Effect of additional progesterone treatment during intravaginal progesterone priming in anestrous ewes

Abstract

Oestrus induction with intravaginal progesterone is the most preferred method in anoestrus sheep. In previous studies it was argued that the decrease in the progesterone level before the sponge is removed reduces the efficiency. This study aimed to test the hypothesis that additional progesterone treatment during the progesterone priming in anestrous ewes could increase the reproductive efficiency of the induction. The study conducted on 261 Kangal sheep, which were pregnant in autumn and gave birth in spring and breastfed their lambs for about 60-75 days. All animals included in the study were randomly divided into 3 different groups as P-7 (n = 86), P-8 (n = 80) and control (n = 95). At the beginning of the study a progesterone impregnated sponge was placed to all ewes (Day 0). During sponge treatment, an injection of progesterone was given to P-7 and P-8 group 7 and 8 days after the was sponge placed, respectively. As for control group, no additional progesterone was given during sponge treatment. All groups received 500 IU pregnant mare serum gonadotropin at the sponge withdrawal. Ram was introduced to all ewes the 10th days of the study. There was no difference between the groups in terms of estrus rate (P = 0.28), pregnancy rate (P = 0.32) and multiple pregnancy rates (P = 0.38) (P = 0.28). We considered that the main reason for unexpected low progesterone concentration at the end of the treatment might be the result of high feed intake and metabolic rate. On the other hand, this additional dose could be caused by an excessive increase in progesterone levels in the sheep, which could be the reason for the decrease in reproductive parameters. Additional progesterone support during progesteronebased synchronization yielded acceptable results. However, progesterone can be administered in injection form in the earlier days of synchronization or before sponge insertion to obtain better results.