Calcium cloprostenol administered at a continuous low dosage induces luteolysis and abortion in bitches

Abstract

The aim of this study was to determine whether calcium cloprostenol administered at a continuous low dosage induced luteolysis and abortion in bitches without a high incidence of adverse effects. Calcium cloprostenol was administered subcutaneously at doses of 0 to 5.26 μg/kg/d delivered by miniosmotic pumps for 7 d. The experimental animals consisted of greyhound bitches in the diestrous control group (0 μg/kg/d, n = 5); diestrous treated group (1.30 to 5.15 μg/kg/d, n = 5); pregnant treated group (2.22 to 5.26 (μg/kg/d, n = 5); and environmental control group (no miniosmotic pump implanted, n = 4). The environmental control bitches were used as controls for environmental effects on cardinal signs (rectal temperature, respiration rate and heart rate). A fifth group comprised various breeds of privately-owned pregnant treated bitches (3.37 to 5.00 μg/kg/d, n = 3). All diestrous and pregnant bitches were in the mid luteal phase (28 to 38 d post estrus). Plasma progesterone concentrations were measured from the day before miniosmotic pump implantation (Day -1) until Days 69 to 73 (diestrous control and diestrous treated groups) or until Days 83 to 93 (pregnant treated group). Cardinal signs were measured in all experimental bitches from Day -1 to Day 8. Vaginoscopy was carried out on all the experimental greyhound bitches on Days -1, 1 and 3, while uterine ultrasonography was performed daily on the pregnant bitches from Day 0 until abortion was complete. The privately-owned pregnant bitches were observed for 6 to 8 h after the implantation of miniosmotic pumps, discharged from hospital and returned 3 to 7 d later for examination. Plasma progesterone concentration and rectal temperature declined simultaneously after miniosmotic pump implantation, and hypothermia (<37.9 °C) was observed in all treated bitches. The plasma progesterone concentrations remained <1 ng/ml in 9 of 10 treated greyhounds from Day 9 onwards. There were no changes in respiration rate or heart rate or other obvious adverse effects associated with calcium cloprostenol administration in the treated greyhounds. The owners of all 3 privately-owned pregnant treated bitches reported polydipsia, and 1 bitch (5.00 μg/kg/d) became lethargic and vomited. All pregnant bitches aborted. This study demonstrated that calcium cloprostenol administered at a continuous low dosage induced luteolysis and abortion and that it was well tolerated by 12 of the 13 bitches.