Two trials were conducted to study factors which influenced the amount of progesterone (P4) remaining in a CIDR intravaginal device used for a treatment period of 15 days and the associated plasma P4 concentrations. In the first trial, the initial P4 content of these devices was varied from 0 to 2.67g P4. In the second trial, animals were treated with either one or three devices which had been moulded to contain the same amount of P4 (1.9g/device). Increasing the initial P4 content of a device increased plasma P4 concentrations, but at a diminishing rate so that devices containing 1.86g P4 maintained similar levels of plasma P4 to devices containing 2.67g P4 (2.48 vs 2.63 ng/ml). This was associated with a quadratic relationship in the residual P4 content in the used devices. Using three devices per animal trebled plasma P4 concentrations and did not alter residual P4 content. These results indicated that P4 release is influenced more by device characteristics than by animal variation.

ST, Bell, MR Cropper, and DP Poppi

Proceedings of the New Zealand Society of Animal Production, Volume 50, , 449-452, 1990
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