Pharmacologically induced ex copula ejaculation in stallions: assessment of new combined protocols

Abstract

Pharmacologically induced ejaculation is an alternative for semen collection in stallions with different physical or behavioral pathologies affecting mounting or copulation. Several protocols have been studied with varying results, so this is still an active research topic. The aim of this study was assessing different protocols to induce ex copula ejaculation. Healthy stallions (n=8, mean age: 8.7 years, range: 5-22 years) were included. Intervals of two days were left between treatments. The following protocols were performed without sexual prestimulation and administering drugs at the same time: xylazine (0.33mg/kg)+butorphanol (0.02mg/kg) (XB), detomidine (0.01mg/kg)+butorphanol (0.02mg/kg) (DB), detomidine (0.01mg/kg)+butorphanol (0.02mg/kg)+oxytocin (20 IU) (DBO) and xylazine (0.33mg/kg)+detomidine (0.01mg/kg)+butorphanol (0.02mg/kg)+oxytocin (20 IU) (XDBO). Other two protocols were imipramine oral administration (2.5mg/kg) followed by xylazine (0.33mg/kg) +butorphanol (0.02mg/kg) (IXB) or detomidine (0.01mg/kg)+butorphanol (0.02mg/kg)+oxytocin (20 IU) (IDBO) 2 hours later. Besides, XB and DBO were also performed with sexual prestimulation (RXB and RDBO) by 10 min of teasing with an estrous mare. Then, stallions were left in their boxes for 5 min, before drug administration. Semen was collected into a non-spermicidal plastic bag. Interval from treatment to ejaculation (min.), volume (ml) and concentration (sperm x10⁶/ml) of the ejaculate were compared between treatments by one-way ANOVA followed by Bonferroni test. The percentage of stallions that ejaculated post-treatment were compared between groups by Chi-Square test. Differences were considered significant with P<0.05. Values are expressed as mean ± SD (Graph Pad). Ejaculation was observed in 37.5% (3/8) of stallions of XB and RXB, in 25% (2/8) of individuals of DBO and RDBO, in 50% of IDBO (4/8) and in 62.5% (5/8) of IXB. Any stallion of DB or XDBO group ejaculated. Effectiveness for triggering ejaculation was not significantly different between treatments (P=0.06). The mean interval from treatment to ejaculation (min) was 2.01±0.9, 1.7±0.5,1.9±0.7, 1.4±0.14, 1.8±0.4 and 1.9±0.4 for XB, RXB, DBO, RDBO, IXB and IDBO, respectively, without significant differences between groups. The mean ejaculate volume was greater in stallions of RXB (31.7±8.5 ml) than in all other protocols (P˂0.01), except for RDBO (13.8±3.8ml). Mean ejaculate concentration was greater in individuals of DBO (723 ± 5 sperm x106/ml), IDBO (672±62 sperm x106/ml) and IXB (786±56 sperm x106/ml), than in those of RXB (262 ± 170 sperm x106/ml) (P˂0.01). In conclusion, except for DB and XDBO, all protocols were effective in triggering ejaculation in some stallions. Sexual prestimulation only increased the ejaculate`s volume in stallions treated with xylazine+ butorphanol. As not all individuals ejaculate with all protocols, several trials using different treatments should be performed in case of failure to obtain semen. The present study provides evidence for different possible alternatives.