Antigen recognition in feral mares previously immunized with porcine zonae pellucidae.

This research studied the responses of free-roaming mares immunized against porcine zonae pellucidae (PZP), observing significant effects on fertility reduction. Post immunization, the majority of these mares did not become pregnant, compared to the untreated and control group, which suggests that these vaccines can inhibit fertility.

Study Design and Participants

• The study was carried out on 26 free-roaming feral mares. The chosen mares were divided into smaller groups and received different numbers of inoculations.
• Eight sexually mature mares were administered 2 inoculations 2 weeks apart, while 18 mares underwent 3 inoculations at intervals of 2 and 4 weeks.
• For comparison, there was also a control group of mares, some of which were subject to sham injections, while others received no treatment at all.

Initial Results and Findings

• The examination of urinary oestrone conjugates (E1C) and non-specific progesterone metabolites (iPdG) in samples collected in October 1988 showed minimal pregnancy rates among the immunized mares.
• None of the 18 mares that received 3 inoculations and only one out of 6 mares that received two inoculations were pregnant.
• In contrast, 3 out of 6 sham-injected control mares and 5 out of 11 untreated mares were pregnant.

Booster Inoculation and Follow-up Findings

• In February and March 1989, the immunized mares that were not pregnant received a single booster inoculation of PZP.
• Urinary analysis of E1C and iPdG, from samples obtained in August and October 1989, revealed just one pregnancy out of the 14 mares given the booster.
• In contrast, around 33% of the mares initially treated in 1988 but not given a booster in 1989, and 7 out of 16 untreated controls, were pregnant.

Conclusion and Implications of the Findings

• By correlating these findings with cases of foaling, the researchers found a significant correspondence.
• This study suggests that mares recognizing PZP antigen post-immunization have elevated antibody titers impacting fertility.
• Subsequent annual PZP inoculations further fuel this effect, reinforcing this fertility-inhibiting effect in mares.