Q. My mare has started peeing in the trailer immediately when I load her after riding. I’ve tried giving her time after untacking to see if she will pee outside before loading, but she won’t. I also don’t have shavings in the trailer (using the logic that horses usually don’t like to pee on solid surfaces that cause splashing). This has turned into an unpleasant habit that’s hard on my trailer mats and floor and makes my trailer stink. I’ve known mares in the past that have peed on command (one would pee when her owner started whistling “Three Blind Mice” prior to loading). Do you have any suggestions for teaching or encouraging my mare to pee before getting in the trailer, and is it possible to break this trailer-peeing habit? –Caroline, via e-mail

A. I have never taught a horse to urinate on command myself, but I have talked to several Thoroughbred trainers and grooms who assure me they do it all the time. After a race when they have to provide a urine sample, they give them a drink, then whistle for up to a minute or so. I have heard a couple of different styles of whistle, either through their teeth or lips. It is a high-pitch vacillating birdlike whistle. I have not heard of someone using a tune, but it probably doesn’t matter what sound you use as long as it is unique and you do it consistently. Working with the horse routinely, whenever it postures to urinate they whistle so the horse associates it with urination. They might also put the horse on fresh bedding.

So if your mare usually pees as soon as you release her into a freshly bedded stall, you could take some bedding with you and spread it out near the trailer. I would give her a long lead, since some horses are reluctant to urinate when you are holding them on a short lead. Like one of my Thoroughbred trainer friends Ben Guessford said, “If that sounds like too much work, just train ‘em to the whistle.”

If neither approach works, you could attach a urine collection device to her tail, watch her on a trailer camera, and when she urinates, stop and empty the bag. You can set one up yourself using a large embroidery hoop and a plastic bag attached to the base of her tail to cover the perineum. When she postures, the urine will usually land in the bag. However, this method still has the potential to cause a mess