Effects of dietary phosphorus intake on bone mineralization and calcium absorption in adult female rats

We investigated the effects of dietary phosphorus (P) intake on the bone mineralization and calcium (Ca) absorption in adult female rats. Fifteen 16-wk-old female Wistar rats were divided into three groups, and respectively fed a low-P diet containing 0.15% P (LP), a control diet containing 0.5% P (C), and a high-P diet containing 1.5% P (HP) for 42 d. The apparent Ca absorption was significantly increased with decreasing dietary P level. The serum parathyroid hormone concentration was significantly lower in the LP group than in the C and HP groups. The serum osteocalcin concentration and urinary excretion of deoxypyridinoline were significantly higher in the HP groups than in the LP and C groups. The bone mineral density of the fifth lumbar vertebra was significantly increased with decreasing dietary P level. These results indicate that the low-P diet increased Ca absorption, this being effective for bone mineralization in adult female rats.     

Effect of dietary calcium: Phosphorus ratio on bone mineralization and intestinal calcium absorption in ovariectomized rats

We investigated the effect of dietary calcium:phosphorus (Ca:P) ratio on bone mineralization and intestinal Ca absorption in ovariectomized (OVX) rat models of osteoporosis and sham-operated rats. Thirty 12-wk-old female Wistar rats were divided into three groups of OVX rats and three groups of sham rats. Thirty days after the adaptation period, OVX rats and sham rats were fed a diet formulated Ca:P, 1:0.5, 1:1 or 1:2 (each diet containing 0.5% Ca), respectively for 42 d. In both sham and OVX rats, serum osteocalcin, a marker of bone turnover, was increased by decreasing Ca:P ratio (1:2). In contrast, rats fed the Ca:P = 1:0.5 diet (dietary P restriction) suppressed the increased serum parathyroid hormone, osteocalcin and urinary deoxypyridinoline, and increased Ca absorption in both sham and OVX rats compared to the Ca:P = 1:1 and 1:2 diets. Especially, in OVX rats, the decreased bone mineral density of the fifth lumbar was also suppressed when rats were fed the Ca:P = 1:0.5 diet. These results indicated that the elevation of dietary Ca:P ratio may inhibit bone loss and increase intestinal Ca absorption in OVX rats.     

Effects of ovariectomy on duodenal calcium transport in the rat: altered ability to adapt to low-calcium diet

Studies were undertaken to determine whether ovariectomy (ovx) would alter the ability of female rats to adapt to low dietary Ca intake by exhibiting an in duodenal active Ca transport. Intact and ovx female rats were fed diets containing 1.5, 0.50, or 0.02% Ca prior to measuring active Ca transport using everted duodenal sacs in vitro. In some experiments, ovx animals were pair-fed to intact animals of the same age consuming the same diet. When ovx animals were allowed to eat ad lib, we found that both growth rate and duodenal active Ca transport increased relative to age-matched, intact controls. However, when growth of ovx animals was maintained at the control rate by pair-feeding, ovx per se did not affect intestinal active Ca transport. Ovx did not alter circulating levels of 1,25-dihydroxyvitamin D (1,25(OH)2D). We found that intact females responded to the low-Ca (0.02%) diet with increased circulating 1,25(OH)2D levels and increased intestinal active Ca transport. Ovx animals exhibited the same increase in circulating concentrations of 1,25(OH)2D in response to low-Ca diet, but did not demonstrate increased duodenal active Ca transport. When ovx animals consumed the diet ad lib, they became larger and exhibited higher Ca transport rates than intact animals fed the high-Ca diet, but there was no difference in Ca transport between ovx animals fed diets containing different Ca contents. The results of these experiments demonstrate that in female rats, the ability to adapt to altered dietary Ca intake is dependent on intact ovarian function and is not necessarily directly related to circulating concentrations of 1,25(OH)2D.     

The effect of diet calcium on fluoride toxicity in growing rats

The effect of dietary Ca in response to fluoride (F) treatment was investigated in rats. Rats were maintained on either adequate (0.5%) or high (2.0%) dietary Ca and given for 5 weeks, NaF in drinking water. The minimum NaF levels that inhibited body growth and reduced survival were 300 mg/L with 0.5% diet Ca and 550 mg/L with 2.0% diet Ca. With these toxic F doses, bone histology showed increased formation surfaces and thickened osteoid seams (osteoid index 6-7%). Fluoride doses 30% below toxic levels (200 and 350 mg/L for 0.5 and 2.0% diet Ca, respectively) had no demonstrable effect on bone. Additional diet Ca reduced F absorption from 76 +/- 3 to 47 +/- 3% for 0.5 and 2.0% diet Ca, respectively. Comparable absorbed doses of F produced comparable effects on bone and body growth but, with additional dietary Ca, these effects were observed with 50% lower serum and bone F levels. Variable response to NaF therapy can be produced in rats by alterations in dietary Ca alone. Results indicate that for clinical treatment the NaF dose needs to be adjusted on an individual basis but neither serum nor bone F levels can be used reliably to establish optimal doses.     

Reduction in dietary calcium/phosphorus ratio reduces bone mass and strength in ovariectomized rats enhancing bone turnover

To clarify the effects of the dietary calcium (Ca)/phosphorus (P) ratio on bone mineralization under the condition of estrogen deficiency, Wistar strain female rats were ovariectomized (OVX) at 12 weeks old. At 16 weeks old, the rats were divided into three dietary groups fed varying levels of P containing 0.5% Ca: 0.25% P, Ca/P = 2; 0.5% P, Ca/P = 1; and 1.0% P, Ca/P = 0.5 respectively. This study indicates that the reduction of the dietary Ca/P ratio impairs trabecular bone turnover accompanying the acceleration of bone formation in OVX rats.     

Interactions between sodium and calcium intake and blood pressure responses to norepinephrine and parathyroid hormone

The present study has examined the vascular responses to infusion of norepinephrine (NE) and parathyroid hormone (PTH 1-34) in animals subjected for a six month period to one of four dietary regimens. Some animals received normal calcium chow (1.0% Ca by weight) and drank water (subgroup A), others consumed the same chow, but water was replaced by 0.5% saline (subgroup B), a third group consumed chow which had 2.0% Ca content and also drank 0.5% saline (subgroup C) and a fourth group consumed the 2.0% Ca chow, but drank water (subgroup D). No differences were found in the pressor response to NE across subgroup A, B, and C, while pressor response to NE in subgroup D was markedly reduced. Depressor responses to PTH were not significantly different across any of the four groups. The ability of changes in calcium homeostasis to affect blood pressure responses to NE and PTH were evaluated in animals consuming reduced dietary calcium (0.1%) for two and four weeks and compared with animals on normal calcium intake (1.0%). This dietary treatment resulted in only mild effects on calcium balance; after four weeks no significant difference in plasma total calcium concentration was observed, but plasma PTH levels were increased in animals on the low Ca diet. No effects on the blood pressure response to NE or PTH infusion were observed after 2 weeks of dietary treatment. At four weeks, NE responses remained unchanged, while responses to PTH were blunted in animals on 0.1% Ca chow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estimation of calcium requirements for optimal productive and reproductive performance,eggshell and tibial quality in egg-type duck breeders

Optimizing the dietary calcium (Ca) level is essential to maximize the eggshell quality, egg production and bone formation in poultry. This study aimed to establish the Ca requirements of egg-type duck breeders from 23 to 57 weeks of age on egg production, eggshell, incubation, tibial, plasma and ovary-related indices, as well as the expression of matrix protein-related genes. Totally, 450 Longyan duck breeders aged 21 weeks of age were allotted randomly into five treatments, each with six replicates of 15 individually caged birds. The data collection started from 23 weeks of age and continued over the following 35 weeks. The five groups corresponded to five dietary treatments containing either 2.8%, 3.2%, 3.6%, 4.0% or 4.4% Ca. The tested dietary Ca levels increased (linear, P <0.01) egg production and egg mass, and linearly improved (P <0.01) the feed conversion ratio (FCR). Increasing the dietary Ca levels from 2.8% to 4.4% increased (P <0.01) the eggshell thickness and eggshell content. The tested Ca levels showed a quadratic effect on eggshell thickness and ovarian weight (P <0.01); the highest values were obtained with the Ca levels 4.0% and 3.6%, respectively. Dietary Ca levels affected the small yellow follicles (SYF) number and SYF weight/ovarian weight, and the linear response (P <0.01) was significant vis-à-vis SYF number. In addition, dietary Ca levels increased (P <0.05) the tibial dry weight, breaking strength, mineral density and ash content. Plasma and tibial phosphorus concentration exhibited a quadratic (P <0.01) response to dietary Ca levels. Plasma calcitonin concentration linearly (P <0.01) increased as dietary Ca levels increased. The relative expression of carbonic anhydrase 2 in the uterus rose (P <0.01) with the increment of dietary Ca levels, and the highest value was obtained with 3.2% Ca. In conclusion, Longyan duck breeders fed a diet with 4.0% Ca had superior eggshell and tibial quality, while those fed a diet with 3.6% Ca had the heaviest ovarian weights. The regression model indicated that the dietary Ca levels 3.86%, 3.48% and 4.00% are optimal levels to obtain maximum eggshell thickness, ovarian weight and tibial mineral density, respectively.     

Tracking dietary transitions in weanling baboons (Papio hamadryas anubis) using strontium/calcium ratios in enamel

Strontium and calcium are incorporated into developing teeth in a manner that reflects changing physiological concentrations in the body. A new model predicts changes in strontium/calcium (Sr/Ca) ratios in response to dietary transitions experienced at birth and during the weaning period. Microsampling of longitudinal thin sections of tooth enamel using laser ablation inductively coupled plasma mass spectrometry provides a basis for the systematic evaluation of variation in Sr/Ca ratios within the tooth crown. Incremental growth markers in enamel are used to determine the age of onset of enamel mineralization at each sampling point. Thin sections of 5 teeth from 2 wild-caught baboons (Papio hamadryas anubis) were systematically analysed using this technique. Intra- and intertooth analyses of Sr/Ca ratios reveal a pattern of dietary development during the period of enamel formation that is consistent with observational data on the timing of weaning behaviour in anubis baboons.     

Testosterone alters duodenal calcium transport and longitudinal bone growth rate in parallel in the male rat.

Duodenal active calcium transport and longitudinal bone growth rate have been shown previously to be regulated in parallel by alteration of gonadal hormone status in sexually maturing female rats. The present study was designed to extend these observations to the sexually maturing male rat. Male rats were orchidectomized (ORX) and given Silastic implants containing either testosterone or estradiol at 6 weeks of age. At 9 weeks of age, duodenal active calcium transport was measured by the everted gut sac method and longitudinal bone growth rate was determined by tetracycline labeling. Decreases in body weight, longitudinal bone growth rate, duodenal calcium transport, and serum Ca and P were exhibited by ORX animals as compared with age-matched control animals. Testosterone administration to ORX animals resulted in an increase in body weight, longitudinal bone growth rate, duodenal calcium transport, and serum Ca and P as compared with ORX animals to a level not significantly different from that of age-matched control animals. Estradiol administration to ORX animals resulted in an additional decrease in body weight, although no significant effect on duodenal calcium transport, serum Ca, or P was noted as compared with ORX animals. There were no statistically significant alterations in the circulating levels of 1,25-dihydroxyvitamin D, parathyroid hormone, or osteocalcin in response to any of the experimental manipulations of gonadal status. These results indicate that, as in the female, gonadal hormone status affects intestinal calcium transport in sexually maturing male rats in parallel with changes in bone growth rate by mechanisms that are independent of circulating levels of 1,25-dihydroxyvitamin D.     

Interaction of dietary calcium,manganese, and manganese source (Mn oxide or Mn methionine complex) on chick performance and manganese utilization

Two trials were conducted to determine the utilization of manganese (Mn) as influenced by the level and source of Mn and the level of dietary calcium (Ca) in broiler chickens. Trial One was a 2 x 2 x 3 factorial arrangement of two Mn sources (Mn methionine or manganous oxide), two levels of dietary Ca (1.8 or 1.0), and three levels of supplemental Mn (30, 60, or 200 mg/kg) fed until 4 wk of age. Total phosphorus (available phosphorus) levels were 0.70% (0.48%) during all ages. High levels of dietary Ca caused a slower early rate of growth (0.53 vs. 0.64 kg) for chicks fed 1.8 vs 1.0% Ca, respectively. Chick weight was equivalent for all diets within the Ca-treatment group, except the dietary combination of high Ca and 200 mg/kg Mn as Mn methionine. Bone and liver Mn were significantly increased as the Mn level increased, but were not affected by the Mn source. Chicks fed 1.8% Ca had higher levels of bone Mn (9.28 ppm) than chicks fed 1.0% Ca (7.23 ppm). High levels of dietary Ca and 200 ppm Mn methionine dramatically depressed early growth, feed intake, and bone ash in this trial, raising the question of a diet x environment (heat-stress) effect. Trial Two was a 2 x 2 factorial arrangement of two levels of dietary Ca (1.8 or 1.0%) and two Mn sources (200 mg/kg Mn as Mn methionine or MnO) up to 3 wk of age in a controlled heat-stress environment. No growth depression in the chicks fed high levels of Ca and Mn methionine was observed. In the presence of high levels of dietary Ca, bone Mn was significantly higher when chicks were fed the MnO source. In summary, dietary Ca did not decrease Mn utilization in these trials, and availability of Mn in Mn methionine as a source compared to MnO depended on dietary Ca levels.     

Reduction in Dietary Calcium/Phosphorus Ratio Reduces Bone Mass and Strength in Ovariectomized Rats Enhancing Bone Turnover

To clarify the effects of the dietary calcium (Ca)/phosphorus (P) ratio on bone mineralization under the condition of estrogen deficiency, Wistar strain female rats were ovariectomized (OVX) at 12 weeks old. At 16 weeks old, the rats were divided into three dietary groups fed varying levels of P containing 0.5% Ca: 0.25% P, Ca/P=2; 0.5% P, Ca/P=1; and 1.0% P, Ca/P=0.5 respectively. This study indicates that the reduction of the dietary Ca/P ratio impairs trabecular bone turnover accompanying the acceleration of bone formation in OVX rats.     

1alpha,25(OH)2-vitamin D3 membrane-initiated calcium signaling modulates exocytosis and cell survival

1alpha,25(OH)(2)-vitamin D(3) (1,25D) is considered a bone anabolic hormone. 1,25D actions leading to bone formation involve gene transactivation, on one hand, and modulation of cytoplasmic signaling, on the other. In both cases, a functional vitamin D receptor (VDR) appears to be required. Here we study 1,25D-stimulated calcium signaling that initiates at the cell membrane and leads to exocytosis of bone materials and increased osteoblast survival. We found that rapid 1,25D-induction of exocytosis couples to cytoplasmic calcium increase in osteoblastic ROS 17/2.8 cells. In addition, we found that elevation of cytoplasmic calcium concentration is involved in 1,25D anti-apoptotic effects via Akt activation in ROS 17/2.8 cells and non-osteoblastic CV-1 cells. In both cases, 1,25D-stimulated elevation of intracellular calcium is due in part to activation of L-type Ca(2+) channels. We conclude that 1,25D bone anabolic effects that involve increased intracellular Ca(2+) concentration in osteoblasts can be explained at two levels. At the single-cell level, 1,25D promotes Ca(2+)-dependent exocytotic activities. At the tissue level, 1,25D protects osteoblasts from apoptosis via a Ca(2+)-dependent Akt pathway. Our studies contribute to the understanding of the molecular basis of bone diseases characterized by decreased bone formation and mineralization.     

Skeletal sensitivity to dietary calcium deficiency is increased in the female compared with the male rat

We investigated potential sex differences in bone resorption and the conservation of whole body bone mass in 24-week-old Sprague-Dawley rats maintained on a 1.0% calcium diet and then fed diets containing 0.02, 0.5, 1.0, or 1.75% calcium for 31 days. Lowering dietary calcium from 1.00% to 0.02% doubled whole skeleton bone resorption (urinary 3H-tetracycline loss). Female rats were more sensitive to calcium stress, exhibiting the maximal resorptive response when fed the 0.5% calcium diet, whereas the 0.02% calcium diet was required to elicit this response in males. Despite the evidence of increased bone resorption, whole skeleton mass was unchanged in females and was significantly increased in males, indicating that switching to even the 0.02% calcium diet did not result in an overt loss of total body bone mass. Compared with controls, the skeleton mass of females (97+/-1.4%) maintained on the 0.02% calcium diet was significantly lower than males (107+/-2.4%), again suggesting a greater impact of calcium deficiency in females. The calculation of the average percentage growth of selected individual bones in male rats indicated a proportional increase in bone mass between the axial and appendicular skeleton of approximately +4% and +18% in animals maintained on 0.02 and 1.75% diets, respectively. By comparison, female rats consuming the 0.02% calcium diet showed an average 14% loss in axial bone and 7.5% gain in appendicular bone mass. The results indicate increased sensitivity to dietary calcium deficiency in female rats which involves a significant loss in axial bone mass not observed in male rats maintained under similar dietary conditions.     

Blood pressure in relation to dietary calcium intake, alcohol consumption, blood lead, and blood cadmium in female nonsmokers

The interrelationship of dietary calcium (Ca) intake, alcohol consumption, blood lead (BPb), blood cadmium (BCd), age, and body mass index (BMI) to blood pressure was examined in 267 peasant women 40-85 years of age. They were residents of two rural areas in Croatia and differed with regard to dietary Ca intake: 100 women with low Ca intake (approximately 450 mg/day) and 167 women with relatively high Ca intake (approximately 940 mg/day). All of the women were nonsmokers and consumed very little or no alcohol. Median and range BPb values were 74 (29-251) microg/L in women with low Ca intake and 59 (21-263) microg/L in women with high Ca intake (p < 0.0002), whereas corresponding BCd values were 0.6 (0.2-3.6) microg/L and 0.6 (0.3-4.5) microg/L (p > 0.10). Results of multiple regression showed a significant (p < 0.05) increase in systolic blood pressure with age, BMI, and BCd, and marginally with alcohol consumption (multiple r = 0.48, p < 10(- 6)). An increase in diastolic blood pressure was significantly (p < 0.05) associated with BMI, age, and residence area (i.e., it was higher in women with low Ca intake), and marginally with BCd, and alcohol consumption (multiple r = 0.38, p < 10(-6)) When the two groups of women with different Ca intake were subdivided into consumers and nonconsumers of alcohol, BPb was related positively to alcohol consumption and inversely to Ca intake. The highest BPb was found in the subgroup of alcohol consumers with low Ca intake, and the lowest BPb in the subgroup of nonconsumers with high Ca intake: 78 (42-251) microg/L and 51 (22-192) microg/L, respectively (p < 10(-8)). Diastolic blood pressure was significantly higher in the former subgroup as compared to the latter: 95 (72-130) mm Hg and 90 (60-120) mm Hg, respectively (p < 0.05). This cannot be explained by age, BMI, or BCd, which were comparable in the two subgroups. The results indicate that alcohol consumption and low Ca intake can increase BPb, which may significantly contribute to an increase in diastolic blood pressure in female nonsmokers even at relatively low-level Pb exposure.     

Effect of dietary calcium and phosphorus restriction on calcium and phosphorus balance in young and old rats

Previous studies have shown that the serum levels of the primary regulators of calcium (Ca) and phosphorus (P) metabolism, 1,25-dihydroxyvitamin D and parathyroid hormone, may change with age. Therefore, the effect of age on the ability of the rat to maintain a positive Ca and P balance was determined. Young (1.5 months) and old (18 months) rats were divided into three groups and fed either a low-Ca, high-P diet; a high-Ca, low-P diet; or a high-Ca, high-P diet. After 14 days, the young rats were in positive Ca and P balance regardless of diet. The old rats on the low-Ca, high-P diet were in negative Ca balance and positive P balance. The old rats on the other diets were in positive Ca and P balance. The negative Ca balance of the old rats was due to decreased intestinal absorption of Ca. Intestinal absorption was assessed by determining the percentage of dietary Ca absorbed in vivo and by measuring the active transport of Ca using the everted gut sac in vitro. Intestinal P absorption showed little change with age, except for a decrease in old rats on the high-Ca, low-P diet. Renal adaptation to dietary Ca and P restriction was similar in both young and old animals. Plasma Ca levels were unchanged with age, but plasma P levels decreased with age regardless of diet. These changes in Ca balance with age may reflect the reported decrease in serum 1,25-dihydroxyvitamin D₃ levels and the slight increase in PTH levels with age. The inability of old rats to maintain a positive Ca balance in the face of Ca deprivation is consistent with a general characteristic of the aging process—the decreased ability of an organism to adapt to changes in the external environment.     

Correlation between loss of alkaline phosphatase activity and accumulation of calcium during matrix vesicle-mediated mineralization

Activity of the bone/liver/kidney isozyme of alkaline phosphatase (AP) is known to be critical for mineralization in developing bone, although its role is unclear. The work now reported explores changes in the activity of this Zn2+-containing enzyme that occur during Ca2+ accumulation by matrix vesicles (MV). A marked loss (up to 65-70%) in AP activity was found to accompany Ca2+ accumulation by MV. These two events were highly correlated, both temporally and quantitatively. Investigation into possible causes revealed that the decline in AP activity during Ca2+ uptake was not due to action of proteases but rather resulted from interaction with the developing mineral phase, loss of metal ions (Zn2+ and Mg2+) from the active site of the enzyme, and concomitant irreversible denaturation of the enzyme. Protease inhibitors did not protect AP from loss of activity during mineralization; in contrast, protease treatments, which progressively destroyed the ability of MV to accumulate Ca2+ actually reduced loss of AP activity. These findings clearly demonstrate that AP is present at the site of MV mineralization and that its catalytic activity is profoundly reduced by the mineralization process.     

OPG-Fc treatment in growing pigs leads to rapid reductions in bone resorption markers, serum calcium, and bone formation markers

Inhibition of the receptor activator of NF-κB ligand (RANKL) is a novel therapeutic option in the treatment of osteoporosis and related diseases. The aim of this study was to evaluate bone metabolism and structure in pigs after RANKL inhibition. 12 growing pigs were assigned to 2 groups with 6 animals each. The OPG group received recombinant human OPG-Fc (5?mg/kg IV) at day 0, the control group was given 0.9% NaCl solution. Serum levels of OPG-Fc, calcium (Ca), phosphorus (P), and bone turnover markers were evaluated every 5 days, and pigs were euthanized on day 20. Serum OPG-Fc concentration peaked at day 5 and coincided with significantly decreased Ca, P, and bone turnover markers. By day 15, measureable OPG-Fc serum levels could only be detected in 2/6 animals. With OPG-Fc clearance starting at day 10, serum Ca and P concentrations were not different between the 2 groups. TRACP5b, P1CP, and BAP levels significantly decreased by 40-70% relative to vehicle controls in the OPG-Fc group between days 5 and 10, indicating that pharmacologic concentration of OPG-Fc led to systemic concomitant inhibition of bone formation and resorption in young growing pigs. Dual X-ray absorptiometry data derived from the proximal femur did not differ between the 2 groups. μCT analysis of selected bone sites demonstrated an OPG-Fc-induced improvement of specific bone architectural indices and bone mineralization.     

Increasing calcium levels in cultured insects

Low calcium (Ca) contents and low calcium:phosphorus (Ca:P) ratios of mealworm larvae and house crickets can result in imbalances of Ca and phosphorus (P) in diets of avian species when these insects form more than a minor proportion of the diet. Appropriate dietary Ca and Ca:P levels are particularly important for normal growth and bone development in chicks, especially of long‐legged species such as bustards. Two experiments were carried out to evaluate the efficacy of a selection of practicable dietary options for increasing the Ca levels and Ca:P ratios of cultured mealworm larvae and immature house crickets used for feeding bustards. Dietary treatments contained higher levels of Ca than the insects' standard culture diet components but similar P levels. Dietary treatment significantly increased Ca level and Ca:P ratio of both mealworm larvae and immature house crickets but did not affect P content of either species. Acceptable insect Ca and Ca:P levels were achieved by maintaining insects on commercial high‐Ca diet products for as little as 24 hours. Other factors that may have influenced the Ca levels of mealworm larvae and house crickets include physical form and overall nutrient composition of their diets. Zoo Biol 19:1–9, 2000. © 2000 Wiley‐Liss, Inc.     

Effect of dietary protein level and source on bone mineralization in rats

Bone mineralization was studied in rats. Animals were divided into three feeding groups: LCP - diet with 13.5% crude protein in DM (5% of gluten, 10% of casein), HCP - diet with 21.2% CP in DM (8% of gluten, 10% of casein), and LSM - diet based on grain meals and meat-bone meal (21% CP in DM). After 28 days feeding, animals were euthanased by cervical dislocation and femur bones were collected, weighed and kept frozen until analyses. Diets with 21% protein (HCP, LSM) significantly increased weight of femur bones. Despite of the substantially higher ash level (7.1%) in the LSM diet than in the LCP diet (3.4%), rats of both groups had the similar bone concentration of Ca (15.7 +/- 1.1 vs. 17.4 +/- 1.1 g/kg) and Zn (178.7 +/- 7.9 vs. 173.0 +/- 8.5 mg/kg). However bone density in LSM rats was significantly higher than in LCP ones. Although rats fed HCP diet had intermediate bone density, the bone concentration of Ca (11.4 +/- 0.5 g/kg) and Zn (145.1 +/- 2.9 mg/kg) was significantly lower, than in animals fed LCP and LSM diets. This was related to the very wide protein/calcium (37:1 g/g) and protein/zinc (5.3:1 g/mg) ratios in HCP diet. Those ratios were narrowest in the LSM diet: 16.2:1 (CP/Ca) and 2.6:1 (CP/Zn). It can be conluded that protein/mineral ratio in a diet is a very important factor in bone development, besides dietary protein and ash contents itselves.     

Effect of crude protein and phosphorus level on growth performance, bone mineralisation and phosphorus, calcium and nitrogen utilisation in grower-finisher pigs

Two experiments in a 2 x 2 factorial arrangement were conducted to evaluate the effect of crude protein (CP) (130 vs. 200 g/kg) and phosphorus (P) (4.0 vs. 6.0 g total P/kg) level in a phytase supplemented diet (500 FTU [phytase units]/kg) in grower-finisher pigs. Owing to the design of the experiment, as dietary P level increased, there was also an increase in dietary calcium (Ca) level in order to maintain a dietary Ca to P ratio of 1.6:1. In Experiment 1, four diets were fed to 56 pigs (n = 14, initial body weight [BW] 36.7 +/- 4.2 kg) to investigate the interaction between CP and P on growth performance, bone mineralisation and digesta pH. Experiment 2 consisted of 16 entire male pigs (n = 4; offered identical diets to that offered in Experiment 1) for the determination of total tract apparent digestibility and nitrogen (N), P and Ca utilisation. There was an interaction between CP and P level on bone ash, bone P and bone Ca concentrations (p < 0.05). Pigs offered low CP-low P diets had a higher bone ash, P and Ca concentrations than pigs offered high CP-low P diets. However, there was no effect of CP level at high P levels on bone ash, P and Ca concentrations. Pigs offered low P diets had a lower ileal pH compared with pigs offered high P diets (p < 0.05). In conclusion, offering pigs a high CP-low P, phytase-supplemented diet resulted in a decrease in bone mineralisation.