i read about a breeder doing this with pitts - bulls, pines, ect... he claimed to have had success with it especially with gravid females. if you are seriously interested, it was about 3 yrs ago on the pitts forum. you could google it or post on there. i'ld bet he is still on that forum.
i also saw a video about feeding rates by a big bin breeder. he also tested vitamins with reported positive effects.
if it's something that interest you, than i say go for it. make it a controlled environment and document the results. than you can share them later.
jonathan
p.s. just as a disclaimer, i have never tried it myself and don't feel the urge to. i prefer plain old fat healthy rats/mice 