Effects of Rams and Luteal or Follicular Phase Ewes on Preovulatory LH Surge Characteristics in Ewes*

This study aimed to investigate whether the preovulatory LH surge mechanism is involved in sheep-to-sheep interaction for oestrous synchronisation. For that purpose, anoestrous ewes were inserted with intravaginal progestagen sponges for 13 days to induce ovulation. Upon sponge withdrawal, they were introduced either to 4 rams (n = 6, ram group), or to 4 ewes which were in follicular period (n = 6, follicular group), or 4 ewes which were in the luteal period (n = 6, luteal group) or else they were kept alone (n = 6, control group). The ewes were weighed and their body conditions were scored prior to the experiment. There were no significant differences in the body weights and body condition scores of the 4 groups. Blood samples were collected at 2 h intervals from sponge withdrawal (0 h) until the 96 h, and twice daily thereafter for 10 days. LH analyses were carried out on blood samples. According to data from the analyses, no LH surge was observed in the follicular and luteal groups within the 96 h following sponge withdrawal. The periods for observation of an LH surge were 162.7 ± 46.2, 224.0 ± 21.5, 58.7 ± 4.6 and 69.7 ± 6.7 h for the luteal, follicular, ram and control groups, respectively (P < 0.001). Although no significant difference was observed between the ram and control groups, the LH surge in these groups occurred significantly earlier than those of the luteal (P < 0.05 and P = 0.075, respectively) and follicular (P < 0.001 for both groups) groups. In conclusion, it appears that female sheep delay the LH surges compared to the ram-introduced or control groups and that female-to-female interaction seems to suppress preovulatory LH surge generation centres.