Management of Morbidity and Mortality in a New Zealand White Rabbit Model of Steroid-Induced Osteonecrosis of the Femoral Head

Steroid-induced osteonecrosis of the femoral head (SONFH) is a condition documented in humans and animals exposed to chronic steroid administration. The rabbit has become a preferred animal model for investigating the pathogenesis and treatment of SONFH due to its shared femoral vascular anatomy with human patients, relative size of the femoral head, and general fecundity. However, morbidity and mortality are frequent during the steroid induction period, prior to surgical manipulation. These problems are poorly reported and inadequately described in the literature. In this study, we report the clinical, gross, and histopathologic findings of New Zealand white (NZW) rabbits undergoing the steroid induction phase of the SONFH model. Severe weight loss (>30%), lipemia, hypercholesterolemia, hyperglycemia, and elevations in ALT and AST were consistent findings across all rabbits, although these changes did not differentiate asymptomatic rabbits from those that became clinically symptomatic or died. Euthanized and spontaneously deceased rabbits exhibited hepatomegaly, hepatic lipidosis/glycogenosis, and hepatocellular necrosis, in addition to a lipid-rich and proteinaceous thoracic effusion. A subset of rabbits developed opportunistic pulmonary infections with Bordetella bronchiseptica and Escherichia coli and small intestine infections with Lawsonia intracellularis superimposed on hepatic and thoracic disease. Together, these findings allowed us to establish a clinical decision-making flowchart that reduced morbidities and mortalities in a subsequent cohort of SONFH rabbits. Recognition of these model-associated morbidities is critical for providing optimal clinical care during the disease induction phase of SONFH.

Osteonecrosis of the femoral head (ONFH), or avascular necrosis of the femoral head (ANFH), is a condition in both humans^4,12,21 and animals⁵ that is associated with inadequate vascularization and subsequent death of trabecular bone and bone marrow of the femoral head. Briefly, diminished or altered vascular supply to the femoral head leads to trabecular bone weakening, with subsequent femoral head collapse and resulting coxofemoral arthritis.¹²Underlying pathogeneses of ONFH can be broadly categorized into traumatic (that is physical trauma) and nontraumatic etiologies.²¹ Nontraumatic etiologies include chronic steroid administration, alcohol consumption, and blood dyscrasias, among others.⁴ Among nontraumatic etiologies, prolonged steroid administration for systemic diseases such as rheumatoid arthritis, systemic lupus erythematosus, and organ transplantation is the most common underlying cause of steroid induced ONFH (SONFH) in human patients.³³ Although various mechanisms have been proposed to explain the pathogenesis of SONFH, the underlying cause(s) remain elusive. A recent literature review categorized proposed pathogenic mechanisms as follows: 1) disorders of lipid metabolism, 2) decreased osteogenic capacity of bone marrow mesenchymal stem cells, 3) insufficient vascular supply, 4) inflammation and apoptosis, and 5) genetic polymorphisms and noncoding RNA.²⁹ The complexity of SONFH and variability of patient demographics suggest the underlying pathogenesis is likely to be multifactorial.¹⁶Several animal models have been developed to study the pathogenesis and potential therapeutic strategies for SONFH.^33,34 Numerous animal species have been explored as candidate models for SONFH including mice, rats, rabbits, chickens, emus, and to a lesser extent, dogs, pigs, and sheep.³⁴ While each species has various advantages and disadvantages, the rabbit is frequently chosen due to its femoral vascular anatomy, which is similar to human patients, relative size of the femoral head, and general fecundity.³⁴ In the rabbit model, SONFH can be established via 3 main induction protocols: 1) intramuscular (IM) injection of methylprednisolone (MPS) alone, 2) IM injection of MPS along with intravenous (IV) lipopolysaccharide (LPS), or 3) IM injection of MPS along with IV allogeneic serum (for example horse serum).³⁴ The two latter induction protocols aim to create the underlying proinflammatory conditions associated with SONFH and are thus used to emulate underlying nontraumatic causes of SONFH in humans.From October 2016 to January 2017, a total of 4 male New Zealand white (NZW) rabbits was submitted to necropsy for unexpected death during the induction phase of a SONFH model. These initial deaths prompted a systematic analysis of a subsequent cohort of rabbits undergoing SONFH induction.Thus, during the period of August 2018 to May 2019, a second cohort of SONFH was established in rabbits. Briefly, the SONFH model was induced in male and female NZW rabbits via a single IM injection of MPS (20 mg/kg). Interventional surgical procedures were scheduled to occur 4 wk after SONFH induction. During the 4-wk induction period, significant comorbidities and deaths occurred in varying subsets of rabbits. Clinical monitoring and intervention were initiated to treat symptomatic rabbits and to identify critical points of interventional therapy. A full complement of diagnostics including bloodwork, radiographs, necropsy, histopathology, microbiologic culture, and PCR testing was implemented to further characterize the nature of any underlying clinical disease(s).Herein we report the clinical presentations, therapeutic interventions, and postmortem findings from rabbits developing comorbidities related to the induction period of SONFH. A literature review over the past 30 y sheds light on the prevalence of SONFH-related complications and/or mortalities reported in primary research articles using this model. Our goal is to help clinicians and pathologists working with rabbit models of SONFH to better understand model-associated comorbidities and help determine points of clinical intervention to minimize model-associated mortalities.     

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Management for oak regeneration: Short-term effects on the bird community and suitability of shelterwood harvests for canopy songbirds

Interest in regenerating oaks (Quercus spp.) has promoted use of partial harvesting techniques that create an open forest structure. From 2007 to 2009, we studied songbirds in mixed-oak forests in southeastern Ohio, comparing shelterwoods recently harvested to 50% stocking and closed-canopy mature second-growth. We surveyed birds using distance-based methods (56 line transects in 18 stands at 4 forests). We intensively investigated suitability of shelterwoods for canopy-nesting species by examining habitat preferences, as measured by settlement patterns, age distributions, and site fidelity; we also examined nesting success. Several midstory and ground-nesting species were 26–73% less abundant in shelterwood than unharvested stands, whereas shrub-nesting species increased >100% several years post-harvesting. Canopy-nesting species were 31–98% more abundant in shelterwoods, but cerulean warbler (Setophaga cerulea) responses varied by forest. Patterns of settlement and site fidelity were generally similar among stands. Proportions of young males were actually greater for several species in shelterwood than unharvested stands, which may have been a consequence of young birds colonizing newly created (or improved) habitat. Even in our predominantly forested study system, nesting success (>700 nests) was low, ranging from 15% to 19% for yellow-throated vireos (Vireo flavifrons) and cerulean warblers, to 27–36% for scarlet tanagers, blue-gray gnatcatchers (Polioptila caerulea) and eastern wood-pewees (Contopus virens). However, nest survival did not differ between shelterwood and unharvested stands, possibly because numbers of avian predators did not change with harvesting. Despite increased numbers of brown-headed cowbirds (Molothrus ater) in shelterwoods, only 2% of canopy nests in which young could be identified were parasitized. Although these results suggest shelterwood harvests containing abundant overstory trees can provide short-term breeding habitat for canopy songbirds, long-term responses of birds to partial harvesting may differ from those documented here depending on different management options employed. Management for oak regeneration will typically remove all overstory trees later in the cutting cycle, initially resulting in loss of nesting substrates and hence breeding habitat for canopy songbirds. © 2011 The Wildlife Society.     

The relationship between anti-predator behaviour and aggression among conspecifics in the three-spined stickleback, Gasterosteus Aculeatus

The response of individual breeding three-spined sticklebacks to territorial intruders of various species was compared with their response to a predator outside the breeding season. The nature of the territorial response to the different intruders, as revealed by factor analysis, was very similar and the level of aggression shown to the different species co-varied across individuals and during each breeding cycle. The level of territorial aggression of the individual fish was positively correlated with their ‘boldness’ towards a predator. These results provide tentative support for the idea that anti-predator behaviour and aggression towards conspecifics are linked in this species. Supporting evidence for and possible adaptive significance of these results are discussed.