In study 3, HP attenuated LH release and reduced ovu-
lation (19.0 vs. 48.4%) in response to GnRH compared
with LP. Combining GnRH and 2 doses of PGF2α in
the 5-d timed AI protocol improved follicle turnover,
luteolysis, and P/AI in heifers. Elevated concentrations
of progesterone suppressed LH release and are linked
with the low ovulatory response to the initial GnRH
treatment of the protoco