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Author Topic: Why does excrement differ so extensively across animal species?  (Read 3248 times)

Offline thedoc

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John Gamel asked the Naked Scientists:
   
During the seven decades of my life, I've discovered a number of salient points about excrement:
 
1.       The droppings of carnivores are denser, more gooey, and more foul-smelling than those of vegetarians.

2.       But, on the other hand, there is wide variation among the latter group. For example, rabbit droppings resemble tiny uniform pills, while (at the opposite end of the spectrum) cows deposit huge semiliquid puddles. During my childhood in Lower Alabama, we termed these "cow flops" (based on the sound they make when they hit the ground) or "cow pies" (based on their appearance when dry).

3.       Horses fall somewhere in the middle by dropping apple-shaped and –sized fibrous turds.

4.       Chickens, in a category of their own, drop small lumps that resemble wads of chewing gum.
 
My question is: since they all eat only vegetable matter, why so much variation?
 
What do you think?
« Last Edit: 29/05/2013 05:30:02 by _system »


 

Offline Don_1

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When it comes to Richard IIIs (turds) I am only an expert in sense that I can ............ Hmmm perhaps I should not continue in this line.

I think you will find that there are several factors which determine how poo will rate in the pong and consistancy charts.

For starters there will be the actual diet. For the herbivores this could be grasses, broad leaf plants, flowers or bark, not to forget seeds, fruit and nuts, or a combination of them. Grasses tend to have a poor nutritional value so many animals will 'chew the cud'. That is they regergitate and re-chew their food. Others, like the rabbit will excrete the indigestable fibre quickly so the more nutritional remains can be moved back to the caecum where bacteria and fungi do their job. The bovine gut has bacteria which can break down the more fiberous grasses.

So it not only the differing diet and gut, but also the differing flora of the gut which will make a great deal of difference to the end product.
 

Offline evan_au

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Australia had a major ecological disaster when cows were introduced here.
  • Australian marsupials tended to have fairly hard droppings.
  • However, "cow pats" were too sloppy for the local dung beetles to dispose of effectively, leading to excess flies, grass die-off in pastureland, etc.
  • This was solved by introducing some overseas dung beetles that could deal effectively with the different texture
Perhaps Australian native animals are very miserly with their water use, while cows came from a wetter climate, consume large amounts of water, and produce a more liquid excrement?

Like Don1 says, it may be related to the different types of bacteria in their intestines.
  • A cow's symbiotic bacteria digest grass effectively, assisted by the cow's multiple stomachs and the cow's habit of regurgitating their food and "chewing the cud" (and they produce lots of methane in the process).
  • I've seen kangaroos that acted like they were re-chewing previously swallowed food, so they probably grind up the food very finely for the bacteria to digest, but they produce a lot less methane than cows.
  • I don't think horses chew their food so thouroughly, so the bacteria in horse intestines can't do such a good job of breaking down the cellulose in the hay they eat. Horses are built for speed, so they can't afford to carry around a large fermentation vat in their guts.
  • Hyenas tend to crunch up a lot of bones - this is reported to produce white, powdery excrement.
  • Chickens and other birds have only a single exit for solid & liquid waste (the cloaca), producing a more liquid waste.
« Last Edit: 22/05/2013 12:51:00 by evan_au »
 

Offline Lmnre

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Offline CliffordK

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Chickens (all birds?) also have a gizzard which may do a better job at pulverizing food than many animals do with their teeth. 

Adaptations for limited water may be with a great number of animals, not just Australian animals.  Deer, for example, have nice round pellets (perhaps perfect for the Australian Dung beetles to take home).  But, I presume they have a much lower water content than bear droppings, for example, which tend to be a nice glob of seeds & etc.  So, the deer would be adapted to less drinking, even when sharing the same environment as the bears.

Certainly each animal has its own preferred foods.  Having distinct preferred foods is likely part of the niches in the animal kingdom that allow different species to co-exist without necessarily out-competing each other.
 

Offline Lmnre

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A couple of people here mentioned rabbits. Actually, rabbits produce two kinds of droppings.
Yewww! Well, I'll never rub noses with my cute little bunny ever again.
 

Offline chris

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I believe koalas feed their droppings to their babies to colonise their guts with appropriate commensals? Evan?
 

Offline evan_au

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Well, if we are delving into the "yuk" factor, there have been questions about where human babies get their commensal bacteria.
Babies often get a dose of human gut bacteria during the birth process - so perhaps the impact of the hygiene hypothesis starts at birth?
« Last Edit: 27/05/2013 22:45:00 by evan_au »
 

Offline CliffordK

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so perhaps the impact of the hygiene hypothesis starts at birth?

For a long time, people have tried to be at least somewhat sterile during the birth process.  Clean towels & etc.  Infant and maternal mortality are HUGE concerns, and have dropped significantly during the last century.

I think gonorrhea or chlamydia used to be major causes of infant blindness until it was treated in both the mother and infant.
 

Offline Lmnre

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Babies often get a dose of human gut bacteria during the birth process

Quote
Children born via cesarean section are slightly more likely than babies delivered vaginally to become heavy or obese

∙∙∙

Why the link?

It's not clear why c-section births are tied to a better chance of being heavy.

One possibility relates to the bacteria babies are exposed to when they are delivered vaginally, which might affect the way they process and store food, said Liu.

Additionally, Liu added, researchers have suggested that c-sections are linked with a lower concentration in the umbilical cord of a hormone important in regulating weight and with a reduced rate of breastfeeding, "both of which are reported to be associated with an increased risk of later obesity."

Babies who are larger than normal are also more likely to be born via cesarean, but most of the studies Liu's team analyzed took into account birth weight.
source
 

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