There is quite a lot of data on this. Remember that 300% only means "3 times". This seems to be true for most of the B vitamins. Some nutrients increase dramatically more, like Vitamin C, which can increase over 30 times or 3000% in a sprout versus dry seed.
Starches reduce because they get used up, and various other vitamins, proteins and minerals become more bioavailable, and fats change. Other phytochemicals also seem to be at their peak at this time - the clever little substances that aren't vitamins, minerals or macronutrients, but things like glucosinolates.
When you think about it, there has to be a lot going on for this tiny little packet of genetic wisdom to transform itself into a fleshy, complex, vital plant that bears no resemblance to a little dry seed. Extraordinary really.
It also depends how long you sprout them for. When humans eat sprouts we take them much further along, whereas for birds we usually just chitt them, but that's still good as most of the important action occurs early in the sprouting process.
I'm making myself want to go and sprout some bird seed for my own lunch...
