The PGF2α agonists luprostiol and D-cloprostenol reliably induce luteolysis in luteal phase mares without evoking clinical side effects or a stress response

In the present study we have evaluated a possible stress reaction in response to two different PGF(2 alpha), analogs luprostiol and D-cloprostenol and their effects on estrous cycle characteristics. In a cross-over-design eight mares received in alternating order either luprostiol (Treatment LUP; 3.75 mg im), D-cloprostenol (Treatment CLO; 22.5 mu g im) or saline (Treatment CON; NaCl 0.9% 0.5 ml im) on day 8 after ovulation. Injection of either LUP or CLO, but not of CON resulted in a significant decline of progesterone concentration in plasma to baseline concentrations within two days (time: p <0.001, treatment: p < 0.01, time x treatment: p < 0.05). The treatment to ovulation interval was significantly shorter in LUP and CLO than in CON cycles (LUP: 9.4 +/- 0.4 d; CLO: 9.4 +/- 1.3 d; CON: 16. +/- 10.8 d; p<0.001). Injection of either LUP or CLO, but not of CON significantly increased salivary cortisol concentration (immediately before injection: CON 1.3 +/- 0.2, LUP 1.4 +/- 0.3, CLO 1.4 +/- 0.3 ng/ml; 60 min after injection: CON 1.0 +/- 0.3, LUP 8.0 +/- .4, CLO 4.2 +/- 0.7 ng/ml; time: p <0.01, treatment: p <0.001, time x treatment: p <0.001). Heart rate decreased over time (p <0.05) independent of treatment and no changes in heart rate variability were detected. Injection of the PGF(2 alpha), analogs CLO and LUP reliably induced luteolysis and apart from a transient increase in salivary cortisol concentration no signs of a physiological stress response or apparent side effects occurred. (C) 2016 Elsevier B.V. All rights reserved.