Vitamin D and bone health in pet rabbits (Oryctolagus cuniculus)

https://helda.helsinki.fi/handle/10138/319570

Rabbit bones are brittle and prone to fissure formation. Radiographs of very young and old rabbits are often indicative of decreased bone density. The aim of this study was to investigate the tibial bone parameters in pet rabbits, and their association with age, sex, castration and dental disease. Eighty-seven (43 female/5 spayed, 44 male/19 castrated) pet rabbits (mean age 2.6 years, range 0.3-9.3 years) of various breeds were studied, of which 37 had dental disease. Right tibiae were scanned with peripheral quantitative CT at the distal (4percent) and mid-shaft sites (50percent of the tibial length). Analysed bone parameters included the total cross-sectional area, cortical bone area and density, trabecular bone density and strength-strain index. The mean diaphyseal cortical density was high (about 1400 mg/cm3) in comparison to many other species. Within the studied age range, age was weakly but positively associated with diaphyseal cortical density, with the juvenile rabbits clearly showing the lowest values. There was no tendency for age-related decrease in trabecular or cortical bone density at least up to six years of age. Neither were sex, castration nor dental disease associated with decreased tibial bone density.

https://onlinelibrary.wiley.com/doi/10.1111/jpn.13120

During the winter time in Finland, sunlight is inadequate for vitamin D synthesis. Many pet rabbits live as house rabbits with limited outdoor access even during summer and may therefore be dependent on dietary sources of vitamin D. The aims of this study were to report the serum 25‐hydroxyvitamin D concentrations in Finnish pet rabbits and to identify factors that influence vitamin D status. Serum 25‐hydroxyvitamin D concentrations from 140 pet rabbits were determined using a vitamin D enzyme immunoassay (EIA) kit. Eleven rabbits were excluded from the statistical analysis because of unclear dietary data. The remaining 129 rabbits were divided into groups depending on outdoor access during summer (no access n = 26, periodic n = 57, regular n = 46) as well as daily diet: little or no hay and commercial rabbit food ≤1/2 dl (n = 12); a lot of hay and no commercial food daily (n = 23); a lot of hay and commercial food <1 dl (n = 59); a lot of hay and commercial food ≥1 dl (n = 35). The range of serum 25‐hydroxyvitamin D concentration was from 4.5 to 67.5 ng/ml with a mean of 26.1 ng/ml. Statistical general linear model adjusted for weight, age and season indicated that diet was associated with vitamin D concentrations (p = 0.001), but outdoor access during summer was not (p = 0.41). Mean 25‐hydroxyvitamin D concentration was significantly higher in the rabbits receiving a lot of hay and commercial food ≥1 dl (33.9 ± 13.2 ng/ml) than in rabbits in other diet groups (24.0 ± 8.5 ng/ml, 21.7 ± 8.1 ng/ml, and 22.2 ± 18.0 ng/ml, respectively). This investigation showed wide variation in 25‐hydroxyvitamin D concentrations among Finnish pet rabbits. Diet remains a main source since outdoor access seems to be too limited to provide adequate vitamin D synthesis for most of them, and the use of vitamin D supplements is rare.

The relationship between serum 25-hydroxyvitamin D and parathyroid hormone concentration in assessing vitamin D deficiency in pet rabbits.

Vitamin D deficiency and related metabolic bone diseases in pet rabbits have been intermittently debated. In human research, the parathyroid hormone concentration in relation to the 25-hydroxyvitamin D concentration is used to determine vitamin D deficiency. Thus, this study aimed to identify the breakpoint in the 25-hydroxyvitamin D concentration indicating a significant change in the parathyroid hormone concentration in 139 pet rabbits. An enzyme immunoassay kit was used for 25-hydroxyvitamin D analysis and the intact parathyroid hormone (PTH 1–84) immunoradiometric assay kit for parathyroid hormone analysis. The mid-tibial cortical bone density was measured using peripheral quantitative computed tomography. A segmented linear regression analysis was performed, with the 25-hydroxyvitamin D concentration as the independent variable, and parathyroid hormone, ionised calcium, total calcium, inorganic phosphorus concentrations and the mid-tibial cortical density as the dependent variables.

Results:

The breakpoint for the parathyroid hormone concentration occurred at a 25(OH)D concentration of 17 ng/mL, whereas the cortical bone density breakpoint occurred at a 25-hydroxyvitamin D concentration of 19 ng/mL. No breakpoints were found for ionised calcium, total calcium or phosphorus.

Conclusions:

These results suggest that a serum 25-hydroxyvitamin D concentration of 17 ng/mL serves as the threshold for vitamin D deficiency in rabbits. Nearly one-third of the rabbits had a serum 25-hydroxyvitamin D concentration below this threshold. Concerns persist regarding the high prevalence of vitamin D deficiency in pet rabbits and the possible health consequences caused by a chronic vitamin D deficiency, including the risk for metabolic bone diseases.