The effects of a low dose of cabergoline on induction of estrus and pregnancy rates in anestrous bitches

Abstract

This is the first report of successful induction of normal estrus and ovulation in breeder bitches with as a low dose as 0.6 μg/kg/day of cabergoline formulation marketed for use in women. Sixty-one pure breed bitches from various breeds were used in the study at their already determined periods of anestrus. Twenty-four dogs formed the control group, while 37 bitches were administered with two different doses of cabergoline (recommended dose group, n = 10, 5 μg/kg/day and low dose group, n = 27, 0.6 μg/kg/day). Induced estrus rates and mean treatment and proestrus durations of dogs in these two dose groups were compared. At the second phase of the study, the effects of 500 IU human chorionic gonadotropin (hCG) administered on days 1 and 3 of estrus induced by the low dose of cabergoline, on the duration of behavioral estrus, ovulation rates, pregnancy rates and the number of offspring were investigated. For this purpose, the dogs with signs of proestrus (22/27) following the treatment in the low dose group were assigned into two subgroups. Five hundred IU of hCG (Pregnyl, Organon, Turkey) was intramuscularly administered to eight of these dogs [low dose (hCG+) group] on days 1 and 3 of estrus. The remaining 14 dogs were not treated with hCG [low dose (hCG−) group]. An aqueous solution of cabergoline (Dostinex, Pharmacia, Italy) was orally administered until 2 day after the onset of proestrus or for a maximum of 42 days. Blood samples were taken daily from all treatment and 11 control bitches during the first five days of behavioral estrus to measure progesterone concentrations. In the recommended dose and low dose groups, estrus was induced between days 8–45 and 4–48 (mean: 23.63 ± 14.33 and 24.41 ± 14.31 days), in the ratio of 80.0 and 81.5%, respectively ( p > 0.05). In both dose groups, post-treatment interestrous intervals were significantly shorter than both those of the control group and their own pre-treatment interestrous intervals ( p < 0.05). Ovulation rates, pregnancy rates and mean number of offspring delivered by the dogs in the recommended dose, low dose (hCG−), low dose (hCG+) and control groups were found to be similar ( p > 0.05). However, the mean duration of behavioral estrus of the dogs in the low dose (hCG+) group was found to be significantly longer compared to dogs in all other groups ( p < 0.05). In both dose groups, no correlation could be found between the anestrus stages and treatment durations ( p > 0.05). Shortly, it has been concluded from the study that (1) normal and fertile estrus can be induced more economically in bitches during different stages of anestrus using as a low dose of 0.6 μg/kg of cabergoline formulation marketed for use in women, and that (2) hCG injections on days 1 and 3 of the estrus induced by this method has no positive effects on the ovulation rates, pregnancy rates and the number of offspring per pregnancy.