Effects Of Dietary Calcium Levels Research Articles

Dietary Calcium Levels and Treatment Interval Determine the Effects of Lead Ingestion on Plasma 1,25-Dihydroxyvitamin D Concentration in Chicks

The combined effects of dietary calcium level and lead level on several indices of vitamin D endocrine function were examined in young, growing chicks. Day-old animals fed a nutritionally adequate diet for 2 wk were fed diets either adequate (1.2%) or low (0.1%) in calcium, and containing 0, 0.2 or 0.8% lead for an additional 1 or 2 wk. In the calcium-adequate group, lead ingestion significantly elevated intestinal calbindin-D28k protein and mRNA levels as well as plasma 1,25-dihydroxyvitamin D concentration compared with the control animals fed a lead-free diet. The effect was apparent after 1 wk of treatment and continued through wk 2. In the calcium-deficient group, the early (1 wk) increases in plasma 1,25-dihydroxyvitamin D and calbindin-D28k protein and mRNA were significantly reversed by lead ingestion over the 2-wk trial period in a dose-dependent fashion. In these circumstances, vitamin D endocrine function is severely compromised. Therefore, lead ingestion may result in either enhanced or diminished circulating 1,25-dihydroxyvitamin D concentrations and ensuing intestinal responses, depending of dietary calcium level and the duration of lead intake. These results provide possible explanations for several apparently conflicting sets of observations regarding lead-calcium interactions.

Effect of dietary calcium level on egg shell quality of aged laying hens housed in conventional cage

Effect of dietary calcium level on egg shell quality of aged laying hens housed in conventional cage

Dietary calcium levels on productive and reproductive traits of european quails

The objective of this study was to determine the effect of dietary calcium levels on productive and reproductive traits of European male quail (Coturnix coturnix). A total of 60 European male quail, at 35 days of age, weighing 248.9g ± 8.1g were distributed in a completely randomized experimental design with five calcium levels (1.5, 2.0, 2.5, 3.0 and 3.5%), and 12 replicates per treatment (one bird each replicate). The experimental period was 35 to 70 days of age. At 70 days of age, the parameters of male productive traits assessed were: feed consumption, calcium consumption, weight gain and body weight of birds. The reproductive traits analyzed were: hatchability and fertility of eggs. Early, intermediate and late embryonic mortality were also evaluated. The diet containing 3.16% of calcium provides higher percentage of hatched eggs and did not show a negative effect on productive performance of European quails.

Organic trace minerals and calcium levels in broilers' diets to 21 days old

This study was undertaken to evaluate the effects of dietary calcium levels and supplementation with organic trace minerals selenium, copper, iron, zinc and manganese on performance, tissue deposition and litter mineral concentration. A total of 2,496 one-day-old male Cobb 500 broilers were randomly assigned to a 3 × 4 factorial experimental design with three levels of dietary Ca [8, 10 and 12 g kg–1, while maintaining the same Ca:nPP (non-phytate phosphorus) ratio (2:1)] and four levels of micromineral supplementation (0.62, 0.72, 0.82 and 0.92 g kg–1). There was a total of 12 treatments, with eight replicates of 26 birds per pen. Micromineral supplementation (MS) was achieved by adding different levels of the product Bioplex TR Se® and Ca supplementation was achieved by adding increasing levels of limestone and dicalcium phosphate. An interaction between Ca and MS levels was observed (p 0.05) for Ca, P or ash concentrations in the tibia, which were influenced only by dietary Ca levels (p < 0.05). The Ca level of 10 g kg–1 promoted higher Ca and P concentration in the tibia and lower micromineral excretion in the litter. The combination of MS level of 0.82 g kg–1 with Ca level of 10 g kg–1 led to the best BWG response. The supplementation conditions that led to higher micromineral levels in the liver and breast varied for each mineral.

Investigating the effect of dietary calcium levels on ileal endogenous amino acid losses and standardized ileal amino acid digestibility in broilers and laying hens.

Two studies were conducted to evaluate the effect of dietary Ca levels (low, 1% and high, 3%) on ileal endogenous amino acid losses (IEAAL) and standardized ileal amino acid digestibility (SIAAD) in broilers (BR) and laying hens (LH) fed nitrogen-free diets (NFD) and distiller's dried grain with solubles (DDGS)-based diets. A total of 384 male Cobb 500 BR and 288 LH were used in a completely randomized design (CRD) with 16 (BR) or 12 (LH) replicate cages with 6 birds/replicate. IEAAL and apparent ileal digestibility (AID) of AA were analyzed using the GLM procedure of SAS appropriate for a CRD while SIAAD values were analyzed using the GLM procedure of SAS appropriate for a 2×2 factorial arrangement of treatments. For BR, IEAAL and N losses (mg/kg of dry matter intake, DMI) were higher (P <0.05) when NFD with high Ca level was fed (total AA was 39%, N was 35% higher). For most of the AA, AID was higher (P <0.05) in BR fed DDGS-based diet with high Ca level. High dietary Ca resulted in higher (P <0.05) SIAAD for all the AA except for Arg, Lys, Met, Cys, and Tyr. For LH, AID of AA was higher (P <0.05) for the DDGS diet with high Ca level in 13 of the 18 AA evaluated. There was interaction (P <0.05) between diet Ca level and correction method on LH SIAAD values for Thr, Asp, Gly, and Ser. The SIAAD values for 8 AA were higher (P <0.05) in birds on high Ca DDGS diet. Correction with low Ca NFD resulted in higher (P <0.05) SIAAD values for all the AA. Result from this study showed that high Ca increased total IEAAL in BR by 39% but decreased same by 27% in LH. Finally, SIAAD values were increased in BR fed high Ca DDGS-based diet while SIAAD value in LH was lower when correction was done using values from high Ca-NFD fed birds.

Effects of dietary calcium levels on growth performance and bone characteristics in pigs in grower-finisher-transitional phase

The objective of this experiment was to determine the effects of dietary calcium (Ca) levels on growth performance and bone development of growing and finishing pigs. A total of 150 crossbred pigs (37.0±4.0kg BW) were randomly assigned to 5 treatment groups: (1) low Ca levels in both grower and finisher phases (LL), (2) low Ca level in grower phase and high Ca level in finisher phase (LH), (3) medium Ca levels in both grower and finisher phases (MM), (4) high Ca level in grower phase and low Ca level in finisher phase (HL), and (5) high Ca levels in both grower and finisher phases (HH). The dietary phosphorus (P) levels were fixed. The animal trial was conducted for 60days. When the average pen BW reached approximately 60kg, the pigs were switched to finisher diets. Pig performance was not affected by dietary treatments during either the grower or finisher phases. During the grower phase, the bone mineral density (BMD) and bending moment of the fourth metacarpal and metatarsal bones were lower (P<0.05) in pigs fed the low Ca diets than in those fed the medium Ca diets. During the finisher phase, P weight, BMD and bending moment of the fourth metacarpal and metatarsal bones were not different for pigs fed the LH and HL diets compared with pigs fed the HH diet. The bending moment of the fourth metacarpal bone and fat-free dry weight of the fourth metatarsal bone were lower (P<0.05) in pigs fed the LH diet compared with those fed the MM diet. In conclusion, a compensatory effect occurred in bone characteristics at the end of the finisher phase when the high Ca diet was introduced in the finisher phase, following a low-Ca diet during the grower phase. However, pigs fed LH diet did not surpass the level of bone mineralization achieved by pigs fed the MM diet.

Effect of dietary calcium level and source on mineral utilisation by piglets fed diets containing exogenous phytase

Calcium and phosphorus are essential minerals, closely linked in digestive processes and metabolism. With widespread use of low P diets containing exogenous phytase, the optimal dietary Ca level was verified. The 40-day study evaluated the effects of Ca level (4, 7 and 10g/kg diet) and Ca source (Ca from CaCO3 and from Lithothamnium calcareum) on mineral utilisation in 72 piglets (7.9±1.0kg BW) fed an exogenous phytase containing diet with 2.9g digestible P/kg. Measured parameters were growth performance, stomach mineral solubility, bone breaking strength and urinary, serum and bone mineral concentration. The apparent total tract digestibility of minerals was also assessed in the two diets with 7g Ca/kg, using 12 additional pigs. Regardless of Ca source, increasing dietary Ca impaired feed conversion ratio, increased urinary pH, increased serum and urinary Ca, decreased serum and urinary P, decreased serum Mg and increased urinary Mg, increased serum AP activity, decreased bone Mg increased bone Zn. Bone breaking strength was improved with 7 compared to 4g Ca/kg. Compared to CaCO3 , Ca from Lithothamnium calcareum increased serum Mg and with, 10g Ca/kg, it limited body weight gain. The dose response of Ca in a diet with 2.9g digestible P/kg and including exogenous phytase indicated that: (i) a low dietary Ca was beneficial for piglet growth, but was limiting the metabolic use of P; (ii) a high dietary Ca level impaired P utilisation; (iii) the optimal P utilisation and bone breaking strength was obtained with a dietary Ca-to-digestible P ratio of 2.1 to 2.4:1; (iv). Increasing dietary Ca reduced Mg utilisation, but not Zn status, when fed at adequate level. Finally, Ca from Lithothamnium calcareum had similar effects on Ca and P metabolism as CaCO3 , but impaired growth when fed at the highest inclusion level.

Effects of dietary calcium levels on growth and tissue mineralization in Japanese seabass,Lateolabrax japonicus

A feeding trial was conducted to investigate the effects of different levels of calcium (Ca) on growth and tissue mineralization in Japanese seabass, Lateolabrax japonicus. Six experimental diets were formulated to contain different levels of Ca (2.9, 4.2, 6.5, 7.9, 10.2 and 31.0 g kg−1) from dietary ingredients and Ca-lactate·5H2O. The diets were fed to three triplicate groups of Japanese seabass (initial weight, 12.5 ± 0.0 g) for 56 days. Dietary Ca had no significant effect on survival or feed efficiency; however, the highest Ca (31.0 g kg−1) diet significantly reduced weight gain, feeding rate and whole-body and muscle protein and lipid contents, as well as serum Ca concentration and alkaline phosphatase activity. A significant reduction in vertebral Ca, P, Zn, Fe and Mn contents and scale Ca, P, Mg and Mn contents was observed in Japanese seabass as dietary Ca level increased. Deformed fish were primarily found in the 2.9 and 31.0 g Ca kg−1 groups, indicating that these fish had poor bone mineralization.

Effects of Dietary Calcium Levels on Productive Performance, Eggshell Quality and Overall Calcium Status in Aged Laying Hens.

This study was conducted to investigate the effects of diets with varying levels of calcium on egg production, shell quality and overall calcium status in aged laying hens. A total of five hundred 70-wk-old Hy-Line Brown layers were divided five groups and fed one of the five experimental diets with 3.5%, 3.8%, 4.1%, 4.4%, or 4.7% Ca, for 10 weeks. There were no significant differences in feed intake, egg production and egg weight among groups. The cracked eggs were linearly reduced as dietary Ca levels increased to 4.7% (p<0.01). A significant linear improvement for eggshell strength and thickness were determined with increasing dietary Ca levels (p<0.01). The contents of serum Ca and phosphorus were not affected by dietary Ca levels. With increase in dietary Ca levels, the tibial breaking strength slightly increased. There were no significant differences in the tibial contents of ash, Ca and phosphorus among groups. In conclusion, eggshell quality, as measured by appearance, strength and thickness of eggshell, were influenced by dietary Ca content as expected (p<0.05). These results suggested that aged laying hens require relatively higher level of Ca than required levels from current Korean feeding standards for poultry.

96 Effects of dietary calcium level and source on environmentally relevant phosphorus excretion in horses

96 Effects of dietary calcium level and source on environmentally relevant phosphorus excretion in horses

Effects of dietary calcium levels on development, haemolymph and antioxidant status of honey bee (Apis mellifera) larva reared in vitro

In order to find out optimal dietary calcium levels for honey bee larvae reared in vitro, we studied the effects of larvae dietary calcium levels on the haemolymph and antioxidant status, as well as growth and development (weight, pupation and emergence rate) of larvae reared in vitro in different growth stages. Eight diet groups were chosen and one group (control) was fed a basal diet containing 43.99 mg/kg calcium; the other seven groups were fed diets with calcium levels ranging from 93.99 to 393.99 mg/kg. Calcium concentration of the haemolymph of larvae significantly (p < .001) increased with increased dietary calcium. When the dietary calcium levels ranged from 193.99 to 243.99 mg/kg, larvae, pupae and emerged bees had the highest weight, and larvae and pupae had a significantly (p < .05) higher total antioxidative capacity. With calcium from 93.99 to 243.99 mg/kg, larvae had a significantly (p < .001) higher pupation rate. Larvae fed diets with calcium levels at 143.99 and 193.99 mg/kg had a significantly higher emergence rate (p < .001). The lowest malondialdehyde concentration of larvae fed 93.99 mg/kg calcium was .19 mmol/ml, while that of pupae 143.99 mg/kg calcium was .15 mmol/ml. We conclude, therefore, that larval dietary calcium levels from 143.99 to 243.99 mg/kg are optimal for larval growth and physiological function.

Effects of dietary clinoptilolite and calcium levels on uric acid and calcium blood concentrations and bone quality of commercial layers

The objective of the present study was to evaluate the effect of clinoptilolite and calcium levels on uric acid and calcium blood profile and bone quality of commercial layers. A total of 576 birds were distributed according to a completely randomized experimental design in a 3x4 factorial arrangement (calcium levels of 2.5, 3.1, or 3.7% and clinoptilolite levels of 0.0, 0.15, 0.25, or 0.50%), into 12 treatments with six replicates of eight birds per cage (experimental unit). The experimental period was 112 days. The experimental diets were based on corn and soybean meal. Results were submitted to analysis of variance and means were compared by the test of Tukey at 5% significance level using SISVAR statistical package. Blood uric acid was significantly influenced by the interaction of the evaluated factors. Clinoptilolite levels significantly increased blood calcium levels. There was no effect of dietary calcium levels on any of the evaluated characteristics. It was concluded that feeding layers with up to 0.50% clinoptilolite does not benefit blood uric acid and calcium concentrations and does not affect their bone quality. When layers at the end of the first laying cycle are fed ad libitum and present 119.50g/hen/day average feed intake, 3.1% dietary calcium promotes 3.7g/hen/day calcium intake, which is sufficient to maintain adequate calcium blood levels and bone quality.

Limestone and oyster shell for brown layers in their second egg production cycle

This study aimed at evaluating the effect of dietary calcium levels and the replacement of calcium sources with different particle size compositions on the performance and egg quality of brown layers in their second egg production cycle. A randomized block experimental design was applied with 12 treatments in a 3x4 factorial arrangement: three calcium levels (2.6, 3.2, 3.8 %) and four combinations of calcium sources (1- 100% fine limestone (FL), 2- 50% FL + 50% coarse limestone (CL), 3- 50% FL and 50% oyster shell (OS), 4- 50% FL and 25% CL+ 25 %OS), with six replicates of eight birds each. Calcium sources were analyzed for geometric mean diameter (GMD) and in-vitro solubility. The following performance and egg quality parameters were evaluated: egg weight (EW, g), egg production (% Eggs), egg mass (EM %), feed intake (FI g), feed conversion ratio (FCR kg/dz and FCR kg/kg), mortality (% Mort.), specific egg gravity (SG), percentages of yolk (Y%), albumen (Alb%) and eggshell (ES%), eggshell thickness (EST), eggshell breaking strength (BS), eggshell weight per surface area (EWSA), Haugh unit (HU), yolk index (YI) and yolk color. Performance and internal egg quality were not affected by the treatments (p>0.05). Blocks had a significant effect on (p<0.05) FI and FCR (kg/dz and kg/kg). Treatments significantly influenced external egg quality, which improved as dietary calcium levels increases and when up to 50% fine limestone was replaced by combinations of coarse limestone with oyster shell.

Effects of dietary calcium levels and limestone particicle size on the performance, tibia and blood of laying hens

A total of 405 23-week-old ISA® Brown layers were distributed in a completely randomized experimental design in a factorial arrangement with nine treatments consisting of three dietary calcium levels (3.5, 3.75, and 4.5%) and three limestone particle sizes (100% fine limestone (FL), 70% FL + 30% coarse limestone (CL) and 50% (FL) + 50% (CL)), with nine replicates of five birds per cage. The following parameters were evaluated: percentage of lay, defective eggs, egg weight, egg mass, feed intake, feed conversion ratio (per kg eggs and per dozen eggs), and mortality. Dietary Ca levels significantly affected lay, with birds fed diets containing 4.5% calcium producing less eggs as compared to those fed 3.0 and 3.75% Ca. Egg production linearly decreased as dietary Ca levels increased, but blood Ca levels (mg/L) increased in 28-week-old birds. The interaction of dietary Ca levels and limestone particle sizes resulted in a reduction in tibial ash Ca content as dietary Ca levels increased and as fine limestone was replaced by coarse limestone. It is concluded that a dietary Ca level of 3.75% and 100% fine particle limestone are required to maintain adequate egg production and available Ca blood level.

Effects of Dietary Calcium Levels on Growth-performance and Digestive Function in Cattle Fed a High-fat Finishing Diet

Plascencia, A., Alvarez, E.G., Montañto, M., Salinas-Chavira, J. and Zinn, R.A. 2009. Effects of dietary calcium levels on growth-performance and digestive function in cattle fed a high-fat finishing diet. J. Appl. Anim. Res., 36: 179–184. A growth performance and digestion trial was conducted to evaluate the influence of dietary calcium level on the feeding value of a high-fat (11%) finishing diet. Treatments consisted of three levels of dietary Ca: 0.50, 0.70 and 0.90% (DM basis). Ca source was limestone and yellow grease was included as supplemental fat. There were no treatment effects (P>0.20) on DMI. Increasing dietary Ca level enhanced ADG (P<0.10) and feed conversion (F:G, P<0.05). There were both linear (P<0.05) and quadratic (P<0.10) effects on dietary NE. Increasing Ca level from 0.7 to 0.9% increased dietary NEg by 8.0%,. Carcass dressing percentage and LM area increased (P<0.10) with increasing dietary Ca level. There were no treatment effects (P>0.10) on total tract digestion of OM, ADF, lipid, starch or N. However, increasing Ca level from 0.7 to 0.9% decreased ruminal digestion of OM (P<0.05), ADF (P<0.10) and feed N (P<0.05), but enhanced (P<0.10) ruminal microbial efficiency and (P<0.01) ruminal N efficiency. Postruminal Cci disappearance tended to be greater (P<0.10) with 0.9% dietary Ca. Increasing dietary calcium level did not affect (P>0.20) either ruminal pH or ruminal soluble Ca. It is concluded that dietary Ca levels greater than 0.7% (DMB) are necessary to achieve optimal performance of feedlot steers fed a high-fat finishing diet.

Calcium levels and limestone particle size in the diet of commercial layers at the end of the first production cycle

This study evaluated the effect of dietary calcium levels and limestone particle size distribution on first-cycle layer performance and egg quality. A completely randomized experimental design in 4x3 factorial arrangement (four Ca levels - 3.0, 3.5, 4.0, 4.5%; and three limestone particle size distributions - 100% fine, 50% fine and 50% coarse, 30% fine and 70% coarse) was applied, totaling 12 treatments with six replicates of eight birds each. The treatments did not influence the most of evaluated performance and internal and external egg quality parameters. However, limestone particle size distribution quadratically affected with percentage of defective eggs, with the lowest percentage obtained with the distribution 61.75% fine limestone and 38.25% coarse limestone. Increasing dietary Ca levels significantly increased eggshell weight per surface area and the percentage of Ca excreted in the feces. It was concluded that the combination of the highest dietary Ca level (4.5%) with 50% replacement of fine-particle limestone by coarse limestone results in better eggshell and increases the number of marketable eggs.

Effects of calcium levels and limestone particle size on the egg quality of semi-heavy layers in their second production cycle

A 112-day trial was carried out to evaluate the effect of dietary calcium level and limestone particle size on the egg quality of 288 Hy-Line Brown semi-heavy layers, with 83 weeks of age at the beginning of the experiment. A completely randomized experimental design was applied in a 2x3 factorial arrangement, with two dietary calcium levels (3.5 and 4.0%) e three limestone particle size compositions (100% fine limestone (FL), with 0.185mm; 30% coarse limestone (CL), with 2.83mm, + 70% FL, with 0.185mm; and 50% CL, with 2.83mm, + 50% FL, with 0.185mm), with six replicates of eight birds each. Mean geometric diameter and in-vitro solubility of the limestone sources were, respectively, 0.185mm and 18.7% for the fine limestone, and 2.83mm and 10.5% for the coarse limestone. At the end of each 28-day period, 72 eggs per treatment were used to determine egg specific gravity, yolk percentage, albumen percentage, eggshell percentage, yolk index, Haugh units, eggshell thickness, and eggshell breaking strength. There was no influence of the treatments on the evaluated parameters. It was concluded that feeding the level of 3.5% calcium usually recommended for layers in their first laying cycle, and the substitution of up to 50% fine limestone by coarse limestone in the feed of semi-heavy commercial Hy-Line Brown layers in their second laying cycle can be applied with no impairment of egg quality.

Bone turnover in growing pigs fed three levels of dietary calcium

The effect of dietary calcium level on bone quality and quantity was evaluated in growing pigs by means of histomorphometric methods as well as basic bone parameters and chemical indicators of bone turnover in the blood. Thirty growing pigs were allocated to three levels of dietary calcium, 3.5, 9.4 and 16.4 g kg−1DM, respectively. Blood was drawn five times throughout 62 d and analyzed for Ca, P, hydroxyproline, alkaline phosphatase and 1-carboxy terminal telopeptide (1CTP). On days 50 and 60 of the experiment, oxytetracycline was injected i.m. and the animals were sacrificed on day 62. Transiliac bone samples were obtained, processed undecalcified and used in morphologic and morphometric analyses. Medium or high dietary calcium resulted in a higher retention of calcium, and more bone mass as indicated by a higher trabecular bone volume and a lower bone resorption. The mineral appositional rate in the bones was also higher in these groups, indicating a fast growth rate. Conversely, a low dietary calcium supply, resulted in lower overall calcium retention, lower bone mass, and a higher extent of resorption lacunae and osteoid extent and width. Higher remodeling activity and osteoid accumulation were due to deficient mineralization as indicated by a lower mineralization rate and prolonged mineralization lag time. Bone markers in the blood were only slightly affected by the dietary calcium differences. It was concluded that the medium level of dietary calcium was sufficient to sustain sound bone development. Key words: Histomorphometric analysis, bone formation, bone resorption, hydroxyproline, cross-links, mineralization

Effect of Dietary Calcium Level on Growth Performance, Phosphorus Digestibility and Bone Mineralization of Lean-Type Growing-Finishing Pigs Fed a Low Phosphorus Diet Supplemented with Phytase

Roberson, K.D., Stalder, K.J., Loveday, H.D. and Masincupp, F.B. 2000. Effect of dietary calcium level on growth performance, phosphorus digestibility and bone mineralization of lean-type growing-finishing pigs fed a low phosphorus diet supplemented with phytase. J. Appl. Anim. Res., 17: 57–68. An experiment was conducted to determine the effect of dietary Ca level and phytase on growth, bone strength and digestibility of P and Ca in growing-finishing pigs. High lean-type pigs were randomly allocated to treatments on the basis of weight and gender. Average initial weight was 23.4kg and the experimental period was 111 days. Each treatment was replicated five times with five pigs per replicate. A corn-soybean meal diet was formulated to contain 0.60% Ca and 0.50% P in the growing period (23.4 to 62.5kg) and 0.50% Ca and 0.40% P in the finishing period (62.5 to 113.4kg). Dietary Ca was decreased by 0, 0.05 or 0.10 percentage units and phytase (Natuphos™) was added at 300 or 250 units/kg in the growing and finishing periods, respectively, when P was decreased by 0.10 percentage units. Daily gain was increased (P<0.05) when 0.55% Ca and 0.40% P were fed with phytase in the growing period. There was no effect (P>0.10) on daily gain or feed intake in the finishing period. Overall, feed intake was higher (P<0.05) when dietary Ca decreased by 0.05 percentage units. Pigs fed the low P diet with phytase had lower fecal P levels (P<0.01), but similar apparent retention of P (P>0.10) compared to the control diet. Dietary Ca level did not affect (P>0.10) femur breaking strength or fecal P output. Dietary Ca, can be reduced by 0.10 percentage units when phytase is fed at 300/250 units/kg and P is reduced from 0.50 to 0.40% and 0.40 to 0.30% in the diets of growing and finishing lean-type pigs, respectively.

Effects of Dietary Calcium Levels on the Histomorphology of Proximal Tibia in Vitamin D-deficient Chicks.

This study was conducted to clarify the effects of dietary calcium levels on tibia histomorphology in young growing chicks fed a vitamin D-deficient diet. Male day-old chicks were fed vitamin D-deficient diets either normal (1.0%) or high (2.0%) in calcium for 4 weeks. Proximal tibiae were excised and longitudinal sections were examined by light microscopy. Morphological differences were quantified by a computerlized histomorphometry. The feeding of the normal calcium diet caused significant increase in the width of epiphyseal cartilage and histomorphometric indices of bone resorption. Osteoclastic resorbing surface and all osteoclast parameters, measured at metaphysis, greatly increased in the normal calcium diet chicks compared to the controls fed the vitamin D-replete diet. The area of osteoblasts remarkably decreased in the normal calcium diet chicks. Changes in these bone cell parameters are thus associated with marked decrease in trabecular bone volume, expressed as percentage of the mineralized bone matrix area. In contrast, tibiae of the high calcium diet chicks were not significantly different from bones of the control chicks with respect to histological features and most parameters. Thus, tibia histomorphology in the high calcium diet chicks showed normalization of bone as observed in the vitamin D-replete diet chicks. These results indicate that in the growing chick continued feeding of a diet with high calcium content can maintain nearly normal epiphyseal cartilage width and metaphyseal bone histomorphology and mineralization in the absence of vitamin D.