Effects of vitamin or mineral deficiency on the morphology of medullary bone in laying hens

Effect of the combination of 25-hydroxyvitamin D3 and higher level of calcium and phosphorus in the diets on bone 3D structural development in pullets

Bone issues such as osteoporosis are major concerns for the laying hen industry. A study was conducted to improve bone-health in pullets. A total of 448 one-day-old Hyline W36 pullets were randomly assigned to four treatments (8 rep; 14 birds/rep) until 17 weeks (wks). Dietary treatments were: 1) vitamin D₃ at (2,760 IU/kg) (D), 2) vitamin D₃ (2,760 IU/kg)+62.5 mg 25-(OH)D₃/ton (H25D), 3) vitamin D₃ (2,760 IU/kg) + 62.5 mg 25-(OH)D₃/ton + high Ca&P (H25D + Ca/P), and 4) vitamin D₃ (2,760 IU/kg) + high Ca&P (D + Ca/P). The high calcium (Ca) and phosphorus (P) diet was modified by increasing both high calcium and phosphorus by 30% (2:1) for the first 12 wks and then only increasing P for 12-17 wks to reduce the Ca to P ratio. At 17 wk, growth performance was measured, whole body composition was measured by dual energy x-ray absorptiometry (DEXA), and femur bones were scanned using Micro-computed tomography (Micro-CT) for bone 3D structure analyses. The data were subjected to a one-way ANOVA using the GLM procedure, with means deemed significant at p < 0.05. There was no significant outcome for growth performance or dual energy x-ray absorptiometry parameters. Micro-computed tomography results indicated that the H25D + Ca/P treatment had lower open pore volume space, open porosity, total volume of pore space, and total porosity in the cortical bone compared to the D + Ca/P. It also showed that a higher cortical bone volume/tissue volume (BV/TV) in the H25D + Ca/P than in the D + Ca/P. Furthermore, the H25D + Ca/P treatment had the lowest trabecular pattern factor and structure model index compared to the other treatments, which indicates its beneficial effects on trabecular structural development. Moreover, the H25D + Ca/P had a higher trabecular percentage compared to the D and 25D, which suggests the additional high calcium and phosphorus supplementation on top of 25D increased trabecular content in the cavity. In conclusion, the combination of 25D with higher levels of high calcium and phosphorus could improve cortical bone quality in pullets and showed a beneficial effect on trabecular bone 3D structural development. Thus, combination of a higher bio-active form of vitamin D₃ and higher levels of high calcium and phosphorus could become a potential feeding strategy to improve bone structural integrity and health in pullets.

The effect of a bisphosphonate on bone volume and eggshell structure in the hen

Bisphosphonates, used in the prevention and treatment of osteoporosis, in man, can prevent bone loss in experimental models of osteoporosis in mammals. In egg-laying hens there is a high incidence of bone fractures which are due to osteoporosis. Alendronate, a bisphosphonate, was given to three groups of hens in mid-lay. Different doses of alendronate were given to each group and group 4 was a control. The birds were killed after 2 weeks of treatment. The hens receiving the highest dosage of alendronate (1 mg/kg every 2nd day) ceased laying and had reduced serum calcium concentrations. Lower dosages of alendronate (0.1 and 0.01 mg/kg every 2nd day) resulted in normal egg production and serum calcium concentrations. Egg shells with ultra-structural features indicative of reduced shell quality were produced by hens on the two higher dosages, but the egg shells from the controls and from the hens on the lowest dosage were considered normal. When alendronate was administered to hens in mid-lay there was no effect on trabecular bone volumes, but there was a reduction in mean medullary bone volume in some groups. In a second experiment, pullets were treated with alendronate (0.01 mg/kg twice a week) before the onset of lay. The pullets were killed after laying their first egg. In the pullets treated with alendronate, this protocol resulted in a significantly greater volume of trabecular (structural) bone at the onset of lay.

Keeping laying hens in furnished cages and an aviary housing system enhances their bone stability

1. Tibia and humerus breaking strength of Lohmann Silver hybrids kept in conventional cages, furnished cages and an aviary with outdoor run were examined in two production cycles. Each trial lasted a full laying period; feeding, management and healthcare were identical for all hens. In both trials bone strength was investigated at the end of laying months 6, 9 and 14. 2. The objective was to determine if bone strength increases when hens are kept in alternative housing systems, especially in furnished cages, and whether hen age affects bone stability. 3. The results indicated that housing system influenced bone breaking strength, which was consistently higher for hens in the aviary compared to hens in conventional and furnished cages. Furthermore, humerus breaking strength was higher for hens in furnished cages compared to conventional cages. No significant difference regarding tibia breaking strength was found between conventional and furnished cages. 4. Our results showed that lack of exercise contributed to the problem of weak bones more than did calcium depletion from eggshell formation. 5. Tibia breaking strength increased during the last third of the production cycle, whereas humerus breaking strength remained unaffected by hen age. 6. Genetic group affected only tibial bone breaking strength, which was lower overall in genetic group A than in group B, which in turn was lower than group C. 7. The increased bone strength in the aviary and in the furnished cages probably reduced the incidence of recently broken bones in these systems compared to the conventional cages. This increase in bone strength can be regarded as an improvement in welfare. Furnished cages, like the aviary system, might be considered an alternative housing system for laying hens, because both resulted in enhanced bone strength.

Secondary nutritional hyperparathyroidism associated with vitamin D deficiency in two domestic skunks (Mephitis mephitis)

Two privately owned domestic skunks (Mephitis mephitis) developed clinical signs of hyperparathyroidism. Survey radiographs, complete blood counts and biochemical profiles, including the concentrations of ionised calcium, parathyroid hormone and 25-(OH)-vitamin D, established that they were deficient in vitamin D and had secondary nutritional hyperparathyroidism. They both responded to treatment, as well as to changes in their diet, and levels of exercise and exposure to sunlight.

Overview of bone biology in the egg-laying hen

In young pullets, long bones elongate by endochondral growth. Growth plate chondrocytes proliferate, then hypertrophy, and are replaced by osteoblasts that form a network of trabecular bone. This bone is gradually resorbed by osteoclasts as the bone lengthens. Long bones widen, and flat bones are formed, by intramembranous ossification in which cortical bone formation by osteoblasts in the periosteal layer is accompanied by osteoclastic resorption at the inner endosteal surface. Growth of structural trabecular and cortical bone types continues up to the onset of sexual maturity in pullets. At this point, the large surge in estrogen changes the function of osteoblasts to forming medullary bone rather than structural bone. Medullary bone is a woven bone that acts as a labile source of calcium for eggshell formation. It lines structural bone and also occurs as spicules within the marrow cavity. It has little inherent strength but can contribute to fracture resistance. Osteoclasts resorb both medullary and structural bone so that during the period the hen remains in reproductive condition there is a progressive loss of structural bone throughout the skeleton, which is characteristic of osteoporosis. The increasing fragility of the bones makes them more susceptible to fractures. The dynamics of bone loss can be affected by a number of nutritional, environmental, and genetic factors. If the hen goes out of reproductive condition, estrogen levels fall, osteoblasts resume structural bone formation, and skeletal regeneration can take place.

Osteoporosis in cage layers

Osteoporosis in laying hens is a condition that involves the progressive loss of structural bone during the laying period. This bone loss results in increased bone fragility and susceptibility to fracture, with fracture incidences of up to 30% over the laying period and depopulation not uncommon under commercial conditions. A major cause of osteoporosis is the switch in bone formation from structural to medullary bone at the onset of sexual maturity, but structural bone loss is accelerated by the relative inactivity of-caged birds. Allowing birds more exercise, as in aviary systems, results in better bone quality but may not decrease the overall fracture incidence. Good nutrition can help to minimize osteoporosis but is unable to prevent it. Best nutritional practice involves transferring birds to a higher calcium diet at lighting up rather than at first egg, providing a source of calcium in particulate form, and not withdrawing feed some days before depopulation. Breeding may be an effective way of combating ostoporosis. Some bone strength traits have been shown to be heritable, and divergent selection for resistance or susceptibility to osteoporosis has resulted in lines with markedly different bone characteristics. After three generations of selection, the lines differ by 19% for keel bone mineral density, 13% for humerus breaking strength, and 25% for tibia breaking strength and show a sixfold difference in fracture incidence under commercial breeding conditions. The difference in bone quality among the lines is maintained under different housing systems.

Medullary bone and humeral breaking strength in laying hens

To test the hypothesis that large amounts of medullary bone in the humeral diaphysis may increase breaking strength, various parameters of bone quality and quantity were examined in two large flocks of hens near end of lay. We conclude that the amount of medullary bone in the humerus of hens during the laying period influences bone strength. This medullary bone may not have any intrinsic strength, but may act by contributing to the fracture resistance of the surrounding cortical bone. Using a quantitative, low dose, radiographic technique, we can predict, from early in the laying period, those birds which will develop large amounts of medullary bone in their humeri by the end of the laying period. The formation of medullary bone in the humeral diaphysis is not at the expense of the surrounding radiographed cortical bone.

Studies on effects of nutritional factors on bone structure and osteoporosis in laying hens

1. A modern hybrid strain of laying hen (Hisex) was fed from point of lay to 68 weeks on a control diet and diets containing oystershell, fluoride, 1,25-dihydroxycholecalciferol, ascorbic acid, a lower concentration of phosphorus and a combination of a lower concentration of crude protein and higher concentration of vitamin K. Hens from a much older strain (Brown Leghorn J-line) were fed on the control diet. 2. Plasma variables were measured during lay. End-of-lay trabecular and medullary bone volumes in the proximal tarsometatarsus and free thoracic vertebra were measured by histomorphometry. 3. The majority of Hisex hens were considered to be osteoporotic by the end of lay. In contrast, none of the J-line were osteoporotic. 4. None of the nutritional treatments affected trabecular bone volumes. Medullary bone volumes were increased significantly by feeding oystershell or fluoride. 5. There was no phenotypic correlation between egg production and trabecular bone volume in the Hisex hens. 6. The experiment provided evidence that osteoporosis in laying hens, as assessed by trabecular bone volumes, is not caused by calcium deficiency and could not be prevented by any of the nutritional treatments studied.

Effects of perches on trabecular bone volume in laying hens

Trabecular bone remodelling is known to be affected by loading or exercise, and thus exercise may effect the trabecular bone loss associated with osteopenia in laying hens. Sixteen ISA Brown hens were housed from 18 to 72 weeks old in cages with perches and 16 in similar cages without perches to examine the effects of the exercise afforded by perch provision on trabecular bone volume. At 72 weeks, mean trabecular bone volume in the proximal tarsometatarsus of birds with access to perches was significantly greater than in control birds, while medullary bone volume was not significantly different in the two groups. However, all the birds were considered osteoporotic, though to varying degrees, and the beneficial effects of perches were relatively minor. It was concluded that while trabecular bone loss may be reduced by perch provision, other factors are probably more influential in the development of the osteoporosis typical of laying hens.

Effects of age, sex and housing on the trabecular bone of laying strain domestic fowl

To determine the effects of age, sex and housing on trabecular bone volume, samples were collected from groups of male and female domestic fowl housed in cages or floor pens from four to 60 weeks old. Between 25 and 60 weeks old, trabecular bone volume decreased by 25 per cent in sections of free thoracic vertebrae (T5) from female birds, the loss occurring at an earlier age in caged birds. Over the sample period, TBV in male caged birds diminished by 35 percent, but male floor birds showed no reduction in trabecular bone volume. At 60 weeks, trabecular bone volume was 30 per cent greater in male caged birds and 40 per cent greater in male floor birds than in the corresponding females. In reproductively active females, no trabecular osteoid was observed, indicating no new trabecular bone formation. However, trabecular osteoid was present in two birds aged 60 weeks which had regressed ovaries. Osteomalacia was not seen in any of the bone samples.