Marybeth Devlin responds to PZP SPIN in High Country News titled: PZP: Where hope, science and mustangs meet http://www.hcn.org/articles/pzp-where-hope-science-and-mustangs-meet
Ms. Wilder is disinformed. PZP does not “cause eggs to reject sperm.” That hypothesis has been disproved. PZP is a registered pesticide whose mechanism-of-action is to cause auto-immune disease. PZP tricks the immune system into producing antibodies that target and attack the ovaries. PZP’s antibodies cause the mare to suffer ovarian dystrophy, oophoritis (inflammation of the ovaries), ovarian cysts, destruction of oocytes in growing follicles, and depletion of resting follicles. Not surprisingly, estrogen levels drop markedly as the ovaries are slowly destroyed. But PZP’s adverse effects are not limited to the individual animal. As a recent study — which included the Little Book Cliffs, Colorado herd and the McCullough Peaks, Wyoming herd — found, PZP extends the birthing season to nearly year-round. Out-of-season births put the life of the foals and the mares at risk. Further, the same study disclosed that the pesticide causes a delay lasting 411.3 days (1.13 years) per each year-of-treatment before mares recover their fertility after suspension of PZP. However, some mares never recover — they are left permanently sterile, and quickly too. Indeed, yet another study found that sterility could occur in some mares from just three years of PZP injections or from just one treatment if the pesticide were given to a filly before she reached puberty. Because PZP messes with the immune system, it ironically works “best” — sterilizes faster — if the mare has a strong immune system. But, conversely, PZP may not work at all in mares whose immune function is weak or depressed. So, the pesticide discriminates against the very horses that Nature has best equipped for survival against disease while favoring and selecting for the immuno-compromised. Worse yet, tests performed via radioimmunoassay indicated that PZP antibodies are transferred from mother to young via the placenta and milk. The transferred antibodies cross-react with and bind to the zonae pellucidae of female offspring, as demonstrated by immunofluorescent techniques.
But there is no need for PZP or any other population-reduction measures. BLM’s wild-horse overpopulation “data” is a fraud. Reviews of BLM’s year-to-year growth-estimates for various herds disclosed biologically-impossible growth-rates. For instance, just recently in Oregon, BLM claimed that the famous Kiger herd’s population grew from 21 horses to 156 horses in just four years — an increase of 643%. Stealthily inserting bogus birth-rates into the data, then wrongly equating the birth-rate with the population growth-rate, and failing to factor in the mortality-rate — that is how BLM creates the false impression of a population-explosion. Another ruse BLM employs is restricting maximum herd-size below minimum-viable herd-size. Then, whenever a herd is made to appear — via false figures — to exceed the arbitrary management level, BLM screams “excess!” and declares an immediate need for mass-removals and sterilizations. It should be noted that more than 70% of the herds are “managed” below minimum-viable size, including Spring Creek Basin.