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Re: [RC] Dark Urine - Susan Garlinghouse, DVM. He has only had about ten rides that I consider real conditioning rides on him. <snip> > so we ended up doing over 25 miles of various terrain. > ><snip> He started to balk at going on the way back. > >His urine was not black or coffee colored, but it was definitely > >darker than it should have been. I tested his CRI and it was fast, tenting was normal, he was poopingand eating and drinking, so why would the urine be darker than normal, and what exactly does that mean and what should I be on the look out for in the future? Based on your description of your ride, your horse had to work harder than he's conditioned for. Eating, drinking, peeing and pooping are good things to watch for after the fact, but assuming the problem isn't spiraling into a catastrophe, they aren't a guaranteed indicator for previous muscle stress that might have occurred. A lot of people also make the mistake of thinking that horses are like an out-of-gas car---just replace the gas and life is good again with no residual damage. Doesn't always work that way, especially when it comes to kidneys. So, when you see dark urine, there are two things that are probably going on. One, when the body is dehydrated, the kidneys compensate by producing as little urine as possible until the deficit is replaced. The urine is more concentrated and thus gets a little darker. Just because a horse has had a drink doesn't mean he's not still dehydrated to one extent or another. Depending on the degree of dehydration, it can sometimes take over 24 hours to fully replace a fluid deficit. However, even concentrated normal urine shouldn't be darker than sort of a deep straw-color. Two, the urine might be darker because of either hemoglobin (the pigment that makes blood red) or myoglobin (similar pigment in muscles). Assuming your horse wasn't actually peeing blood cells, the dark urine can be due to myoglobin from damaged muscle. The muscles could have been damaged either because they were overworked for his level of conditioning; because concurrent dehydration reduced blood flow to the muscle groups and THAT contributed to muscle cell damage; and/or because of an increase in body temperature that damaged muscle cells. All of those all come down to the same thing, which is too acidic an environment in the cell and disruption of the surrounding membranes. Don't worry about the little details, just hang onto the big picture. There lots of other things that can also result in myoglobin in the urine (it's called myoglobinuria, by the way), but in your case, heat, dehydration and overwork are the most likely issues. So what happens is that when muscle cells are damaged, they dump the cell contents into the bloodstream, where they are filtered out by the kidneys and released in the urine. The more muscle damage, the more myoglobin, the darker the urine. The tricky part is that myoglobin is toxic to the nephron tubules inside in the kidneys, both directly and secondary to any clogging up that occurs because of all this gunk getting sludged on through. If there's enough of it, it causes something called tubular necrosis. Enough of THAT and your horse's kidneys are irreparably damaged---because unlike liver, kidneys do not regenerate. To a certain extent, they can compensate, but not regenerate. In my opinion, more than a few horses that have raced at very high levels for a season or two, and then dropped dead or couldn't later tolerate even low levels of performance, were the victims of tubular necrosis to one extent or another. And, we won't know the true costs of endurance racing on horses until we've answered that question one way or another. But, off my soapbox. :-) I know what you're thinking and No, just because your horse's urine was a little dark this time, it doesn't mean his kidneys are shot, or he suffered terrible muscle damage or his endurance career is over. Take it as a warning sign---he's gonna be sore for a few days, and in the future, he needs easier workouts until he's ready for them. Pay a lot of attention to electrolyting, even during conditioning to encourage him to drink at every opportunity, plan your rides to offer water regularly and do what you can to keep him cool with sponge-downs and such. Don't feed a super high protein ration, keep him body clipped when feasible and maybe think about not riding on really hot days until he's acclimated to a higher level of work. All that sort of stuff. Good luck! Susan G, DVM =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Ridecamp is a service of Endurance Net, http://www.endurance.net. Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp Ride Long and Ride Safe!! =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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