How Fast Should We Grow Giant Tortoises? How Fast Should We Grow Long-Lived Tortoises?
In captivity, we are capable of feeding a young tortoise ample quantity of nutritious foods with high fiber content on a daily basis in order to maximize growth. Is this what is best for the tortoise?? Many stewards of giant or long-lived tortoise hatchlings seem to want their tortoises to grow large as possible as quickly as possible, feeding quantities of tortoise pellets, produce, and other nutritious and easily digested foods daily to achieve rapid growth. Feeding to achieve this goal will likely result in premature mortality and morbidity. Care in the first ten years is critical. Consider a male Galapagos may hatch at a weight of 70 grams and potentially grow to 500 plus lbs. (227 kg), a multiple in excess of 3200. Females more likely will achieve a potential growth factor of nearer 1500. Proper husbandry in the first 10% of life is critical for these tortoises to achieve their genetic potential. How best to achieve this remains controversial.
The Galapagos tortoises have been the subject of more documented research than the Aldabra tortoises but there are many similarities. The reader will have to determine if any of the following is applicable to tortoise species with which they are working. The author does not claim expertise but rather is attempting to share knowledge and insight acquired over time. Clearly some experienced breeders on the Tortoise Forum incorporate husbandry practices similar to those found appropriate with these gentle giants. The following remarks will be confined to the Galapagos tortoises (Chelonoidis nigra) which has been the subject of study, observations, and publications over many years. Nomenclature continually changes regarding species and subspecies. Certain subspecies are extinct, with the others being listed as Critically Endangered, Endangered, or Vulnerable. Nomenclature will be left to others and for purposes of this discussion, all subspecies are considered together. They have been extensively studied in the wild in their various habitats as well as in captivity. Studbook data confirms in many cases, we (author included) have not done a good job with husbandry of young animals in the past. Adults are much more forgiving. Fortunately, we know much more than we did 20-30 years ago and hopefully we will continue to learn.
Several thousand of the various subspecies of Galapagos tortoises have been hatched and raised in captivity on the Galapagos Islands. There are research stations on both Santa Cruz and Isabella islands. Tortoises have been hatched and “head started”, initially for 5 years or more and later as much as 8 years before release to their native habitat. Hatchlings are raised under conditions to promote growth and conditioning similar to what they might achieve in the wild. When they are large enough to likely escape predation and survive, they are repatriated to the wild. There is still significant mortality following repatriation, largely related to adverse environmental factors. Sun, exercise (including climbing for food), and limited groceries are part of the islands’ husbandry programs in these formative years.
There are several videos of the Galapagos rearing facilities available on YouTube.
Zoo Zurich, Zurich, Switzerland, kept their Aldabra and Galapagos tortoises together and they received the same diet. They changed their adult giant tortoise diet following a 1983 death of a giant Aldabra tortoise with renal failure and severe visceral gout. The first two Galapagos hatchlings born there in 1992 died after 14 and 15 months, one with chronic interstitial pneumonia, the other with “slight interstitial nephritis and thymitis. In addition, both animals developed signs of Metabolic Bone Disease (MBD). They also reported on four Aldabra tortoises who arrived in 1964 as 6 month old imports. They required euthanasia at between 10 and 12 years due to MBD described as rickets combined with osteodystrophy. The diet prior to 1983 consisted of 15% (by volume) lettuce, 20 % bananas, 30% tomatoes, 30% apples and pears, 5% minced meat, green corn in summer, and grass 3x/week in summer. Ca-grit was used as a supplement. The new diet of 1984 consisted of Kale, red cabbage 15%, carrots 45%, various vegetables 30%, carob 5%, shredded horn, shrimpmeal 3%, Ca-grit 1.5%, Carnicon 0.5% as well as grass , fresh leaves 3x /week in summer and chopped hay 3x / week in winter. (https://dokumen.tips/documents/mana...ne-elephantopus-and-geochelone-gigantean.html)
In 2004, the Zoo Zurich published a report on the growth rates of their captive raised tortoises as compared to the growth rates of tortoises raised at the Charles Darwin Research Station (CDRS) in the Galapagos Islands, Ecuador. They found considerable discrepancies in growth rates between the ages of 1-4 years. (https://doi.org/10.1002/zoo.10130)
Comparison of the weights of Galapagos giant tortoises from Zoo Zurich and CDRS
https://www.researchgate.net/figure/Comparison-of-the-weights-of-Galapagos-giant-tortoises-from-Zoo-Zurich-and-the-CDRS-Bars_fig1_230045908
Comparison of the carapace lengths of Galapagos giant tortoises from Zoo Zurich and the CDRS
https://www.semanticscholar.org/paper/Comparative-Study-on-the-Growth-of-Juvenile-Giant-(-Furrer-Hatt/ee9109b00009b95ae31c01c186bbbb7a90e25a75/figure/1
At 4 years of age, the Zurich Zoo raised tortoises weighed about 10 times as much as the CDRS animals and were twice as long. Subsequently the zoo diet was modified to produce a more natural growth rate.
There are multiple photos of deformed tortoises fed a diet of primarily of dog food or other inappropriate diets in the veterinary literature.
Twenty plus years ago the author raised a group of young Galapagos tortoises in South Florida in a large wire enclosed outdoor aviary in which parrots were housed overhead in suspended cages. This arrangement protected the young tortoises from predators. It was a particularly rainy year (warm and humid). Part of the aviary was covered, and part exposed to sun and rains. The parrots’ feed areas were under cover such that food remained dry. The tortoises had a heated “night box” for inclement weather. In addition to daily produce and occasional seed, the parrots were fed a diet primarily of Kaytee parrot pellets. Some of what they spilled was eaten by the tortoises. Veterinary and experienced reptile breeder consultation was obtained. At the time this was an ideal environment and minor adjustments were made when suggested. There was plenty of room for exercise. Grass and occasional germinated spilled seed were plentiful, far more than this small group of young tortoises would eat. The extra protein and nutrition from the spilled parrot pellets and other foods resulted in rapid growth. Unfortunately, shell deformity and MBD also resulted in several. Subsequently some cannot walk normally and are stunted. Some of these animals will never grow to their potential or be able to breed.
Examples of deformities
It is felt this abnormal growth was iatrogenic, a direct result of malnutrition resulting from an excess of easily digested groceries (protein) likely without adequate crude fiber. One of the parent tortoises of this group was known to produce occasional deformed offspring and undoubtedly there may be a genetic predisposition. In addition to desiccating basking lamps or sun in conditions of low humidity, other factors such as vitamin toxicity or deficiency, minerals, lack of sun, fast growth rates, lack of exercise, genetics, etc., have been suggested as contributing factors to pyramiding and shell deformity. Likely there are many factors which can influence the growth and development of the scutes and bone in these formative years.
Jarchow (http://www.deserttortoise.org/ocr_DTCdocs/1984Proceedings-OCR.pdf page 83-94) compared the crude fiber content of grocery store produce typically fed captive tortoises with that of typical wild foods of the desert tortoise. The grocery store produce being fed had a significantly lower crude fiber percentage than plants consumed in the native diet. Some of the captive fed foods had higher fat content and lower calcium-phosphorus ratios or lower calcium levels than levels expected from the native diet. He felt this diet related to the incidence of documented MBD in the captive raised tortoises.
The potential morbidity of rapid growth in giant tortoises has been recognized for at least the past ten years. Hiatt cautioned“The fast growth observed in giant tortoises must controlled by limiting the amount of food and reducing digestibility. Giant tortoises are well adapted to a high fiber, herbivore diet. Special attention must be given to the mineral supplementation and photoenvironment.” (http://www.zora.uzh.ch/id/eprint/10240/2/ZAWAM_6V.pdf, 2008).
Previously Hatt etal measured digestibility in different fiber fractions using a high crude fiber diet (20.5% dry matter). Their studies showed an increase in crude fiber reduced digestibility in juvenile Galapagos tortoises. They suggested but did not study diets of 30-40% crude fiber for Galapagos tortoises. They showed juvenile Galapagos tortoises demonstrated a digestion of crude fiber of similar efficiency as domestic horses.(https://www.researchgate.net/profil...tive-Galapagos-tortoises-Geochelone-nigra.pdf)
At the 2014 ARAV meeting, Adams C.H.,etal. (Failing the Galapagos Tortoise(Chelonoidis nigra): Death and Body Changes Resulting from Poor Husbandry)(https://propertibazar.com/queue/fai...f-reptilian-and_5b196434d64ab24602eec1da.html) reported many of the hundreds of captive F1 offspring produced over the last 30 years have failed to survive. They reported health issues related to husbandry. These animals have often exhibited rapid growth, ambulatory issues, edema, and morphological abnormalities. There has been a high incidence of associated fatal hepatological and cardiac disease. For purposes of this discussion, this will be called “Rapid Growth Syndrome” (RGS) although clearly more is involved than nutrition alone.
Adams, etal. suggested use of husbandry techniques to” better mimic wild conditions and accommodate the massive growth potential, long life, and impressive mobility of giant tortoises. This includes the elimination of highly digestible food stuffs from the captive diet, reducing the volume of food offered, providing a hard, rough substrate, and mandating routine exercise.”
Below is one of two genetically valuable animals sent to our facility with advanced “RGS” disease. They were quite edematous on arrival and were virtually unable to walk. The thought was that they were going to die, there was nothing to lose, and perhaps they might improve on the ranch setting. They were initially kept in a quarantine area. One tortoise never made meaningful recovery, succumbing to her hepatic and heart failure. After a prolonged quarantine period in which some ability to ambulate was restored, the second tortoise, a Chelonoidis nigra becki(whose genetically valuable mother has been dead for many years) was treated with “tough love”. As a beckishe is genetically smaller than other subspecies of Galapagos tortoises. One cannot judge her age by the scute “rings”. She has reached maturity to the point that her shell is developingbeckiflaring in the anterior and posterior portions of her carapace. Due to her goiter she has had some empiric iodine supplementation but otherwise her diet has consisted almost entirely of grasses (primarily Byhalia). She has spent an inordinate amount of time in the water compared to the other tortoises. She spent most of her days in the water last summer and fall. When it warmed enough in spring, she wallowed out mud soaks. Currently (August) she spends her nights and much of her day in her mud wallow or pond (as do many of the Galapagos tortoises). She can now raise her posterior and walk rapidly enough to easily outrun a larger male. She does not fully rise on her hind legs and still has some lateral sweep. The edematous throat is now a sack which sometimes contains fluid. What were massive areas of edema over her front and back legs are now flaps of skin which sometimes contains fluid but certainly is quite different from the tense interstitial edema she had for years. Videos are from April and August of this year. Notice she is unable to get her back legs completely under her plastron and raise herself fully on the hind legs, instead using a lateral sweeping motion of her back legs. This has allowed an elongation of her back claws; however, she can rapidly ambulate wherever she wants. How much the cardiomyopathy will reverse and how she will do in the long term is unknown. She has made marked symptomatic improvement with her prolonged soakings, grass, exercise, and sun. The amount of fluid in her residual skin flaps seems to vary from week to week. This improvement suggests this “RGS” manifested by rapid growth, edema, morphological changes, impaired ambulation and inability to fully stand, hepatic, and cardiac disease may be partially reversible with husbandry changes, confirming Adams, etal., recommendation regarding husbandry.
Videos
There has not been agreement on diets for giant tortoises in various institutions and breeder facilities. Some tortoises have been raised on easily digested bagged feeds, produce and greens with limited space, exercise, and crude fiber. Some facilities give extra protein periodically. Other facilities do an excellent job in providing for these tortoises with grasses, hay, supplements, exercise, and UV light.
AZA Galapagos Studbook (2012) Appendix on diet suggestions include:
At the Isabella research station the 2-4 yo tortoises being “head started” are fed three days per week with a “traditional diet” based on Xanthosoma sagittifoliun (otoy,yautia or malanga) elephant ear.( http://www.annexpublishers.co/artic...-in-Captivity-at-Isabela-Island-Galapagos.pdf)
(This species appears on the Florida Noxious Weed List and is legally prohibited in Florida.) Various other diets have also been trialed including ones listed in the above referenced paper.
It is difficult to test for a vitamin or mineral deficiency or toxicity from a single or limited blood samples. It may be reasonable to periodically give a multivitamin with minerals or similar supplement. Toxicity can occur from over supplementation. There is little good data. Nutritional secondary hyperparathyroidism is reported to be a very common cause of metabolic bone disease in reptiles due to either inadequate calcium intake or low calcium to phosphorus ratios, and lack of adequate ultraviolet light. This results in lack of appropriate levels of vitamin D3. It may be prudent to provide calcium supplementation. If Opuntia is not regularly fed or if there is any question of adequate calcium intake with a high calcium to phosphorus ratio, supplementation with calcium carbonate (food grade ground limestone) may be considered. This may also be considered when foods high in oxalates are fed. Sun or an adequate source of ultraviolet light is required. There are many ways to appropriately supplement calcium, vitamins, and trace minerals.
Exercise (on a non-slick surface) is mandatory for young tortoises. They show be observed for signs of problems associated with “RGS”. If too rapid growth is evidenced by failure to stand fully on the hind legs or ambulate appropriately, husbandry changes should be made as soon as possible to try to prevent disease progression.
The author has not witnessed the “RGS” in primarily grass/pasture raised Galapagos tortoises. Unfortunately, despite fencing, pasture raised animals are subject to predators, particularly raccoons.
In summary, slow and steady growth of giant tortoises is preferable to rapid growth for health reasons, some of which are illustrated above. Bagged tortoise chow and grocery store produce are not the dietary answer during these formative years. Adults can usually safely graze grasses free choice if no sudden dietary changes are made. It is questionable if 1-5-year-old tortoises, even those raised on high crude fiber diets or grass, should be fed to satiety on a daily basis. There is much to suggest that slow growth on a high crude fiber diet over the first 10% of these tortoises’ lives is advantageous to tortoises’ long-term health.
In captivity, we are capable of feeding a young tortoise ample quantity of nutritious foods with high fiber content on a daily basis in order to maximize growth. Is this what is best for the tortoise?? Many stewards of giant or long-lived tortoise hatchlings seem to want their tortoises to grow large as possible as quickly as possible, feeding quantities of tortoise pellets, produce, and other nutritious and easily digested foods daily to achieve rapid growth. Feeding to achieve this goal will likely result in premature mortality and morbidity. Care in the first ten years is critical. Consider a male Galapagos may hatch at a weight of 70 grams and potentially grow to 500 plus lbs. (227 kg), a multiple in excess of 3200. Females more likely will achieve a potential growth factor of nearer 1500. Proper husbandry in the first 10% of life is critical for these tortoises to achieve their genetic potential. How best to achieve this remains controversial.
The Galapagos tortoises have been the subject of more documented research than the Aldabra tortoises but there are many similarities. The reader will have to determine if any of the following is applicable to tortoise species with which they are working. The author does not claim expertise but rather is attempting to share knowledge and insight acquired over time. Clearly some experienced breeders on the Tortoise Forum incorporate husbandry practices similar to those found appropriate with these gentle giants. The following remarks will be confined to the Galapagos tortoises (Chelonoidis nigra) which has been the subject of study, observations, and publications over many years. Nomenclature continually changes regarding species and subspecies. Certain subspecies are extinct, with the others being listed as Critically Endangered, Endangered, or Vulnerable. Nomenclature will be left to others and for purposes of this discussion, all subspecies are considered together. They have been extensively studied in the wild in their various habitats as well as in captivity. Studbook data confirms in many cases, we (author included) have not done a good job with husbandry of young animals in the past. Adults are much more forgiving. Fortunately, we know much more than we did 20-30 years ago and hopefully we will continue to learn.
Several thousand of the various subspecies of Galapagos tortoises have been hatched and raised in captivity on the Galapagos Islands. There are research stations on both Santa Cruz and Isabella islands. Tortoises have been hatched and “head started”, initially for 5 years or more and later as much as 8 years before release to their native habitat. Hatchlings are raised under conditions to promote growth and conditioning similar to what they might achieve in the wild. When they are large enough to likely escape predation and survive, they are repatriated to the wild. There is still significant mortality following repatriation, largely related to adverse environmental factors. Sun, exercise (including climbing for food), and limited groceries are part of the islands’ husbandry programs in these formative years.
There are several videos of the Galapagos rearing facilities available on YouTube.
Zoo Zurich, Zurich, Switzerland, kept their Aldabra and Galapagos tortoises together and they received the same diet. They changed their adult giant tortoise diet following a 1983 death of a giant Aldabra tortoise with renal failure and severe visceral gout. The first two Galapagos hatchlings born there in 1992 died after 14 and 15 months, one with chronic interstitial pneumonia, the other with “slight interstitial nephritis and thymitis. In addition, both animals developed signs of Metabolic Bone Disease (MBD). They also reported on four Aldabra tortoises who arrived in 1964 as 6 month old imports. They required euthanasia at between 10 and 12 years due to MBD described as rickets combined with osteodystrophy. The diet prior to 1983 consisted of 15% (by volume) lettuce, 20 % bananas, 30% tomatoes, 30% apples and pears, 5% minced meat, green corn in summer, and grass 3x/week in summer. Ca-grit was used as a supplement. The new diet of 1984 consisted of Kale, red cabbage 15%, carrots 45%, various vegetables 30%, carob 5%, shredded horn, shrimpmeal 3%, Ca-grit 1.5%, Carnicon 0.5% as well as grass , fresh leaves 3x /week in summer and chopped hay 3x / week in winter. (https://dokumen.tips/documents/mana...ne-elephantopus-and-geochelone-gigantean.html)
In 2004, the Zoo Zurich published a report on the growth rates of their captive raised tortoises as compared to the growth rates of tortoises raised at the Charles Darwin Research Station (CDRS) in the Galapagos Islands, Ecuador. They found considerable discrepancies in growth rates between the ages of 1-4 years. (https://doi.org/10.1002/zoo.10130)
Comparison of the weights of Galapagos giant tortoises from Zoo Zurich and CDRS
https://www.researchgate.net/figure/Comparison-of-the-weights-of-Galapagos-giant-tortoises-from-Zoo-Zurich-and-the-CDRS-Bars_fig1_230045908
Comparison of the carapace lengths of Galapagos giant tortoises from Zoo Zurich and the CDRS
https://www.semanticscholar.org/paper/Comparative-Study-on-the-Growth-of-Juvenile-Giant-(-Furrer-Hatt/ee9109b00009b95ae31c01c186bbbb7a90e25a75/figure/1
At 4 years of age, the Zurich Zoo raised tortoises weighed about 10 times as much as the CDRS animals and were twice as long. Subsequently the zoo diet was modified to produce a more natural growth rate.
There are multiple photos of deformed tortoises fed a diet of primarily of dog food or other inappropriate diets in the veterinary literature.
Twenty plus years ago the author raised a group of young Galapagos tortoises in South Florida in a large wire enclosed outdoor aviary in which parrots were housed overhead in suspended cages. This arrangement protected the young tortoises from predators. It was a particularly rainy year (warm and humid). Part of the aviary was covered, and part exposed to sun and rains. The parrots’ feed areas were under cover such that food remained dry. The tortoises had a heated “night box” for inclement weather. In addition to daily produce and occasional seed, the parrots were fed a diet primarily of Kaytee parrot pellets. Some of what they spilled was eaten by the tortoises. Veterinary and experienced reptile breeder consultation was obtained. At the time this was an ideal environment and minor adjustments were made when suggested. There was plenty of room for exercise. Grass and occasional germinated spilled seed were plentiful, far more than this small group of young tortoises would eat. The extra protein and nutrition from the spilled parrot pellets and other foods resulted in rapid growth. Unfortunately, shell deformity and MBD also resulted in several. Subsequently some cannot walk normally and are stunted. Some of these animals will never grow to their potential or be able to breed.
Examples of deformities
It is felt this abnormal growth was iatrogenic, a direct result of malnutrition resulting from an excess of easily digested groceries (protein) likely without adequate crude fiber. One of the parent tortoises of this group was known to produce occasional deformed offspring and undoubtedly there may be a genetic predisposition. In addition to desiccating basking lamps or sun in conditions of low humidity, other factors such as vitamin toxicity or deficiency, minerals, lack of sun, fast growth rates, lack of exercise, genetics, etc., have been suggested as contributing factors to pyramiding and shell deformity. Likely there are many factors which can influence the growth and development of the scutes and bone in these formative years.
Jarchow (http://www.deserttortoise.org/ocr_DTCdocs/1984Proceedings-OCR.pdf page 83-94) compared the crude fiber content of grocery store produce typically fed captive tortoises with that of typical wild foods of the desert tortoise. The grocery store produce being fed had a significantly lower crude fiber percentage than plants consumed in the native diet. Some of the captive fed foods had higher fat content and lower calcium-phosphorus ratios or lower calcium levels than levels expected from the native diet. He felt this diet related to the incidence of documented MBD in the captive raised tortoises.
The potential morbidity of rapid growth in giant tortoises has been recognized for at least the past ten years. Hiatt cautioned“The fast growth observed in giant tortoises must controlled by limiting the amount of food and reducing digestibility. Giant tortoises are well adapted to a high fiber, herbivore diet. Special attention must be given to the mineral supplementation and photoenvironment.” (http://www.zora.uzh.ch/id/eprint/10240/2/ZAWAM_6V.pdf, 2008).
Previously Hatt etal measured digestibility in different fiber fractions using a high crude fiber diet (20.5% dry matter). Their studies showed an increase in crude fiber reduced digestibility in juvenile Galapagos tortoises. They suggested but did not study diets of 30-40% crude fiber for Galapagos tortoises. They showed juvenile Galapagos tortoises demonstrated a digestion of crude fiber of similar efficiency as domestic horses.(https://www.researchgate.net/profil...tive-Galapagos-tortoises-Geochelone-nigra.pdf)
At the 2014 ARAV meeting, Adams C.H.,etal. (Failing the Galapagos Tortoise(Chelonoidis nigra): Death and Body Changes Resulting from Poor Husbandry)(https://propertibazar.com/queue/fai...f-reptilian-and_5b196434d64ab24602eec1da.html) reported many of the hundreds of captive F1 offspring produced over the last 30 years have failed to survive. They reported health issues related to husbandry. These animals have often exhibited rapid growth, ambulatory issues, edema, and morphological abnormalities. There has been a high incidence of associated fatal hepatological and cardiac disease. For purposes of this discussion, this will be called “Rapid Growth Syndrome” (RGS) although clearly more is involved than nutrition alone.
Adams, etal. suggested use of husbandry techniques to” better mimic wild conditions and accommodate the massive growth potential, long life, and impressive mobility of giant tortoises. This includes the elimination of highly digestible food stuffs from the captive diet, reducing the volume of food offered, providing a hard, rough substrate, and mandating routine exercise.”
Below is one of two genetically valuable animals sent to our facility with advanced “RGS” disease. They were quite edematous on arrival and were virtually unable to walk. The thought was that they were going to die, there was nothing to lose, and perhaps they might improve on the ranch setting. They were initially kept in a quarantine area. One tortoise never made meaningful recovery, succumbing to her hepatic and heart failure. After a prolonged quarantine period in which some ability to ambulate was restored, the second tortoise, a Chelonoidis nigra becki(whose genetically valuable mother has been dead for many years) was treated with “tough love”. As a beckishe is genetically smaller than other subspecies of Galapagos tortoises. One cannot judge her age by the scute “rings”. She has reached maturity to the point that her shell is developingbeckiflaring in the anterior and posterior portions of her carapace. Due to her goiter she has had some empiric iodine supplementation but otherwise her diet has consisted almost entirely of grasses (primarily Byhalia). She has spent an inordinate amount of time in the water compared to the other tortoises. She spent most of her days in the water last summer and fall. When it warmed enough in spring, she wallowed out mud soaks. Currently (August) she spends her nights and much of her day in her mud wallow or pond (as do many of the Galapagos tortoises). She can now raise her posterior and walk rapidly enough to easily outrun a larger male. She does not fully rise on her hind legs and still has some lateral sweep. The edematous throat is now a sack which sometimes contains fluid. What were massive areas of edema over her front and back legs are now flaps of skin which sometimes contains fluid but certainly is quite different from the tense interstitial edema she had for years. Videos are from April and August of this year. Notice she is unable to get her back legs completely under her plastron and raise herself fully on the hind legs, instead using a lateral sweeping motion of her back legs. This has allowed an elongation of her back claws; however, she can rapidly ambulate wherever she wants. How much the cardiomyopathy will reverse and how she will do in the long term is unknown. She has made marked symptomatic improvement with her prolonged soakings, grass, exercise, and sun. The amount of fluid in her residual skin flaps seems to vary from week to week. This improvement suggests this “RGS” manifested by rapid growth, edema, morphological changes, impaired ambulation and inability to fully stand, hepatic, and cardiac disease may be partially reversible with husbandry changes, confirming Adams, etal., recommendation regarding husbandry.
Videos
There has not been agreement on diets for giant tortoises in various institutions and breeder facilities. Some tortoises have been raised on easily digested bagged feeds, produce and greens with limited space, exercise, and crude fiber. Some facilities give extra protein periodically. Other facilities do an excellent job in providing for these tortoises with grasses, hay, supplements, exercise, and UV light.
AZA Galapagos Studbook (2012) Appendix on diet suggestions include:
Grass, hay & leafy browse = 85% of diet
– Offer daily
Cactus & grocery store greens = 13% of diet
– Offer in moderation (no more than what can be eaten in ten minutes) 2 X week
Tortoise chow & others = 2% of diet
– Feed like bonbons
– No more than once weekly
Suggested food items
• Grass
• Hay: Bermuda, Timothy, Alfalfa
• Edible leaves & flowers
• Hibiscus
• Turk’s cap
• Local species (?)
• Opuntia cactus pads
• Green leafy grocery store veggies
In moderation only
• Tortoise Chow: Soaked, Volume as big as tortoise’s head X once weekly
• Carrot or sweet potato: Most benign, given in moderation, but only as a tool to condition or stimulate exercise
• Apple and other fruits: Should be considered as treats. Only with exercise, no more than once weekly
– Offer daily
Cactus & grocery store greens = 13% of diet
– Offer in moderation (no more than what can be eaten in ten minutes) 2 X week
Tortoise chow & others = 2% of diet
– Feed like bonbons
– No more than once weekly
Suggested food items
• Grass
• Hay: Bermuda, Timothy, Alfalfa
• Edible leaves & flowers
• Hibiscus
• Turk’s cap
• Local species (?)
• Opuntia cactus pads
• Green leafy grocery store veggies
In moderation only
• Tortoise Chow: Soaked, Volume as big as tortoise’s head X once weekly
• Carrot or sweet potato: Most benign, given in moderation, but only as a tool to condition or stimulate exercise
• Apple and other fruits: Should be considered as treats. Only with exercise, no more than once weekly
At the Isabella research station the 2-4 yo tortoises being “head started” are fed three days per week with a “traditional diet” based on Xanthosoma sagittifoliun (otoy,yautia or malanga) elephant ear.( http://www.annexpublishers.co/artic...-in-Captivity-at-Isabela-Island-Galapagos.pdf)
(This species appears on the Florida Noxious Weed List and is legally prohibited in Florida.) Various other diets have also been trialed including ones listed in the above referenced paper.
It is difficult to test for a vitamin or mineral deficiency or toxicity from a single or limited blood samples. It may be reasonable to periodically give a multivitamin with minerals or similar supplement. Toxicity can occur from over supplementation. There is little good data. Nutritional secondary hyperparathyroidism is reported to be a very common cause of metabolic bone disease in reptiles due to either inadequate calcium intake or low calcium to phosphorus ratios, and lack of adequate ultraviolet light. This results in lack of appropriate levels of vitamin D3. It may be prudent to provide calcium supplementation. If Opuntia is not regularly fed or if there is any question of adequate calcium intake with a high calcium to phosphorus ratio, supplementation with calcium carbonate (food grade ground limestone) may be considered. This may also be considered when foods high in oxalates are fed. Sun or an adequate source of ultraviolet light is required. There are many ways to appropriately supplement calcium, vitamins, and trace minerals.
Exercise (on a non-slick surface) is mandatory for young tortoises. They show be observed for signs of problems associated with “RGS”. If too rapid growth is evidenced by failure to stand fully on the hind legs or ambulate appropriately, husbandry changes should be made as soon as possible to try to prevent disease progression.
The author has not witnessed the “RGS” in primarily grass/pasture raised Galapagos tortoises. Unfortunately, despite fencing, pasture raised animals are subject to predators, particularly raccoons.
In summary, slow and steady growth of giant tortoises is preferable to rapid growth for health reasons, some of which are illustrated above. Bagged tortoise chow and grocery store produce are not the dietary answer during these formative years. Adults can usually safely graze grasses free choice if no sudden dietary changes are made. It is questionable if 1-5-year-old tortoises, even those raised on high crude fiber diets or grass, should be fed to satiety on a daily basis. There is much to suggest that slow growth on a high crude fiber diet over the first 10% of these tortoises’ lives is advantageous to tortoises’ long-term health.