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The Digestive function of venom
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by Naja_oxiana on July 30, 2001
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I was origionally gonan post this over at the hide, but my stoopid IE5.5 doesn't want to access it right now, so I post here, in as worthy a forum as any that exists elsewhere.
One of the functions of venom is digestion. An interesting question is whether venom is meant to kill quickly or immobilize quickly and kill slowly. Take, for instance, the black widow spider. It uses venom to paralyze prey so that it can extract hemolymphs and other boduly fluids. For ease, the prey must still be alive for this. (In other words, it would be a lot harder were the prey dead.)
Venomous snakes are a little different in that their venom is designed to do more than just paralyze, but also kill the prey. This is why the venom can take so long to take effect. (In Elapid bites a human death is unusual in under four hours, and in viper bites, death is unusual in under 12 hours.) A snake injects the venom, which first immobilizes the prey but it stay's alive long enough for the venom to circulate throughout the bloodstream.
While I generally dislike generalizing types of venom into neuro- and heamotoxic, I will here for ease. Vipers generally have heamotoxic venoms which are enjected via longer fangs, which allow for the venom to be injected deeper into the prey and be absorbed into more of the body tussue. (ie, into muscle tissue and the blood stream.) Clearly if the venom was designed to kill immediatly, this would not work. However, a speedy immobilization is advantagous to the snake as the prey may not get very far.
Early workers in toxinology noticed how quickly envenomated mice underwent digestion when the snakes regergitated them. Interestingly, Reichert noted in Bothrops jaracussu that when live prey was fed, the given digestive cycle was 4 to 5 days, but when pre-killed prey was given the cycle was 12-14 days. Zeller even quotesa a report by Stimmler-Morath which indicates that in Vipera aspis, there is an increase of 2-5 days in digestion time of envenomated and non-envenomated prey. Also interesting was the studies of Thomas and Pough, which demonstrated that the venom of Crotalus atrox accelerated the rupture of the visceral contents of the prey. This keeps bacteria from building up in the prey's stomach. Aditionally the venom aided the loosening of hair. Little things like this aid in the snake's digestion of it's prey.
What have I deduced from this? Venoms which act mainly on the blood stream and permiable tissues are probably the more advanced venoms, as opposed to those that work primarily on neuromuscular tissues and transmissions. The more advanced venom aids ina quicker digestion cycle by breaking down the prey before the snake begins to eat it. (I know of no studies of the digestive functions of more neuromuscular venoms.) Aditionally, I now understand why solenoglyphy is considered the more advanced of the glyphous conditions.
Anyone have anything to add to or correct?
CHeers
Roger Hallman
(BTW, I've been getting my information from Findlay Russel's book.)
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RE: The Digestive function of venom
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by Mojo on July 30, 2001
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I thought it was really interesting and informative. The only part I did not like was using humans as evidence to support that envenomations do not kill in a short period of time (not saying that the statement is not true), since humans have never been the prey of venomous snakes. It would have been more logical to use how long an envenomated mouse, rat, amphibian etc. takes to die from a bite. Despite that I found the material interesting and would like to check the book out myself. Could you let me know where you got it at and what the name is? Thanks.
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RE: The Digestive function of venom
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by DON on July 31, 2001
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Very good Roger. Your information makes some very interesting points.
One I've never considered is the loosening of hair. I know it does happen because of my snakebite experience with larger mammals. Within hours of a rattlesnake bite to a hairy mammal, the bitten area loses all the hair and the underlying tissue begins to look like raw, purplish meat as the skin rapidly degenerates. It only stands to reason that venom will also seperate the hair from a prey animal and destroy the integrity of the skin thus aiding in the digestive process.
Another good point is the visceral rupture. This makes a lot of sense, especially in vipers that may exist in cooler areas and cannot always rely on a high ambient temperature to speed digestion. The intact gut of a prey animal could indeed putrify quite rapidly.
I've fed my young C. atrox prekilled/thawed prey and the digestive rate has occasionally slowed to the point it appeared to be non-existent. On two occasions, when he was very young, I eventually had to follow a prekilled meal with a tiny (3 gram), live pink mouse as a type of laxative just to get him going again.
In observing the behavior of this snake, it appears that he's learning to initially inject just enough venom to confuse and inhibit the motor capabilities of the prey, following that with addition envenomations to aid in the predigestion. He is definitely developing a preference for administration of very numerous bites to different areas of the prey animal. His last four feedings (all in July) were rats weighing between 48.5 and 75 grams. He bit these four rats a total of 20 times. Kill times for these rats averaged 31 minutes each. His growth rate and weight gain this month has been unbelievable.
Please see my 7/29 post over at the hide about his latest feeding. 9 bites over the course of 61 minutes with death occurring at the 65 minute point.
I learned quite some time ago that digestion of prekilled prey is greatly inhibited. Now I'm definitely seeing things that seem to verify the longer a prey animal remains alive, the more complete the predigestion and the greater the rate of feed conversion.
Thanks for the info.
Don
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RE: The Digestive function of venom
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by Naja_oxiana on July 31, 2001
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Hey Don,
How long does it take for the initial imobilization of the prey? Does the snake show a prefference of what partof the prey it strikes first? (Head, rear, middle?) I would find this information to be extremely interesting.
Cheers
Roger
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RE: The Digestive function of venom
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by DON on August 1, 2001
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Hi Roger,
Mice are immobilized relatively quickly, within several minutes. Expiration usually occured in a range of 6-22 minutes. I've completely gotten away from feeding mice now that he's large enough to take a readily available size of rat. I've always preferred to feed rats but properly sized rat pups for a small snake are very difficult to find.
Rats become disoriented, passive and uncoordinated within several minutes but generally aren't completely immobilized until shortly before death.
The snake seems to exhibit a preference for landing the initial strikes in the area of the upper front quarters. After that, he generally works it over from front to back. The rats generally finish up looking fairly well peppered. He avoids the top of the head but will bite on the face.
Don
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RE: The Digestive function of venom
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by TAIPAN78 on August 1, 2001
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Hi guys,
Very interesting thread guys and great ideas Roger! It does make alot of sense that a Crotalid or Viperade would need to let the venom circulate and properly digest the mouse before consumption. Being such inactive animals, they definately need the extra help.
Also, elapids haveing a much faster metabolizm and being able to digest food alot more efficantly without the aid of venom, makes perfect sense as to first, why almost all have primarily neruo(I know I know)venom and 2, why they have such a powerfull cocktail.
Thanks fo sheding some light guys!!! and Roger, whats the name of that book again? Need to order a copy. Sounds like some great reading.
Take care you all.
later,
Jeremy
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RE: The Digestive function of venom
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by GREGLONGHURST on August 3, 2001
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The book Roger mentioned is :"Snake Venom Poisoning" by Findlay E. Russell, M.D., PhD. A better book on this topic is not out there, in my opinion. It first came out in 1980, but is as valid today as then, The ISBN is 0-87936-015-1. Publisher is Scholium International.
It has been my experience that in some snakes, their venoms seem to be species specific, in that, it works better & faster on the type animal they prey upon than on others. Cobra venom in cobras that prey upon amphibians does not knock down rodents as quickly as cobra venom from a type that generally feeds on rodents.
~~Greg~~
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