Ý ß Glossary & References / Miscellaneous Documents List / D151 - Published Papers: Studies on Released Rehabilitated Hedgehogs / Text Sections:
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Published
Papers: Studies on Released Rehabilitated Hedgehogs |
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Wildpro Reference Code: J3.138.w2 Health
and welfare of rehabilitated juvenile hedgehogs (Erinaceus europaeus) before and after release into the wild † Materials
and Methods Thirteen wild caught
juvenile hedgehogs were treated and overwintered in a rehabilitation centre
and 12 were released into the wild and monitored by radiotelemetry. Clinical
examinations were carried out before they were released and twice
afterwards, and any hedgehogs found dead were examined post mortem. The
health of the animals was generally good but dental disease, obesity and
minor injuries were common. One hedgehog died before it was released and had
cardiovascular and respiratory lesions, and one was euthanased 28 days after
its release and had verminous enteritis and parasitic bronchitis. Three
hedgehogs were killed by badgers, two were killed by road traffic and four
were known to have survived when the study ended. The European hedgehog (Erinaceus europaeus) is probably the most frequently rehabilitated mammalian species in the UK (British Wildlife Rehabilitation Council 1993). Morris and others (1993a, b) investigated the survival of released adult hedgehogs, which had had previous experience of the wild, and found that the animals managed to feed and apparently behave normally; Morris and others (1993b) found that of four hedgehogs released one had died within three weeks and, in a separate study, eight hedgehogs were released of which three died and four were unaccounted for by 12 weeks after their release (Morris and others 1993a). However, in both studies, the deaths were not necessarily linked to the release, for example, road traffic killed some of the hedgehogs but many wild hedgehogs die from this cause every year. The annual mortality of wild adult hedgehogs is approximately 30 per cent (P. A. M., unpublished observations). Neither of the above studies investigated in detail the health of the hedgehogs before or after their release, and the causes of most of the deaths were not investigated post mortem. A
large percentage of the hedgehogs 'rescued' by rehabilitation centres are
juveniles, sometimes nestlings, which are taken into captivity in the
autumn. These may have been abandoned by their dam or may have been judged
to have insufficient fat resources to survive hibernation. Morris (1984)
showed that hedgehogs which weigh less than 450 g in the autumn are unlikely
to survive the winter. Whatever their origin, many of these young hedgehogs
have had little experience of life in the wild when they are released in the
following spring. Thirteen
hedgehogs, seven males and six females, had been overwintered at the Royal
Society for the Prevention of Cruelty to Animals Wildlife Hospital at West
Hatch, Somerset. They had weighed less than 350 g when taken into captivity
the previous autumn. They were anaesthetised on April 2, 1993 for a clinical
examination and fitted with radiotransmitters (Morris and Warwick 1994) so
that they could be tracked. The
animals were released at Helecombe Farm, near Clayhanger in Devon (NGR ST
0224) where previous uncontrolled releases had taken place. The date of
release varied for each animal (Morris and Warwick 1994). Six of the
hedgehogs (four females and two males, 221, 244,
270, 298, 312 and 324) were
released directly but six (two females and four males, 211,
228, 256, 288,
332 and 353) were held in pre-release cages for five nights before they were
released as described by Morris and Warwick (1994). One male (341) died
while it was in the pre-release cage. The movements of the hedgehogs were
monitored every night after their release for approximately five weeks by
radiotracking and less frequently thereafter for approximately four weeks.
They were caught for examination and weighed, usually every night for at
least the first four weeks, and less often thereafter. Resident wild
hedgehogs found during the monitoring procedures were weighed and marked
individually by spraying a patch of spines with paint (Morris and Warwick
1994). Behavioural interactions between resident and released hedgehogs were
recorded. Clinical
examinations The
13 hedgehogs were anaesthetised for a clinical examination either on the day
of their release or up to 10 days before. Seven of them were re-examined
five weeks after the release programme started and four of these were
examined again two weeks later. Anaesthesia
was induced in an anaesthetic chamber with 4 per cent halothane (Halothane; RMB
Animal Health) and
maintained with approximately 2 per cent halothane administered through a
malleable face mask. The bodyweight of the hedgehogs was measured and the
condition of each animal was scored on the basis of the amount of
subcutaneous fat and the muscle thickness of the abdominal wall and limbs as
follows: 1 thin, no subcutaneous fat and wasted musculature; 2 moderate, no
subcutaneous fat but good muscle thickness; 3 good, some subcutaneous fat; 4
fat, a thick covering of subcutaneous fat. The
oral cavity was examined for signs of disease including dental disease.
Scoring systems were used for recording the severity of dental calculus in
the oral cavity as follows: 1 mild calculus on some teeth; 2 mild calculus
on all teeth; 3 severe calculus on some teeth; 4 severe calculus on all
teeth. For gingivitis the scoring was: 1 mild inflammation of some gingival
margins; 2 mild inflammation of all gingival margins; 3 severe inflammation
of some gingival margins; 4 severe inflammation of all gingival margins. Microbiology
and parasitology Faecal swabs were cultured for bacteria by plating on to 5 per cent horse blood agar (Oxoid CM331; Unipath) and xylose lysine desoxycholate medium (Oxoid CM469). When appropriate, skin samples were plated on to Sabouraud's dextrose agar with chloramphenicol (Oxoid CM41) for fungal isolation. When the faeces were unformed or liquid, blood-free Campylobacter selective agar (Oxoid CM739) was used. The unformed faeces were also examined for the presence of cryptosporidia by the modified Ziehl-Neelsen technique, using a direct smear of a faecal homogenate. Direct smears were prepared from all the faecal samples and examined microscopically for parasite larvae and ova. The McMaster technique was used to estimate the number of nematode eggs per gram of faeces. Pathology Detailed
systematic post mortem examinations were carried out on four hedgehogs which
died during the course of the study. Bacteriological and parasitological
examinations were carried out on the rectal contents by the methods
described above. Tissues for histological examination were fixed in neutral
buffered 10 per cent formalin, embedded in paraffin wax, sectioned and
stained with haematoxylin and eosin. The
results of the clinical and post mortem examinations and the fate of each
hedgehog are given in Table 1. Calculus
and gingivitis were common findings and were severe in one case in which the
gingivae bled on being touched. Eight of the 13 hedgehogs had cuts,
abrasions or subcutaneous abscesses or evidence of recently healed injuries
before they were released. These minor injuries were treated with antiseptic
(povidone iodine) and topical chlortetracycline hydrochloride (Aureomycin
topical powder; Cyanamid) when required. Hedgehogs 332 and
353 were treated
with ampicillin (Amfipen; Gist-brocades Animal Health) by intramuscular
injection before they were released, for an inflamed prepuce and an inflamed
foreleg, respectively. All of the injuries were considered to be due to bite
wounds caused by other hedgehogs. After they were released, the injuries
that were examined during routine nightly monitoring or at subsequent health
assessments, were found to have healed without complications.
Hedgehog 324 was killed by a car four weeks after its release. It had already lost 35 per cent of its bodyweight and its condition had been of concern before its death. Its stomach and small intestine were empty, suggesting that it had not fed recently, and there was no subcutaneous or abdominal fat. Hedgehog 341 died while under anaesthesia when its radio-transmitter was being fitted, before it was released. It had chronic abscessation of the lung with bronchopneumonia and a chronic low-grade myocarditis. Its intestinal tract was empty. No
serious aggressive encounters were observed among any of the hedgehogs,
resident or released, after the release had occurred (Morris and Warwick
1994). Courtship and mating behaviour between resident and released
hedgehogs was observed (Morris and Warwick 1994). Three
animals were found to be pregnant 26, 29 and 49 days after their release,
suggesting that they had conceived after they were released, because the
gestation period of the hedgehog is 31 to 35 days (Deanesly 1934);
furthermore the hedgehogs had been housed as single sex groups while in
captivity. In each of the pregnant hedgehogs there were five to 10, 5 to 10
mm diameter, roughly circular, tonic conceptual swellings in the uterus,
separated by a similar length of uterine body. One animal (228) was palpated
again 15 days later and the swellings had grown to approximately 15 x 40 mm
tubular-shaped bodies and showed significantly less uterine tone. Another
hedgehog (312) was not pregnant 15 days after a positive diagnosis but it is
not known whether it had given birth or had aborted. The
study identified two substantial health problems: periodontal disease and
injuries. These problems indicate that the animals' management while in
captivity could be improved. All the 13 hedgehogs had peridontal disease
when they were first examined, and hedgehog 298 had severe calculus and
gingivitis and had lost several teeth. This was a surprising finding
considering their young age. The incidence and prevalence of periodontal
disease in wild hedgehogs has not been investigated but it would seem
unlikely that it would be high in young animals. It is possible that the
soft diet offered at the rehabilitation centre led to a build up of plaque
on the teeth, and subsequently to the formation of calculus and gingivitis (Kertesz
1993). The diet included puppy dog food (Puppy Chum; Pedigree Pet Foods),
day-old chicks and a mix designed for insectivorous birds (Prosecto; J.
Haiths). A more natural diet of beetles, caterpillars, earthworms, flies,
spiders, centipedes and slugs (Yalden 1976) might be better, but the
production and supply of this diet would be impractical. At the time of the
first health assessment it was considered that the preferable course of
action for the hedgehogs would be to return them to the wild where they
would receive a more natural diet which would improve their oral health.
There is a clear need to investigate and provide a more suitable diet for
captive hedgehogs. Dental disease is painful and in the long term could
affect the survival of hedgehogs by reducing their feeding efficiency. In
addition, many people place food in their gardens for wild hedgehogs (Morris
1983) and it is important to ensure that such supplementary diets do not
cause dental disease. Cuts,
abrasions and subcutaneous abscesses, probably caused by bites from other
hedgehogs, were common before the hedgehogs were released, and although
these minor injuries responded well to treatment, methods of husbandry that
reduce the chances of aggressive behaviour should be used. The requirements
for the housing of hedgehogs in captivity have not been well documented
although there is some information (Morris 1967). The
health of the hedgehogs after their release was generally good but several
findings indicated suboptimal welfare.
Both Capillaria species and strongyle type (Crenosoma species)
nematodes have been previously recorded from hedgehogs in the UK (Boag and
Fowler 1988, Majeed and others 1989, Keymer and others 1991). In the present
study ova of Capillaria species nematodes were more commonly found in
the faeces than the ova and larvae of strongyle nematodes. Although the
species were not identified and the life cycles are not known for certain,
it is likely that most of the hedgehogs had an infestation of egg-producing
adults before their release because there was only a short interval between
the animals' release and the detection of nematodes in the faeces. The
verminous gastroenteritis and parasitic bronchitis found post mortem in
hedgehog 256 suggests that further monitoring of parasitic infestations
during the over-wintering period in the rehabilitation centre would be
useful and possibly that those found to be infested should be treated before
release to increase their chances of survival in the wild. In general, the
bacteriological and mycological examinations yielded no organisms considered
to be of clinical significance but the intestinal flora of hedgehog 256 may
have played a secondary role in the pathogenesis of the gastroenteritis
observed post mortem. The
poor condition of hedgehog 324 may have had a bearing on its inability to
avoid a collision. Unfortunately, the carcase had been partially eaten by
scavengers and it was not possible to establish the cause of the loss of
bodyweight. Despite the severe head and other injuries inflicted on hedgehog
332 by a vehicle they were not evident externally in the field at night; the
animal was found alive and only noted as dead two hours later. It is known
that large numbers of hedgehogs die in road collisions and, in a review,
Morris (1993) quoted estimates for the UK of between 100,000 and 1.3
million such casualties annually. The lesions of bronchopneumonia and
myocarditis found post mortem in hedgehog 341 were thought to have been
severe enough to have caused its death under anaesthesia; it had been
particularly active in the pre-release cage in an attempt to escape, which
may explain the absence of intestinal contents, and the resultant stress may
have affected its survival under anaesthetic. The benefits or otherwise of
the use of pre-release cages in this study were discussed by Morris and
Warwick (1994). The
ability to reproduce is considered to be a sign of good welfare (Moberg
1985). Although three hedgehogs were found to be pregnant, neither their
litter sizes nor the survival of the young were measured. If
possible, obesity is avoided in captive animals. However, obesity may have
improved the survival chances of the hedgehogs released in this study.
Assuming a daily maintenance requirement of 145 kcal/day, then, for example,
300 g of fat deposits would provide for approximately 19 days without food
(Kirkwood 1991). The three hedgehogs which weighed more than 1000 g before
being released survived to the end of the study, but an analysis of weight
in comparison with survival is complicated by the causes of death; the risk
of predation and road accidents may not be affected by weight. Three
hedgehogs were killed by badgers. In two cases the predation was established
from an examination of the carcase and in the third case the badger was
encountered in the act (Morris and Warwick 1994). The relative
susceptibility of the hedgehogs to this cause of death was discussed by
Morris and Warwick (1994). There
was no evidence that the release of the hedgehogs adversely affected the
welfare of the resident wild hedgehogs. Despite the release of 12 additional
animals at a site where hedgehogs were present, no aggressive encounters
were observed between the released and wild animals (Morris and Warwick
1994). A single wound, thought to be the result of an aggressive interaction
between hedgehogs, was found on one female (228). It is likely that the
resident animals were already exposed to the infectious agents identified in
the hedgehogs before their release; nematodes have been described in wild
hedgehogs (Boag and Fowler 1988). Studies in which both the released and the
resident animals are monitored in detail are required to clarify this issue. The
release process in this study was unusual in several ways; one animal (256)
found to be ill after its release was returned to the rehabilitation centre;
another (298) remained within a farm building for three days and had to be
'rescued' while a third was retrieved after having moved out of the
monitored area of farmland (Morris and Warwick 1994). These interventions
were necessary for welfare or practical reasons, but in similar
non-monitored releases these animals might have suffered compromised welfare
or died. Similarly, the hedgehog which died while under anaesthesia, with
cardiovascular and respiratory lesions, would have been released without
knowledge of its poor health. Boag
B & Fowler P A (1988) Journal of zoology, London 215,
379 British Wildlife Rehabilitation Council (1993) Wildlife Casualty Recording Scheme Quarterly Return, January-March 1993 Deansley
R (1934) Philosophical Transactions of the Royal Society B 223,
239 Harris S (1989) Proceedings of the Inaugural Symposium of the British Wildlife Rehabilitation Council. Eds S. Harris, T. Thomas. London, British Wildlife Rehabilitation Council. p 94 Kertesz
P (1993) Veterinary Dentistry and Oral Surgery. London, Wolfe Publishing. p
73 Keymer
I F, Gibson E A & Reynolds D J (1991) Veterinary Record 128,
245 Kirkwood
J K (1991) Journal of Nutrition 121 (IIS), S29 Kirkwood J K (1993) Veterinary Record 132, 235 Lewis
J C M & Stocker L (1993) Veterinary Record 133, 23 Majeed
S K, Morris P A & Cooper J E (1989) Journal of Comparative
Pathology 100, 27 Moberg G P (1985) Animal Stress. Ed G. P. Moberg. Bethesda, American Physiological Society. p 245 Morris
B (1967) The UFAW Handbook: the Care and Management of Laboratory Animals.
3rd edn. Edinburgh, E & S Livingstone. p 478 Morris
P A (1983) Hedgehogs. London, Whittet Books. p 70 Morris
P A (1984) Journal of zoology, London 203, 291 Morris P A (1993) A Red Data Book for British Mammals. London, Mammal Society. p 10 Morris
P A, Meakin K & Sharafi S (1993a) Animal Welfare 2,53 Morris
P A, Munn S & Craig-Wood S (1993b) Field Studies 8,89 Morris P A & Warwick H (1994) Animal Welfare 3,163 Yalden D W (1 976) Acta Theriologica 21, 401 † |
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