Horses & Hormones

DanteDante, rescued from a PMU farm and now living at Lockwood Animal Rescue Center

When NEAVS began looking into women’s health as part of our Common Ground campaign, one area stood out as particularly egregious due to its unnecessary use of horses in drug development. Hormone replacement therapy (HRT) can be prescribed to increase estrogen levels, most commonly to treat menopausal symptoms, but also for post-hysterectomy and transgender patients. The urine from pregnant mares, due to its high estrogen concentration, is a key ingredient in some popular HRT drugs.

Horse Treatment and Slaughter

On pregnant mare urine (PMU) farms, mares are used as breeding machines, confined in stalls so narrow they cannot turn around for most of their pregnancy. Attached urine collection bags can cause chafing lesions, and they are denied free access to water to increase estrogen concentration.1 Although care guides allow for exercise, the type or amount is self-regulated by farms and too often is completely inadequate.2 Female foals (fillies) are used to replace their mothers, or sold at auction for slaughter along with male foals (colts) and “spent” mares. Occasionally foals are adopted out, but Pfizer Pharmaceutical – one of the largest HRT producers – has prohibited working with animal rescue organizations.3 According to one rescue group, a PMU filly in North America has a less than one-in-ten chance of escaping slaughter. Colts have a less than one-in-fifty chance.4

This suffering is unnecessary because plant-based and synthetic HRTs exist, with comparable benefits and risks. If women switched to alternatives, thousands of mares and foals in North America – as well as tens of thousands of horses abroad – would be spared annually. Some examples of alternative drugs include, but are not limited to, Estrace, Estratab, Climara, Cenestin, and Ortho-Est.

Take Action

  • If you are taking or considering starting an HRT regimen, ask your doctor about HRT drugs that do not derive from animal suffering. Alternative drugs with comparable risks and benefits are available. Contact us for postcards to send to your doctors before your next visit. Or download them here: postcard front/postcard back.
  • PMU drugs like Premarin and Duavee are typically labeled “conjugated estrogens …  in their naturally occurring conjugated form,” rather than specifying they are made from pregnant mare urine. This lack of transparency prevents a consumer’s informed choice. Use this form to ask Pfizer to correctly label their PMU drugs, as well as end PMU drug production.
  • Are you a physician who cares about animals? Consider signing our Physicians' Pledge to recommend alternatives to PMU drugs. If you have physician friends or family members, please spread the word!
History of the HRT Industry

HRT drug Premarin, once the most frequently dispensed drug in the U.S., generates over $1 billion in annual revenue for Pfizer Pharmaceutical.8,9 In its peak year Pfizer earned $2 billion from Premarin made from the urine of 60,000-70,000 pregnant mares in the U.S. and Canada, as well as an unknown number in China and India.10,11 Sales plummeted after a 2003 Women’s Health Initiative (WHI) study, the largest HRT study in the U.S., showed long-term estrogen and progestin use increased risk of breast cancer, stroke, and heart attack.12 Around the time of the WHI study, increased exposure of suffering on PMU farms by animal protection groups also contributed to a decline in Premarin sales.

Tara and TieTara (l) and Tie (r), rescued from a PMU farm and now living at Lockwood Animal Rescue Center

With the release of conflicting studies that disagree on whether HRT use outweighs risks, and which hormone combinations are safest, Premarin sales climbed back to over $1 billion in 2012 (once again a top seller for Pfizer).5 Other PMU drugs in the Premarin family include Prempro, Premphase, and most recently Duavee.

Today, Pfizer contracts 26 PMU farms in Canada totaling 2,000 mares, each giving birth to about one foal per year.13 In addition, Pfizer has purchased conjugated equine estrogens in bulk from China and India since the 1980s. And according to a 2010 report there are “plans to ramp up production of PMU facilities in China, Kazakhstan, and Poland.”14,15 The most recent information available indicates well over 600 large-scale PMU farms in China provide estrogen mainly to Pfizer and emerging Chinese competitor Xinzi Source Biological Pharmaceutical Co., Ltd. Animal welfare regulations are subpar in China, even compared to the U.S. which requires only bare minimum regulations be met.

Pfizer’s Premarin patent expired at the end of 2012, allowing any company to make a generic version from equine estrogens. Since, Pfizer has developed and gained FDA approval for its latest PMU drug Duavee (formerly Aprela), marketed as treatment for “menopause [symptoms] and the prevention of … osteoporosis.”16

NEAVS Care for Rescued PMU Horses

Part of NEAVS’ mission is to provide lifetime care for animals rescued from the research, testing, and pharmaceutical industries. Accordingly, we were honored to provide financial support for the 2013 rescue of Tara, a pregnant mare at a PMU farm. Tara was 800 lbs underweight and pregnant when rescued by the Lockwood Animal Rescue Center (LARC), founded by NEAVS Vice President Dr. Lorin Lindner. Now safe in sanctuary, Tara has since given birth to her foal Tie Dye. In addition, Tara and Tie live with Dante, a PMU farm rescue for whom NEAVS provides Lifetime Care support who would likely have been sent to slaughter as a young male colt.

Watch a Dateline segment on PMU Horses:

1 Premarin Mares and Foals Fact Sheet. Horse Fund. Retrieved from <>.
2 The North American Equine Ranching Information Council. (2013). Recommended Code of Practice for the Care and Handling of Horses in PMU Operations. Retrieved from <>.
3 About Premarin. Red Rover. Retrieved from <>.
4 What is a P.M.U. Horse? Gentle Giants Draft Horse Rescue. Retrieved from <>.
8 Pfizer Inc. (2013). Appendix A 2012 Financial Report. Retrieved from <>.
9 What is Premarin(e)? (March 5, 2004). Retrieved from <>.
10 About Premarin. Red Rover. Retrieved from <>.
11 PMU Foal Controversy. EquiSearch. Revrieved from <>.
12 Findings from the WHI Postmenopausal Hormone Therapy Trials. (Sep. 21, 2010). Women’s Health Initiative. Retrieved from <>.
13 About the Equine Ranching Industry. (2013). NAERIC. Retrieved from <>.
14 Pfizer consigns PMU horses to killing fields of Asia. (March 31, 2012). Tuesday’s Horse. Retrieved from
15 Premarin Timeline Update for 2010. (June 2, 2010). Tuesday’s Horse. Retrieved from
16 Pfizer Inc. (2013). Pfizer Inc. Announces FDA Approval of DUAVEETM (conjugated estrogens/bazedoxifene) For The Treatment Of Moderate-To-Severe Vasomotor Symptoms (Hot Flashes) Associated With Menopause And The Prevention Of Postmenopausal Osteoporosis [Press Release]. Retrieved from <>.