الكاتب: Multiple References

The use of dexamethasone to induce parturition in beef cattle has given highly repeatable results when it is injected after 255 days of gestation. However, a high frequency of retained placentas and concomitant endometritis are a common sequelae (1, 2, 7, 15, 21). Blood serum estradiol and estrone concentrations in cattle increase approximately tenfold during the month before parturition, with the most dramatic rise occurring during the last five days of gestation (5, 9, 10, 13, 18, 20). It has been suggested that cows induced with corticoids prior to normal term, may calve without sufficient estrogen concentrations to result in normal placental delivery (4, 11, 16). However, the use of estrogens in various induction regimes in an attempt to mimic normal hormonal events at parturition has yielded conflicting results (11, 12, 14, 16, 19). This inconsistency of results may be due to uncontrolled experimental error such as breed and age differences of cattle used in the experiments, the number of days before predicted calving when induced, small numbers of experimental animals and variations in the type, dose and method ofadministration ofestrogens. Estrogens dissolved in oils or absolute alcohol and administered intramuscularly may not have been present long enough or in high enough concentrations to have the desired result.