Effects of estrogen treatment on dominance relationships in cows.

The effects of prolonged estrogen treatment were studied in two groups of eight ovariectomized heifers. In Group I, four animals were treated with increasing doses of estradiol benzoate (300 micrograms/day to 1.5 mg/day) for 180 days. In Group II, four animals were treated with 1.5 mg/day for 90 days. In each group the other four animals received the vehicle only. Ninety percent of the dominance relationships between treated and control animals was reversed. The delay was, nevertheless, longer than those observed previously following androgen treatment. As is the case following androgen treatment, changes in social rank could not be explained by an increase in aggressiveness by treated animals, but rather could be explained by a lowered reactivity to aggressions and perhaps by a decrease in fear reactions.