The effects of UV light on calcium metabolism in ball pythons (Python regius)

Abstract

Despite the popularity of keeping snakes in captivity, there has been limited investigation into the effects of UV radiation on vitamin D levels in snakes. The aim of this study was to investigate the effects of UV-b radiation on plasma 25-hydroxyvitamin D3 levels and ionised calcium concentrations in ball pythons (Python regius). Blood samples were taken from 14 ball pythons, which had never been exposed to UV-b light, to obtain baseline 25-hydroxyvitamin D3 levels and ionised calcium concentrations. Blood samples were then taken again from the same snakes 70 days later after one group (Group 1, n=6 females) were exposed to UV-b radiation daily, and the other group (Group 2, n=5 males and 3 females) were exposed to no UV-b radiation. Mean±sd 25-hydroxyvitamin D3 levels on day 0 in Group 1 were 197±35 nmol/l, and on day 70 were 203.5±13.8 nmol/l. Mean±sd 25-hydroxyvitamin D3 levels in Group 2 on day 0 were 77.7±41.5 nmol/l, and on day 70 were 83.0±41.9 nmol/l. Mean±sd ionised calcium levels at day 0 were 1.84±0.05 mmol/l for Group 1, and on day 70 were 1.78±0.07 mmol/l. Mean±sd ionised calcium levels at day 0 were 1.79±0.07 mmol/l for Group 2, and on day 70 were 1.81±0.05 mmol/l. No association was demonstrated between exposure to UV-b radiation and plasma 25-hydroxyvitamin D3 and ionised calcium concentrations. These results may provide baseline parameters for future studies in this and other snake species to determine ability to utilise UV-b light for vitamin D production.

Full text

doi: 10.1136/vr.101555
25, 2013 2013 173: 345 originally published online SeptemberVeterinary Record
J. Hedley and K. Eatwell
metabolism in ball pythons (Python regius)
The effects of UV light on calcium
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October 12, 2013 | Veterinary Record
Paper
Paper
The effects of UV light on calcium metabolism in
ball pythons (
Python regius
)
J. Hedley, K. Eatwell
Despite the popularity of keeping snakes in captivity, there has been limited investigation
into the effects of UV radiation on vitamin D levels in snakes. The aim of this study was
to investigate the effects of UV-b radiation on plasma 25-hydroxyvitamin D3 levels and
ionised calcium concentrations in ball pythons (
Python regius
). Blood samples were taken
from 14 ball pythons, which had never been exposed to UV-b light, to obtain baseline
25-hydroxyvitamin D3 levels and ionised calcium concentrations. Blood samples were then
taken again from the same snakes 70 days later after one group (Group 1, n=6 females) were
exposed to UV-b radiation daily, and the other group (Group 2, n=5 males and 3 females)
were exposed to no UV-b radiation. Mean±sd 25-hydroxyvitamin D3 levels on day 0 in Group 1
were 197±35 nmol/l, and on day 70 were 203.5±13.8 nmol/l. Mean±sd 25-hydroxyvitamin
D3 levels in Group 2 on day 0 were 77.7±41.5 nmol/l, and on day 70 were 83.0±41.9 nmol/l.
Mean±sd ionised calcium levels at day 0 were 1.84±0.05 mmol/l for Group 1, and on day 70
were 1.78±0.07 mmol/l. Mean±sd ionised calcium levels at day 0 were 1.79±0.07 mmol/l
for Group 2, and on day 70 were 1.81±0.05 mmol/l. No association was demonstrated
between exposure to UV-b radiation and plasma 25-hydroxyvitamin D3 and ionised calcium
concentrations. These results may provide baseline parameters for future studies in this and
other snake species to determine ability to utilise UV-b light for vitamin D production.
Introduction
Vitamin D is essential for the absorption of dietary calcium in near-
ly all terrestrial vertebrates (Ullrey and Bernard 1999) and a lack of
Vitamin D3 has been associated with secondary hyperparathyroidism
in lizards (Hoby and others 2010) and chelonians (McArthur 2004).
UV-b radiation in the spectrum of 290–315 nm is important in the
conversion of provitamin precursors in the skin (7-dehydrocholesterol)
to previtamin D3 (Holick 1995). Previtamin D3, in turn, is converted
to vitamin D3 (cholecalciferol) via a temperature-sensitive isomerisa-
tion (Havinga and others 1960). Cholecalciferol binds to plasma pro-
teins to be transported to the liver where it is converted to calcediol
(25-hydroxyvitamin D3). Calcediol is then transported to the kidneys
where it is converted to calcetriol (1,25 dihydroxyvitamin D3), the
active form of Vitamin D (Bentley 1976).
Different reptile species appear to have varying abilities to utilise
UV-b light to produce endogenous vitamin D3 or to absorb dietary
forms. Many lizard and chelonian species, such as iguanas, Iguana iguana
(Laing and others 2001), bearded dragons, Pogona vitticeps (Oonincx
and others 2010), panther chameleons, Furcifer pardalis (Ferguson and
others 2003) and red-eared sliders, Trachemys scripta elegans (Acierno
and others 2006), have been shown to produce endogenous vitamin
D3 in response to UV-b radiation. However, oral supplementation of
vitamin D3 to bearded dragons has been shown to be ineffective at
increasing 25-hydroxyvitamin D3 and 1,25 dihydroxyvitamin D3 to
the concentrations observed in UV-b-exposed animals (Oonincx and
others 2010), whereas black-throated monitor lizards, Varanus albigula-
ris, appear able to both use UV-b light to produce vitamin D and also
to use oral forms (Ferguson and others 2009).
Snakes are thought to have originally evolved from a group of liz-
ards that became subterranean and adapted to a fossorial lifestyle (Vitt
and Caldwell 2009). Despite the popularity of keeping snakes in cap-
tivity, there has, however, been limited investigation into the effects
of UV radiation on vitamin D levels in snakes, and as a consequence
many reptile care guides and popular websites recommend keeping
snakes in captivity without exposure to UV-b light (Flank 1998,
Kruzer 2012). In a previous study, exposure to UV-b light led to a sig-
nificant increase in 25-hydroxyvitamin D3 levels in colubrid snakes
(corn snakes, Elaphe guttata), suggesting that this species has evolved
and retained or recreated the ability to utilise UV-b light (Acierno and
others 2008). However, different snake species have been shown to
vary considerably in their amount of UV-b exposure in their natural
habitats (Ferguson and others 2009).
The ball python, Python regius, is one of the most common boid
species kept in captivity, and so far, no research has been performed
on the effects of UV radiation on this species. Boid snakes have fol-
lowed a different evolutionary path to colubrid snakes and retain more
primitive characteristics (Vitt and Caldwell 2009), so it is unknown if
they would be able to respond to UV-b light in the same way as corn
snakes.
The aim of this study was, therefore, to investigate the effects of
UV-b radiation on plasma 25-hydroxyvitamin D3 levels and ionised
calcium concentrations in ball pythons.
Materials and methods
Fourteen captive ball pythons were used in the study consisting of
five males and nine females, all over four years old, weighing between
Veterinary Record (2013) doi: 10.1136/vr.101555
J. Hedley, BVM&S DZooMed MRCVS,
K. Eatwell, BVSc (hons) DZooMed Dip
ECZM MRCVS,
Royal (Dick) School of Veterinary Studies
and The Roslin Institute, The University
of Edinburgh, Hospital for Small Animals,
Easter Bush Veterinary Centre, Roslin,
Midlothian EH25 9RG, UK
E-mail for correspondence:
Hedley@ed.ac.uk
Provenance: Not commissioned;
externally peer reviewed
Accepted September 3, 2013
group.bmj.com on October 11, 2013 - Published by veterinaryrecord.bmj.comDownloaded from group.bmj.com on October 11, 2013 - Published by veterinaryrecord.bmj.comDownloaded from group.bmj.com on October 11, 2013 - Published by veterinaryrecord.bmj.comDownloaded from group.bmj.com on October 11, 2013 - Published by veterinaryrecord.bmj.comDownloaded from

Paper
Veterinary Record | October 12, 2013
0.91 and 2.36 kg. These animals belonged to three local collections,
and were all due to be health screened as part of their recommended
preventative medicine protocol. Their diet and housing was standard-
ised between the collections. Snakes were housed in wooden vivaria
(115×49×43 cm) with sliding glass doors and plastic ventilation panels
in dedicated thermostatically controlled reptile rooms. Temperature
gradients of 20–30°C were maintained using heat mats towards one
end of the vivaria. Humidity was maintained within 50–80 per cent
by regular misting of the enviroment. Handling was minimised. All
snakes were standardly offered one pre-killed 25–30 g mouse once per
week as was the normal routine. All the snakes had been kept indoors
and had never previously been exposed to any supplemental or natu-
ral UV light. None of the snakes had any current health concerns. The
study was approved by the institutional Veterinary Ethics and Review
Committee.
On Day 0 (July 26, 2012) all snakes were weighed, choanal tem-
peratures were checked with an infrared thermometer (RayTemp 4,
Electronic Temperature Instruments) and a full clinical examination
was performed, before a blood sample was collected via cardiocente-
sis. Approximately 1 ml of blood was collected from each snake for
routine haematology and biochemistry. Samples were processed using
a point-of-care analyser (i-STAT 1, Abbot Diagnostics, Maidenhead,
Berkshire, UK) with a blood gas cartridge (CG8+, Abbot Diagnostics,
Maidenhead, Berkshire, UK) which had been kept in a fridge at 4°C,
but allowed to reach room temperature prior to use. The parameters
measured included pH (power of hydrogen), PaCO2 (partial pressure
of arterial carbon dioxide) (mm Hg), PaO2 (partial pressure of arte-
rial oxygen) (mm Hg), SaO2 (arterial oxygen saturation) (per cent),
Na (sodium) (mmol/l), K (potassium) (mmol/l), iCa (ionised calcium)
(mmol/l), Glu (glucose) (mg/dl), Hct (haematocrit) (per cent) and Hb
(haemoglobin) (mg/dl) in addition to total and differential white
blood cell counts which were performed manually using a phloxine
B technique to count heterophils and eosinophils (Campbell 2004).
The remaining plasma was separated and stored frozen at −20°C for
25-hydroxyvitamin D3 analysis at the end of the study.
One group of snakes (Group 1, n=6 females) were then exposed
to UV-b radiation daily. From day 1, Group 1 snakes were removed
from their usual enclosures and placed individually into commercially
available snake terrrariums where they were continually exposed to
a commonly marketed artificial UV light source (ReptiSun 5.0 UV-b
Fluorescent bulb, Zoo Med, USA) placed at a 10 cm distance from each
snake for eight hours per day. After the eight hour period the snakes
were returned to their usual enclosure for the rest of the day and over-
night. Environmental temperature was maintained within the same
range as that of the snake’s usual enclosure. UV output was measured
(mW/cm2) at weekly intervals with a Solarmeter 6.2 (Solartech, USA)
throughout the terrarium at the distance of 10 cm from the bulb at
which the snakes were basking. The remaining snakes (Group 2, n=5
males and 3 females) were maintained in their usual enclosures for the
duration of the study. The feeding regime remained the same for both
groups throughout the study.
On day 70 (October 4, 2012), snakes were re-examined, and a sec-
ond blood sample was taken for a repeat evaluation of their health sta-
tus. The same parameters were measured as previously, and separated
plasma submitted for 25-hydroxyvitamin D3 analysis.
Statistical analysis
Data was analysed using Minitab (Minitab, Pennsylvania, USA) and
P<0.05 was taken to indicate statistical significance. Data for body
weight, ionised calcium, 25-hydroxyvitamin D3 levels and UV-b
measurements were evaluated by use of an Anderson-Darling test and
found to be normally distributed. A paired sample two-tailed t test
was used to determine whether these variables changed in individual
animals between day 0 and day 70. A two-sample t test was used to
compare the body weight, ionised calcium, 25-hydroxyvitamin D3
levels between Groups 1 and 2 at both timepoints.
The mean, sd and observed range for ionised calcium levels were
calculated using an Excel-based tool (Reference Value Advisor V.2.1,
Reference Value Advisor add in for Microsoft Excel V.2.1) (Geffre and
others 2009, 2011). The data was evaluated by use of an Anderson-
Darling test and was found to be normally distributed. Therefore, in
accordance with Reference Value Advisor V.2.1 recommendations,
the reference intervals were created parametrically. Outliers were
retained in accordance with Reference Value Advisor’s recommenda-
tions, as all snakes were clinically normal and these were not deemed
to be aberrant observations. If outliers were present, Reference Value
Advisor’s robust method was used, as this is less sensitive to the pres-
ence of outliers.
Results
All snakes remained healthy and continued feeding throughout the
duration of the study and no abnormalities were detected on rou-
tine haematological and biochemical health screening. Mean±sd
number of mice eaten by Group 1 snakes were 7.5±1.38 and by
Group 2 snakes 7.8±1.38. Mean±sd choanal temperatures were
27.1±2.0°C. Mean±sd weights at day 0 were 1.86±0.53 kg for Group
1 and 1.42±0.39 kg for Group 2. Mean±sd weights at day 70 were
1.80±0.47 kg for Group 1 and 1.46±0.37 kg for Group 2. Body
weight in Groups 1 and 2 did not differ significantly between the two
groups at the start of the study (P=0.120) or at the end of the study
(P=0.176). There were also no significant changes in body weight
within each group over the course of the study (Group 1; P=0.165,
Group 2; P=0.113).
UV-b radiation reduced over time as measured at the basking
surface from 70.86±11.78 (52–90) µW/cm2 on day 0 to 57.57±10.71
(45–71) µW/cm2 on day 70 (mean ±1sd (range)). This reduction was
statistically significant (P=0.049).
Mean±sd 25-hydroxyvitamin D3 levels on day 0 in Group 1 were
197±35 nmol/l, and in Group 2 on day 0 were 77.7±41.5 nmol/l.
Mean±sd 25-hydroxyvitamin D3 levels on day 70 in Group 1 were
203.5±13.8 nmol/l, and in Group 2 on day 70 were 83.0±41.9 nmol/l.
25-hydroxyvitamin D3 levels in Groups 1 and 2 did not differ sig-
nificantly within each group between day 0 and day 70 (Group 1;
P=0.406, Group 2; P=0.452) (Table 1). However, there were signifi-
cant differences between the two groups both at the start of the study
(P<0.001) and at the end of the study (P<0.001) with Group 1 snakes
having consistently higher 25-hydroxyvitamin D3 values at both day
0 and day 70 (Fig 1).
Mean±sd ionised calcium levels at day 0 were 1.84±0.05 mmol/l
for Group 1 and 1.79±0.07 mmol/l for Group 2. Mean±sd ionised
calcium levels on day 70 in Group 1 were 1.78±0.07 mmol/l and in
Group 2 on day 70 were 1.81±0.05 mmol/l. Ionised calcium levels in
Groups 1 and 2 did not differ significantly within each group between
day 0 and day 70 (Group 1; P=0.109, Group 2; P=0.634) (Table 2).
There were also no significant differences between the two groups
either at the start of the study (P=0.140) and at the end of the study
(P=0.497) (Fig 2). All ionised calcium data was therefore pooled for
calculation of the mean, sd and an observed interval as calculated by
Reference Value Advisor were found to be 1.81±0.06 (1.67–1.94).
TABLE 1: Plasma 25-hydroxyvitamin D
3
(25OHD
3
) concentrations
(nmol/l) in ball pythons that received (Group 1; n=6) or did
not receive (Group 2; n=8) supplemental UV radiation over the
course of the study
Sex 25OHD3 on day 0 25OHD3 on day 70
Group 1 exposed to UV-b
1 Female 224 225
2 Female 224 224
3 Female 143 177
4 Female 230 244
5 Female 173 154
6 Female 188 197
Group 2 not exposed to UV-b
7 Female 128 139
8 Female 134 127
9 Female 68.4 98.2
10 Male 32.6 44.5
11 Male 25.7 32.9
12 Male 78. 5 44.7
13 Male 4 9. 5 61.4
14 Male 105 116

Paper
October 12, 2013 | Veterinary Record
Discussion
Results of this study showed no significant effects of UV radiation on
plasma 25-hydroxyvitamin D3 and ionised calcium concentrations in
six female ball pythons. Both 25-hydroxyvitamin D3 levels and ion-
ised calcium concentrations did not differ significantly between the
group of female snakes which were exposed to UV, and the mixed
group of male and female snakes which were not.
The range of 25-hydroxyvitamin D3 levels were similar to those
previously recorded in corn snakes (Acierno and others 2008). That
study, however, indicated that exposure to UV-b light was associated
with a significant increase in 25-hydroxycholecalciferol levels. In the
current study, all snakes in Group 1 were exposed to UV-b radiation
over 70 days, and although the amount of radiation did reduce over
time, all bulbs were still emitting an output >41µW/cm2 measured
at snake level on day 70. This is greater than in the previous study
in corn snakes which showed an effect of UV-b radiation even when
exposed for only 30 days at much lower levels (~10µW/cm2).
There are various possible explanations for the results of this
study. Ball pythons are nocturnal snakes (Leck and Klingenberg 2000),
so less likely to need the ability to utilise UV-b light, whereas corn
snakes have more diurnal or crepuscular habits, so will be exposed
to some natural sunlight (Love and Love 2000). Gender may have
accounted for the elevated 25-hydroxycholecalciferol levels in Group 1
snakes. In green iguanas, reproductively active females were found to
have elevated 25-hydroxycholecalciferol levels compared with males
(Nevarez and others 2002). The reproductive status of the snakes in
this study was not evaluated, but the study was performed between
July and September which is the season that some of these snakes had
produced eggs in previous years.
Mean, sd and reference intervals for ionised calcium as calculat-
ed by Reference Value Advisor were found to be 1.81±0.06 (1.67–
1.94) which is higher than recorded values in iguanas (Dennis
and others 2001) and similar to recorded values in Testudo species
(Eatwell 2009). Ionised calcium levels did not vary between the two
groups despite differences in 25-hydroxyvitamin D3 levels. Ionised
calcium is, however, physiologically maintained within a tight ref-
erence range so changes in this would not be expected despite dif-
ferences in 25-hydroxyvitamin D3. Ionised calcium levels have not,
to the authors knowledge, been published previously in any snake
species.
Although no significant effects of UV-b exposure on plasma
25-hydroxyvitamin D3 and ionised calcium concentrations were
demonstrated in this study, exposure to UV light has been shown
to have other beneficial effects in reptiles. Behavioural changes have
been demonstrated in iguanids and agamids (Moehn 1974), and
increased activity levels in corn snakes exposed to UV light (Nail
2011). The potential positive behavioural effects of UV-b radiation
in ball pythons have not been examined before and would be a use-
ful future study. In this study, snakes were only exposed to UV-b
radiation for eight hours per day due to time limitations, but a more
natural photoperiod would be 12 hours UV-b:12 hours darkness,
and the effect of different photoperiods would also need further
investigation.
It is important to be aware of possible side effects of supplying
excessive UV light. Photokeratoconjunctivitis and photodermatitis
have been reported in a ball python associated with exposure to a UV
bulb (Gardiner and others 2009). That bulb, however, had a much
higher UV-b output than the bulbs tested in this study, and a dispro-
portionately high output of UV-b below 300 nm which is within
the action spectra for photokeratoconjunctivitis, photodermatitis
and DNA damage (Setlow 1974). Body weight in the two groups did
not differ significantly over the course of the study, and all snakes
remained clinically healthy, so there was no evidence of problems
with UV exposure at the level used in this study.
The effects of UV-b radiation on ball pythons would ideally be
obtained by assessment of two randomised gender-balanced groups.
One limitation of this study is that only female snakes were exposed
to UV-b radiation. Future studies would be necessary to examine
larger numbers of snakes and investigate the effect of UV-b radiation
on the different genders. Further studies would also be necessary to
examine the effect of environmental temperature in combination
with UV-b radiation.The pythons in the current study were provided
with a temperature gradient of 20–30°C, and measured choanal tem-
peratures were 27.1±2.0°C (mean±sd), but higher temperatures may
be necessary for production of cholecalciferol.
250
200
150
100
Plasma 250HD3 concentrations (nmol/L)
50
0
Group 1 day 0Group 2 day 0Group 1 day 70 Group 2 day 70
FIG 1: Boxplot to illustrate plasma 25-hydroxyvitamin D3 (25OHD3)
concentrations (nmol/l) in ball pythons that received (Group 1; n=6)
or did not receive (Group 2; n=8) supplemental UV radiation over
the course of the study
TABLE 2: Ionised calcium concentrations (mmol/l) in ball pythons
that received (Group 1; n=6) or did not receive (Group 2; n=8)
supplemental UV radiation over the course of the study
Sex Ionised Ca day 0 Ionised Ca day 70
Group 1 exposed to UV-b
1 Female 1.8 1.73
2 Female 1.9 1.85
3 Female 1.79 1.8
4 Female 1.81 1.84
5 Female 1.91 1.81
6 Female 1.84 1.67
Group 2 not exposed to UV-b
8 Female 1.8 1.8
9 Female 1.75 1.79
10 Female 1.71 1.88
11 Male 1.86 1.8
12 Male 1.79 1.7 7
13 Male 1.75 1.7 3
14 Male 1.92 1.8
15 Male 1.74 1.89
1.95
1.90
1.85
1.80
Ionised calcium (mmol/L)
1.75
1.70
Group 1 day 0Group 2 day 0Group 1 day 70 Group 2 day 70
FIG 2: Boxplot to illustrate ionised calcium concentrations (mmol/l)
in ball pythons that received (Group 1; n=6) or did not receive
(Group 2; n=8) supplemental UV radiation over the course of the
study

Paper
Veterinary Record | October 12, 2013
In conclusion, no association has been demonstrated between
exposure to UV-b radiation and plasma 25-hydroxyvitamin D3 and
ionised calcium concentrations in the female ball pythons in this
study. These results may, however, provide baseline parameters for
future studies in this and other snake species to determine ability to
utilise UV-b light for vitamin D production.
Acknowledgements
The authors would like to thank the staff at Edinburgh Butterfly
and Insect World, Five Sisters Zoo and the Exotic Animal Teaching
Facility at the Royal (Dick) School of Veterinary Studies, Edinburgh
for their help with this study, and Dr Darren Shaw for advice on the
statistics.
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