Sam Sweet
Platinum member Cage humidity and dehydration. A couple of recent threads on basking behavior and acclimating newly-acquired monitors have slopped over into comments on cage humidity, and it is not uncommon (especially on other fora) to hear of people soaking their animals to “rehydrate” them. It might be worth considering this as a separate issue, as there seem to be some misconceptions afoot.
Monitors can only acquire water by mouth (from food or by
drinking). Unless they drink, soaking does not rehydrate them, as their skins are effectively impermeable to water. Notice that we humans, with a much thinner skin keratin layer, do not bloat from taking a
bath. Raising the ambient humidity can reduce the rate of dehydration, but it cannot reverse it.
As I noted in another post, monitors lose body water in feces (not much), by evaporation from their eyes (quite a bit), and by exhaling. Air inhaled by a monitor is almost always cooler than the animal’s body temperature. Even if that inhaled air is saturated (100% rh), the temperature increase will reduce the rh of the air in the lungs, and thus body water will be extracted to bring the lungful of air to saturation at the new temperature. When that air is exhaled, the body water goes with it, either all the way out of the body or at least as far as the nasal chamber. Some desert-adapted monitors (like V. griseus) have recurved nasal passages that may help condense and trap exhaled water vapor, but this is absent in species from the wet tropics, and is never as fancy as the water traps in the noses of many desert mammals.
A monitor basking in a cage is inhaling hot, locally dry air, and losing body water each time it exhales. A monitor resting in a cooler part of the cage, especially in a mostly-enclosed burrow or box or hollow, is inhaling nearly saturated air that is at the same temperature as its body and thus it is not dehydrating as quickly. It is pretty likely that monitors are aware of differences in relative humidity at various potential hiding places within a cage.
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#2 2008-08-28 00:37:03
simqc
Silver member Re: Cage humidity and dehydrationSo Sam, does that means that keeping a monitor in too hot condition, without retreat, will automatically dehydrate it, whatever saturated the air is?
Thank you for that post, I am sure it will clear so misunderstanding. Dehydration is probably a big cause of death for captive animals.
Simon
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#3 2008-08-28 01:10:18
Sam Sweet
Platinum member Re: Cage humidity and dehydrationYes it will lose water, because the air in the lungs is *always* saturated, while the air in the cage (at least in the hottest parts) will not be saturated.
Still, that wouldn't matter as long as the animal drinks regularly. A lot of monitors are finicky about
drinking -- either they won't drink from a bowl or tub at all, or won't touch it unless it has just been cleaned and refilled. Lots of smaller species will drink from a dripping tube, or will drink droplets from spray or condensation.
The 'heat-um-n-feed-um' principle can create a problem that I suspect is pretty common among captive monitors. Once they've eaten, monitors like nearly all reptiles will bask as long as they can to speed up digestion. While they're doing that (and not
drinking), they are dehydrating. At the same time the proteins in their food are being digested, and the nitrogenous waste is being converted from ammonia at the cellular level to urea in the bloodstream to uric acid in the kidneys or cloaca. Urea is made of two ammonia molecules, and uric acid is made of two urea molecules, so at each step the concentration of the solution falls by half, and the available water is reabsorbed; above a certain concentration uric acid begins to crystallize out of solution, allowing recovery of almost all the metabolic water. This is why lizard (and bird) 'pee' is white and semisolid. The problem is that uric acid crystals are not easily dissolved once they form, and they plog up the works.
Normally this last crystallization step occurs in the cloaca. However, if an animal is dehydrated you can get crystallization of uric acid in the kidneys, which impairs their function, and even elsewhere in the animal's body if dehydration is severe. This condition is termed visceral gout, and it is basically irreversible. It is insidious, because tiny bits of crystalline uric acid act as templates for further crystyal growth, and so any time the animal is even slightly dehydrated, a bit more can form. After a while it becomes a big problem and can kill the animal.
It is probably fair to say that captive monitors get to bask longer than do wild ones, since there is not much else to do and nothing to run away from, and so they are more likely to be a little bit dehydrated than are wild animals, at least now and then. A wild monitor that is dehydrated will usually hole up and not eat, and thus is not processing nitrogenous wastes while its body fluids are in the danger zone for uric acid crystal formation.
Many old captive individuals of nonaquatic monitors show some evidence of visceral gout on necropsy, and a fair few die from it. Even a day or two of basking without access to water that they will accept to drink can add to the problem; it's often hard to know, for picky individuals, if they aren't
drinking because they're not
thirsty, or because there is something they don't like about the water source they have.
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#4 2008-08-28 08:20:13
simqc
Silver member Re: Cage humidity and dehydrationWhat would be symptoms of visceral gout?
Simon
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#5 2008-08-28 14:54:37
Sam Sweet
Platinum member Re: Cage humidity and dehydrationThat's the problem, Simon -- by the time symptoms are evident it's pretty late in the game. Kidney failure will cause or accompany gout, and one sign of kidney problems in monitors can be a slightly bulging appearance of the eyes, particularly if the conjunctival tissues bordering the eye have a swollen appearance. Plasma assays for uric acid can show abnormally high values, although the normal values vary with time since feeding, with a transient peak about 2-3 days after a large meal.
A number of antibiotics are nephrotoxic in reptiles, leading to acute kidney failure. This would lead to gout if the animal lives long enough, but the usual scenario is chronic kidney failure that is the progressive result of uric acid deposition associated with a long-term history of dehydration.
Any of the usual signs of dehydration are warnings about the likelihood of gout, especially if the animal is chronically dehydrated as a result of poor husbandry. The dehydration often seen in newly-imported monitors is less a concern for gout, since these animals have not been feeding and thus did not have a lot of uric acid to process. In that connection, this is one reason why it is important to address
hydration first in treating new captives, and begin feeding only after the animals have recovered enough body water to process nitrogenous wastes properly.
Most of the uric acid deposition that leads to gout occurs on serosal membranes (those that secrete fluids into body cavities, such as the peritoneal lining, pericardial and pleural membranes, and the linings of joint capsules), and also the inner walls of kidney tubules and blood vessels. The joint capsule variety (articular gout) seems to be less common in monitors than visceral gout, but shows up as obviously impeded movements. There is a video somewhere (I will try to find it) of one of the adult lace monitors at Bronx Zoo that shows advanced articular gout. Visceral gout is unfortunately best diagnosed at necropsy. It can be avoided, but is difficult to cure, since reptiles and birds lack any physiological mechanism to convert uric acid back to urea.
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#6 2008-08-28 18:42:08
simqc
Silver member Re: Cage humidity and dehydrationThanks alot Sam for taking the time to write all that down.
Hope I can read one of your book soon
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#7 2008-08-29 08:33:58
kriminaal
Silver member Re: Cage humidity and dehydrationYes Sam, that's for that info. Very enlightening stuff.
--------------------------------------------------------------------------------
Mike D
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#8 2008-08-30 05:50:52
cumingi
Gold member Re: Cage humidity and dehydrationThanks for the info Sam! Very intressting topic!
As i wrote earlier this year I have a spenceri that has a constipation. I've treated it since april(I think it was) and it is now finally seams to getting better. I stopped the parafin oil and I'm down to one
bath a week. This was primary to helping it poo in the water as it seams easier for it. Do you think the spenceri drink any of the water while soaking. It getts realy ballony after the soaking but it getts down after 5-10 minuts.
I know realise that it can have got this uric acid. Some of the feces is realy hard like small stones can this be because of that.
I think it's getting better though because its allso have more ''normal'' feces that I've found in the cage.
/Mike
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#9 2008-08-30 10:17:45
Krusty1
Platinum member Re: Cage humidity and dehydrationMonitors puff up with air when you put them in a
bath. I think they're trying to not drown and float. I doubt your lizard is "soaking" water as it either has to enter the mouth or vent.
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#10 2008-08-30 12:18:52
cumingi
Gold member Re: Cage humidity and dehydrationSorry, a bit unclear hear. I didnt mean it was soaking water through its body. I ment if it was
drinking water when it was
bathing or if they try to do all they can not to swallow any water. I never seen it acctualy drink the water while it is in the water. I seen it drink water from the bowl in the cage.
The vet told me that it was very important for it to get water daily. The first months I had to give it both water and parafin with a syringe. Now it does seam better and it acts much more like a monitor should with hissing whipping and running away. Plus it has grown abit.
/Mike
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#11 2008-09-13 17:22:50
Aeries
New member Re: Cage humidity and dehydrationHey there,
Will the monitor sense the changes in humidity throughout the terrieum, and be able to choose the level that is 'right' for him? (aka The air is significantly less humid around my basking lights than it is over by the water dish)
And...since soaking doesn't 'rehydrate', does soaking still have positive benefits for the monitor? I've read elsewhere that it does, but it seems my Ackie absolutly hates it, he runs at the walls the entire time, and will climb up my arm instantly if I let him. The only other explanation I could think of for this is that he can't the the sides of the tub because it has no contours.
Thanks for the Advice!
-Aeries, the amateur Ackie owner trying to learn more and do better!
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#12 2008-09-13 21:33:50
Sam Sweet
Platinum member Re: Cage humidity and dehydrationIt's pretty likely that monitors become aware of differences in humidity in the same ways that we do -- dry nose, frequency of needing to blink, thirst, etc. It's not going to be an instantaneous sensation, more an 'uncomfortable/comfortable' thing. Other factors are probably going to be more important in determining what the animal does at any particular time, but accumulated experience can certainly affect choice of hides and so on.
Soaking does no harm, and can assist in shedding (especially on the toes and tail) as well as removing accumulated dust and dirt that can act like sunblock in reducing UV uptake. Lots of dry country monitors are wary of standing water, since the only times they encounter it out bush would be during flash floods, and the correct response then is to find something to climb up. Most larger species seem to enjoy soaking.
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