectly in line with the adult's investment period but, in cattle, that's not the case.  With cattle, the juvenile won't even reach half of it's mature size during that period.  I would contend that the 'investment in offspring' ultimately has a greater impact on the size of the adult who's making the investment than it does on the offspring who's the recipient. For the juvenile, compensatory gains will, obviously to an extent, allow it to reach it's growth potential regardless of the adult's initial level of investment.  Alternatively, by calving at two and forcing the adult to invest reasonably in the juvenile, we will have more permanently limited the adult's size which the benefits of should be fairly obvious to anyone feeding cows out of pocket.

By just selecting against investment per offspring, I think you're just as likely to end up with large, poor milking cattle that have a tremendously long compensatory growth curve as you are to successfully undermine the size paradox. 

I agree with that.