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Paleopathological investigations of conditions linked to vitamin D deficiency have increased in the last twenty years, and a suite of skeletal lesions has been established to aid in the diagnosis of vitamin D deficiency disease in subadults and adults. This paper analyzes the occurrence of these lesions in a large skeletal series comprising 3541 Roman period individuals (1st-6th century AD). Sixteen lesions reported in rickets in subadults, and 13 associated with residual rickets and osteomalacia in adults, were analyzed. Among subadults, there were clear associations among post-cranial lesions. Porotic cranial changes were associated with each other, but not with post-cranial lesions. A range of conditions could have produced the cranial lesions. There was a general paucity of correlations between indicators found in adults, and the difficulty in recording bending deformities was clear. Pseudofractures appear to provide a useful means of investigating osteomalacia in adults. In general, a simple algorithmic approach using presence or absence of lesions is unlikely to provide an adequate means of diagnosing vitamin D deficiency in paleopathology. Knowledge and consideration of the underlying physiological mechanisms involved in lesion formation, combined with individual judgement, will be required to differentially diagnose cases., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Vitamin D deficiency rickets was considered endemic in the industrialized cities of 19th century England, but was rarely reported in more rural and suburban areas. The commercial excavation of St. John's Church, Redhill, Surrey, UK provided an opportunity to examine to what extent suburban children were affected by rickets and the factors responsible for its development. Seventy-nine non-adults (0-17 years) from St. John's Church were subjected to macroscopic and radiographic analysis to identify skeletal manifestations of vitamin D deficiency. Rachitic lesions were identified in 14/79 individuals (17.7%) aged from six months to six years. Active cases occurred from six months to two years of age with healed cases observed from three to six years. One seven month old infant also displayed healed lesions. The age-specific pattern of active and healed rickets suggests the population was vulnerable to the seasonal restriction of sunlight hours, with the considerably low vitamin D content of the infant diet unable to provide sufficient amounts to maintain metabolic functions. This research demonstrates that rickets was not simply a disease of industrialization but that a variety of factors contributed to its development in groups previously considered to be low risk., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Teeth are mineralized organs composed of three unique hard tissues, enamel, dentin, and cementum, and supported by the surrounding alveolar bone. Although odontogenesis differs from osteogenesis in several respects, tooth mineralization is susceptible to similar developmental failures as bone. Here we discuss conditions fitting under the umbrella of rickets, which traditionally referred to skeletal disease associated with vitamin D deficiency but has been more recently expanded to include newly identified factors involved in endocrine regulation of vitamin D, phosphate, and calcium, including phosphate-regulating endopeptidase homolog, X-linked, fibroblast growth factor 23, and dentin matrix protein 1. Systemic mineral metabolism intersects with local regulation of mineralization, and factors including tissue nonspecific alkaline phosphatase are necessary for proper mineralization, where rickets can result from loss of activity of tissue nonspecific alkaline phosphatase. Individuals suffering from rickets often bear the additional burden of a defective dentition, and transgenic mouse models have aided in understanding the nature and mechanisms involved in tooth defects, which may or may not parallel rachitic bone defects. This report reviews dental effects of the range of rachitic disorders, including discussion of etiologies of hereditary forms of rickets, a survey of resulting bone and tooth mineralization disorders, and a discussion of mechanisms, known and hypothesized, involved in the observed dental pathologies. Descriptions of human pathology are augmented by analysis of transgenic mouse models, and new interpretations are brought to bear on questions of how teeth are affected under conditions of rickets. In short, the rachitic tooth will be revealed.

We describe a case of lamellar ichthyosis with bilateral genu valgum. The association of genu valgum with congenital ichthyosis is rare. Our patient, a 22-year-old girl, had lamellar ichthyosis and was born with a collodion membrane. She developed progressive valgus deformity of the knees of 5 years duration associated with difficulty in walking. On evaluation, she had generalised scaly skin lesions along with bilateral genu valgum and biochemical evidence of vitamin D deficiency. Skin serves as an important site for vitamin D synthesis and thus skeletal deformities secondary to vitamin D deficiency may occur in cases of congenital ichthyosis, causing a diagnostic dilemma due to the unusual association. This case serves as a reminder that clinicians need to be aware of such an association in order to prevent, appropriately diagnose and adequately treat the rare case of congenital ichthyosis with rickets and osteomalacia.

Rickets can be attributed to nutritional, genetic, hormonal, or toxic disturbances and is classified as a metabolic bone disease. Rickets is most often associated with inappropriate dietary levels of calcium, phosphorus, and/or vitamin D. During a 27-month period (January 2010 through March 2012), the Iowa State University Veterinary Diagnostic Laboratory investigated causes of sudden, unexpected death and lameness in growing pigs throughout the Midwestern United States. Clinical observations from 17 growing pig cases included weakness, lameness, reluctance to move, muscle fasciculations and/or tremors, tetany, and death. Ribs were weak, soft, and bent prior to breaking; rachitic lesions were apparent at costochondral junctions in multiple cases. Acute and/or chronic bone fractures were also noted in multiple bones. Failure of endochondral ossification, expanded physes, infractions, thin trabeculae, and increased osteoclasts were noted microscopically. Decreased bone ash and serum 25(OH)D(3), combined with clinical and microscopic evaluation, confirmed a diagnosis of vitamin D-dependent rickets in all cases. In 3 cases, disease was linked to a specific nutrient supplier that ultimately resulted in a voluntary feed recall; however, most cases in the current investigation were not associated with a particular feed company. The present report describes vitamin D-associated rickets and its importance as a potential cause of weakness, lameness, muscle fasciculations, recumbency or sudden unexpected death in swine, and describes appropriate samples and tests for disease diagnosis.

Rickets and osteomalacia are increasing in prevalence in people because of cultural practices, breast-feeding, decreased sun exposure, and increased sunscreen usage. Several hereditary forms of rickets owing to either renal phosphate wasting or defects in vitamin D metabolism are also reported in people. Rickets is well recognized in domestic animals, but published reports are not always supported by microscopic findings, and diagnoses based on clinical signs and radiology are unreliable. Most cases in domestic animals are caused by dietary deficiency of either vitamin D or phosphorus, but occasional inherited forms are reported in pigs, sheep, cats, and dogs. There is variation between species in susceptibility to dietary vitamin D and phosphorus deficiency and in the ability to manufacture vitamin D in their skin. A number of mouse models have been discovered or created to study human skeletal diseases and skeletal homeostasis. With the discovery that vitamin D is involved in not only calcium and phosphorus homeostasis but also in the immune system and cancer, there is great potential for new and existing animal models to generate valuable information about vitamin D and its many functions. This review presents an overview of vitamin D metabolism and rickets in domestic and laboratory animals and makes comparisons where appropriate with the disease in humans.

Hypovitaminosis D is increasing worldwide and is associated with low bone mass. The effects of hypovitaminosis D on bone might be direct or mediated through decreased muscle mass and function and/or secondary hyperparathyroidism. This study systematically investigated the relative contribution of lean mass, PTH, and the direct effect of vitamin D as predictors of vitamin D mediated osteopathy in elderly individuals. 460 ambulatory subjects aged 65-85 years had their bone mass and lean body mass measured by a dual-energy X-ray absorptiometry. Serum calcium, phosphorus and alkaline phosphatase, intact parathyroid hormone (PTH) and 25-hydroxyvitamin D (25 OHD) were also measured. Serum 25 OHD correlated with lean body mass in men, r = 0.24, P = 0.002, but not in women; and with bone mass at all skeletal sites in men, r = 0.20-0.30, P < 0.02. Correlations were also noted at all skeletal sites in women except for the spine, r = 0.13-0.18, P < 0.04. In both genders, BMD at sites enriched in cortical bone was 0.4-0.7 SD lower in the group with the lowest vitamin D tertile than that in the group in the highest tertile. After controlling for PTH, the magnitude of the correlations between BMD and 25 OHD remained significant in both genders. After controlling for lean body mass, the magnitude of these correlations did not change in women and decreased but remained significant in men. After adjustment for age and height, both lean body mass and PTH had significant independent contributions to BMD variance at all skeletal sites. After adjustment for age, height, lean mass, and PTH, 25 OHD did not have any significant residual contribution to BMD variance except at the trochanter in men. This study demonstrates that vitamin D osteopathy in the elderly is in large part mediated through lean mass in men and through PTH levels in both genders, with a greater contribution of PTH in women than in men. There was little demonstrable independent relation between serum 25 OHD and bone mass.

The treatment of choice for pseudo-vitamin D deficiency rickets (PDDR), caused by mutations in the 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1; 1alpha-OHase) gene, is replacement therapy with 1,25(OH)2D3. We have previously engineered an animal model of PDDR by targeted inactivation of the 1alpha-OHase gene in mice. Replacement therapy was performed in this model. The 1alpha-OHase-/- mice and heterozygote controls were treated with 500 pg of 1,25(OH)2D/g body weight/day for 2 weeks, followed by 100 pg of 1,25(OH)2D3/g body weight/day for an additional 3 weeks before death at 8 weeks of age. Blood biochemistry analysis revealed that the rescue treatment corrected the hypocalcemia and secondary hyperparathyroidism. The daily injections of 1,25(OH)2D3 induced strong expression of CYP24, the 25-hydroxyvitamin D 24-hydroxylase gene. Bone histology and histomorphometry confirmed that the rickets and osteomalacia were cured. The rescue regimen also restored the biomechanical properties of the bone tissue within normal parameters. These results show that chronic treatment with the active 1,25(OH)2D3 metabolite is effective to rescue the PDDR phenotype of 1alpha-OHase mutant mice.

To study the 'in vivo' importance of vitamin D on the natural killer (NK) activity, rats were submitted to privational rickets induced by a diet deficient in vitamin D and phosphorus (D-P-). Thirty days after the beginning of treatment the animals showed low body weight, changes in the bone development, and decreased levels of 25-hydroxyvitamin D(3) (25-OH D(3)). NK activity, evaluated using a cytotoxicity assay against 51Cr-labeled Yac.1 target cells, was not modified by the rickets-inducing treatment during the first 30 days. Following a long-term treatment (60 days) the rachitic rats (D-P-) exhibited higher NK activity than control animals (D+P+) (P<0.05). On the other hand, D-P+ animals showed higher cytotoxic activity than D-P- and D+P+ groups. Feed replacement to the rachitic rats by a complete diet (D-P-/D+P+) led to a partial recuperation of growth, bone development, and 25-OH D(3) serum levels. The NK activity was also influenced by vitamin D intake, decreasing after treatment.

Pseudovitamin D-deficiency rickets is caused by mutations in the cytochrome P450 enzyme, 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-OHase). Patients with the disease exhibit growth retardation, rickets, and osteomalacia. Serum biochemistry is characterized by hypocalcemia, secondary hyperparathyroidism, and undetectable levels of 1alpha,25-dihydroxyvitamin D(3). We have inactivated the 1alpha-OHase gene in mice after homologous recombination in embryonic stem cells. Serum analysis of homozygous mutant animals confirmed that they were hypocalcemic, hypophosphatemic, hyperparathyroidic, and that they had undetectable 1alpha,25-dihydroxyvitamin D(3). Histological analysis of the bones from 3-week-old mutant animals confirmed the evidence of rickets. At the age of 8 weeks, femurs from 1alpha-OHase-ablated mice present a severe disorganization in the architecture of the growth plate and marked osteomalacia. These results show that we have successfully inactivated the 1alpha-OHase gene in mice and established a valid animal model of pseudovitamin D-deficiency rickets.

Bone sialoprotein (BSP) and osteopontin (OPN) are two major noncollagenous matrix proteins in mineralized connective tissue that have discrete roles in bone matrix formation, mineralization, and remodeling. The osteotropic secosteroid, 1,25-dihydroxyvitamin D3, a potent regulator of bone remodeling required for normal bone development, has been shown to exert differential effects on OPN and BSP expression by bone cells in vitro. To investigate these effects in vivo, we induced vitamin D3 deficiency in a transgenic mouse line (rBSP2.7Luc) that has a 2.7 kb rat BSP promoter linked to a luciferase reporter gene in its genome. Pregnant rBSP2.7Luc mice were fed vitamin D3-deficient food and demineralized water for 6 weeks. Their offspring were weaned at 3 weeks of age and then fed vitamin D-deficient food for an additional week. The control group were fed normal rodent pellets and water during the entire experimental procedure. Bone tissues from 40, 4-week-old offspring in each group were analyzed for BSP, OPN and luciferase expression. Vitamin D3-deficient mice displayed a rachitic phenotype that included reduced size and malformation of bones. Assays of the BSP promoter transgene in calvariae, mandibles, and tibiae of the rachitic mice showed increases in luciferase activity of 3.1-, 1.9-, and 4.6-fold, respectively, when compared with control littermates. Semiquantitative reverse transcriptase polymerase chain reaction assays of BSP mRNA revealed increases of 7-, 74-, and 66-fold, respectively, in the same rachitic bones, while OPN mRNA was reduced 12.5-fold in calvariae and 2-fold in tibiae and mandibles. In situ hybridization using mouse cRNA probes revealed that the increased BSP expression and decreased OPN expression in the vitamin D3-deficient mice was primarily in osteoblastic cells on the surface of calvariae and endosteal spaces of alveolar bone, on newly formed epiphyseal bone, and in cementoblasts and in hypertrophic chondrocytes. These studies are the first to show that BSP and OPN are differentially regulated by vitamin D3 in vivo, reflecting the diverse roles of these protein in bone remodeling. Moreover, the increased expression of the BSP transgene in the rachitic mice demonstrates that vitamin D3 regulation of BSP expression is mediated, in part, by element(s) within the 2.7 kb promoter region.

The epiphyseal plates of rachitic chicks fed a vitamin D-deficient and low-calcium diet were examined ultrastructurally at 4, 7, 14, 18 and 21 days old. On and after 14 days, changes were observed. Chondrocytes in resting, proliferating and maturing zones commonly showed a reduction in cell organelles, suggestive of a decrease in synthetic activity of matrix components. In addition, the resting zone cells had numerous intracytoplasmic microfilaments. Mitotic figures were present but not increased in number in the proliferating zone. Autolysosome-like dense bodies in the chondrocytes and clusters of degenerative and necrotic chondrocytes were observed in the proliferating and maturing zones. In the calcifying zone of the rachitic epiphyseal plate, initial calcification was observed characterized by the deposition of apatite crystals in matrix vesicles and the formation of spherical crystal clusters. The crystal clusters were separated from each other by collagen fibrils on which only small amounts of apatite crystals had been deposited. In this zone, hypertrophic chondrocytes responsible for the initial calcification were seen, but not the stellate chondrocytes responsible for the progression of matrix calcification after its initiation. These findings suggest that accumulation of the proliferating and maturing zone cells as a characteristic lesion of the epiphyseal plate in rachitic chicks is caused by a disturbance of cell maturation. Such disturbance in the calcifying zone may explain the progression of the defect in matrix calcification.

We examined the effects of 1, 25-dihydroxyvitamin D3 on the growth and differentiation of cultured human hair follicle cells from a patient with vitamin D-dependent rickets type II [DDR-II] with alopecia. In the presence of 100 nM 1, 25-dihydroxyvitamin D3, the clonal growth of normal hair follicle cells was inhibited and terminal differentiation was markedly stimulated. However, the cells from a patient with DDR-II with alopecia did not respond to the hormone, suggesting a lack of the specific receptors in the cells. The difference in the cellular response to the hormone between the normal hair follicle cells and those from a patient were clear and easily distinguished, and these studies may provide a basis for the rapid diagnosis of DDR-II. Large number of hairs were difficult to obtain from patients with alopecia, and we developed a new culture method to accomplish these studies. Our system may be useful in the culture of HFC from only a few hair follicles.

In the present study, we have evaluated the role of calcium and phosphorus concentrations in serum on the mineralization of bone in the absence of vitamin D. This was accomplished by feeding mother rats and subsequently their pups vitamin D-deficient diets varying in calcium, phosphorus, and lactose content. After 5-7 wk on these diets, serum concentrations of 25-hydroxyvitamin D [25(OH)D] and 1,25-hydroxyvitamin D [1,25(OH)2D] were undetectable. Rats fed a vitamin D-deficient diet containing 0.44% calcium and 0.3% phosphorus showed a serum calcium of 4.9-5.9 mg/dl and a serum phosphorus of 7.3-8.2 mg/dl; rickets (wide epiphysial plates) had developed as well as osteomalacia (wide osteoid seams). Rats maintained on a vitamin D-deficient diet containing 3% calcium and 0.65% phosphorus had normal serum calcium, low serum phosphorus, and severe rickets, but osteomalacia was not seen. Rats fed a diet containing 20% lactose, 4% calcium, and 1% phosphorus showed normal serum calcium, somewhat low serum phosphorus, normal serum PTH, normal width of the epiphysial plate, normal volume density of trabecular bone, and normal volume density of osteoid seams. These data confirm the findings of others, using a different experimental model, that serum calcium and phosphorus concentrations are the determining factors in mineralization defects and not the absence of 25(OH)D or 1,25(OH)2D. In these rats thyroparathyroidectomy is well tolerated, which makes for an ideal model for the study of the effects of calcium-regulating hormones on bone histology, cytology, and biochemistry.

This study involved comparison of the distribution and integrity of perforating epiphyseal and marrow vessels with the stage of development and integrity of chondrocytes and the distribution of insoluble calcium in the proximal tibial growth plate of 3-week-old vitamin-D3-deficient hypocalcemic chicks and 3-week-old D3-deficient chicks 12, 36, 72, and 120 hours after an oral dose of 10,000 units vitamin D3. The aim was to clarify the mechanisms responsible for chondrocyte hypertrophy and cartilage calcification in the avian growth plate. Within 12 hours after administration of vitamin D3, serum calcium levels rose to normocalcemic levels. The following morphologic changes were first recognizable at the times indicated. Distal portions of previously elongated perforating epiphyseal vessels and adjacent proliferative and maturing chondrocytes underwent necrosis by 12 hours. Chondrocyte necrosis was not preceded by hypertrophy. By 36 hours, vascular and chondrocyte necrosis involved large portions of the thickened proliferating and maturing zone, and perforating epiphyseal vessels were shortened to a normal length. By 72 hours, chondrocyte hypertrophy and calcification resumed around the shortened epiphyseal vessels. By 120 hours, marrow had removed the necrotic cartilage, and morphologically normal growth plate was restored, with perforating epiphyseal and marrow vessels, both ending in a narrow hypertropic cartilage zone. The results indicate that proximity of chondrocytes to perforating epiphyseal vessels is necessary for their viability, but loss of these vessels does not cause hypertrophy. Since hypertrophy and calcification both occur in the proximity of perforating epiphyseal vessels in normocalcemic animals but not in hypocalcemic animals, it is likely that the vessels influence hypertrophy and calcification by delivering calcium to chondrocytes.

Using routine transmission electron microscopy and light and electron microscopic techniques for the histologic demonstration (localization) of catalase (a peroxisomal enzyme), peroxisomes in chick duodenal epithelial cells were identified and studied. In these cells, peroxisomes were seen to be small, ovoid structures, delimited by a single unit membrane. They were concentrated in the supranuclear cytoplasm in initimate association with the smooth endoplasmic reticulum. As demonstrated histochemically, the heterogeneous matrix of these organelles was catalase positive. In addition, most of the larger peroxisomes revealed central nucleoids; however, the smaller peroxisomes were generally anucleoid. It thus appears that two classes of peroxisomes exist in chick intestinal absorptive cells: (1) small, anucleoid microperoxisomes, and (2) larger, nucleoid-containing peroxisomes. In addition to the above morphological characteristics, both peroxisome types were numerous in normal and vitamin-D-replete tissues, but were conspicuously decreased or absent from the apical cytoplasm of rachitic epithelial cells. From these observations it is hypothesized that these organelles may be involved in the overall vitamin-D response of the small intestine.

Day-old broiler chicks were fed a vitamin D-deficient diet for 30 days. Gross, microscopic, and radiographic examinations of the proximal tibiotarsus were done at 2, 3, and 4 weeks of age. In 2-week-old chicks, there was variable lengthening and disorganization of the proliferating-prehypertrophied zone (P-PHZ), resorption of cartilage spicules in the degenerating hypertrophied zone and primary spongiosa, and lengthening of bone spicules in the secondary spongiosa; many bone surfaces were lined with increased osteoid. In 3-week-old chicks, there was a tendency for the P-PHZ to decrease in relative length and for cartilage spicules to increase in length. In 4-week-old chicks, however, there was marked lengthening of the P-PHZ, resorption of cartilage spicules, and replacement of the metaphysis with irregularly oriented islands of woven bone, osteoid, and loose fibrous connective tissue.

An outbreak of rickets in sheep under a year old (hoggs) appeared clinically as stiffness and rotation of the carpal joints. Histological studies confirmed the diagnosis and biochemical analyses of blood demonstrated a primary vitamin D deficiency.

Plasma levels of the vitamin D metabolites were related to changes in bone morphology during the development of rickets in rats deprived of phosphorus and vitamin D. Weanling rats were studied at 1, 3, and 5 wk after onset of diets deficient in phosphorus or in both phosphorus and vitamin D. Bone histology and morphometry were carried out and measurements were made of 45Ca and 32P absorption, serum Ca and P, and plasma 25(OH)D3, 24,25(OH)2D3 and 1,25(OH)2D3. After 1 wk of vitamin D restriction, the plasma levels of 25(OH)D3 and 24,25(OH)2D3 were non-detectable (less than 0.5 and less than 0.8 ng/ml). The plasma 1,25(OH)2D3 level was elevated at 1 wk (105.5 pg/ml) and fell to 19 pg/ml by 5 wk. At 1 wk mild rachitic lesions in epiphyseal cartilage were observed despite the elevated 1,25(Oh)D3 level. Serum Ca and P levels and values for 45CA and 32P absorption decreased and the severity of the rickets increased with the fall in plasma levels of 1,25(OH)2D3. In Vitamin D replete, phosphate deficient rats the epiphyseal cartilage was normal throughout the 5 wk study period. Our results provide further evidence that physiological levels of 1,25 (OH)2 D3 will not prevent rickets without adequate plasma concentrations of either 25(OH)D3 or 24,25(OH)2D3.

Defective mineralization of bone and cartilage is the classical histological finding in vitamin D deficiency. Whether this represents a direct effect on mineral deposition or is a consequence of the decreased calcium and phosphorus levels that result from impaired intestinal absorption is not clear. A method has been developed in which vitamin D-deficient rats have plasma calcium and phosphorus levels maintained in the normal range by continuous infusion. Histomorphometric analysis of undecalcified tibiae from these animals was compared with that of rats given vitamin D. Epiphyseal growth plate thickness, trabecular osteoid volume, and mean osteoid seam width were not increased. Moreover, the administration of two time-spaced courses of tetracycline revealed that the mineralization rate and the time interval between apposition and subsequent mineralization of osteoid (mineralization lag time) were identical to those in rats treated with vitamin D. Trabecular bone volume was increased (osteosclerosis) in the vitamin D-deficient rats. In vitamin D-deficient controls without infusions, the osteosclerosis was mostly osteoid, whereas the excess bone was well mineralized in the vitamin D-deficient rats infused with calcium and phosphorus. Osteosclerosis in vitamin D-deficient animals may result from both decreased bone resorption and increased osteoid apposition. This study provides firm evidence that vitamin D is not essential for mineralization in young growing rats. Decreased availability of calcium and phosphorus thus may be the sole basis of the mineralization defect seen in vitamin D deficiency.

Turkey poults were fed a vitamin D-deficient diet and examined for clinical signs and structural changes of bone and parathyroid glands. Vitamin D-deficient poults developed ricketic changes during days 10 to 14. Control poults (deficient diet plus vitamin D) did not develop rickets. In deficient poults, lengths of proliferating-prehypertrophied zones of growth plates increased significantly in the proximal tibiotarsus but were only slightly elongated in the distal tibiotarsus. Unmineralized hypertrophic chondrocyte zones increased in length rapidly in conjunction with a decrease in the length of mineralized hypertrophic degenerative zones; this occurred more rapidly in proximal than in distal tibiotarsus. Other ricketic changes included decreases in bone ash, total femoral bone ash (calcium, phosphorus, magnesium), bone length, and body weight. Plasma alkaline phosphatase was increased, calcium was normal, and phosphorus was normal or elevated. Parathyroids were hyperplastic and had foci of degeneration. Vitamin D3 metabolites 25OHD3, 1,25(OH)2D3, and 24,25(OH)2D3 were rapidly depleted. Increase in bone ash Ca/P ratios in deficient poults suggests that phosphorus may be selectively released from ricketic bone. Low 25OHD3 and 1,25(OH)2D3 of control poults early in the experiment suggests that 1,400 IU of vitamin D3/kg of feed may not be an adequate level of vitamin D3 for growing turkey poults.