Vitamin E primary affects the sex hormones of the animal, sex hormones naman will affect the libido, egg production etc. Vitamin E is just a part of the whole picture. To increase egg production you must also have enough energy so eggs can be release from the ovaries. Vitamin E could help increase litter size and return to heat of the animal.
The commercial available vitamin b in the market are multivitamins, usually andun na yun iba't ibang B vitamins plus other minerals. B complex with liver extract is fine. Just compare the cost if it is practical naman.