In other words, you place the hens in a broody pen. Such treatment may return a hen to production, but one or two weeks of eggs are usually lost. Hens which have had one broody period are likely to have more. There is some older work suggesting that progesterone, or perhaps estrogens, may have some effect on broodiness, but this has not really been carefully studied. VIP is the brain hormone which controls secretion of prolactin.
Prolactin is the pituitary hormone which causes broodiness.
If you immunize a turkey against VIP, there will be no stimulation of prolactin during the reproductive cycle, and no broodiness. This technique was worked out by Dr. M. E. El Halawani at the University of Minnesota, and is being commercialized for turkey breeders based on his patent. As far as I know, it has not been tried with chicken breeders, but it should work the same. When you wash an egg, you remove part of the cuticle that covers the shell. It is important that the temperature of the wash water be approximately 20 degrees F higher than that of the egg.