Summary
Lactating Holstein cows and replacement
heifers were treated with a novel synchronized
ovulation protocol, which involves one fixedtime
insemination without heat detection. One
injection of GnRH (Cystorelin®) was given,
followed in 7 days with an injection of PGF2a
(Lutalyse®). Approximately 32 to 36 hr later,
ovulation was induced with a second injection
of GnRH, and one fixed-time insemination was
given 18 hr later. Control cattle were given one
injection of PGF and inseminated at observed 2a
estrus. Pregnancy rates measured by palpation
between 38 and 52 days after insemination in
controls (47.1%) were slightly, but not significantly,
greater than those in the synchronized
ovulation treatment (35.3%). The
treatment worked much better in lactating cows
than in virgin heifers. This treatment may be
particularly well suited to cows in which estrus
is rarely observed, as well as for synchronizing
first or repeat services.
