Assuming a "good" breeding or insemination (i.e. the semen has been placed correctly in the uterus - which happens in both live cover and AI) unless your mare stands on her back legs and jumps up and down 4 or 5 times immediately after breeding (in which case you perhaps shouldn't have bred her anyway ), the semen is not coming back out!!!
The vet that told you to walk the mare, if they suggested that in connection with "losing" semen, are also probably of the school of thought that throwing a bucket of ice cold water over her rear end after breeding is good too, as she will clamp her tail down and "prevent" semen loss... That or perhaps they tend not to get those "good" AI's I mentioned above...
Please note that opinions, product information, advice or suggestions posted on this bulletin board are not necessarily those of the management at Equine-Reproduction.com nor does the maintenance of the post position indicate an implicit or any endorsement of that information, opinion or product.
Further, although we have the greatest respect for the posters offering assistance here, you are advised to seek a consultation with your veterinarian prior to using information obtained from this board if it is of a veterinary nature.Proud to be sponsored and supported by: