Support of embryonic chick survival by vitamin D metabolites

Twenty-five hydroxycholecalciferol as a cholecalciferol substitute in broiler breeder hen diets and its effect on the performance and general health of the progeny

An experiment was conducted with broiler breeder hens to determine the relative biological value of 25-hydroxycholecalciferol (25-OHD3) compared with cholecalciferol (vitamin D3) for hen-day egg production, hatchability, embryo mortality (early, 1 to 10 d of incubation, late, 11 to 21 d), and body ash of the progeny. The study was conducted with 73-to-90-wk-old molted Ross broiler breeder hens in an environment excluding ultraviolet light. A basal vitamin D3 deficient diet supplemented with 4 levels of vitamin D3 (0, 3,125, 12,500, and 50,000 ng/kg of diet) and 2 levels of 25-OHD3 (3,125 and 12,500 ng/kg of diet) was fed. The relative biological values of 25-OHD3 in comparison to vitamin D3, using slope ratio techniques, were 138, 133, 128, and 111% for hen-day egg production, hatchability, late embryo mortality, and body ash of the progeny,, respectively (average = 128%). When comparing 25-OHD3 against D3 at the 3,125 ng/kg level, the relative biological values were 209, 167, 400, and 108% for the same criteria, respectively (average = 221%). However, at the 12,500 ng/kg level no statistical differences between 25-OHD3 and D3 were observed (average = 108%). Four trials were conducted to determine the effect of the maternal diet on the performance and leg abnormalities of the hens' progeny. In experiment 1, no vitamin D was added to the corn-soybean meal basal diet fed to the chicks, and in experiments 2, 3, and 4 the basal diet was supplemented with 27.5 microg of D3/kg of diet. In the progeny study, the average relative biological value of 25-OHD3 at the 3,125 and 12,500 ng/kg levels were 115 and 101%, respectively. The potency of 25-OHD3 in relation to vitamin D3 depended on the level tested. When comparing vitamin D sources, 25-OHD3 had greater potency than D3 only at very low levels of supplementation.

Calcium uptake by chorioallantoic membrane: effects of vitamins D and K

The chorioallantoic membrane (CAM) of birds is an epithelial tissue that actively transports large amounts of Ca during embryonic development. In this study the effect of vitamins D and K on Ca uptake by the CAM was studied. Four dietary treatments were used to produce eggs that are the following: deficient in vitamins D and K (-D/-K), sufficient in both (+D/+K), or deficient in one and sufficient in the other (-D/+K or +D/-K). Vitamin D-deficient (-D) Japanese quail embryos (from hens fed 1,25-dihydroxyvitamin D3) do not hatch because of severe Ca deficiency resulting from their inability to obtain Ca from shell, whereas vitamin K deficiency results in only 14% reduction in hatchability. The results demonstrate that Ca uptake by CAM is vitamin D dependent and only slightly vitamin K dependent. Ca-binding activity of CAM extracts was unchanged by vitamin K deficiency, and only a small increase was provided by vitamin D treatment. Vitamin D stimulated both Ca entry and exist from the chorion cells as indicated by the increased accumulated 45Ca in +D embryos. We conclude that vitamin D is essential for the utilization of eggshell Ca by the developing embryo and hence its survival, suggesting that Ca transport across the CAM is largely a vitamin D-dependent process.

The role of vitamin D in chorioallantoic membrane calcium transport

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) is essential for the transport of eggshell calcium to the embryo across the chorioallantoic membrane (CAM). CAM contains the vitamin D receptor that increases following 1,25-(OH)2D3 injection into embryos at day 10 of incubation. Further, a single injection of 100 ng of 1,25-(OH)2D3 into vitamin D-deficient quail eggs at day 10 of incubation resulted in a significant increase in both body and yolk calcium. This is accompanied by an increase in carbonic anhydrase from low levels in deficiency to normal levels. Acetazolamide (AZ), a specific carbonic anhydrase inhibitor injected into the quail embryos, caused hypocalcemia and hyperphosphatemia. This is similar to the hypocalcemia and hyperphosphatemia found in vitamin D-deficient embryos. These results suggest that one mechanism of action of vitamin D in the mobilization of eggshell calcium is the activation of carbonic anhydrase that acidifies the calcium carbonate shell.

Survival of vitamin D-deficient embryos: time and choice of cholecalciferol or its metabolites for treatment in ovo

Vitamin D-deficient (-D) Japanese quail embryos [from hens fed 1,25-dihydroxycholecalciferol (1,25-(OH)2D3)] die at Day 15 of incubation from severe calcium deficiency. Single doses of 125 ng cholecalciferol, 600 ng 24,25-dihydroxycholecalciferol [24,25-(OH)2D3], or 100 ng 1,25-(OH)2D3 were found to increase hatchability when injected into eggs prior to incubation. Cholecalciferol could be used from 125 to 1,250 ng per egg with no detrimental effects on hatchability, whereas single doses of 1,25-(OH)2D3 lower or higher than 100 ng per egg reduced hatchability. Injection of 125 ng cholecalciferol per egg supported the hatching of -D embryos when eggs were treated as late as 10 days of incubation. Sharply reduced hatchability occurred when cholecalciferol was injected at Day 11 or 12 of incubation. Experiments designed to evaluate the physiological state of 1-day-old quail treated with a single dose of cholecalciferol metabolites in ovo prior to incubation revealed that chicks had hypocalcemia, reduced total calcium content, and a six- to sevenfold increase in renal 25-hydroxycholecalciferol-1-hydroxylase activity. On the other hand, chicks from eggs treated with cholecalciferol were relatively normal. It appears that cholecalciferol administered in ovo is the compound of choice for supporting sustained development of the skeleton, mobilization of shell calcium, and prevention of hypocalcemia, probably because cholecalciferol is utilized slowly as needed to support development of the chick skeleton.

Use of slow-release pellets to administer calcitriol to avian embryos: effects on plasma calcium, magnesium, and phosphorus

Calcitriol (1,25-dihydroxycholecalciferol) was administered to embryos of domestic fowl by slow-release pellets inserted into eggs on Day 10 of incubation. Mortality among embryos receiving 10 pg/day was no different from that of controls, but mortality among embryos receiving 100-1000 pg/day was elevated in later stages of incubation. Concentrations of calcium in plasma did not vary over the course of incubation among surviving embryos receiving carrier, but concentrations of magnesium and inorganic phosphorus declined with time. All doses of calcitriol elicited increases in plasma Ca and Mg on Day 12, and embryos may have responded also with a dose-dependent hypophosphatemia. The increases in plasma Ca and Mg were not sustained for the remainder of incubation, but the hypophosphatemia seemingly was of longer duration. This study demonstrates a new procedure for administering hormones to avian embryos and reveals that embryonic chickens respond in the expected manner to very small quantities of calcitriol.

Vitamin D deficiency in the chick embryo: effects on prehatching motility and on the growth and differentiation of bones, muscles, and parathyroid glands

Vitamin D-deficient chicken embryos were obtained by feeding laying hens diets in which 3-7 micrograms calcitriol replaced the vitamin D3 supplement. A large proportion of the D-deficient embryos failed to complete the prehatching positional changes required to start pulmonary respiration. For this reason most of them became cyanotic and had subcutaneous edema and hemorrhages in the head and neck and died without hatching. Total as well as leg-bone and muscle weights were significantly lower in the deficient embryos than in the controls and these changes probably explain the inability of the embryos to complete the movements required to place the beak in contact with the air chamber and start pulmonary respiration. The histological study of the tibiae showed decreased mineralization with narrower trabeculae and enlarged osteoid seams; bone resorption at the inner surface was also significantly decreased. The ultrastructural study of parathyroid glands showed increased functional activity reflected by increased number and size of cisternae of rough endoplasmic reticulum. Injection of 10 ng calcitriol, 1 microgram 24,25-(OH)2D3, or 2 micrograms 25OHD3 to deficient embryos on the 14th day of incubation improved hatchability, bone and muscle weights, and both bone mineralization and resorption.

Indexes of vitamin D deficiency in Japanese quail embryos

Effects of vitamin D deficiency (-D) on mineral homeostasis were investigated in Japanese quail embryos. The -D embryos from 1,25(OH)2D3-fed hens became progressively calcium deficient, as documented by hypocalcemia and reduced calcium accumulation by the skeleton, yolk sac, and allantoic fluid. Plasma phosphate was progressively elevated between days 11 and 15. Increased calcium accumulation by the skeleton, yolk sac, and allantoic fluid occurred between days 12 and 15 in +D embryos. Phosphate and adenosine 3',5'-cyclic monophosphate (cAMP) concentrations of allantoic fluid increased in +D embryos during the period of shell calcium mobilization. Further increases in phosphate and cAMP excretion into allantoic fluid occurred in -D embryos, although no calcium was absorbed from the shell. Renal 25(OH)D-1-hydroxylase activity increased between days 11 and 13, whereas the adenylate cyclase response to parathyroid hormone was lost in -D embryos by day 14. These changes in renal function are indicative of secondary hyperparathyroidism in the -D embryos. Differentiation of villus cavity and capillary covering cells occurred in the chorionic epithelium of -D embryos, but eggshell calcium was apparently not absorbed. In contrast, 75% of the total body calcium of newly hatched (+D) chicks was obtained from the eggshell. Thus the dissolution and/or transport of eggshell calcium is dependent on vitamin D in quail embryos.

Lack of response of bone mineralization of chicks fed egg yolks from hens on dietary 1,25 dihydroxycholecalciferol

White Leghorn hens, age 34 wk, fed 0 to 3 micrograms/kg of 1,25 dihydroxycholecalciferol (1,25(OH)2D3) as the only source of dietary vitamin D3 with 2.5 or 3.5% calcium failed to achieve normal embryonic survival and hatchability of their fertile eggs. Improved egg production was observed over a 24-wk period as the level of 1,25(OH)2D3 was increased. Eggs of hens fed the vitamin D-deficient diet showed significantly lower (P less than .01) egg weight and shell strength with a higher percent of soft shell eggs than those of hens fed 1,25(OH)2D3 or vitamin D3. To study the possibility that 1,25(OH)2D3 cannot be transferred into the egg yolk, yolks from the hens receiving varying levels of 1,25(OH)2D3 and vitamin D3 were fed to day-old chicks. A standard vitamin D3 assay was developed and bone ash was determined on fat-free tibial bone. Significantly lower (P less than .01) vitamin D activity per gram of yolk was observed in yolks from hens fed 0 to 3 micrograms of 1,25(OH)2D3 than in yolks of hens fed vitamin D3. These results demonstrate that insufficient 1,25(OH)2D3 is incorporated in the egg yolk to support normal embryonic survival and hatchability. This may be due to a decrease in available receptor sites in the egg yolk or to the inability of 1,25(OH)2D3 to cross the vitelline membrane.

Studies on the role of 1,25-dihydroxyvitamin D in chick embryonic development

Vitamin D-deficient laying hens were repleted with 25-hydroxy[26,27-3H]vitamin D3 or 1,25-dihydroxy[26,27-3H]vitamin D3. Egg production returned to normal for both groups of hens by the third week. Eggs from hens fed either 25-hydroxy[26,27-3H]vitamin D3 or 1,25-dihydroxy[26,27-3H]vitamin D3 contained 1,25-dihydroxy[26,27-3H]vitamin D3. Eggs from hens fed 25-hydroxy[26,27-3H]vitamin D3 contained substantial amounts of 25-hydroxy[26,27-3H]vitamin D3, while those from hens fed 1,25-dihydroxy[26,27-3H]vitamin D3 contained none. Plasma from 18-day embryos from hens fed 1,25-dihydroxy[26,27-3H]vitamin D3 contained little or no 1,25-dihydroxy[26,27-3H]vitamin D3, while that from 18-day embryos from hens given 25-hydroxy[26,27-3H]vitamin D3 had normal levels of 1,25-dihydroxy[26,27-3H]vitamin D3. No eggs from hens fed 1,25-dihydroxy[26,27-3H]vitamin D3 hatched, while eggs from hens fed 25-hydroxy[26,27-3H]vitamin D3 achieved a hatchability of 90%. It appears that embryos from hens maintained on 1,25-dihydroxyvitamin D3 as their sole source of vitamin D are essentially vitamin D deficient.

The action of various vitamin D3 metabolites on calcium and phosphorus metabolism in chick embryo calvariae

Chick embryos from vitamin D-deficient hens given physiological doses of 1,25-dihydroxyvitamin D3 or 24,25-dihydroxyvitamin D3 or both become severely hypocalcemic, hyperphosphatemic and fail to hatch as compared to those derived from hens given 25-hydroxyvitamin D3 or 24,25-difluoro-25-hydroxyvitamin D3. Calvariae from the former contain less mineral and on incubation in vitro produce significantly lower calcium and higher phosphate concentration in the medium than do the calvariae derived from the embryos of hens supported on 25-hydroxyvitamin D3 or 24,24-difluoro-25-hydroxyvitamin D3.

Effect of vitamin D3 metabolites on calcium and phosphorus metabolism in chick embryos

The biochemical nature of the physiological defect found in chick embryos from hens supported on 1,25-dihydroxyvitamin D3 as their sole source of vitamin D is described. Vitamin D-deficient hens (44-wk-old) were divided into six groups of five and dosed daily for 19 wk with either 2.0 micrograms of 25-hydroxyvitamin D3, 2.0 micrograms of 24,24-difluoro-25-hydroxy-vitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3, 2.0 micrograms of 24,25-dihydroxyvitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3 plus 2.0 micrograms of 24,25-dihydroxyvitamin D3, or vehicle only. Normal embryonic development was found in eggs from hens given 25-hydroxyvitamin D3 or 24,24-difluoro-25-hydroxyvitamin D3, whereas embryos from hens given 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or their combination were abnormal and failed to hatch. Embryos from hens fed 1,25-dihydroxyvitamin D3 and/or 24,25-dihydroxyvitamin D3 had vitamin D deficiency: low bone ash, low plasma calcium, low total body calcium, and extremely high plasma phosphorus. Because the shell is the major source of calcium for the developing embryo, calcium transport from the shell to the embryos across the chorioallantoic membrane apparently fails, giving rise to the observed defects in embryonic development.