Management of the estrous cycle is now
more practical than it was a decade ago because
of our understanding of follicular waves.
With availability of three gonadotropin-releasing
hormone (GnRH) products and two prostaglandin
products, the cycle can be controlled for
fixed-time inseminations with little loss in conception
rate compared to inseminations after
detected estrus. Various systems are effective
for programming first inseminations with or
without some heat detection. With the incorporation
of transrectal ultrasonography for early
pregnancy diagnosis 28 to 30 days after insemination,
routine heat detection programs could
be eliminated by reprogramming each cow after
an open diagnosis. The most limiting factor in
the control of the cycle is the proportion of
missed heats in estrus-synchronization programs
that rely partly or solely on heat detection.
Pregnancy rate (the proportion of cows that
become pregnant of all cows programmed for
insemination) is the best measure of an estrussynchronization
program, because it measures
total number of pregnancies achieved per unit of
time rather than simple conception success at
any given insemination.
