Our purpose was to determine if giving
an additional injection of GnRH to beef
heifers synchronized with the Cosynch
protocol would increase pregnancy rate to
timed A.I. Eighty yearling beef heifers
received an injection of GnRH, 7 days before
receiving an injection of PGF (Cosynch).
One half of the heifers were also given an
injection of GnRH 14 days prior to the PGF
injection (2×GnRH-Cosynch). All heifers
were given a GnRH injection 2 days after
PGF and inseminated at that time. Pregnancy
rate for the 2×GnRH-Cosynch group (40%)
was not different than that for the Cosynch
group (50%) and was actually numerically
lower. This trial suggested that an additional
injection of GnRH 1 week prior to the
Cosynch protocol was not beneficial in
increasing the pregnancy rate of heifers to
timed A.I.
