Daily oral cabergoline in lactating ewes - efficacy on prolactin levels and reproductive parameters

Abstract

Background: Ewes exhibit a seasonal breeding pattern and the management strategy of the postpartum period seriously affects the reproductive performance and lambing interval in lactating ewes. Suckling or lactating causes an increase in prolactin levels (hyperprolactinemia) in the early postpartum period in ewes. The increase in prolactin level has a suppressive effect on gonadotropins. Dopamine agonists such as cabergoline are ergot-derivated alkaloids that exert an antiprolactinergic effect. The objective of this study was to investigate the effects of daily oral cabergoline administrations on prolactin suppression and reproductive parameters for 7 days at 60 days postpartum in lactating ewes.

Materials, Methods & Results: This study was conducted in 60 mature ewes that received 2 different doses (CABlow, n = 20; or CABhigh, n = 10) of cabergoline at 60 +/- 2 days post partum. Twenty ewes in the low dose group (CABlow) received daily oral 0.5 mg cabergoline and 10 ewes in the high dose group received daily oral 1 mg cabergoline (CABhigh) for 7 days. Ewes in control groups (CONlow, n = 20; CONhigh, n = 10) received any hormonal application during the study. Blood samples were collected from all ewes to determine prolactin measurement at 60 +/- 2 and 67 +/- 2 days postpartum. Estrous detection was performed at 12 h intervals for 15 days after ram introduction. Pregnancy diagnoses were performed via ultrasonography at 102 +/- 2 and 132 +/- 2 days postpartum. Any adverse effects of cabergoline were not observed in our study. The estrous responses within the 1st 5 and 15 days after introducing rams to flock were 15%, 100%; 10%, 90%; 20% and 100%; 20% and 100% in CABlow, CONlow, CABhigh and CONhigh groups, respectively (P > 0.05). Pregnancy rate was 100%, 85%, 90%, and 100% in CABlow, CONlow, CABhigh, and CONhigh groups, respectively. Similar to the estrous response, both doses of cabergoline did not statistically affect the pregnancy rates (P > 0.05). Serum prolactin levels were 81.44 +/- 11.99, 96.67 +/- 9.41, 52.28 +/- 3.08, and 94.95 +/- 9.92 ng/mL at the onset of study in CABlow, CONlow, CABhigh, and CONhigh groups, respectively. These levels reduced (P > 0.05) in all groups (61.01 +/- 11.80, 74.66 +/- 7.24, 37.07 +/- 3.15, and 73.90 +/- 8.55 ng/mL, respectively) at the end of the application.

Discussion: Our results showed that administration of oral cabergoline was not effective in improving estrus response and pregnancy rate in ewes. The subsequent increase in estrus response and pregnancy rate in ewes in the CAB groups after introducing rams was unlikely produced by the rebound of PRL because there was a parallel increase in estrus response and pregnancy rate in ewes in the CON groups. Firstly, the failure of cabergoline to improve reproductive parameters and to reduce prolactin levels possibly could have resulted from the administration of oral route. Secondly, higher estrous response and pregnancy rate in control (CON) groups could be masked by the increment of reproductive parameters in treatment groups (CAB). The follicular wave is synchronized for about 3 days with manipulation of a single dose of estradiol-17 beta in anestrous ewes after introduction of rams. Although cabergoline did not contribute to the increment of estrous response and pregnancy rate, improvement of reproductive parameters in both control and treatment groups could be explained by the ram effect.