Holstein cows and virgin heifers were
treated with GnRH and PGF in a novel 2a
ovulation synchronization protocol, which
involves one fixed-time insemination. One
injection of GnRH is given on a Monday
morning, followed in 7 days with an injection
of PGF . Approximately 32 hr later, ovula- 2a
tion is induced with a second injection of
GnRH, and one insemination is made 18 hr
later. Control cattle were given one injection
of PGF and inseminated at estrus. Preg- 2a
nancy rates measured between 28 and 35
days after insemination by ultrasonography
were slightly, but not significantly, higher in
controls (52.9%) than in the ovulation synchronization
treatment (44.3%). This treatment
may be particularly well suited to cows
in which estrus is rarely observed, as well as
for synchronizing first or repeat services