Evaluation of progesterone controlled internal drug release dispensers for synchronization of estrus in sheep

Abstract

Three experiments were conducted to evaluate 366 mg progesterone, type S, controlled internal drug release dispensers (CIDR-S) for estrous synchronization. In Experiment 1, synchronization of estrus was investigated in early fall. Of 129 ewes treated for 12 days, 117 (91%) were bred within 5 days of dispenser removal. A total of 118 (91%) ewes lambed with 74% of lambings occurring within 6 days of each other. In Experiment 2, duration of progesterone release from CIDR-S was examined over a 45-day period. In ovariectomized ewes, plasma progesterone levels were 2.8 ng/ml 3 days after insertion and then decreased gradually to 0.3 ng/ml by day 30. In cycling ewes, Day 3 levels were 4.5 ng/ml due to contribution of luteal progesterone. Exogenous progesterone blocked estrus and ovulation for 27 to 31 days, after which ovulation occurred without estrus. Estrus with ovulation occurred by Day 38 to 45. In Experiment 3, cycling ewes were treated for 0, 4 or 12 days and progesterone residue in adipose, liver, kidney and muscle tissues was measured. Residues differed ( P < 0.05) among treatment groups and tissue types with no interaction. Tissue progesterone levels of ewes treated for 4 days were greater than those in ewes treated for 0 and 12 days. Adipose tissue contained over 10 times as much progesterone as other tissues. Progesterone residues were related ( r = 0.5, P < 0.05) to circulating progesterone levels at time of death but with neither total nor peak levels reached during the treatment period. CIDR-S had a 92% retention rate and provided a simple and effective delivery of natural progesterone.