Pelleted diets... yea... again

[EJ]

Exactly... in the form of cholecalciferol. All my tortoises indoors do not have UV.

Originally Posted by samstar

Wow never knew that, so absolutely no sun throughout the year? Than they would not need the UVB bulb?

[samstar]

Originally Posted by EJ

Exactly... in the form of cholecalciferol. All my tortoises indoors do not have UV.

Whats cholecalciferol?

[EJ]

Another name for cholecalciferol is vitamin D3.

I'll go so far as to repost this... The easiest explanation for calcium metabolism... enjoy.

From: "Juan F. Sanz-Cervera"
Date: Sat Aug 18, 2001 1:14 am
Subject: Calcium forms and metabolism
This is from Voet & Voet's 2nd. edition of Biochemistry, John Wiley & Sons, 1995, pp.
1265-1267.

Calcium Metabolism Is Regulated by Parathyroid Hormone, Vitamin D, and Calcitonin.
Ca2+ [Calcium cation] forms hydroxyapatite, Ca5(PO4)3OH, the major mineral constituent of bone, and it is an essential element in many biological processes including the mediation of hormonal signals as a second messenger, the triggering of muscle contraction, the transmission of nerve pulses, and blood clotting. The extracellular concentration of Ca2+ must therefore be closely regulated to keep it at its normal level of ca. 1.2 mM [millimolar; a common concentration unit]. The hormones have been implicated in homeostasis:
1. Parathyroid hormone (PTH), an 84-residue polypeptide secreted by the parathyroid gland, increases serum concentration of Ca2+ by stimulating the resorption from bone and kidney and by increasing the dietary absorption of Ca2+ from the intestine.
2. Vitamin D, a group of steroid-like substances that act in a synergistic manner with PTH to increase serum concentration of Ca2+.
3. Calcitonin, a 33-residue polypeptide synthesized by specialized thyroid gland cells, decreases serum Ca2+ concentration by inhibiting the resorption of Ca2+ by bone and kidney.
The bones, the body's main Ca2+ reservoir, are by no means metabolically inert. The are continually "remodeled" through the action of two types of bone cells: osteoblasts, which synthesize the collagen fibrils that form the bone's organic matrix, the scaffolding upon which its hydroxyapatite mineral phase is laid down; and osteoclasts, which participate in bone resorption. PTH inhibits collagen synthesis by osteoblasts and stimulates bone resorption by osteoclasts. The main effect of PTH, however, is to increase the rate that the kidneys excrete phosphate, the counterion of Ca2+ in bone. The consequent decreased serum phosphate concentration causes hydroxyapatite to leach out of bone through mass action and thus increase serum Ca2+ concentration. Finally, PTH stimulates teh production of the active form of vitamin D by kidney which, in turn, enhances the transfer of intestinal Ca2+ to the blood.
Vitamin D is a group of dietary substances that prevent rickets, a disease of children characterized by stunted growth and deformed bones stemming from insufficient bone mineralization (vitamin D deficiency in adults is known as osteomalacia, a condition characterized by weakened, demineralized bones). Although rickets was first described in 1645, it was not until the early 20th. century that it was discovered that animal fats, particularly fish liver oils, are effective in preventing this deficiency disease. Moreover, rickets can also be prevented by exposing children to sunlight or just UV light in the wavelength range 230 to 313 nm, regardless of their diets. [I think that here they mean "regardless of their vitamin D intake"; obviously, if there is not enough Ca2+ ingested in the diet, serious consequences derive!]
The D vitamins, which we shall see are really hormones, are sterol derivatives in which the stearol B ring is disrupted at its 9,10 position. The natural form of the vitamin, vitamin D3 (cholecalciferol), is nonenzimatically formed in the skin of animals through the photolitic action of UV light on 7-dehydrocholesterol. Vitamin D2 (ergocalciferol), which differes from vitamin D3 only by a side chain double bond and a methyl group, is formed by the UV irradiation of the plant sterol ergosterol. Since vitamins D2 and D3 have essentially identical biological activities, vitamin D2 is commonly used as a vitamin supplement, particularly in milk.
Vitamins D2 and D3 are hormonally inactive as such; they gain biological activity through further metabolic processing, first in the liver and then in the kidney:
1. In the liver, vitamin D3 is hydroxylated to form 25-hydroxycholecalciferol in an oxygen-requiring reaction catalyzed by cholecalciferol-25-hydroxylase.
2. The 25-hydroxycholecalciferol is transported to the kidney, where it is further hydroxylated bya mitochondrial oxygenase, 25-hydroxycholecalciferol-1alpha -hydroxylase, to yield the active hormone 1alpha,25-hydroxycholecalciferol [1,25(OH)2D]. The activity of this hormone is regulated by PTH, so this reaction is an important control point in Ca2+ homeostasis.
1,25(OH)2D acts to increase serum Ca2+ concentration by promoting the intestinal absorption of dietary Ca2+ and stimulating Ca2+ release from bone. Intestinal Ca2+ absorption is stimulated through increased synthesis of Ca2+-binding protein, which functions to transport Ca2+ across the intestinal mucosa. [...]
Vitamin D, unlike the water-soluble vitamins, is retained by the body so that an excessive intake of vitamin D over long periods causes vitamin D intoxication. The consequent high Ca2+ serum concentrations results in aberrant calcification of a wide variety of soft tissues [!!!]. The kidneys are particularly prone to calcification, a process that can lead to the formation of kidney stones and ultimately kidney failure. in addition, vitamin D intoxication promotes bone demineralization to the extent that bones are easily fractured. The observation that the level of skin pigmentation in indigenous human populations tends to increase with their proximity to the equator is explained by the hypothesis that skin pigmentation functions to prevent vitamin D intoxication by filtering out excessive solar radiation.
Calcitonin has essentially the opposite effect of PTH; it lowers serum Ca2+ concentration. It does so primarily by inhibiting osteoclastic resorption of bone. Calcitonin also inhibits kidney from resorbing Ca2+ but in this case the kidney cells that calcitonin influences differ from those that PTH stimulates to resorb Ca2+.

Originally Posted by samstar

Whats cholecalciferol?

[samstar]

Ed,
Thanks for the full explanation. Would you be kind enough to post photos of your Stars enclosures? Also how big is their enclosure?

[EJ]

This is my setup. The near/darker set... second from the top... is my Star Tortoises. I use aspen bedding and a water bowl... that's it.

The enclosure is 2 x 4 feet.

Originally Posted by samstar

Ed,
Thanks for the full explanation. Would you be kind enough to post photos of your Stars enclosures? Also how big is their enclosure?

[samstar]

Originally Posted by EJ

This is my setup. The near/darker set... second from the top... is my Star Tortoises. I use aspen bedding and a water bowl... that's it.

The enclosure is 2 x 4 feet.

Hi Ed,
Thanks. I was just looking through all your posts and already found it in this thread: http://shelledwarriors.co.uk/forum/s...ad.php?t=10195
Curious, dont you feel they might be happier with rocks, huts etc etc... to me the simpler, the better but I have my enclosure filled with stuff for them to keep busy, explore...

[EJ]

I have mixed feelings on that. Sometimes all the toys takes away space. The current setup was supposed to be temporary with the idea of adding rocks for them to climb and a humid hide... we're going on 4 years of 'temporary'. It will change but all I plan to add is those 2 things. The rocks are going to be a single 'hill'.

Originally Posted by samstar

Hi Ed,
Thanks. I was just looking through all your posts and already found it in this thread: http://shelledwarriors.co.uk/forum/s...ad.php?t=10195
Curious, dont you feel they might be happier with rocks, huts etc etc... to me the simpler, the better but I have my enclosure filled with stuff for them to keep busy, explore...

[samstar]

Originally Posted by EJ

I have mixed feelings on that. Sometimes all the toys takes away space. The current setup was supposed to be temporary with the idea of adding rocks for them to climb and a humid hide... we're going on 4 years of 'temporary'. It will change but all I plan to add is those 2 things. The rocks are going to be a single 'hill'.

Ok, no fake plants? Why just the rocks? you give me the impression that the more simple their enclosure=the better but in the wild they get plants to hide under etc etc, please correct me if I'm wrong.

[EJ]

I worry about them trying to eat the plants.

With a large collection... I believe the simpler the better in an indoor enclosure.

Originally Posted by samstar

Ok, no fake plants? Why just the rocks? you give me the impression that the more simple their enclosure=the better but in the wild they get plants to hide under etc etc, please correct me if I'm wrong.

[Alex]

Nice growth on them Ed.

Unrelated question I just remembered some time back your Pyxis planicauda group laid an egg, did it come to anything, did they lay any more?