Four experiments were performed to
determine whether cooling cows during
final maturation of oocytes and early embryonic
development or injection of vitamin
E at AI prevented adverse effects of
heat stress on pregnancy rates in lactating
Holstein dairy cows. In Experiment
1, cows were placed in a cooling facility
containing sprinklers and forced ventilation
or received shade only from 2 to 3 d
before until 5 to 6 d after breeding.
Although cooling had no effect on detection
of estrus, pregnancy rates were increased
slightly for cooled cows (8 of 50
cows; 16.0%) compared with those for
cows exposed to shade only (2 of 32
cows; 6.2%). In Experiments 2 through
4, cows were administered 3000 IU of
vitamin E or placebo i.m. at AI during
two consecutive summers and one winter
in Florida. Administration of vitamin E
had no consistent beneficial effect on
pregnancy rates during summer or winter.
Short-term cooling improved pregnancy
rates slightly in heat-stressed
cows, but administration of vitamin E
had no beneficial effects on pregnancy
rates during heat stress. Further improve