Quantitative requirement for cholecalciferol in the absence of ultraviolet light

Genotype-dependent impact of dietary vitamin D3 on laying hens

Vitamin D₃ has an integral part in calcium and phosphorus homoeostasis, which in turn plays a key role in egg production of hens. The present study aimed to investigate whether an additional vitamin D₃ supplementation improves the laying performance and egg quality of hens according to their genetic potential. For this purpose, four layer lines (low performing: R11 and L68; high performing: WLA and BLA) supplemented either with 300 or 3000 IU vitamin D₃ per kg feed were compared concerning serum 25-hydroxyvitamin D₃ (25-OHD₃), calcium, phosphorus and alkaline phosphatase (ALP), laying performance and egg quality. The higher supplementation of vitamin D₃ increased 25-OHD₃ serum concentrations in all genotypes, except for R11 and WLA hens in week 49, and also elevated vitamin D₃ and 25-OHD₃ content in the egg yolk (p < 0.05). In week 29, 3000 IU vitamin D₃ decreased pooled least squares means (LSMeans) of serum calcium concentrations considering all genotypes and increased the ALP concentrations in BLA hens (p < 0.05). Considering the whole experimental period daily egg mass of R11 hens was increased by an additional vitamin D₃ supplementation (p < 0.001). Regarding all genotypes and the whole experimental period the pooled LSMeans of breaking strength of eggs from hens fed 3000 IU vitamin D₃ were higher than those of hens fed 300 IU (p = 0.044). In conclusion, present results give evidence that the higher vitamin D₃ supplementation might have genotype-dependently beneficial effects on calcium and phosphorus homoeostasis of hens, which might improve feed efficiency in the early laying period and promote the persistence of the laying period irrespectively of genotype. The increase of serum 25-OHD₃ by the higher vitamin D supplementation supported the higher transfer of vitamin D in the egg yolk and improved genotype-dependently the breaking strength of the eggshell.

Phytase dose-dependent response of kidney inositol phosphate levels in poultry

Phytases, enzymes that degrade phytate present in feedstuffs, are widely added to the diets of monogastric animals. Many studies have correlated phytase addition with improved animal productivity and a subset of these have sought to correlate animal performance with phytase-mediated generation of inositol phosphates in different parts of the gastro-intestinal tract or with release of inositol or of phosphate, the absorbable products of phytate degradation. Remarkably, the effect of dietary phytase on tissue inositol phosphates has not been studied. The objective of this study was to determine effect of phytase supplementation on liver and kidney myo-inositol and myo-inositol phosphates in broiler chickens. For this, methods were developed to measure inositol phosphates in chicken tissues. The study comprised wheat/soy-based diets containing one of three levels of phytase (0, 500 and 6,000 FTU/kg of modified E. coli 6-phytase). Diets were provided to broilers for 21 D and on day 21 digesta were collected from the gizzard and ileum. Liver and kidney tissue were harvested. Myo-inositol and inositol phosphates were measured in diet, digesta, liver and kidney. Gizzard and ileal content inositol was increased progressively, and total inositol phosphates reduced progressively, by phytase supplementation. The predominant higher inositol phosphates detected in tissues, D-and/or L-Ins(3,4,5,6)P4 and Ins(1,3,4,5,6)P5, differed from those (D-and/or L-Ins(1,2,3,4)P4, D-and/or L-Ins(1,2,5,6)P4, Ins(1,2,3,4,6)P5, D-and/or L-Ins(1,2,3,4,5)P5 and D-and/or L-Ins(1,2,4,5,6)P5) generated from phytate (InsP6) degradation by E. coli 6-phytase or endogenous feed phytase, suggesting tissue inositol phosphates are not the result of direct absorption. Kidney inositol phosphates were reduced progressively by phytase supplementation. These data suggest that tissue inositol phosphate concentrations can be influenced by dietary phytase inclusion rate and that such effects are tissue specific, though the consequences for physiology of such changes have yet to be elucidated.

Application of Ultraviolet Light for Poultry Production: A Review of Impacts on Behavior, Physiology, and Production

The application of ultraviolet (UV) light in poultry production is garnering increased interest with the drive toward improved poultry welfare and optimized production. Poultry can see in the UV spectrum (UVA wavelengths: 320–400 nm) thus inclusion of these shorter wavelengths may be viewed as more natural but are typically excluded in conventional artificial lights. Furthermore, UVB wavelengths (280–315) have physiological impact through stimulation of vitamin D pathways that can then improve skeletal health. However, better understanding of the effects of UV supplementation must occur before implementation practically. This non-systematic literature review aimed to summarize the impacts of UV supplementation on the behavior, welfare, and production of laying hens, meat chickens (breeders and growers), and other domestic poultry species including directions for future research. The literature demonstrated that UVA light has positive impacts on reducing fear and stress responses but in some research, it significantly increases feather pecking over age during the production phase. UVB light will significantly improve skeletal health, but an optimum duration of exposure is necessary to get this benefit. Supplementation with UVB light may have more distinct impacts on egg production and eggshell quality when hens are experiencing a dietary vitamin D3 deficiency, or if they are at the terminal end of production. The relative benefits of UVB supplementation across different ages needs to be further verified along with commercial trials to confirm beneficial or detrimental impacts of adding UVA wavelengths. Further research is warranted to determine whether adding natural light wavelengths to indoor poultry production is indeed a positive step toward optimizing commercial housing systems.

Implications of Vitamin D Research in Chickens can Advance Human Nutrition and Perspectives for the Future

The risk of vitamin D insufficiency in humans is a global problem that requires improving ways to increase vitamin D intake. Supplements are a primary means for increasing vitamin D intake, but without a clear consensus on what constitutes vitamin D sufficiency, there is toxicity risk with taking supplements. Chickens have been used in many vitamin-D-related research studies, especially studies involving vitamin D supplementation. Our state-of-the-art review evaluates vitamin D metabolism and how the different hydroxylated forms are synthesized. We provide an overview of how vitamin D is absorbed, transported, excreted, and what tissues in the body store vitamin D metabolites. We also discuss a number of studies involving vitamin D supplementation with broilers and laying hens. Vitamin D deficiency and toxicity are also described and how they can be caused. The vitamin D receptor (VDR) is important for vitamin D metabolism; however, there is much more to understand about VDR in chickens. Potential research aims involving vitamin D and chickens should explore VDR mechanisms that could lead to newer insights into VDR. Utilizing chickens in future research to help elucidate vitamin D mechanisms has great potential to advance human nutrition. Finding ways to increase vitamin D intake will be necessary because the coronavirus disease 2019 (COVID-19) pandemic is leading to increased risk of vitamin D deficiency in many populations. Chickens can provide a dual purpose with addressing pandemic-caused vitamin D deficiency: 1) vitamin D supplementation gives chickens added-value with the possibility of leading to vitamin-D-enriched meat and egg products; and 2) using chickens in research provides data for translational research. We believe expanding vitamin-D-related research in chickens to include more nutritional aims in vitamin D status has great implications for developing better strategies to improve human health.

Effect of ultraviolet radiation on vertebrate animals: update from ethological and medical perspectives

Many animals under human care are kept indoors to prevent infectious diseases vectored by wildlife, facilitate environment control, or due to the lifestyle of their owners. However, ultraviolet radiation has documented effects on animal vision, vitamin synthesis, immunity, behavior, psychogenic disorders and on their environment. Ultraviolet-emitting lights are commercially available and the documentation of their effect on indoor-housed animals is increasing. This article reviews published information about ultraviolet effects in vertebrate animals from veterinary and ethological perspectives, and techniques used to assess ultraviolet exposure across animal taxa.

Vitamin D3 enhanced intestinal phosphate cotransporter genes in young and growing broilers

The influence of dietary vitamin D₃ (VD3) levels on growth, bone performance, and duodenal type IIb sodium-dependent phosphate cotransporter (NaPi-IIb) genes in broiler chicken were studied. One-day-old male Ross308 broilers (n = 432) were allocated into 6 treatment groups with each group consisting of 6 cage pens. Each treatment group received diet containing different amounts of VD3 (80, 200, 500, 1,250, 3,125, or 7,813 IU per kg of diet) from a day-old to 31 D of age. Dietary available phosphorus and calcium were kept the same across all treatments in each phase. At 14 D, influence of VD3 on BW gain was found in the birds that received VD3 of 3,125 IU/kg and 200 IU/kg (P < 0.05). Toe ash and tibia ash linearly increased (P < 0.05) at 14 D with increase in dietary VD3_. There was no significant influence of dietary VD3 on tibia breaking strength. In both phases, relative expression of duodenal NaPi-IIb linearly increased (P < 0.01) with increase in dietary VD3. At 14 D, highest expression of 3.2 folds was observed in birds treated with VD3 at 7,813 IU/kg of feed. At 31 D, birds that received VD3 levels of 3,125 and 7,813 IU/kg of feed showed 2.9 folds higher in NaPi-IIb expression compared with those fed lowest level of VD3 at 80 IU/kg of feed. When dietary calcium and phosphorus were maintained at the standard requirement, increase in dietary VD3 did not improve growth performance. For optimum growth and bone characteristics, dietary inclusion of VD3 at 500 IU/kg was adequate for both starter and grower broiler diets. Vitamin D₃ enhanced the expression of NaPi-IIb at higher doses and thus improving the tibia ash content in high VD3 treatment groups. This study reported for the first time an increased in the expression of duodenal NaPi-IIb in 31-day-old broilers in response to high dietary VD3 levels.

Developing a novel oral vitamin D3 intake bioassay to re-evaluate the vitamin D3 requirement for modern broiler chickens

The present study was conducted to develop a non-traditional vitamin D3 (D3) intake bioassay with the objective of increasing the precision of D3 delivery to the chickens. For this purpose, newly hatched chickens (5 birds per cage) were allocated in battery brooders and randomly distributed into 8 treatments and 6 replicates per treatment. A basal corn-soy diet devoid of D3 containing calculated calcium and non-phytate phosphorus concentrations of 0.90 and 0.45%, respectively, was fed throughout a 21-D period. The first 9 D of the study served to deplete the maternal stores of D3 followed by a 12-h fasting period. From day 10 to the end of the trial, the birds were gavaged with graded levels of D3 obtained from a highly purified pharmaceutical grade D3 standard (99.8%) purchased from Sigma-Aldrich and dissolved in corn oil. Daily gavage treatments were based on estimated intake of 0, 50, 100, 200, 400, 800, 1,600, and 3,200 IU D3/kg of feed consumed over the last 12 D of the study. Precise cholecalciferol intake per kg of diet was adjusted based on actual daily feed intake per pen of birds. Performance data were evaluated from day 10 to 21. Percent tibia bone ash (TBA), tibia breaking strength (TBS), total mineral content, and total bone mineral density were obtained at day 21. The D3 treatments improved (P < 0.05) weight gain and feed efficiency. There was no linear or quadratic effect for any of the productivity performance variables. Graded levels of D3 improved (P < 0.05) TBA and TBS. Both were linearly increased (P < 0.05) in response to graded levels of D3. A quadratic response was observed for TBS only. Under the conditions of the present experiment and the average of 3 regression models, the D3 requirement for starter broilers was estimated at 285 IU D3/kg of feed when bone mineralization responses (TBA and TBS) were used as criteria to estimate the requirement.

Influence of light sources on body characteristics of female Japanese quail (Coturnix coturnix japonica) in different reproductive ages

The aim of the study was to evaluate the influence of different light sources on organ characteristics, bone development, chemical body composition and hepatic function of female Japanese quail (Coturnix coturnix japonica) in different reproductive ages. In total, 210 female 1-day-old birds were housed in a brick shed, which was divided into six rooms during 12 weeks. Each room was equipped with a different type of light bulb (incandescent; compact fluorescent; and white, blue, red and green light-emitting diodes (LEDs)) and contained seven cages with five birds in each. The light intensity was 15 lx and the photoperiod was 23 h light and 1 h dark (23L:1D) during the first week, 10 L:14D from the second to the fifth week, and 17L:7D until the end of the experiment. The experimental design was completely randomised, with six treatments and seven replicates of each bird. The morphophysiological conditions of the birds were evaluated at the beginning (8 weeks) and during peak production (12 weeks). At 8 weeks, a higher intestine weight and length and liver weight were observed in birds maintained in white LED (P &lt; 0.05). Lower breast weight (P &lt; 0.01) was also observed with this type of lamp. White and red LEDs decreased (P &lt; 0.05) the percentage of ash in the tibia, but this reduction did not affect (P &gt; 0.05) bone resistance. At 12 weeks, higher bone resistance was obtained (P &lt; 0.01) with white LED and higher eye diameter was observed (P &lt; 0.05) with incandescent and white LED lamps. There was no influence (P &gt; 0.05) of light sources on the circulating levels of aspartate aminotransferase and alanine aminotransferase. Fluorescent bulbs resulted in the highest (P &lt; 0.05) level of γ-glutamyltransferase, while blue LED resulted in the lowest level. There was no influence (P &gt; 0.05) of light sources on chemical body composition in any of the evaluated ages. It was concluded that the photostimulation of Japanese quail with white LED is more efficient to stimulate their organ development, especially the intestine, until 8 weeks of life, resulting in birds with better bone development during peak production.

THE EFFECT OF UVB RADIATION ON SERUM VITAMIN D AND IONIZED CALCIUM IN THE AFRICAN SPOONBILL (PLATALEA ALBA)

Metabolic bone disease (MBD) was diagnosed in two chicks produced by a captive breeding colony of African spoonbills (Platalea alba). The birds were housed indoor during the winter breeding season and had no access to natural sunlight. When the index cases occurred, the nesting birds and chicks had a mean 25-hydroxyvitamin D (25-OHD) concentration of 9.9 ± 2.7 nmol/L and a mean ionized calcium (iCa) concentration of 0.98 ± 0.12 mmol/L (winter pretreatment). For comparison purposes, serum was collected the following summer; mean 25-OHD was 20.8 ± 3.9 nmol/L and mean iCa was 1.32 ± 0.05 mmol/L (summer). During the following breeding season, ultraviolet B (UVB) lighting was provided to the flock, resulting in a mean 25-OHD of 19.0 ± 5.6 nmol/L and mean iCa of 1.23 ± 0.06 mmol/L (winter treatment 1). Both 25-OHD and iCa were significantly higher compared with winter pretreatment, and 25-OHD was not significantly different from summer, indicating that treatment during the winter months succeeded in increasing 25-OHD levels to summer levels. However, winter treatment 1 and summer iCa were significantly different. During the next breeding season (winter treatment 2), the birds were exposed to a light with higher UVB output. The mean 25-OHD of the flock was 16.5 ± 7.2 nmol/L, and the mean iCa increased to 1.34 ± 0.04 mmol/L. Both were comparable to summer values. Healthy chicks were hatched during both breeding seasons, and no further cases of MBD occurred during the course of the study. Provision of a UVB light source to captive African spoonbills maintained indoors during the winter months can increase 25-OHD and iCa to levels equivalent to those seen in the summer months, when birds have unrestricted access to natural sunlight. UVB lighting is recommended for all breeding spoonbills that do not have access to natural sunlight.

Increasing dietary vitamin D3 improves the walking ability and welfare status of broiler chickens reared at high stocking densities

A study was conducted to evaluate the effects of varying dietary vitamin D3 and stocking density on growing performance, carcass characteristics, bone biomechanical properties, and welfare responses in Ross (308) broilers. Experimental diets, containing 1, 10, or 20 times the NRC recommended level of vitamin D3 (200 IU/kg), were formulated with low, medium, or high vitamin D3 levels for 3 growing phases. Two stocking densities were 10 and 16 birds/m(2). One-day-old hatchlings (1,872 males) were randomly assigned to 6 pens in each treatment. Results showed that high stocking density decreased the feed intake, BW gain (P < 0.01), breast muscle yield (P = 0.010), and tibial development (P < 0.01), whereas increasing feed conversion ratio (P < 0.001), and the scores of gait, footpad and hock burn, and abdominal plumage damage (P < 0.01), particularly toward the age when birds attained their market size. Increasing dietary vitamin D3 improved the birds' walking ability and tibial quality (P < 0.05), and reduced the development of footpad or hock dermatitis and abdominal plumage damage (P < 0.01), some aspects of which were age-dependent and appeared to vary with stocking density. These data indicate that increasing supplemental vitamin D3 has a favorable effect on walking ability and welfare status of high stocking density birds, but not on performance.

Effects of 25-hydroxycholecalciferol and soy isoflavones supplementation on bone mineralisation of quail

1. The effects of 25-hydroxycholecalciferol (25-OH-D(3)) and soy isoflavones supplementation on performance, carcase recovery, bone mineral density, and tibia ash, Ca, P, and serum vitamin D concentrations and alkaline phosphatase activity in the Japanese quail (Coturnix coturnix japonica) exposed to high ambient temperature were evaluated. 2. A total of 270 ten-d-old Japanese quail were randomly assigned to 9 treatment groups, 6 replicates of 5 birds each in a 2 x 3 x 3 factorial arrangement of treatments. Birds were kept in a temperature-controlled room at either 22 degrees C (thermo-neutral) or 34 degrees C (heat stress) for 8 h/d (09:00-17:00 h) and given a basal (control) diet or the basal diet supplemented with one of three levels of 25-OH-D(3) (0, 250 and 500 IU/kg of diet) combined with one of three levels of soy isoflavones (0, 400 and 800 mg/kg of diet). 3. Birds kept at 34 degrees C consumed less feed and gained less weight than control birds. An increase in body weight, feed intake (and improvement in feed efficiency and carcase recovery were found in soy isoflavones and 25-OH-D(3)-supplemented quail reared under heat stress conditions. Bone mineral density, tibia ash, Ca, and P were linearly improved by 25-OH-D(3) and soy isoflavones supplementation in both thermoneutral and heat stress groups. Serum vitamin D levels and alkaline phosphatase activity were improved by 25-OH-D(3) and soy isoflavones supplementation in both thermoneutral and heat stress groups in quail. 4. In conclusion, a combination of 25-OH-D(3) and soy isoflavones supplementation to basal diet significantly improved bone mineralisation in quail.

The Vitamin D3 Requirement of Broiler Breeders

An experiment was conducted with 25- to 66-wk-old Ross broiler breeders in an environment excluding ultraviolet light to determine the cholecalciferol (D3) requirements for hen day egg production; hatchability; body weight of the progeny at 1 d; embryo mortality during the early (1 to 10 d of incubation), middle (11 to 15 d of incubation), and late stages (16 to 21 d of incubation) of development; egg weight; specific gravity; and body ash of the progeny at 1 d of age. Five levels of vitamin D3 (125, 250, 500, 1,000, and 2,000 IU/kg of diet) were fed to hens from 25 to 66 wk of age. One additional group was fed no supplemental D3 until 36 wk of age and was then changed to 4,000 IU/kg of diet. Separate regression analyses were performed for wk 27 to 36 (peak original design) and for wk 37 to 66 (postpeak production modified design). The D3 levels for the predicted maximum hen day egg production during peak and postpeak were 1,424 and 2,804 IU/kg, respectively. The D3 levels for the predicted maximum hatchability were 1,390 IU/ kg (peak) and 2,708 IU/kg (postpeak). The level of D3 that resulted in the minimum early embryo mortality was 1,288 IU/kg at peak; however, no significant effect was observed at postpeak. The D3 levels for minimum middle stage embryo mortality were 1,130 IU/kg (peak) and 2,568 IU/kg (postpeak) and for late stage embryo mortality were 1,393 IU/kg (peak) and 2,756 IU/kg (postpeak). The D3 level for maximum egg weight was 1,182 IU/kg (peak) and for specific gravity was 1,337 IU/kg (peak) and >2,000 IU/kg (postpeak). The D3 level for maximum body ash of progeny at d 1 was >2,000 IU/kg. Analysis of the data from the original design of the experiment (treatments providing 0, 125, 250, 500, 1,000, and 2,000 IU of vitamin D3/kg for the 27- to 36-wk-old birds) indicates a requirement of approximately 1,400 IU of D3/kg of feed for broiler breeder hens. When the data from the modified experiment (37 to 66 wk of age) include conversion of the treatment provided at 0 IU of D3/kg to a treatment providing 4,000 IU of D3/kg, the requirement may be approximately 2,800 IU of D3/kg.

Effect of the level of cholecalciferol supplementation of broiler breeder hen diets on the performance and bone abnormalities of the progeny fed diets containing various levels of calcium or 25-hydroxycholecalciferol

Four experiments were conducted using Ross x Ross chicks hatched from broiler breeder hens fed various levels of cholecalciferol (vitamin D3; 0 to 4,000 IU/kg of diet) to determine the effect of the maternal diet on the performance and leg abnormalities of the progeny. Chicks hatched from eggs laid by the hens at different ages were used in experiments 1 to 4. The studies were conducted in an ultraviolet light-free environment as split plot designs, with Ca levels or 25-hydroxycholecalciferol (25-OHD3) in the chicks' diet as the whole plot, and vitamin D3 in the maternal diet as a subplot. Chicks in experiments 1 and 2 were fed 2 levels of Ca (0.63% or 0.90%) and chicks in experiments 3 and 4 were fed 6 levels of 25-OHD3 (0 to 40 microg/kg of diet). Significant increases in body weight gain (BWG) of the progeny were observed in experiments 1, 2, and 4 as the vitamin D3 level in the maternal diet increased. Chicks hatched from eggs laid by hens fed the highest levels of D3 had the highest tibia ash. Significant reductions in Ca rickets incidence (experiments 1 and 2) and tibial dyschondroplasia (TD) incidence (experiment 1) were observed as the level of vitamin D3 in the maternal diet increased. Chicks fed lower levels of Ca had lower BWG and tibia ash and higher incidences of TD and Ca rickets than chicks fed higher levels of Ca. Increasing the level of 25-OHD3 in the chicks' diet significantly improved BWG, tibia ash, and plasma Ca and reduced TD and Ca rickets incidence. An overall evaluation of the study indicates that chicks from hens fed the highest levels of vitamin D3 and fed high levels of Ca or 25-OHD3 had the highest BWG, tibia ash, and plasma Ca, and the lowest incidences of TD and Ca rickets.

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.

Effects of vitamin D3 dietary supplementation of broiler breeder hens on the performance and bone abnormalities of the progeny

Six experiments were conducted using Ross x Ross chicks hatched from eggs laid by broiler breeder hens fed various levels of vitamin D3 (0 to 4,000 IU/kg of diet) to determine the effects of vitamin D3 level in the maternal diet on the performance and leg abnormalities of their progeny. Chicks hatched from eggs laid when hens were 27, 41, 29, 36, 45, and 52 wk of age were used in experiments 1, 2, 3, 4, 5, and 6, respectively. The studies were conducted in a ultraviolet (UV)-light-free environment. Experiments 1 and 2 were conducted as complete randomized designs with the maternal diets as the treatments, and experiments 3, 4, 5, and 6 were conducted as split plot designs, with vitamin D3 in the chick diets as the whole plot and vitamin D3 in the maternal diet as a subplot. Chicks in experiments 1 and 2 were fed a vitamin D3-deficient diet, whereas chicks in experiments 3 and 4 were fed 4 levels of vitamin D3 (0 to 400 IU/kg of diet), and chicks in experiments 5 and 6 were fed 6 levels of vitamin D3 (0 to 3,200 IU/kg of D3). The highest body weight gains and tibia ash were observed in chicks hatched from hens fed the highest levels of vitamin D3 in all experiments. Reductions in the incidence of Ca rickets were observed in experiments 3 and 6, whereas increases in tibia ash were observed in experiments 2 and 6 as the level of vitamin D3 in the maternal diet increased. Body weight gain and tibia ash increased and Ca rickets incidence decreased as the vitamin D3 level in chick diets increased. An evaluation of the study indicates that chicks hatched from eggs laid by hens fed 2,000 or 4,000 IU of D3/kg as the maximum level of vitamin D3 had the highest body weight gains, and chicks fed 3,200 IU had the highest body weight and tibia ash and the lowest TD and Ca rickets incidences.

The effect of particle size of commercial soybean meal on performance and nutrient utilization of broiler chicks

An experiment was conducted to determine the effects of soybean meal (SBM) particle size on broiler performance, particularly P utilization. This experiment utilized a 2 x 2 x 2 factorial design with the following variables: SBM particle size, P level, and diet type, either corn-SBM or semipurified. SBM was obtained from a processing plant before (geometric mean diameter 1,239 microm) and after (891 microm) hammer milling. The P levels were 0.5% total P for deficient diets and 0.7% total P for adequate P diets. The coarse SBM improved bone ash (P < 0.05), gain:feed ratios (P < 0.1), and plasma P levels (P < 0.1). The diets with 0.5% P resulted in overall poorer performance as 16-d BW was reduced, gain:feed ratio decreased, bone ash decreased, and rickets incidence increased. Chicks fed the semipurified diets also had lower 16-d BW, lower gain-to-feed ratio, and lower bone ash. There was a significant interaction between the diet type and the soy particle size when the corn-SBM meal diets were fed because the coarse SBM increased plasma P levels, whereas there was little effect when the semipurified diets were fed. There were also significant interactions observed between these variables on growth and gain:feed ratio in that the coarse SBM elicited a much more dramatic response when incorporated into the semipurified diets as opposed to the corn-SBM diets. The results suggest that large particle size soybean meal may be more efficiently utilized than fine particle size soybean meal.

Effectiveness of twenty-five-hydroxycholecalciferol in the prevention of tibial dyschondroplasia in Ross cockerels depends on dietary calcium level

Five experiments were conducted to evaluate the efficacy of 25-hydroxycholecalciferol [25-(OH)D3] to minimize the development of tibial dyschondroplasia (TD) and improve phytate phosphorus retention in Ross cockerels during the starter period. In experiment 1, chicks were fed a TD-inducing (0.67% calcium) diet with or without exposure to ultraviolet light and no supplemental cholecalciferol. Dietary 25-(OH)D3 was added at 0, 10, or 70 microg/kg for both light treatments. In experiment 2, 25-(OH)D3 was added at 0, 10, 40, or 70 microg/kg to a TD-inducing diet containing 27.5 microg/kg added cholecalciferol. Experiment 3 was similar to experiment 2 except a diet marginal (0.85%) in calcium was fed, and cholecalciferol was added at 55 microg/kg. In experiments 4 and 5, 25-(OH)D3 was added at 0, 18, 36, 54, 72, or 90 microg/kg to a diet marginal in calcium. Dietary 25-(OH)D3 decreased the incidence of TD similarly at 40 and 70 microg/kg 25-(OH)D3 and improved phytate phosphorus retention when the TD-inducing diet was fed. The incidence of TD was decreased when 70 microg/kg 25-(OH)D3 was added to a diet marginal in calcium in experiment 3 only. Phytate phosphorus retention was generally not affected by dietary 25-(OH)D3 when a diet containing marginal calcium, adequate phosphorus, and high cholecalciferol was fed. The effectiveness of 25-(OH)D3 to reduce the incidence of TD in young broilers was higher when the dietary calcium level was below 0.85%. The incidence of TD in Ross cockerels was low (< 25%) when dietary calcium was greater than 0.85%.

The expression of calbindin in chicks that are divergently selected for low or high incidence of tibial dyschondroplasia

Three experiments were conducted with broiler chicks that were divergently selected for low or high incidence of tibial dyschondroplasia (LTD and HTD, respectively) to determine if the expression of intestinal calbindin-28 kD mRNA and protein differed between the 2 strains. In addition, levels of intestinal vitamin D receptor mRNA and plasma thyroid hormone concentrations were also examined. In experiment 1, LTD and HTD chicks were fed a corn-soybean meal diet that was adequate in all nutrients except cholecalciferol (D3), which was titrated to 5 or 40 microg/kg diet in a completely randomized 2 x 2 factorial arrangement. At 4 and 8 d of age, HTD chicks fed 5 microg of D3/kg of diet had a lower (P < 0.05) expression level of calbindin-28 kD mRNA than the LTD chicks fed the same diet. At 4 and 8 d of age, HTD chicks fed 5 microg of D3 had the lowest intestinal expression of calbindin-28 kD protein. Expression of vitamin D receptor mRNA did not differ for broiler strains at either level of D3 supplementation. In experiment 2, there was no significant difference in the expression of calbindin-28 kD mRNA or vitamin D receptor mRNA between day-of-hatch LTD, HTD, and commercial broiler chicks. Experiment 3 was similar in design to the first experiment except that the birds were fed for 18 d. Calbindin-28 kD and vitamin D receptor mRNA expression levels at 18 d were similar to those observed in experiment 1. Plasma triiodothyronine and free-triiodothyronine concentrations were greater for LTD chicks, regardless of dietary D3 supplementation levels. These results suggest that divergent selection of broilers for LTD or HTD alters the physiological response to nutritionally inadequate levels of dietary D3.

Effects of u.v. irradiation of very young chickens on growth and bone development

Six experiments were conducted to study the effects of exposure of young chickens to u.v. radiation. Chickens were fed a cholecalciferol (D3)-deficient diet and exposed to u.v. radiation from fluorescent lights giving total radiance (285-365 nm) at 0.15 m of 99.9 mJ/s per m(2). In Expt 1, chickens had increased body weight, bone ash and plasma Ca and decreased incidence of rickets and tibial dyschondroplasia (TD) when exposed to fluorescent light radiation 24 h per d, 24 h every 2 d, or 24 h every 3 d starting with exposure on day 1 after hatching. However, when not exposed on day 1, but on days 4, 7, 10, 13 and 16, the bone ash was reduced, and the incidence of TD and rickets was increased, compared with chickens exposed on day 1 after hatching. When chickens were exposed at 1 d of age to radiation from two lamps, each of which gave a radiance (285-365 nm) at 0.26 m of 856 mJ/s per m(2), both the length of time of radiation and location of the lamps (above or below the chicken) influenced the response as measured by body weight, bone ash, plasma Ca and incidence of rickets. When chickens that received a TD-inducing diet were exposed to 30 min u.v. radiation from below at 1 d of age they developed significantly less TD than did those not exposed when fed either 27.5 or 55.0 microg D3/kg diet.

Graded levels of phytase past industry standards improves broiler performance

This study evaluated the overall performance of 0-to-16-d-old, mixed-sex, Cobb x Cobb broiler chicks when dietary phytase levels were supplemented in excess of industry standards. The experimental diet used consisted of a basal corn-soybean meal diet that contained an analyzed 22.2% CP, 0.88% Ca, a deficient total P (tP) level of 0.46% (phytate P = 0.272%), and calculated ME of 3.123 kcal/g diet on an as-is basis. In addition to a positive control diet [0.70% tP], the dietary phytase levels evaluated were 0, 93.75, 187.5, 350, 750, 1,500, 3,000, 6,000, and 12,000 U/kg of diet. Supplementing phytase from 0 to 12,000 U significantly increased body weight gain from 287 to 515 g/chick, feed intake from 381 to 595 g/chick, gain to feed from 0.755 to 0.866, plasma P from 2.5 to 7.1 mg/100 mL, tibia ash from 26 to 41%, tibia ash weight from 0.200 to 0.601 g/tibia, tP retention from 51 to 80%, phytate P disappearance from 40% to 95%, apparent N retention from 58 to 78%, AMEn from 3,216 to 3,415 kcal/kg diet, and reduced P rickets from 80 to 3%. Using nonlinear regression analysis on log-transformed phytase levels, gain to feed, apparent N retention, and AME, responded linearly with respective R2 values of 0.76, 0.82, and 0.72, whereas body weight gain, feed intake, plasma P, P rickets, tP retention, phytate P disappearance, tibia ash percentage, and tibia ash weight responded quadratically with respective R2 values of 0.93, 0.88, 0.85, 0.84, 0.91, 0.96, 0.96, and 0.98. Few statistical differences existed between response data for broilers consuming the positive control diet or diets containing 1,500 to 12,000 U of phytase (P > 0.05). This finding indicates that broilers consuming a tP-deficient corn-soybean meal diet can achieve maximum performance when phytase is supplemented to 12,000 U/kg diet and that current phytase supplementation levels within the poultry industry may need to be reevaluated.

Studies on the efficacy of cholecalciferol and derivatives for stimulating phytate utilization in broilers

Studies were conducted to determine the effect of dietary supplementation with cholecalciferol (D3), 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], 1alpha-hydroxycholecalciferol (1alpha-OHD3), and 25-hydroxycholecalciferol (25-OHD3) on utilization of phytate P by broiler chickens. Three experiments were conducted with corn-soybean meal type diets with D3 and 1,25-(OH)2D3 being tested in one experiment and 1,25-(OH)2D3, 1alpha-OHD3, and 25-OHD3 being tested in two experiments of exactly the same design. In the first experiment, high levels of D3 (110 microg and 220 microg/kg of diet) increased phytate P utilization, but the increase was not as great as that obtained from 1,25-(OH)2D3 supplementation. In the other two experiments, 1,25-(OH)2D3, D3 and 1alpha-OHD3 were consistently effective in increasing phytate P utilization as measured by plasma Ca and P, incidence of P rickets, bone ash, and retention of Ca, P, and phytate P. Supplementation with 25-OHD3 in general gave smaller and more inconsistent responses to these criteria, indicating some inconsistency in its ability to improve phytate P utilization.

Quantitative evaluation of 1-alpha-hydroxycholecalciferol as a cholecalciferol substitute for broilers

Two experiments were conducted using a corn-soybean meal diet that meets or exceeds the NRC (1984) requirements for all nutrients except cholecalciferol (D3) to determine the effectiveness of 1-alpha-hydroxycholecalciferol (1alpha-OHD3) as a substitute for D3 in the diet of young broilers. Ross x Ross mixed-sex, 1-d-old chicks were reared in Petersime battery brooders not exposed to ultraviolet light with feed and water supplied ad libitum for 16 d. In Experiment 1, D3 was fed at 0, 2.5, 5, 10, 20, and 40 microg/kg and one source of 1alpha-OHD3-(Hoffmann-LaRoche, Inc.; HLR) was fed at 0.625, 1.25, 2.5, 5, and 10 microg/kg of diet. In Experiment 2, the D3 was fed at 0, 2.5, 5, and 10 microg and two sources of 1alpha-OHD3-[HLR and Majestic Research Inc. (MRI)] were fed at 0, 0.625, 1.25, and 5 microg/kg of diet. Slope ratio analysis of data from the measurement of 16-d body weight, plasma Ca, rickets, and bone ash indicated bioavailability of the 1alpha-OHD3 as compared to D3 from 1.88 to 21.2. Percentage bone ash gave the most precise values in both experiments. Considering all the data from both experiments, the 1alpha-OHD3 appears to be approximately eight times as effective as D3 for satisfying the requirements of several criteria in two experiments with broiler chickens.

Evaluation of cholecalciferol sources using broiler chick bioassays

Three experiments were conducted to test the potencies of nine sources of cholecalciferol using a chick bioassay. The tested products were compared with a Sigma Reference Standard (SRS). All of the diets fed to the chicks were prepared from corn-soybean meal. Each of the products was in premix form containing cholecalciferol. Their physical characteristics reflected the methods used to produce the premixes. They were categorized as spray-dried or drum-dried in the beadlet or flake form. Basal diets without cholecalciferol were used in all experiments. For Experiments 1 and 2, the designs were a 2 x 3 factorial arrangement using three different cholecalciferol products and two levels of 200 and 400 IU/kg dietary cholecalciferol. For both experiments, three additional SRS levels of 600, 800, and 1,000 IU/kg were included in the studies as positive controls as there is a possibility that the cholecalciferol products being tested may exhibit activity higher than the amount stated. In Experiment 3, a 3 x 4 factorial arrangement was used, which was represented by three cholecalciferol products and four levels of dietary cholecalciferol at 150, 300, 600, and 1,200 IU/kg. By using the slope ratio analysis, the potencies of the products from the three experiments were between 86 and 118%. In Experiment 3, the requirement of chicks for cholecalciferol using the three tested products, as determined by a nonlinear regression model based on bone ash, were 843+/-85, 911+/-106, and 986+/-131 IU/kg of diet as compared with 915+/-82 IU/kg when using the SRS. The results from these studies indicate that the chemical assays used to determine the cholecalciferol activity of these products were very reliable.

Nutrition and skeletal problems in poultry

Several excellent reviews regarding nutrition and skeletal disorders have appeared in the last 20 yr. This review will cover several areas of vitamin D research, the area of feed deprivation, and bone abnormalities, because there has been considerable interest in these areas during the past 10 yr. Studies indicate that the quantitative requirement for cholecalciferol (D3) for broiler chickens is much greater than previously thought. Ascorbic acid may play a role in stimulating 1-hydroxylation of 25-hydroxycholecalciferol [25-(OH)D3], but the evidence is not clear under exactly what conditions this relationship is important in practical prevention of tibial dyschondroplasia. Studies indicate that dietary supplementation with 1,25-dihydroxycholecalciferol [1,25(OH)2D3] will reduce the incidence of tibial dyschondroplasia in three different strains of broilers bred to develop a high incidence of the disease. But it did not prevent the disease totally in the strains, unless high enough levels of 1,25-(OH)2D3 were fed to reduce growth rate. These studies indicate that these high tibial dyschondroplasia strains have a defect(s) in vitamin D metabolism. Studies continue to elucidate the role of ultraviolet light in preventing leg abnormalities. Only a few studies have been conducted on the efficacy of various vitamin D3 derivatives to prevent tibial dyschondroplasia. Feed deprivation continues to be an intriguing method of preventing tibial dyschondroplasia, and examination of exactly how this prevents the bone abnormality could open avenues for explaining the disease.

Composition of vitamin supplements in Spanish poultry diets

1. The composition of 106 vitamin supplements used in about 85% of the Spanish poultry production diets were studied. Vitamin supplements were grouped by production classes and, for broilers and pullets, also by feeding periods. 2. Four vitamins (niacin, alpha-tocopherol, pantothenic acid, and riboflavin) comprised over 87% of the vitamin supplements by weight (choline excluded), whereas alpha-tocopherol and retinol represented from 51% to 60% of the total vitamin cost. 3. The highest and lowest vitamin supplementation rates were for broilers in the starter and withdrawal periods (106 and 44 mg/kg, respectively) and the mean values for breeders, pullets and layers were 104, 58, and 48 mg/kg, respectively. 4. Supplements with higher vitamin contents showed less variability in their composition. Retinol, cholecalciferol, riboflavin and pantothenic acid showed the lowest variability within supplements (6% to 36% CV), whereas alpha-tocopherol, menadione, thiamin and biotin showed the highest (40% to 224% CV). 5. Vitamin supplementation rates were compared with requirements, taking into account the dietary contribution. In general, vitamin fortification exceeded the NRC recommendations, using a high safety margin for some vitamins such as vitamin A (from 2.6 to 7.8) and for some poultry classes such as breeders (3.2).

Effects of steam pelleting and extrusion of feed on phytate phosphorus utilization in broiler chickens

Three experiments were conducted to determine the effects of pelleting and extrusion of feeds on the utilization of phytate P by broilers. The first experiment investigated the effects of pelleting the whole corn-soybean meal (SBM) diet, the corn, or SBM separately on phytate P utilization. The P-deficient basal diet contained 0.5% total P and 0.2% phytate P. Steam pelleting the whole diet, the corn, or SBM separately did not decrease the severity of the P deficiency obtained and there were no indications of increased phytate P utilization. In the second experiment, the whole corn-SBM P-deficient diet was extruded. Extrusion of the diet did not influence bone ash and P rickets, both sensitive criteria of P deficiency. Extrusion decreased Ca, P, and phytate P retention and decreased the ME value of the diet. In the third experiment, phytate P retention by chickens fed three commercial pelleted diets was compared to chicks fed the corn-SBM P-deficient diet. Phytate P retention by the chickens fed the commercial diets was much lower than retention by chickens fed the corn-SBM P-deficient diet. These studies gave no indication that pelleting or extrusion of corn-SBM diets would increase phytate P utilization by broiler chickens.

Vitamin D3 requirement of young chicks receiving diets varying in calcium and available phosphorus

1. Three battery experiments were conducted with broiler chicks during the 2nd and 3rd week of life. Graded amounts of cholecalciferol (D3) were added to maize-soyabean meal diets that were designed to be (a) severely deficient in available phosphorus (P), (b) marginally deficient in calcium (Ca) or (c) adequate in both available P and Ca. 2. With diets containing 1.0 g available P and 6.3 g Ca/kg (assay 1), graded doses of D3 between 0 and 37.5 mu/kg produced linear (P < 0.05) positive responses in both weight gain and tibia ash. With a D3 concentration of 1250 micrograms/kg, 250 times the requirement recommended by the NRC, bone ash was increased (P < 0.05) over that of birds fed 37.5 micrograms/kg, and neither weight gain nor food intake were reduced. 3. With a P-adequate diet (4.5 g available P/kg) containing 8.5 g Ca/kg (assay 2), weight gain and bone ash increased linearly (P < 0.05) upon supplementing the basal diet with 0, 2.5 and 5.0 micrograms D3/kg. Higher doses of D3 did not elicit further responses, and chicks fed on a diet containing 1250 micrograms D3/kg gained as fast and had bone ash values that did not differ from those of chicks receiving 5, 10, 20 or 40 micrograms D3/kg. 4. When the maize-soyabean meal basal diet was fortified with Ca and P to achieve adequate amounts of Ca (10.1 g/kg) and P (4.5 g available P/kg) in assay 3, dietary additions produced results similar to those obtained in assay 2 where P was adequate and Ca was slightly deficient. Again, chicks receiving a surfeit of D3 (1250 micrograms/kg) exhibited weight gains and bone ash values that were as great as those of chicks receiving 5, 10, 15 or 30 micrograms D3/kg. 5. It is apparent that young chicks have a high tolerance for excess D3, and chicks fed on diets that are severely deficient in available P continue to respond to D3 in excess of 37.5 micrograms/kg.

Effects and interactions of dietary levels of vitamins A and E and cholecalciferol in broiler chickens

Four experiments were conducted to determine the effects and interactions of feeding different levels of vitamins A, cholecalciferol (vitamin D3), and E on broiler chicks. In Experiment 1, chicks were fed marginal vitamin D3 (500 IU/kg) and increasing dietary levels of vitamin A (5,000, 10,000, 20,000, 40,000, 80,000, and 160,000 IU/kg). Bone ash was reduced by 10,000 IU/kg of vitamin A in the diet and at vitamin A levels above 20,000 IU/kg of diet body weight was reduced. In Experiment 2, two levels of vitamin A (1,500 and 15,000 IU/kg) and six levels of vitamin E (10, 500, 1,000, 2,500, 5,000, and 10,000 IU/kg) were added to the basal diet. High levels of vitamins A and E significantly (P < 0.001) reduced bone ash. The vitamin A x E interaction was significant (P < or = 0.05) for rickets. In Experiment 3, the same two levels of vitamin A as Experiment 2 and six levels of vitamin D3 (500, 1,000, 1,500, 2,000, 2,500, and 3,000 IU/kg) were added to the basal diet that contained 10,000 IU/kg of vitamin E. Body weight and bone ash were increased by increasing vitamin D3 with a corresponding reduction (P < or = 0.05) in rickets. In Experiment 4, three levels of vitamin A (1,500, 15,000, and 45,000 IU/kg), three levels of vitamin D3 (500, 1,500, and 2,500 IU/kg), and three levels of vitamin E (10, 5,000, and 10,000 IU/kg) were added to the basal diet. Significant negative responses (P < or = 0.05) to increasing dietary vitamin A were observed for bone ash, rickets, and plasma and liver vitamin E. A significant (P < 0.001) increase in bone ash and plasma calcium with a corresponding reduction in rickets was observed by increasing vitamin D3. Increasing dietary vitamin E adversely affected (P < or = 0.01) bone ash, plasma calcium, and plasma and liver vitamin A concentrations. These results indicate the need for making feed with the proper ratios of vitamins A, D3, and E.

Effects of different levels of vitamins A and E on the utilization of cholecalciferol by broiler chickens

Three experiments were conducted to determine the effects of high dietary levels of vitamins A and E on the utilization of cholecalciferol by broiler chicks. In Experiment 1, chicks were fed six levels of vitamin A (5,000, 10,000, 20,000, 40,000, 80,000, and 160,000 IU/kg). Cholecalciferol (vitamin D3) was not added to the basal diet but all birds were exposed to ultraviolet (UV) fluorescent light. Body weight was decreased only at levels of vitamin A of 80,000 IU/kg or above. In Experiment 2, birds were exposed to UV fluorescent light or no UV light, two levels of dietary vitamin A (1,500 and 45,000 IU/kg) and three levels of dietary vitamin D3 (0, 500, and 2,500 IU/kg) in a 2 x 2 x 3 factorial arrangement. The high level of vitamin A reduced (P < 0.001) bone ash but only at a marginal level of vitamin D3 (500 IU/kg) and when the birds were not exposed to UV light. In Experiment 3, birds were exposed to UV fluorescent light or no UV light, two levels of dietary vitamin E (10 and 10,000 IU/kg) and three levels of dietary vitamin D3 (0; 500 and 2,500 IU/ kg) in a 2 x 2 x 3 factorial arrangement. The high level of vitamin E significantly (P < 0.05) reduced body weight, bone ash, plasma calcium, and increased rickets but only at 500 IU/kg of vitamin D3. Feeding 2,500 IU/kg of vitamin D3 overcame the effects of the high level of vitamin E, causing a significant (P < 0.05) interaction. Ultraviolet light also prevented the detrimental effects of the high level of vitamin E. The results of these studies indicate that high dietary levels of vitamins A and E negatively affected the utilization of vitamin D3 only when D3 was present at a marginal level (500 IU/kg) in the diet but not when it was synthesized in the bird by exposure to UV light or supplemented at 2,500 IU/kg in the diet.

The influence of vitamin A on the utilization and amelioration of toxicity of cholecalciferol, 25-hydroxycholecalciferol, and 1,25 dihydroxycholecalciferol in young broiler chickens

Three experiments were conducted to determine the influence of vitamin A on the utilization and amelioration of toxicity of cholecalciferol (vitamin D3), 25-hydroxycholecalciferol [25-(OH)D3], and 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] in young broiler chicks. Two levels of vitamin A (1,500 and 45,000 IU/kg or 450 and 13,500 microg) were fed in all experiments. In Experiment 1, chicks were fed six levels of vitamin D3 (0, 5, 10, 20, 40, and 80 microg/kg). High dietary vitamin A decreased bone ash (P < 0.001), and increased the incidence of rickets (P < or = 0.02). Linear and quadratic responses to vitamin D3 levels were significant (P < 0.01) for body weight, bone ash, incidence and severity of rickets, and plasma calcium. In Experiment 2, six levels of 25-(OH)D3 (0, 5, 10, 20, 40, and 80 microg/kg) were added to the basal diet. Adding 25-(OH)D3 increased (P < 0.001) body weight, bone ash, and plasma calcium, and decreased rickets and plasma vitamin A. Adding 25-(OH)D3 overcame the reduction in bone ash produced by high dietary vitamin A showing a significant (P < 0.02) interaction. In Experiment 3, six levels of 1,25-(OH)2D3 (0, 2, 4, 8, 16, and 32 microg/kg) were added to the basal diet. High dietary vitamin A increased (P < 0.01) the incidence and severity of rickets. Adding 1,25-(OH)2D3 increased (P < 0.01) body weight, bone ash, plasma calcium, and reduced rickets and plasma and liver vitamin A. Adding 1,25-(OH)2D3 overcame the reduction in bone ash, and the increase in rickets produced by high vitamin A was significant (P < or = 0.05). These results indicate that high dietary vitamin A (45,000 IU/kg) interferes with the utilization of vitamin D3, 25-(OH)D3 and 1,25-(OH)2D3, increasing the requirement for each of them. Moreover, 45,000 IU/kg of dietary vitamin A ameliorated the potential toxic effects of feeding high levels of vitamin D3, 25-(OH)D3 and 1,25-(OH)2D3 to young broiler chickens. Further work is necessary to find the minimum levels of these vitamins needed to cause these effects.

Effect of 1,25-dihydroxycholecalciferol, cholecalciferol, and fluorescent lights on the development of tibial dyschondroplasia and rickets in broiler chickens

Experiments were conducted to determine whether dietary 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] will alleviate a cholecalciferol deficiency induced by low dietary cholecalciferol and no fluorescent lighting and to determine cholecalciferol requirements as influenced by fluorescent lighting or 1,25-(OH)2D3. In each study, nutritionally complete basal diets were fed to broiler cockerels from 1 to 16 d of age. Experiment 1 had a 2 x 2 x 2 factorial arrangement of treatments with 1,25-(OH)2D3 at 0 and 10 micrograms/kg, cholecalciferol at 2.75 and 27.5 micrograms/kg, and fluorescent lights on or off. Experiments 2 to 4 had four levels of dietary cholecalciferol (0, 5.0, 27.5, and 50.0 micrograms/kg) and fluorescent lights on or off (Experiment 2) or 1,25-(OH)2D3 at 0 and 10 micrograms/kg (Experiments 3 and 4). In Experiment 1, fluorescent lighting increased bone ash, and decreased the incidence and severity of rickets at 2.75 micrograms/kg cholecalciferol and 0 microgram/kg 1,25-(OH)2D3 and reduced the severity of TD at both levels of cholecalciferol and 0 microgram/kg 1,25-(OH)2D3. In all cases 1,25-(OH)2D3 improved bone ash. The metabolite also decreased the incidence and severity of TD at both cholecalciferol levels with lights off and decreased the incidence and severity of rickets at 2.75 micrograms/kg cholecalciferol and lights off. In the absence of fluorescent lighting and 1,25-(OH)2D3 27.5 micrograms/kg cholecalciferol reduced the incidence and severity of rickets to levels equivalent to those produced by either fluorescent lighting or 1,25-(OH)2D3 alone (Experiments 2, 3, and 4). However, even 50.0 micrograms/kg cholecalciferol was not as effective as fluorescent lights or 1,25-(OH)2D3 in reducing the incidence and severity of TD.

The effects of ultraviolet light and cholecalciferol and its metabolites on the development of leg abnormalities in chickens genetically selected for a high and low incidence of tibial dyschondroplasia

Four experiments were conducted to investigate the effects of ultraviolet (UV) light exposure and several cholecalciferol metabolites on the development of tibial dyschondroplasia (TD) and other parameters associated with vitamin D metabolism in chickens selected for high (HTD) and low (LTD) incidence of TD. In Experiment 1, exposure of chickens to UV light reduced the incidence and severity of TD more in LTD chickens than in HTD chickens, as evident by the significant interactions (P < 0.10 and 0.04). In Experiment 2, the addition of cholecalciferol to diets that were deficient in cholecalciferol linearly decreased the incidence of vitamin D rickets and increased bone ash, but increased the incidence of severe TD. The LTD chickens had a higher maximal bone ash of 40.0 +/- 0.7% than did the HTD chickens, which had a maximal bone ash of 37.0 +/- 0.7%. In Experiment 3, the addition of 5 micrograms/kg of 25-hydroxycholecalciferol [25-(OH)D3], 1-alpha-hydroxycholecalciferol, or 1,25- dihydroxycholecalciferol decreased the incidence and severity of TD in the LTD chickens and had no effect on TD in HTD chickens. In Experiment 4, increasing dietary 25-(OH)D3 increased plasma 25-(OH)D3 levels in both lines, but HTD chickens had higher plasma 25-(OH)D3 levels at 20 and 40 micrograms/kg of dietary 25-(OH)D3. The incidence and severity of TD were reduced in the LTD chickens by dietary 25-(OH)D3, but little effect was noted in HTD chickens. The LTD chickens reached a maximal bone ash at 9.7 +/- 1.9 micrograms/kg and HTD chickens reached the same bone ash at 33.0 +/- 7.0 micrograms/kg. These results indicate that UV light and vitamin D metabolites are not effective in preventing TD in HTD chickens, but that altered vitamin D metabolism does exist between HTD and LTD chickens.