Influence of estradiol administration to lactating cows on bacterial growth in milk whey

Bacterial growth (E. coli) in whey was studied by turbidometric technique during estradiol benzoate administration (0.02 mg/kg of body weight/day for 12-19 days) to 13 ovariectomized cows at three stages (early, mid and late) of the 1st- and 3rd-lactations. Whey samples from cows at early stage (60-90 days) of 1st-lactation promote the growth of E. coli during the estradiol treatment. This included a significant increase in the maximum turbidity and a decrease in the generation time. Bacterial growth was inhibited in whey from cows at other stages of lactation during the hormone treatment. The degree of inhibition varied at different stages of lactation. No significant alterations in the ability of whey to support bacterial growth were observed in 3 ovariectomized cows treated with the drug vehicle (arachis oil) alone. Majority of the quarters included in the present study were bacteriologically negative throughout the study.