Abstract
Progesterone (P<inf>4</inf>)-impregnated controlled internal drug-releasing device for goats and sheep (CIDR-G) is used in the estrus synchronization protocol; however, it is not commercially available in Japan. In this study, we investigated whether a modification of CIDR-B, designed for cattle, could be used as a P<inf>4</inf> release device for synchronizing estrus in goats. An in vitro analysis showed that the dissolution rate was not significantly different between CIDR-G and modified CIDR-B (CIDR-M). The administration of CIDR-G or CIDR-M to dairy goats resulted in plasma P<inf>4</inf> concentrations being maintained at the functional luteal phase levels (>2 ng/ml) in both groups for 12 days after administration. However, P<inf>4</inf> concentrations at 2, 4, and 8 days after the administration of CIDR-G were significantly higher than those after the administration of CIDR-M. These results suggest that the CIDR-M examined in this study can maintain P<inf>4</inf> levels for 12 days after its administration as a P<inf>4</inf> release device.