October 29, 2010
By Laurie Dixon
Research indicates the long-term horse contraceptive, porcine zona pellucida (PZP), extends the breeding season in wild horses, raising concerns over the social consequences of the drug on herds.

PZP, which is derived from pig eggs, is increasingly being used in wild horse herds . . .

Read more: http://www.horsetalk.co.nz/news/2010/10/220.shtml#ixzz38YJwjAdY