Use of timed AI programs has become
commonplace on most dairy farms either
because cows are not watched sufficiently to
detect estrus, or because expression of estrus
is limited by confinement housing. A number
of programs are available to set up firstpostpartum
inseminations that include some
timed AI or timed AI of all cows once the end
of voluntary waiting period (VWP) is reached.
One approach may include a period of heat
detection and AI until, for example, 100 days
in milk, when a timed AI protocol is applied
to all previously non-inseminated cows.
Another approach includes injections of
prostaglandin F2α, followed by periods of heat
detection and AI, until a timed AI protocol is
applied to all previously non-inseminated
cows. Another approach may use a timed AI
protocol that is applied so all cows can be first
inseminated after the end of the VWP. The
most sophisticated system involves presynchronizing
estrous cycles during the latter part of the
VWP and then applying a timed AI protocol.
When protocols are applied correctly, ensuring
that each cow is injected and inseminated
appropriately, conception rates are either
equal to, or slightly less, than those achieved
when inseminations are based solely on
behavioral signs of estrus (i.e., standing
estrus). In contrast, pregnancy rates are
almost always greater because more cows are
inseminated (PR = AI submission rate ×
conception rate). Early application of
Ovsynch before pregnancy status is known
can allow all open cows to be re-inseminated
by 2 to 3 days after their nonpregnant status is
confirmed. This last program can essentially
eliminate heat detection; when heats are
observed, however, it becomes a bonus to the
system.
