Pregnancy rates and semen usage in rectally guided and endoscopic inseminations

Abstract

Reducing sperm numbers in the inseminate increases the number of mares bred per ejaculate, maximizes the use of frozen semen from dead stallions, increases the fertility of some stallions with sub-optimal semen quality, aids in the use of epididymal sperm harvested from dead stallions and reduces the incidence of post-breeding endometritis in mares with delayed uterine clearance. Two techniques have been used for reducing sperm numbers in the inseminate: (1) rectally guided insemination (RGI) and (2) hysteroscopic insemination (HI). The objective of this study was to analyze frozen semen data from three breeding seasons in a large commercial farm in order to compare the two insemination techniques, RGI or HI. Semen frozen in 0.5-ml straws and concentrations of 50 to 150× 106 per straw was available from 88 stallions whose fertility with frozen semen was between 0 and 100%; 2544 inseminations were performed. Fertility was assessed by embryo recovery on days 7 or 8 post ovulation in 48% of the mares or by the ultrasonographic presence of an embryonic vesicle at 14 days post insemination in 51% of the mares. RGI (n= 1279) resulted in 43% fertility rate and 5.1 straws/pregnancy. Fertility of the mares bred by the HI technique was 45%. Although there was a consistent advantage across years for the HI technique over the RGI, the difference was not statistically significant (p> 0.05). However, there was a significant difference (p< 0.05) in the number of straws used per cycle 2.2 and 1.4 for RGI and HI respectively resulting in a significant reduction in the number of straws required to establish a pregnancy 5.1 vs 3.1 straws/preg for RGI and HI respectively). Although it would appear that the HI results in a higher fertility and requires approximately 40% less semen to establish a pregnancy than the RGI technique, it is difficult to justify the routine use of HI considering the additional expense in personnel and equipment needed to conduct the procedure. Our results indicate that although there is a slight and consistent advantage of the HI technique, veterinarians must weigh the advantages and disadvantages as well as semen availability before deciding what technique to use. However, if the volume is ≤250 l, it is strongly suggested to deposit the semen by HI. The results of this analysis agree with previous reports in which the HI resulted in a 4% increase in fertility compared to the RGI procedure. In conclusion, the two techniques described in the present study are comparable and can result in the establishment of pregnancies on a commercial basis. It is clear that the two techniques are a viable option to maximize the use of frozen semen, and with proper equipment, technique and skills the hysteroscopic insemination technique further maximizes the use of semen. This could prove to be economically beneficial when using semen of very valuable or deceased stallions.