Is there equine estrogen in estradiol?

In a sense, yes. Conjugated equine estrogens are collected from pregnant mare urine and then are used to supplement women going through menopause.

This product was marketed as Premarin and sold by Wyeth Pharmaceuticals.

The pregnant mares are restrained and their urine collected. The by-product, of course, is the mare's foal. Some PMU (pregnant mare urine) foals are bred to be pedigreed and sell well. Other less responsible breeders do not put much thought into the resulting foal, which led a lot of animal rights groups to question the practice.

EC