Effect of active immunisation of ewes against synthetic luteinising hormone releasing hormone.

At the start of the breeding season 13 intact and four ovariectomised ewes were immunised against LH-RH which was rendered immunogenic by conjugation to bovine serum albumin using carbodiimide. The immunogen was emulsified with Freund's complete adjuvant prior to multi-site intradermal injection into a shaved area on the back of each animal. All the ewes were boosted using an identical procedure six and twelve weeks later. LH-RH antibody titres were monitored from weekly blood samples. Oestrous cycles were shown to stop in all but one of the intact ewes after anti-LH-RH titres had developed, but before the seasonal anoestrus. Laparoscopy of the ewes at this time showed that the ovaries and uteri were in various stages of regression. Plasma gonadotrophin levels of ovariectomised ewes fell significantly after immunisation and in intact immunised ewes ovariectomy failed to result in any increase in plasma gonadotrophins. Injection of 150μg synthetic Lh-RH or 6μg of an immunologically distinct analogue of LH-RH failed to induce LH or FSH responses approaching those previously demonstrated with identical doses in non-immunised anoestrous ewes. These results suggest that immunisation against LH-RH could provide an alternative to ovariectomy for the suppression of unwanted oestrous symptoms and ovulation but that reversal of the effects of immunisation might be difficult to achieve routinely.