Oxytocin is not involved in luteolysis and early maternal recognition of pregnancy (MRP) in alpacas

Pregnancy maintenance depends on the maternal recognition of pregnancy (MRP), a physiological process by which the lifespan of the corpus luteum is prolonged. This mechanism is not well characterized in camelids. The objectives of the present research were to determine if exogenous oxytocin prolongs the corpus luteum activity in alpacas and to evaluate expression and localization of oxytocin receptors within the endometrium at 9 and 14 days post-mating. In the oxytocin studies, plasma progesterone profiles were determined after ovulation in the same alpacas on 2 cycles: one cycle without oxytocin treatment and one cycle with oxytocin treatment. Oxytocin was administered daily by intramuscular injections (IM) at a dose of 20 IU (experiment 1, n = 6) or 60 IU (experiment 2, n = 7 from day 3 through day 10 after induction of ovulation with GnRH IM. There was no significant difference in the length of the luteal phase (i.e. corpus luteum lifespan) between the treated and control cycles using either 20 or 60 IU of oxytocin. In the final experiment, uteri from open and pregnant alpacas (n = 4 per group) at 9 and 14 days post-mating were evaluated for expressions of oxytocin receptors by immunohistochemistry. No significant difference (P ≤ 0.05) in the expression of oxytocin receptors was observed between open and pregnant animals in either staining intensity or tissue localization. We conclude that oxytocin is not involved in luteolysis and early MRP in alpacas.