Meal-feeding and phosphorus ingestion influence calcium bioavailability evaluated by calcium balance and bone breaking strength in pigs

Use of fixed calcium to phosphorus ratios in experimental diets may create bias in phytase efficacy responses in swine

The objective of this study was to investigate the effects of two dietary total Ca/P ratios on available P release by phytase, measured using growth performance and bone mineralization with 528 barrows and gilts according to a randomized complete block design. Three were 11 diets in a factorial of 2 by 4 plus 3, including 3 reference diets consisting of 0.25% (control), 0.70%, or 1.15% monocalcium phosphate (MCP) and 8 diets from combining 4 phytase doses (500, 1,000, 2,000, and 3,000 FYT/kg) with 0.25% MCP and 2 dietary Ca/P ratios (1.05 and 1.20). Each diet was fed to 6 pens of 8 pigs. All diets contained 3 g/kg TiO₂, and fecal samples were collected from each pen on d 13–15 of trial. At the end of trial, one pig per pen was sacrificed to collect a tibia and urine in the bladder. The results showed that MCP improved growth performance linearly (P < 0.01), whereas both a linear and quadratic response was observed with the addition of phytase. The MCP increased the percent bone ash and weights of bone ash, Ca, and P linearly (P < 0.01). At both Ca/P ratios, increasing supplementation of phytase increased the percent bone ash and weights of bone ash, Ca, and P both linearly and quadratically (P < 0.05). Both MCP and phytase significantly increased digestibility of Ca and P as well as digestible Ca and P in diets and reduced the digestible Ca/P ratio. The dietary Ca/P ratio of 1.20 resulted in poorer feed utilization efficiency, more digestible Ca, greater percent bone ash, Ca, and P and heavier weights of bone Ca and P than the ratio of 1.05 (P < 0.05). The ratio of 1.20 elicited numerically higher available P release values from phytase, with percent bone ash and bone P weight as the response variables, but significantly lower values with gain:feed. The urinary concentration of Ca increased linearly (P < 0.01) with increasing digestible Ca/P ratios whilst urinary concentration of P decreased quadratically (P < 0.01). In conclusion, fixing the same total Ca/total P ratio in diets supplemented with increasing phytase dosing created an imbalance of digestible Ca and P, which could have an adverse effect on bone mineralization and thus compromise the phytase efficacy relative to mineral P.

Effect of Microbial Phytase on Ileal Digestibility of Minerals, Plasma and Urine Metabolites, and Bone Mineral Concentrations in Growing-Finishing Pigs

The study was conducted to evaluate the effects of added phytase in the diet of pigs on utilization of minerals and to determine the essential levels of this supplement in compound feed. An additional aim of the study was a critical assessment of current recommendations regarding the level of phosphorus in the diet of pigs, taking into account the use of phytase. A total of 432 pigs were allotted to six dietary treatments, with nine replicate pens per treatment according to body weight (BW) and sex. The treatments included a negative control (NC) with reduced content of digestible phosphorus; the NC diet supplemented with 6-phytase produced by a genetically modified strain of Aspergillus oryzae in the amount of 250 (NC + 250), 500 (NC + 500), 1000 (NC + 1000), or 1500 (NC + 1500) FTU/kg of feed; and a positive control (PC) diet formulated to meet NCR nutrient requirements for pigs. The results showed that, the higher the phytase activity in the diet (NC+), the lower the concentration of P, Ca, and Mg in the chyme (p < 0.05). Pigs fed the PC and NC+ diets had higher plasma levels of P and Ca than group NC in both fattening periods (p < 0.05). The content of phosphorus in the femur of pigs increased with the level of phytase added to the diet (p < 0.05). The content of Cu and Zn in the femur of pigs in the growing period was higher in groups NC + 500 and NC + 1000 than in the remaining experimental groups (p < 0.001). The content of P and Ca in the feces was higher in pigs fed the PC diet in comparison to the remaining experimental groups in both fattening periods (p < 0.001). There was a decrease in the content of P, Ca, and Mg in the excreta of pigs fed NC+ diets in both fattening periods (p < 0.05). A linear decrease in excretion of zinc in the feces was noted in the case of high levels of phytase, i.e., 1000 and 1500 FTU (p < 0.001). Increasing the level of phytase decreased the Cu (p < 0.001) content in the urine of growing−finishing pigs. In conclusion, the analysis of the effects of the use of phytase in a range of 0−1500 FTU/kg in low-phosphorus diets for fattening pigs indicates that 1000 FTU is the most effective level of phytase for increasing utilization of minerals and reducing excretion of elements into the environment.

Influence of Phytase Supplementation at Increasing Doses from 0 to 1500 FTU/kg on Growth Performance, Nutrient Digestibility, and Bone Status in Grower-Finisher Pigs Fed Phosphorus-Deficient Diets

Simple Summary

The current study investigates the growth performance and bone status of grower–finisher pigs supplemented with phytase, an enzyme which increases the bioavailability of phosphorus in animal feeds. The study results provide new information with regards to the positive role phytase supplementation to livestock feed plays in the achievement of the maximum effectiveness of the feed, as well as numerous positive effects on bone characteristics (geometry, mineralization, and mechanical strength) in grower–finisher pigs.

Abstract

The objective of the current study is to assess the effects of the inclusion of 6-n phytase to a phosphorous-deficient diet on the growth performance (feed intake, average daily gain, and feed conversion ratio), apparent digestibility of calcium and phosphorus, and bone characteristics of grower–finisher pigs. The experimental diets included a phosphorus-deficient diet containing 0 (negative control), 250, 500, 1000, or 1500 FTU/kg of 6-phytase, and a diet formulated to meet the phosphorus nutrient requirements of pigs (positive control). Pigs were fed the experimental diets from the time they were ~35 kg body weight until they reached slaughter weight of ~110 kg. Bone status of the metacarpal (ash, mineral content) and femur (mineralization, geometry, and mechanical strength) bones were assessed. There was no effect of dietary treatment on feed intake. Feed conversion ratio was improved following inclusion of phytase at a dose of 500 FTU/kg or higher. Phytase inclusion at a dose of 1000 FTU/kg increased the average daily weight gain of grower–finisher pigs. Phytase inclusion at a dose of 500 FTU/kg was sufficient to increase metacarpal phosphorus content. Femur mid-diaphysis ash percentage was significantly increased even after the inclusion of the lowest dose of phytase. Analysis of structural parameters of femur mechanical strength (Young’s modulus, yield stress, yield strain, ultimate stress, ultimate strain) showed that the inclusion of a phytase dose of 500 FTU/kg in growing/finishing diets was sufficient to significantly improve bone status of grower–finisher pigs at slaughter.

Intracellular Phosphate Dynamics in Muscle Measured by Magnetic Resonance Spectroscopy during Hemodialysis

Of the 600-700 mg inorganic phosphate (Pi) removed during a 4-hour hemodialysis session, a maximum of 10% may be extracted from the extracellular space. The origin of the other 90% of removed phosphate is unknown. This study tested the hypothesis that the main source of phosphate removed during hemodialysis is the intracellular compartment. Six binephrectomized pigs each underwent one 3-hour hemodialysis session, during which the extracorporeal circulation blood flow was maintained between 100 and 150 ml/min. To determine in vivo phosphate metabolism, we performed phosphorous ((31)P) magnetic resonance spectroscopy using a 1.5-Tesla system and a surface coil placed over the gluteal muscle region. (31)P magnetic resonance spectra (repetition time =10 s; echo time =0.35 ms) were acquired every 160 seconds before, during, and after dialysis. During the dialysis sessions, plasma phosphate concentrations decreased rapidly (-30.4 %; P=0.003) and then, plateaued before increasing approximately 30 minutes before the end of the sessions; 16 mmol phosphate was removed in each session. When extracellular phosphate levels plateaued, intracellular Pi content increased significantly (11%; P<0.001). Moreover, βATP decreased significantly (P<0.001); however, calcium levels remained balanced. Results of this study show that intracellular Pi is the source of Pi removed during dialysis. The intracellular Pi increase may reflect cellular stress induced by hemodialysis and/or strong intracellular phosphate regulation.

Reversal of osteoporotic changes of mineral composition in femurs of diabetic rats by insulin

Insulin plays an important role in bone prevention of diabetic osteoporosis, but little is known about the relation between the bone mineral density (BMD) increase and the change of mineral element content after treated with insulin. To address this problem, male Wistar rats were randomly divided into three groups: normal group (n = 6), streptozotocin-induced diabetic group (n = 5), and streptozotocin-induced diabetic group with insulin treatment (n = 5). The femoral BMD was measured by dual energy X-ray absorptiometry, and the element content was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The results showed that the femoral BMD in diabetic group was significantly lower than that in normal group (P < 0.01) but restored by insulin treatment (P < 0.01 vs diabetic group). ICP-AES analysis revealed that the element content of calcium (Ca), phosphorous (P), magnesium (Mg), strontium (Sr), and potassium (K) in diabetic group were remarkably lower than those in normal group (P < 0.01) but only Ca, P, and Mg content were significantly increased compared with diabetic group (P < 0.05) after insulin treatment. However, no significant differences were observed in element zinc (Zn) content among three groups. Our findings suggested that the loss of Ca, P, Mg, Sr, and K content accounted for the lower BMD in streptozotocin-induced diabetes rats, insulin treatment could restore BMD by increasing the content of Ca, P, and Mg.

Higher calcium urinary loss induced by a calcium sulphate-rich mineral water intake than by milk in young women

It is well known that the intestinal availability of Ca from Ca-rich mineral waters is equivalent to that of milk Ca. However, the effect of associated anions on Ca urinary loss needs to be addressed. The aim of the current study was to compare, under ordinary conditions of consumption, milk and a SO4-rich mineral water as the Ca provider in a large number of subjects consuming the same quantity of Ca from the two sources in a crossover study lasting for an extended period. Thirty-seven healthy women completed a 12-week protocol, divided into four periods of 3 weeks (W). In the first (W1-3) and third (W6-9) periods, dietary Ca intake was restricted to 600 mg/d. In the second (W4-6) and final (W10-12) periods, either 400 ml/d medium-fat milk or 1 litre of a Ca- and SO4-rich mineral water, each providing about 480 mg Ca/d, was added to the diet in a random manner. Dietary evaluation, blood and urinary measures were performed during the last week (W6 and W12) of each Ca supplementation period. The urinary excretion of Ca was higher (0.5 mmol/d more) with water than with milk (P<0.001). An examination of all the dietary factors known to influence calciuria suggested that the acidogenic action of SO4 was responsible for this increased calciuria. Thus, despite an equal Ca intake and assuming an unchanged intestinal absorption, these results suggest that Ca balance is better with milk consumption than with CaSO4-rich water.

The effect of estrogens and dietary calcium deficiency on the extracellular matrix of articular cartilage in Göttingen miniature pigs

Clinical observations have suggested that estrogens are involved in the pathogenesis of postmenopausal osteoarthritis (OA). However, positive and negative associations between the incidence of OA and serum estrogen concentrations have been reported. In contrast to this, osteoporosis is regarded as a disease with a strong estrogen-dependent component. Moreover, there is an interaction between estrogen and calcium deficiency: calcium supplementation potentiates the effect of estrogen therapy. The present study was designed to investigate how estrogen deficiency affects the articular cartilage depending on calcium supply. The distribution of different types of glycosaminoglycans and collagens can be used as an indicator for extracellular matrix changes induced by estrogen deficiency. Different levels of dietary calcium were therefore fed to intact and ovariectomized Göttingen miniature pigs for one year before articular cartilage was harvested. The histochemical staining for heavy sulfated glycosaminoglycans in the extracellular matrix of ovariectomized miniature pigs, especially of those fed with a low calcium diet, was stronger in comparison to intact animals. In intact animals type II-collagen was immunodetected in all zones of unmineralized and mineralized articular cartilage, while immunostaining for this protein was negative to weak in the deep radiated fiber zone of ovariectomized minipigs. These results suggest that the synthesis of heavy sulfated glycosaminoglycans and immunohistochemically detectable type II-collagen is possibly influenced by estrogen deficiency. In conclusion, under estrogen deficiency, the extracellular matrix of articular cartilage underwent similar changes to those observed in physiologically aging cartilage where keratan sulfate is increased as a heavy sulfated glycosaminoglycan.

Statistical optimization of gastric floating system for oral controlled delivery of calcium

The development of an optimized gastric floating drug delivery system is described. Statistical experimental design and data analysis using response surface methodology is also illustrated. A central, composite Box-Wilson design for the controlled release of calcium was used with 3 formulation variables: X1 (hydroxypropyl methylcellulose [HPMC] loading), X2 (citric acid loading), and X3 (magnesium stearate loading). Twenty formulations were prepared, and dissolution studies and floating kinetics were performed on these formulations. The dissolution data obtained were then fitted to the Power Law, and floating profiles were analyzed. Diffusion exponents obtained by Power Law were used as targeted response variables, and the constraints were placed on other response variables. All 3 formulation variables were found to be significant for the release properties (P <.05), while only HPMC loading was found to be significant for floating properties. Optimization of the formulations was achieved by applying the constrained optimization. The optimized formulation delivered calcium at the release rate of 40 mg/hr, with predicted n and T50% values at 0.93 and 3.29 hours, respectively. Experimentally, calcium was observed to release from the optimized formulation with n and T50% values of 0.89 (+/- 0.10) and 3.20 (+/- 0.21) hours, which showed an excellent agreement. The quadratic mathematical model developed could be used to further predict formulations with desirable release and floating properties.

Osteopenic disease in growing pigs: diagnostic methods using serum and urine calcium and phosphorus values, parathoromone assay, and bone analysis

This research was performed to evaluate the utility of several serum and urine parameters as well as bone ash and plasma parathormone assay to diagnose and monitor diet-related osteopenia in growing pigs. Five diets were tested as follows: calcium-deficient, phosphorus-replete; moderate-deficiency of calcium and phosphorus; marked deficiency of calcium and phosphorus; calcium replete, phosphorus deficient; and vitamin D deficient. Parameters monitored included serum calcium and phosphorus as well as ratios of urine calcium to creatinine, phosphorus to creatinine, calcium to phosphorus, and percent fractional excretions of calcium and phosphorus. Plasma parathormone (PTH) levels were monitored in 2 of 3 experiments. Osteopenic bone differences at necropsy were evaluated by bone density, percent ash, ash per milliliter bone, calcium per milliliter bone, and phosphorus per milliliter bone. Marked change in urine mineral parameters, especially the calcium-to-phosphorus ratio, typically occurred within 1 to 2 days of treatment and preceded significant change in serum mineral or plasma PTH by 2 to 3 weeks. When monitored, plasma PTH levels were elevated following treatment, which confirms the hyperparathyroid state induced by the test diets. Significant differences in bone mineralization between control and treatment diets at necropsy were generally observed. The results of this study indicate that the analysis of urine minerals offers an early, noninvasive technique to investigate diet-associated osteopenic disease in growing pigs, which can be supported further by bone mineral analysis at postmortem using techniques herein described. Several urine mineral reference intervals for application to field investigations are included. Research into application of similar techniques to evaluate calcium and phosphorus homeostasis in pigs of all ages, including gestating and lactating gilts and sows, appears warranted.

The bioavailability of dietary calcium

This update focuses on the bioavailability of dietary calcium for humans. Fundamentals of calcium metabolism, intestinal absorption, urinary excretion and balance are recalled. Dietary factors, especially lactose and other milk components, influencing calcium bioavailability at intestinal and renal levels are reviewed. A critical examination of all the methods used for evaluating calcium bioavailability is made. This includes in vitro assays, classical and isotopic balances, urinary excretion, isotope labeling in the urine, plasma and bones, long term evaluation of bone mineralization and the use of biological bone markers. Importance and advantages of animal models are discussed. The state of the art in the comparative bioavailability of calcium in foods is detailed including a comparison of sources of calcium (dairy products and calcium salts) in human studies and in some animal studies, casein phosphopeptides, proteins, lactose and lactase and their relation with calcium bioavailability (in humans and rats). An update on the consumption of dairy products and bone mass is presented. Emphasis on peculiarities and advantages of calcium in milk and dairy products is given.

Calcium-regulating hormones, bone mineral content, breaking load and trabecular remodeling are altered in growing pigs fed calcium-deficient diets

Studies on calcium nutrition in appropriate large animal models can be directly relevant to humans. We have examined the effect of dietary Ca deficiency on various bone and bone-related variables, including plasma markers, histomorphometry, mineral content and breaking strength in pigs. Three groups of eight 38-d-old female pigs were fed adequate (0.9%; control), low (0.4%; LCa) or very low (0.1%; VLCa) Ca diets for 32 d. Plasma Ca significantly decreased over time only in the VLCa-deficient pigs. The concentrations of the parathyroid hormones (PTH) and calcitriol increased as Ca deficiency developed, and the plasma PTH and calcitriol levels varied inversely with dietary Ca. The total bone ash contents, bending moments, trabecular bone volume and the mineral apposition rate all decreased as the calcium intake decreased. The osteoclast surface areas were greater than those of controls in both Ca-deficient groups, whereas the osteoblast surface areas were greater only in the VLCa group. The plasma osteoblast-related markers (alkaline phosphatase, carboxy-terminal propeptide of type I procollagen and osteocalcin) were either greater or unaffected in the Ca-deficient pigs. The results indicate that deficient bone mineralization combined with an increased bone resorption led to bone loss and fragility. The differences in the changes in bone cells (number and activity) between LCa and VLCa groups might be due to differences (time and extent) of circulating PTH and calcitriol. The defective mineralization in both Ca-depleted groups resulted mainly from the lack of Ca because their osteoblast activity was either maintained or stimulated. The results also underline the progressive sensitivity of pigs to Ca supply and the usefulness of this model.

A high sucrose diet decreases the mechanical strength of bones in growing rats

High sucrose diets alter mineral metabolism in humans and animals. We examined the effect of a high sucrose diet on bone growth, composition and mechanical strength in growing rats. Weanling Wistar rats received a high sucrose (43 g/100 g) diet (9 males, 11 females). In the control diet (8 males, 8 females), sucrose was replaced with potato starch, providing an equal energy value. At the onset of the experiment, bones were marked by tetracycline. After 5 wk, the tibias and femurs were weighed, and maximum breaking strengths were determined. Tibias were cut at the tibia-fibular junction; the widths of the bone at the start of the experiment, the periosteal bone formation during the experiment, the widths of the medullary cavity and the final bone width were determined from tetracycline lines. Bone ash weight, Ca and P contents were determined. The breaking strengths of both bones were significantly lower in the sucrose-fed groups of both sexes. In females, the weight of both bones and the final width of the tibias were significantly lower in the sucrose-fed group. The Ca concentration in both bones and the P concentration in tibias were significantly lower in the sucrose-fed group. It was concluded that the metabolic interference induced by sucrose was the reason for the differences. The alterations were more pronounced in females, but independent of body weight.

Experimental models of fracture repair

Many mammalian and avian species have been used as models to study fracture healing. The individual animals, based on their size and other characteristics, are used to show the effects of different interventions on healing bone. The models may have fractures created by closed or open means or osteotomies. Fracture healing can be evaluated through histologic, mechanical, chemical, or biological studies. Internal fixation, external skeletal fixation, or no fixation may be used in the experiments. Results of fracture healing studies among animal species may conflict even when the same model is used in each species. These differences may be explained by anatomic, biochemical, and gene expression differences. Evaluation of the animal model is an important consideration when applying the results of any particular study to humans. Consensus regarding fracture healing develops from agreement between results of animal models and human clinical studies.

Mineral bioavailability and bone mineral contents in pigs given calcium carbonate postprandially

We have further investigated the "meal effect" on mineral bioavailability in pigs by mineral balance studies and measurements of bone ash contents and bending moment. A group of seven pigs (CAA) was given all its dietary Ca as CaCO3 5 h after the first daily meal for 8 weeks. The control group of seven pigs received CaCO3 in the meal. Both groups were given normal P within the meals. Ca and P absorption and retention were evaluated by a 10-day balance trial. Several bones were collected at slaughter to determine bone ash, Ca, and P contents and bending moment (three-point bending test). Ingesting Ca after the meal did not affect Ca bioavailability or phosphorus absorption, but did reduce P retention, which in turn decreased the bone scores. Osteopenia, indicated by decreased total mineral contents of bones (and decreased ash:bone volume ratio), was associated with elevated plasma osteocalcin in the CAA group. Thus, CaCO3 need not be incorporated into a meal for high Ca absorption, provided that Ca is given after a meal, but simultaneous intakes of Ca and P are required for the best mineral retention.