Delayed luteal regression in ewes immunized against oxytocin

Area of Science:

• Reproductive endocrinology
• Immunology
• Animal science

Background:

• The oestrous cycle in sheep is regulated by complex hormonal interactions.
• Oxytocin's role in the luteal phase and its potential involvement in luteolysis require further elucidation.
• Understanding these mechanisms is crucial for reproductive management in livestock.

Purpose of the Study:

• To investigate the effects of active immunization against oxytocin on the oestrous cycle of sheep.
• To determine if blocking oxytocin influences luteal phase length and progesterone concentrations.
• To explore the potential role of endometrial oxytocin receptors in oestradiol-17 beta-mediated luteolysis.

Main Methods:

• Sheep were actively immunized against oxytocin.
• Oestrous behaviour and circulating progesterone concentrations were monitored to assess cycle length.
• Antibody specificity was confirmed through cross-reactivity tests.
• Oxytocin and antibody levels in circulation and cerebrospinal fluid were measured.

Main Results:

• Active immunization against oxytocin significantly prolonged the luteal phase of the oestrous cycle in sheep.
• Mean oestrous cycle length was extended by 3.7 days.
• Circulating oxytocin concentrations increased 10-fold post-immunization, with specific antibodies showing minimal cross-reactivity.
• Low levels of oxytocin antibodies were detected in cerebrospinal fluid.

Conclusions:

• Active immunization against oxytocin effectively extends the luteal phase in sheep, suggesting a critical role for oxytocin in cycle regulation.
• The findings support the hypothesis that oestradiol-17 beta may induce luteolysis by increasing endometrial oxytocin receptor concentration.
• This research provides insights into the neuroendocrine control of the ovine oestrous cycle and potential targets for reproductive manipulation.