12 ovariectomized cows plasma samples were collected immediately prior to insertion every 24 hours after insertion immediately prior to insert removal on day 7 and 24 hours following insert removal progesterone content in the plasma was determined by direct radio immuno assay coat a count dpc usa the poly u03b5 caprolactone insert was evaluated clinically over three separate rounds of treatment in a commercial dairy herd number of animals treated number of inserts lost number of cows submitted for artificial insemination number of cows diagnosed as pregnant and conception rate were recorded residual amounts of progesterone remaining in the inserts after administration were determined by soxhlet extraction cidr u2122 inserts or gravimetric analysis poly u03b5 caprolactone inserts upon insertion of the poly u03b5 caprolactone or cidr u2122 intravaginal inserts plasma progesterone concentrations were observed to rise rapidly fig9 elevations in plasma progesterone initially declined from approximately 5 ng ml over the first 3 to 4 days and thereafter sustained constant concentrations of approximately 2 ng ml to the seventh day these concentrations had returned to undetectable basal levels within 24 hours of insert removal analysis of the pharmacokinetic parameters auc c max and t max showed that there were no significant differences between the test and reference product within or between rounds table 3 in addition both inserts released the same amount of progesterone over the insertion period table 3 the large scale clinical trial showed that poly u03b5 caprolactone insert retention was significantly greater compared to the cidr insert of the 361 animals that received the poly u03b5 caprolactone insert only 1 was lost compared to 16 for the 387 animals that received the cidr insert this study has shown that an intravaginal insert comprising poly u03b5 caprolactone and containing 10.