Because it didn’t do a very good job of correlating the observed facts.
The heliocentric model wasn’t perfect but it did a better job of explaining the motions of the heavenly bodies.
Euclidian geometry works well within the confines of the village but fails at larger distances because the surface of the earth is curved.
Likewise, the sperm-blocking theory of PZP doesn’t do a good of correlating the observed facts, especially the skewing of sex ratios in favor of females, and therefore deserves a fair share of skepticism.
Better yet, it should be tossed out along with its adherents in favor of the ovary-killing theory, which is not perfect but does a better job of explaining the observed facts.
RELATED: Sperm-Blocking Theory Doesn’t Account for Self-Boosting Mares.
Western Horse Watchers Association 