The highest protein and nutritional value is achieved when the tip of the root first appears. As the root gets longer, and the shoot appears, the level of protein and vitamins sinks rapidly. This high protein level is one reason that sprouted seed is so useful to breeding birds, with their higher protein requirements. Birds in a non-breeding situation can be fed less sprouts. I would give about a tablespoonful to a bird out of breeding condition, but as much as they want to eat during breeding season, at least a cup full.
Sprouted seed is also of value to moulting birds, which have an increased protein requirement.
Common sense dictates that animals in the peak of health are more likely to reproduce than those that are only marginally healthy. In numerous studies of cattle, the addition of sprouts to the diet was found to increase the production of milk and to restore fertility to cows that were sterile. This is not surprising because wheat sprouts, for example, supply more and higher-quality vitamin E than does wheat germ, a noted source of the fertility vitamin. The vitamin E content of wheat triples when it is sprouted. Oats and rye also are excellent sources of the fertility vitamin as are all sprouted seeds and nuts.