| Summary: | Two experiments tested the efficacy of gonadotropin-releasing hormone
(GnRH) or estradiol cypionate (ECP) administration in combination with
controlled internal drug release (CIDR) inserts on pregnancy rate to fixed-time
artificial insemination (FTAI) in beef heifers. In the first experiment, heifers in the
two ECP groups received ECP in conjunction with the CIDR insert. The CIDR
insert was removed and PGF was administered on either d 7 or 9. Heifers
received ECP 24 h after CIDR removal and were inseminated 30 h after ECP.
Heifers in the two GnRH groups received GnRH in conjunction with the CIDR
insert. Heifers received PGF on either d 6 or 7, and the CIDR insert was
removed on d 7. Heifers were inseminated and received GnRH 48 h after CIDR
removal. Pregnancy rates to FTAI were higher for heifers treated with GnRH.
Pregnancy rate to FTAI was highest for heifers in the GnRH group that received
PGF on d 6 and was lowest for the group that received ECP in combination with
a 7-d CIDR insert. In the second experiment, heifers received GnRH in conjunction with the
CIDR insert. CIDR inserts were removed and PGF was administered on d 7.
Heifers were inseminated 60 h later, with one group receiving GnRH at
insemination. Pregnancy rate to FTAI was higher for heifers that received GnRH
at insemination.
The final experiment tested the efficacy of estradiol 17_ (E17) or GnRH in
combination with a CIDR insert on pregnancy rate to FTAI in Brahman cows.
Either E17 or GnRH was administered in conjunction with the CIDR insert.
CIDR inserts were removed on d 7. Cows in the GnRH group received PGF on
d 6 and GnRH at insemination which occurred 48 h after CIDR removal. Cows
in the E17 group received PGF on d 7, E17 24 h later, and were inseminated 30
h after E17 administration. Pregnancy rate to FTAI was higher for cows treated
with E17.
These data indicate acceptable pregnancy rates were obtained when the
CIDR insert was combined with either GnRH in beef heifers or with E17 in
Brahman cows.
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