Cows exposed to heat stress before or
after calving or both are prone to reduced
fertility because of reduced expression of
estrus and less embryonic survival if pregnant.
Cows calving on three dairy farms
during the summer of 1998 were studied.
First inseminations were programmed to
occur between 50 and 70 days in milk using
the Ovsynch protocol, which included a timed
artificial insemination. Control cows were
treated similarly but did not receive the second
injection of gonadotropin-releasing
hormone and were inseminated only after
estrus was detected (Select Synch). The
Ovsynch protocol increased pregnancy rates
from 17.6 to 31.3%, because AI submission
rates were 100% and conception rates were
not different from those of control (Select
Synch) cows.
