PMU means Pregnant Mare Urine.  PMU farms are the mass collection and production of pregnant mareurine. The urine collected contains a hormone variant called Premarin.

 

This estrogen hormone is gathered through a catheter, then given to women in hope to alleviate menopause symptoms. Premarin is given in several forms; pills, creams, injections, patches and vaginal rings.
 
full Text:
http://thepersianhorse.wordpress.com/2011/08/04/stop-cruelty-to-premarin-horses-please-sign-petition/
Petition:
http://www.ipetitions.com/petition/premarin/