Cerebellar herniation in captive lions (Panthera leo)

CASE-CONTROL STUDY OF THE FREQUENCY AND ETIOLOGY OF ATAXIA IN ASIATIC LIONS (PANTHERA LEO PERSICA) BETWEEN 2002 AND 2020

The Asiatic lion (Panthera leo persica) is an endangered species with a slowly increasing captive and wild population. Several zoos from within the European Association of Zoos and Aquaria Ex Situ Program reported Asiatic lions with neurological signs such as (progressive) ataxia, and stargazing. The aim of this study was to evaluate the frequency (prevalence and incidence) and etiology of these clinical signs within the captive Asiatic lion population. The medical history of 74 Asiatic lions (36 healthy and 38 affected) was retrieved and reviewed for blood tests (biochemical, hematological, and retinol), diagnostic imaging (MRI and CT scans) and postmortem examinations. The data of the affected lions was compared with those of healthy lions. Between 2002 and 2020, the prevalence of ataxia ranged from 0.6% in 2004 to 13.0% in 2020. The incidence of ataxia was variable per year between 2002 and 2020 and ranged between 0 and 40%. Besides ataxia, stiffness and lameness were the most described signs in this study. Blood results showed lower total protein, ALT and creatinine, and higher phosphate in lions with neurological signs. Moreover, neurologically affected lions showed a significant lower blood retinol than the control lions (0.59-0.81 µmol/L). The most important finding in diagnostic imaging and necropsy included caudal fossa hyperostosis and cerebellar herniation. These abnormalities are similar as found in African lions (Panthera leo) with calvarial hyperostosis syndrome associated with vitamin A deficiency. Leucomyelopathy, syringomyelia (in one case combined with cerebellar herniation) and incidental mineralization of the dura mater were also described. A possible congenital/hereditary component should not be excluded.

Welfare concerns associated with captive lions (Panthera leo) and the implications for commercial lion farms in South Africa

Breeding and housing wild animals in captive environments can pose challenges for their welfare. In South Africa, thousands of lions (Panthera leo) are bred and raised at commercial captive breeding facilities, so called 'lion farms', for use in tourism, trophy hunting and traditional medicine. To gain a better understanding of the potential welfare challenges faced by lions on farms we reviewed 91 peer-reviewed articles relating to lion welfare, identified via a systematic review of the scientific literature. Across these studies, we identified 170 different terms relating to negative behaviours and physical health afflictions. The majority of these terms were associated with disease and injury (124; 73%), followed by negative behaviours (19; 11%), negative mental experiences (15; 9%), nutritional concerns (7; 4%), and environmental challenges or discomfort arising from the animal's surroundings (5; 3%). Of the 91 articles, 32 (35%) focused on data concerning captive lions. Only two studies focused specifically on data obtained from lion farms in South Africa, whilst the remainder reported on data collected from zoos, wildlife parks, sanctuaries, game reserves and private ownership. Our preliminary review of the scientific literature draws attention to some of the challenges associated with caring for lions in captivity, and outlines the potential significance of these welfare challenges for commercial lion farms. Our data highlight the apparent lack of scientific research involving captive lion welfare generally, particularly data collected at commercial breeding facilities in South Africa and the consequences this could have for the welfare of thousands of lions within the industry.

Effects of reduced mobility on trabecular bone density in captive big cats

Bone responds to elevated mechanical loading by increasing in mass and density. Therefore, wild animals should exhibit greater skeletal mass and density than captive conspecifics. This expectation is pertinent to testing bone functional adaptation theories and to comparative studies, which commonly use skeletal remains that combine zoo and wild-caught specimens. Conservationists are also interested in the effects of captivity on bone morphology as it may influence rewilding success. We compared trabecular bone volume fraction (BVF) between wild and captive mountain lions, cheetahs, leopards and jaguars. We found significantly greater BVF in wild than in captive felids. Effects of captivity were more marked in the humerus than in the femur. A ratio of humeral/femoral BVF was also lower in captive animals and showed a positive relationship to home range size in wild animals. Results are consistent with greater forelimb than hindlimb loading during terrestrial travel, and possibly reduced loading of the forelimb associated with lack of predatory behaviour in captive animals. Thus, captivity among felids has general effects on BVF in the postcranial skeleton and location-specific effects related to limb use. Caution should be exercised when identifying skeletal specimens for use in comparative studies and when rearing animals for conservation purposes.

Magnetic Resonance Imaging in 50 Captive Non-domestic Felids - Technique and Imaging Diagnoses

Magnetic resonance imaging (MRI) is the recognized gold standard for diagnostic imaging of the central nervous system in human and veterinary patients. Information on the use of this modality and possible imaging abnormalities in captive non-domestic felids is currently limited to individual case reports or small case series. This retrospective study provides information on technique and imaging findings in a cohort of cases undergoing MRI at an academic Veterinary Medical Center. The University of Tennessee College of Veterinary Medicine MRI database was searched for non-domestic felids undergoing MRI of the brain or spine from 2008 to 2021. Medical record data were recorded, and MRI studies were reviewed. Fifty animals met the inclusion criteria. The most common brain diseases were Chiari-like malformation (n = 8) and inflammatory conditions (n = 8). Other abnormalities included pituitary lesions (n = 5), brain atrophy (n = 2), and one each of metabolic and traumatic conditions. Fourteen animals had a normal brain MRI study. The most common spinal abnormality was intervertebral disc disease (n = 7). Other disorders included vertebral dysplasia (n = 2), presumptive ischemic myelopathy (n = 1), subdural ossification causing spinal cord compression (n = 1), and multiple myeloma (n = 1). Spinal cord swelling of undetermined cause was suspected in two animals, and seven patients had a normal MRI study of the spine. MRI is a valuable tool in the diagnostic workup of non-domestic felids with presumptive neurologic disease.

A RETROSPECTIVE STUDY OF BRAIN LESIONS IN CAPTIVE NONDOMESTIC FELIDS

This retrospective study identified and characterized brain lesions in captive nondomestic felids from a large cat sanctuary. Necropsy reports from January 2002 through December 2018 were examined, and gross images and microscopic slides were reviewed from individual cats, where available. In total, 255 cats met the following inclusion criteria: complete necropsy report available, brain examined grossly or microscopically, and age of >1 mon. Of the 255 cats, 49 cats (19%) were determined to have brain lesions. Eleven different felid species, as well as one captive-bred hybrid (liger), were included in the study, with tigers (Panthera tigris) (55%) and lions (Panthera leo) (18%) being the most common species. Lesions were grouped into six etiologic categories: neoplastic (32%), vascular (26%), inflammatory or infectious (20%), congenital (9%), idiopathic (7%), and metabolic (6%). Not included in these categorized lesions were previously undescribed amphophilic globules in the cerebral cortex of many cats with and without other brain lesions; these were in 95% of lion and 93% of tiger brains where the cerebral cortex was available for histologic examination. These globules were not associated with clinical disease. The histopathologic and gross brain changes documented in this study provide insight into specific diseases and pathologic processes that affect the brains of captive large cat populations.

Radiographic analysis of the thickness of the cranial bones in captive compared to wild-living cheetahs and in cheetahs with hypovitaminosis A

Captive cheetahs often demonstrate a high incidence of diseases in which vitamin A imbalances are implicated. These can occur even under controlled and optimised feeding regimens, which is why surveillance of vitamin A status is mandatory in the successful health management of cheetahs. Serum levels of the vitamin do not reflect the true vitamin A status and liver tissue analysis is rather impractical for routine application in large felids. A biomarker for evaluating overt and subclinical vitamin A deficiency in cheetahs is needed. This study evaluates whether increased calvarial bone thickness can be detected on routine skull radiographs of vitamin A deficient cheetahs compared to unaffected animals, and secondly, evaluates whether there is increased bone thickness in clinically sound captive cheetahs in general compared to wild-living controls. Bone thickness in the neuro- and splanchnocranium was measured in 138 skull radiographs. Significant thickening of the parietal bones was found in latero-lateral radiographs of immature cheetahs (< 12 months) with vitamin A deficiency. This finding may allow a presumptive diagnosis of hypovitaminosis A in immature cheetahs. A general difference in skull thickness between free-living and captive cheetahs was not found.

Shape of the feline cerebellum and occipital bone related to breed on MRI of 200 cats

Objectives The MRI features of the feline cerebellum and occipital bone have not previously been described in the literature. The aims of this study were three-fold. Firstly, to document variations in cerebellar shape on MRI in neurologically normal cats to support our hypothesis that crowding of the contents of the caudal fossa or herniation of the cerebellar vermis through the foramen magnum occurs frequently as an anatomical variant. Secondly, to document variations in the morphology of the occipital bone. Thirdly, to see whether these variations in shape of the feline cerebellum and occipital bone could be associated with head conformation, such as brachycephaly. Methods The imaging records of the small animal clinic at the Animal Health Trust between 2000 and 2013 were searched retrospectively to identify adult cats that had undergone high-field (1.5 T) MRI investigation which included the brain. Exclusion criteria included evidence of intracranial disease or the presence of cervical syringomyelia. Midline sagittal T2-weighted and transverse images were used to assess the occipital bone morphology and cerebellar shape, and to measure the width to length ratio of the cranial cavity. Results Fourteen different breeds were represented. A cerebellar shape consistent with crowding of the contents of the caudal fossa, or herniation through the foramen magnum was present in 40% of the entire population. Persians (recognised as a brachycephalic breed) had a higher proportion of cerebellar crowding or herniation than all other breeds. There was no significant difference in the distribution of occipital bone morphology between these breed groups. Conclusions and relevance It is important to recognise morphological variations of the feline cerebellum and occipital bone in order to avoid false-positive diagnoses of raised intracranial pressure and pathological herniation on MRI.

Congenital vestibular disease in captive Sumatran tigers (Panthera tigris ssp. sumatrae) in Australasia

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The Sumatran tiger is a critically endangered species.

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A congenital vestibular syndrome was identified in captive Sumatran tiger cubs.

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Vestibular signs included head tilt, circling, falling, ataxia, strabismus and nystagmus.

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Clinical signs persisted for a median of 237 days and resolved by 2 years of age.

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Pedigree and segregation analysis supported a genetic cause with an autosomal dominant mode of inheritance.

The Sumatran tiger (Panthera tigris ssp. sumatrae) is a critically endangered species in the wild. To ensure that demographic and genetic integrity are maintained in the longer term, those Sumatran tigers held in captivity are managed as a global population under a World Association of Zoos and Aquariums Global Species Management Plan (GSMP). A retrospective study, including segregation and pedigree analysis, was conducted to investigate potential cases of congenital vestibular disease (CVD) in captive Sumatran tigers in Australasian zoos using medical and husbandry records, as well as video footage obtained from 50 tigers between 1975 and 2013. Data from the GSMP Sumatran tiger studbook were made available for pedigree and segregation analysis.

Fourteen cases of CVD in 13 Sumatran tiger cubs and one hybrid cub (Panthera tigris ssp. sumatrae × Panthera tigris) were identified. Vestibular signs including head tilt, circling, ataxia, strabismus and nystagmus were observed between birth and 2 months of age. These clinical signs persisted for a median of 237 days and had resolved by 2 years of age in all cases. Pedigree analysis revealed that all affected tigers were closely related and shared a single common ancestor in the last four generations. A genetic cause for the disease is suspected and, based on pedigree and segregation analysis, an autosomal dominant mode of inheritance is likely. Further investigations to determine the world-wide prevalence and underlying pathology of this disorder are warranted.

The three-dimensional morphological effects of captivity

Many captive animals are fed diets that are drastically different in mechanical properties than their wild diet. Most captive pantherines are fed a nutritionally supplemented diet consisting almost entirely of ground meat. While many zoos supplement this diet with bones, the fact remains that large captive felids are fed diets that require substantially less masticatory effort than those of their wild counterparts. The osteological effects of this dietary difference have not been fully evaluated. To this end, we compared linear measurements and 3D geometric morphometric landmarks of captive and wild lions and tigers. Using Principal Component (PC) analysis of the linear measurements, not only were the sexes and species statistically distinct, but so too was the population clearly divisible in terms of captivity status. The 3D analysis supported these findings: although the most influential variable in the sample (PC1, 21.5% of the variation) separates the two species, the second most influential contributor (PC2) to the overall skull shape is driven not by the sex differences in these highly dimorphic species, but rather by their captivity status. In fact, captivity status drives nearly twice as much of the 3D variation as sexual dimorphism (14.8% vs. 8.0% for PC2 vs. PC3). Thus the shape is influenced nearly twice as much by whether the animal was captive or wild than by whether it was male or female. If a causal relationship can be demonstrated between dietary mechanical properties and morphology, people who oversee the diets of captive carnivores should consider modifying these diets to account for not only nutritional but also the mechanical properties of a carcass-based diet as well. In addition to the husbandry implications, our analyses show the ways in which captive specimens are different than their wild counterparts--ndings that have implications for morphologists when considering anatomical samples.

Comparative skull analysis suggests species-specific captivity-related malformation in lions (Panthera leo)

Lion (Panthera leo) populations have dramatically decreased worldwide with a surviving population estimated at 32,000 across the African savannah. Lions have been kept in captivity for centuries and, although they reproduce well, high rates of stillbirths as well as morbidity and mortality of neonate and young lions are reported. Many of these cases are associated with bone malformations, including foramen magnum (FM) stenosis and thickened tentorium cerebelli. The precise causes of these malformations and whether they are unique to captive lions remain unclear. To test whether captivity is associated with FM stenosis, we evaluated 575 lion skulls of wild (N = 512) and captive (N = 63) origin. Tiger skulls (N = 276; 56 captive, 220 wild) were measured for comparison. While no differences were found between males and females or between subadults and adults in FM height (FMH), FMH of captive lions (17.36±3.20 mm) was significantly smaller and with greater variability when compared to that in wild lions (19.77±2.11 mm). There was no difference between wild (18.47±1.26 mm) and captive (18.56±1.64 mm) tigers in FMH. Birth origin (wild vs. captive) as a factor for FMH remained significant in lions even after controlling for age and sex. Whereas only 20/473 wild lions (4.2%) had FMH equal to or smaller than the 5^th percentile of the wild population (16.60 mm), this was evident in 40.4% (23/57) of captive lion skulls. Similar comparison for tigers found no differences between the captive and wild populations. Lions with FMH equal to or smaller than the 5^th percentile had wider skulls with smaller cranial volume. Cranial volume remained smaller in both male and female captive lions when controlled for skull size. These findings suggest species- and captivity-related predisposition for the pathology in lions.

Vitamin A deficiency and hepatic retinol levels in sea otters, Enhydra lutris

Vitamin A deficiency has rarely been reported in captive or free-ranging wildlife species. Necropsy findings in two captively housed southern sea otters (Enhydra lutris nereis) included irregular thickening of the calvaria characterized by diffuse hyperostoses on the internal surface. One animal also had moderate squamous metaplasia of the seromucinous glands of the nose. There was no measurable retinol in the liver of either sea otter. For comparison, hepatic retinol concentration was determined for 23 deceased free-ranging southern and northern (Enhydra lutris kenyoni) sea otters from California and Alaska. Free-ranging otters were found to have similar hepatic retinol concentrations (316 +/- 245 mg/kg wet weight) regardless of their location and subspecies. All of these values were significantly higher than the levels in the affected animals. Consumption of a diet with very low vitamin A concentrations and noncompliance in daily supplementation are hypothesized as the causes of vitamin A deficiency in these two sea otters.

Needle biopsy for hepatic vitamin A levels in lions (Panthera leo)

Hypovitaminosis A (HA)-related skull malformations resulting in neurologic abnormalities and death have been, and still are, reported in captive lions (Panthera leo) worldwide. Liver vitamin A (VA) concentration is the most reliable indicator of animals' VA status, and its assessment is essential in prevention and treatment of HA in lions. A percutaneous needle liver biopsy using high-performance liquid chromatography ultraviolet retinoid analysis for VA concentration measurement was validated. It was first assessed in vitro using chicken liver. Later, the safety and feasibility of ultrasound-guided percutaneous needle liver biopsy was assessed in living lions. Hepatic VA concentrations in lion liver were measured using the above laboratory method. Mean chicken hepatic VA concentration in needle biopsy (NB) and wedge biopsy (WB) of the same liver lobes were 108.66 and 60.89 microg/g wet tissue, respectively, and were significantly (P = 0.03) correlated (r = 0.74). The calculated linear regression for predicting VA concentration in WB using NB VA for chicken liver was 25.194 + 0.3234x NB (microg/g). Four ultrasound-guided percutaneous needle liver biopsies were obtained from each of the four lions under general anesthesia. Mean hepatic VA concentration was 8.25 microg/g wet tissue (range 1.43-25.29 microg/g). Mean serum VA concentration, measured in these four lions was 1,011.1 nmol/L with a standard deviation of 337.91 nmol/L (range 590.26-1,077.2 nmol/L). The lions recovered uneventfully, and no complications were observed during a 4-yr follow-up period. In conclusion, the percutaneous needle liver biopsy technique is a reliable, practical, safe tool for obtaining liver tissue samples antemortem for assessment of the VA status in lions and can be used in future studies.

Serum vitamin A concentrations in captive sea otters (Enhydra lutris)

Individual dietary preferences and difficulty with animal training create challenges and nutritional concerns when evaluating a captive sea otter (Enhydra lutris) diet. The importance of vitamin A within the body reflects the necessity that it be ingested in adequate amounts to ensure optimal health. To compare levels of serum vitamin A concentrations from captive sea otters on daily oral vitamin A supplementation, serum samples from eight adult sea otters from three institutions were evaluated for serum vitamin A concentrations. The eight animals were fed a total of four different diets and received oral supplementation via three different methods. Multiple diet items were analyzed for vitamin A content and were found to have low to nondetectable levels of vitamin A. Oral vitamin A supplementation, as a slurry with dietary items, was shown to be effective and a mean serum concentration of approximately 170 +/- 51 microg/L was obtained for serum vitamin A concentrations in captive sea otters. Captive diets can be modified to increase vitamin A concentration and supplementation and, if accepted, can be used as a means to ensure adequate vitamin A intake.

Computed tomographic analysis of calvarial hyperostosis in captive lions

Osseous malformations in the skull and cervical vertebrae of lions in captivity are believed to be caused by hypovitaminosis A. These often lead to severe neurologic abnormalities and may result in death. We describe the characterization of these abnormalities based on computed tomography (CT). CT images of two affected and three healthy lions were compared with define the normal anatomy of the skull and cervical vertebrae and provide information regarding the aforementioned osseous malformations. Because bone structure is influenced by various factors other than the aforementioned disease, all values were divided by the skull width that was not affected. The calculated ratios were compared and the most pronounced abnormalities in the affected lions were, narrowing of the foramen magnum, thickening of the tentorium osseus cerebelli and thickening of the dorsal arch of the atlas. CT is useful for detection of the calvarial abnormalities in lions and may be useful in further defining this syndrome.

Degenerative myelopathy and vitamin A deficiency in a young black-maned lion (Panthera leo)

Degenerative myelopathy and vitamin A deficiency were diagnosed in a 1-year-old, female, black-maned lion (Panthera leo). Diffuse white matter degeneration characterized by dilated myelin sheaths, Wallerian degeneration, and reactive astrocytosis was present at all levels of the spinal cord. With luxol fast blue-resyl echt violet stain, bilaterally symmetrical demyelination was observed in the fasciculus cuneatus of the cervical spinal cord and in peripheral white matter of cervical, thoracic, and lumbar segments. Additionally, the ventral gray columns and brain stem nuclei contained rare chromatolytic neurons with abnormal neurofilament accumulation. Leptomeninges of the cervical spinal cord were focally adhered to the dura and thickened by fibrosis and osseous metaplasia. Vitamin A deficiency was diagnosed based on hepatic vitamin A concentration of 1.71 microg/g dry weight. Adequate hepatic vitamin A concentration for yearling to adult domestic animals ranges between 150 and 1000 microg/g dry weight. Lesions were distinct from those previously described in young captive lions with vitamin A deficiency, which had thickened skull bones and cerebellar herniation. The pathogenesis of vitamin A-associated myelopathy in this lion may be similar to that described in adult cattle, which is believed to result from spinal cord compression secondary to elevated pressure of cerebrospinal fluid.