Cloprostenol in Equine Reproductive Practice: Something More Than a Luteolytic Drug

Abstract

Prostaglandin F(2α) and its analogues (PGF) are widely used in equine reproductive practice. The interval from PGF treatment to ovulation (ITO) varies greatly with a range from 2 to 16 days. Clinical observation suggests that mares mated and ovulated soon after PGF treatment may have poor fertility. Reproductive records of 329 cyclic Thoroughbred mares were analysed retrospectively. The following parameters were analysed: (i) use of cloprostenol; (ii) ITO and (iii) number of ovulations per cycle. According to these parameters, mares were classified into four groups. (i) mares with spontaneous ovulations, n = 57; (ii) mares induced with cloprostenol and ITO = 4-7 days, n = 77; (iii) ITO = 8-10 days, n = 89 and (iv) ITO = ≥ 11 days, n = 106. Differences in pregnancy (PR) and multiple ovulation (MO) rates among groups were tested using chi-squared test. PR rates for groups 1-4 were: 73.7%, 46.7%, 64% and 71.7% respectively (p < 0.05). Groups 1 and 2 had lower (p < 0.05) MO rate (24.6% and 20.8%) than groups 3 and 4 (40.4% and 44.3%). It appears that ovulation soon after PGF-induced luteolysis is detrimental to PR rates. It was found highly significant that in cloprostenol-treated mares, the MO rate was enhanced without subsequent increase in multiple pregnancies.

The period of the follicular phase during which the uterus of mares shows estrus-like echotexture influences the subsequent pregnancy rate

“…Furthermore, the second hypothesis was also accepted: this correlation was significant in both PGF-induced and spontaneous estrous periods. Similarly, the ITO length was also positively correlated with PR, which is in agreement with previous reports [9,10,14]. As seems logical, the ITO had a fairly good correlation with the duration of the follicular phase with estrus-like echotexture.…”

“…The interval from PGF treatment to ovulation (ITO) is also greatly variable, ranging from 2 to 16 days [8][9][10], regardless of the day of the estrous cycle on which treatment is administered [7]. Several reports have analyzed the effect of PGF treatment to induce estrus on pregnancy rates (PRs), and although the overall PR of mares after PGF-induced cycles was not different to that of spontaneous cycles [9][10][11][12][13], when the PR of PGF-induced cycles were analyzed according to the ITO, it was observed that the PR increased as the ITO became longer [9,10,14]. It is likely that the ITO correlates well with the period in which the mare shows estrus-like echotexture.…”

The effect of mare's age on multiple ovulation rate, embryo recovery, post-transfer pregnancy rate, and interovulatory interval in a commercial embryo transfer program in Argentina

“…As the IOI was shorter, the ERR was reduced. A similar relationship has been reported in Thoroughbred mares (Cuervo-Arango and Newcombe, 2010). In the latter study, the interval from PGF treatment to ovulation also influenced the pregnancy outcome of the mating of the subsequent estrus.…”

“…Since PGF shortens the IOI (Ginther, 1992) the Day of embryo flushing is likely to influence the subsequent IOI. Furthermore, evidence shows that the interval from PGF treatment to ovulation may influence the pregnancy rate (PR) (CuervoArango and Newcombe, 2010). However, the relationship between the IOI and the subsequent embryo recovery rate (ERR) has not been investigated in donor mares during an EET programs.…”

Likelihood of pregnancy after embryo transfer is reduced in recipient mares with a short preceding oestrus

“…Several studies have shown a positive correlation between the length of the follicular phase and likelihood of establishing pregnancy in mares following PGF-induced [4,7,8] or spontaneous luteolysis [7]. Several studies have shown a positive correlation between the length of the follicular phase and likelihood of establishing pregnancy in mares following PGF-induced [4,7,8] or spontaneous luteolysis [7].…”