Effect of dexamethasone on experimental Escherichia coli mastitis in the cow.

The effect of intramuscular administration of dexamethasone on milk production and on several clinical and hematologic indicators in cows with experimental Escherichia coli mastitis was studied. Two groups of three cows each were intramammarily inoculated with 20 x 10(5) cfu E. coli 0101 K99 F41 in rear quarters. Immediately after inoculation one groups received 30 mg dexamethasone intramuscularly, whereas the other group was injected similarly with pyrogen-free saline. Fourteen days later milk production losses were markedly less in the dexamethasone-treated group. Dexamethasone treatment reduced local clinical signs of inflammation, significantly increased rectal temperatures, and diminished inhibition of rumen amplitude during the acute phase of infection. Moreover, cows treated with dexamethasone showed diminished neutropenia, more pronounced hypozincemia, and delayed onset in the decrease in plasma iron concentrations. Possible mechanisms by which these changes are accomplished are discussed.