Determination of the proper time for mating after oestrous synchronisation during anoestrous or oestrous by measuring electrical resistance of cervical mucus in ewes

The purpose of the present study was to investigate whether the electrical resistance values of the cervical mucus and/or blood οestradiol-17β and progesterone concentrations at mating, after oestrous synchronisation during the anoestrous or oestrous period in ewes, are related to fertility. Oestrus was induced by medroxyprogesterone acetate-impregnated intravaginal sponges (Veramix, Upjohn, USA), either for 12 days (12-day group; 24 Kymi and 28 Chios) or for 14 days (14-day group; 24 Kymi and 28 Chios), plus 400 IU equine chorionic gonadotropin (Intergonan, Intervet, the Netherlands) i.m., at the time of sponge removal. In each case, one blood sample was collected from all ewes at sponge insertion, at sponge removal and at oestrus, for the determination of serum οestradiol-17β and progesterone concentrations, using a radioimmunoassay. The electrical resistance of the cervical mucus was measured once, just after oestrus detection by teaser rams, using a digital heat detector. All ewes found to be in oestrus were mated to fertile rams. Pregnancy was determined by transabdominal ultrasonography 35-40 days after mating. Kymi ewes were in anoestrous, while those of Chios were in the oestrous period. The 14-day treatment resulted in better outcome as concerns oestrus detection and pregnancy rate than the 12-day treatment, in either oestrous or anoestrous period ewes. Oestradiol-17β concentrations at sponge removal and at oestrus were lower (P < 0.05) in the 14-day group than in the 12-day group, in both oestrous or anoestrous period ewes. Progesterone concentrations at sponge insertion and removal were higher (P < 0.05), while progesterone concentrations and electrical resistance values of the cervical mucus at oestrus were lower (P < 0.05) in ewes of both groups who conceived compared to those that did not, either in oestrous or in the anoestrous period. Linear regression analysis revealed a positive relation between the electrical resistance values of the cervical mucus and blood serum progesterone concentrations in both oestrous or anoestrous period ewes. The electrical resistance of cervical mucus could be useful for the detection of the proper time for mating after oestrous synchronisation in ewes.