Characterization of the Chicken Small Intestine Type IIb Sodium Phosphate Cotransporter

1,25-dihydroxyvitamin D3 enhances the expression of phosphorus transporters via vitamin D receptor in ligated duodenal loops of Arbor Acres male broilers

1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] could promote phosphorus (P) absorption in the duodenum of broilers. The vitamin D receptor (VDR) mediates the action of 1,25-(OH)2D3. However, it remains unknown whether and how VDR is involved in promoting P absorption in the duodenum of broilers by 1,25-(OH)2D3. The objective of the current study was to investigate the effect of added 1,25-(OH)2D3 levels on P absorption, mRNA or protein expression levels of VDR, retinoid X receptor (RXR), type IIb sodium-phosphate cotransporter (NaPi-IIb), inorganic phosphate transporter (PiT) 1 and PiT-2, and the enrichments of VDR bound to DNA promoters of the above P transporters in the ligated duodenal loops of Arbor Acres male broilers. The duodenal loops were perfused with solutions (pH = 6.0) containing 0 (control), 12.5, or 25.0 ng/L of 1,25-(OH)2D3 for up to 40 min. The results indicated that the addition of either 12.5 or 25.0 ng/L 1,25-(OH)2D3 to the perfusates increased (P < 0.04) P absorption percentage and rate, as well as the mRNA expression levels of VDR, RXR, NaPi-IIb, and PiT-2, alongside protein expression levels of VDR, NaPi-IIb, and PiT-2, whereas it did not affect (P > 0.10) PiT-1 mRNA and protein expression levels. Moreover, 1,25-(OH)2D3 administration increased (P < 0.01) the enrichments of VDR bound to NaPi-IIb and PiT-2 DNA promoter regions in the ligated duodenal loops of broilers, which were in line with their mRNA expression levels. These findings suggest that 1,25-(OH)2D3 increased P absorption possibly through VDR-mediated transactivation of NaPi-IIb and PiT-2 genes in the duodenum of Arbor Acres male broilers.

Long-Term Effects of Early Low-Phosphorous Nutritional Conditioning on Broiler Chicken Performance, Bone Mineralization, and Gut Health Under Adequate or Phosphorous-Deficient Diets

Phosphorous is essential for many metabolic functions and the constitution of bones. Poultry have limited ability to use phosphorous from diets, which is mainly excreted and causes environmental concern. For this reason, diets are commonly supplemented with inorganic phosphorus and phytases. It has been suggested that chickens can adapt to an early nutrient restriction by increasing its efficiency of utilization, an adaptation that has been defined as nutritional conditioning. The aim of this study was to investigate a strategy of phosphorous nutritional conditioning by feeding low phosphorous diets during the first week of life as a strategy to improve the efficiency of phosphorous utilization later in life. To test this, 600 male broiler chickens were fed either a standard (control group) or a phosphorous-deficient diet (conditioned group) during the first week of life. Later in life, the effect of conditioning was tested using standard or P-deficient diets during the finishing phase (21-43 d). Conditioning did not affect overall performance, despite finding evidence for reduced relative phosphorous excretion between days 19 to 21, increased duodenal gene expression for the phosphorous transporter SLC34A2 at day 30 (-6% and +17%, respectively), and tendencies for improved phosphorous digestibility (+7%) and tibia mineralization (+6%) at the end of the trial. It is concluded that phosphorous nutritional conditioning early in life can increase subsequent dietary phosphorous utilization and bone mineralization in poultry, although it may not be able to counteract severe phosphorous deficiencies. Further research is required to assess the extent to which phosphorous supplementation in post-conditioning diets may be reduced with this strategy without compromising performance.

Ileal phosphorus digestibility of soybean meal for broiler chickens remains consistent across institutions in a collaborative study regardless of non-phytate phosphorus concentration in the pre-experimental starter diet

The same experimental protocol was used in 4 institutions to evaluate the impact of non-phytate phosphorus (nPP) concentration in the starter diet on regression method-derived ileal P digestibility of soybean meal (SBM) during the subsequent grower phase. A total of 1,536 Ross 308 male broiler chickens on d 0 post hatching were allotted to 2 pre-experimental starter diets that contained 3.5 or 4.5 g nPP/kg (96 replicate cages per diet, 8 birds per cage) for 18 d. Subsequently, 576 birds from each starter diet were selected and allocated to 3 experimental semi-purified grower diets containing 400, 510, or 620 g SBM/kg (32 replicate cages per diet, 6 birds per cage) for 3 d until collection of ileal digesta. Statistical analysis was conducted as a randomized complete block design with the starter period as whole plot and the grower period as split-plot. The only significant 2-way interaction was between grower diet and experimental institution (P < 0.05) on BW gain and gain to feed ratio. The main effect of institution and grower diet impacted (P < 0.05) feed intake, the digestibility of DM, P, and calcium, and disappearance of inositol hexakisphosphate (InsP6) in the grower diets. Birds fed the 3.5 g nPP/kg starter diet had lower (P < 0.05) BW gain and feed intake during the grower period, but presented higher (P < 0.05) digestibility of P and disappearance of InsP6 compared with the birds that were fed the 4.5 g nPP/kg starter diet. Regression method-derived ileal P digestibility of SBM was determined to be 46 or 42% for the respective 3.5 or 4.5 g nPP/kg pre-experimental starter diet and was not affected by the nPP concentration or by the institution. In conclusion, the experimental protocol used in the current study resulted in similar estimates across multiple institutions and is thus endorsed for future application in studies that aim to expand the database of digestible P content in plant source feed ingredients.

Ileal mineral digestibility and expression of nutrient transporter genes of broiler chickens in response to variable dietary total Ca and phytase supplementation are influenced by time on experimental diet and age of the birds

Two experiments were conducted to determine the impact of Ca, phytase, sampling time, and age on the digestibility (AID) of Ca and P and the expression of their transporters. Cobb 500 male chicks (N = 600) were used in each experiment and allocated to cages with 10 (Exp 1, 8-11 d) or 5 (Exp 2, 21-24 d) birds/cage and 10 (Exp 1) or 20 (Exp 2) reps/treatment. Treatments were a 2 × 3 factorial arrangement, with low (LOW) or standard (STD) Ca level and 3 phytase (PHY) levels (0, 300, or 3,000 FYT/kg). Ileal digesta were collected at 8, 12, 24, 48, and 72 h, and jejunum tissues at 12, 48, and 72 h after the start of feeding experimental diets. In Exp 1, there was no effect of Ca or phytase on the AID of Ca at 8, 12, or 24 h. Phytase increased the AID of P (P < 0.05) at all time points, and the magnitude was influenced by Ca. At 12 h, the mRNA level of P (NaPi-IIb) and Ca (CaSR) transporters was greatest in the LOW diets without phytase (Ca × PHY, P ≤ 0.06). In Exp 2, the STD diet decreased the AID of Ca and P (P < 0.05) at 8, 24, 48, or 72 h. Phytase increased the AID of Ca (P < 0.05) at 8, 12, and 24 h, and decreased the AID of Ca (quadratic, P < 0.05) in the STD diet (48 h). The AID of P (P < 0.05) increased with phytase at all sampling times. At 48 h, 3,000 FYT/kg decreased (P < 0.05) mRNA expression of NaPi-IIb and Ca transporter ATP2B1 in the STD diet (Ca × PHY, P < 0.05). In conclusion, to avoid adaptation of broilers to Ca and P deficiencies, the optimal time on experimental diets is ≤ 48 h for young broilers and ≤ 24 h in older birds due to up- or down-regulation of Ca and P transporters in response to dietary Ca, P, and phytase.

Approaches to determine the efficiency of novel 3-phytase from Klebsiella pneumoniae and commercial phytase in broilers from 1 to 14 d of age

This study aimed to evaluate the effects of a laboratory 3-phytase (the expression of the phyK gene, Lab-Phy) and a commercial 6-phytase (Quantum Blue 40 P, Com-Phy) alone and in combination (corn-soy-based diets) in broilers. A total of 400, day-old Ross 308 male broilers were randomly assigned to 5 treatments with 10 replicate cages (8 chicks/cage) for a 14-day trial. Experimental treatments included the positive control (0.95% Ca and 0.48% nonphytate phosphorus (nPP), PC), negative control (0.90% Ca and 0.22% nPP, NC), and NC which was supplemented with Lab-Phy 250 FTU/kg and Com-Phy 250 FTU/kg alone or in combination of Lab-Phy 125 FTU/kg and Com-Phy 125 FTU/kg. The inclusion of Lab-Phy in the NC diet significantly improved the P and Ca content in the tibia compared to the NC group. Moreover, the inclusion of Com-Phy alone and in combination with Lab-Phy in the NC diet significantly increased the P and Ca content in the tibia compared to the Lab-Phy. The mRNA expression of NaPi-IIb was upregulated in the duodenum by the reduction of nPP and downregulated by the inclusion of any phytase, whereas other nutrient transporters were not influenced by the reduction of nPP or the addition of phytase in the small intestine mucosa. Broilers receiving the NC diet obtained the lowest body weight (BW) and body weight gain (BWG) at 8 to 14 and 1 to 14 d of age. The NC group showed the lowest villi height and surface area, Newcastle disease (ND) antibody titer, and digestibility of nutrients compared to the PC group at 14 d of age. Supplementing the NC diet with the Lab-Phy and Com-Phy individually, or in combination tended to improve BW, BWG, tibia characteristics, villi characteristics, ND, and retained CP and P, and apparent ileal digestibility of CP, P, methionine, and threonine. The present research indicated that the studied traits by the combination of phytases were slightly better than the average of the 2 individually, suggesting there might be some value in combining the laboratory and commercial phytases.

Physiological regulation of calcium and phosphorus utilization in laying hens

Commercial laying hens can produce one egg approximately every 24 h. During this process, regulatory systems that control vitamin D3 metabolism, calcium and phosphorus homeostasis, and intestinal uptake of these minerals work in concert to deliver components required for eggshell calcification and bone mineralization. Commercial production cycles have been extended in recent years to last through 100 weeks of age, and older hens often exhibit an increased prevalence of skeletal fractures and poor eggshell quality. Issues such as these arise, in part, through imbalances that occur in calcium and phosphorus utilization as hens age. As a result, an in-depth understanding of the mechanisms that drive calcium and phosphorus uptake and utilization is required to develop solutions to these welfare and economic challenges. This paper reviews factors that influence calcium and phosphorus homeostasis in laying hens, including eggshell formation and development and roles of cortical and medullary bone. Metabolism and actions of vitamin D3 and physiological regulation of calcium and phosphorus homeostasis in key tissues are also discussed. Areas that require further research in avian species, such as the role of fibroblast growth factor 23 in these processes and the metabolism and action of bioactive vitamin D3, are highlighted and the importance of using emerging technologies and establishing in vitro systems to perform functional and mechanistic studies is emphasized.

Broiler physiological response to low phosphorus diets at different stages of production

Phosphorus (P) inclusion in broiler diets needs to meet the physiological demands at a specific developmental stage to ensure the performance, health, and welfare of the birds and minimize nutrient losses. Toward a more efficient utilization of P in broiler husbandry, a timed nutritional conditioning strategy might enhance the endogenous mechanisms of mineral homeostasis and thus reduce dietary P supply of mineral sources. In this study, following a variable P supply in the starter phase, the effects of a dietary P depletion of broiler chickens were investigated at different developmental stages. Physiological adaptation mechanisms were elucidated based on zootechnical performance, endocrine parameters, regulation of intestinal P transport, bone characteristics, and health aspects. The results revealed a marked response to P depletion at the earliest developmental phase, after which indications of effective compensatory mechanism were detectable with advancing ages. Potential mechanisms that enable broilers to maintain mineral homeostasis primarily include endocrine control mediated by calcitriol actions, as well as intestinal P uptake and mineral mobilization from the bone. Conclusively, the precise timing, duration, and extent of a P depletion strategy in the broiler chicken might be considered for optimized nutrient utilization.

The temporal gene expression profiles of calcium and phosphorus transporters in Hy-Line Brown layers

Calcium and phosphorus homeostasis is crucial for the performance and bone health of laying hens. The calcium and phosphorus transporters play an important role in calcium and phosphorus absorption, reabsorption, and excretion. In the present study, Hy-Line Brown layers were sampled at brooding period (1, 4, 6 wk), growing and developing period (12, 18 wk) and laying period (20, 28, 80 wk) respectively, and the calcium transporters CaBP-D28k and PMCA1b and phosphorus transporters NPt2a and NPt2b were respectively measured in duodenum, jejunum, ileum and kidney. The result showed that serum calcium increased (P < 0.0001) and phosphorus level fluctuated (P = 0.0019), while alkaline phosphatase activity decreased with age (P < 0.0001). The mRNA and protein expressions of CaBP-D28k in small intestine elevated after maturity (P ≤ 0.0001). In contrast, the PMCA1b mRNA showed a trend to increase with age in jejunum (P = 0.0059) and ileum (P = 0.0825) whereas there was a decrease for PMCA1b protein in 12-18 wk (P ≤ 0.0009). The peak of NPt2b mRNA were observed at 28 wk in duodenum (P = 0.0001) and jejunum (P = 0.0622) and 1 wk in ileum (P < 0.0001). The NPt2b protein expression reached the top point at 4 or 6 wk and 20 wk and decreased to the lowest point around 12 wk (P ≤ 0.0850). In kidney, CaBP-D28k mRNA was not influenced by age (P = 0.4999), while PMCA1b highly expressed in 6-12 wk (P = 0.0003). The protein expressions of CaBP-D28k (P = 0.0148) and PMCA1b (P = 0.0003) decreased with age and lowly expressed in 12-18 wk and increased thereafter. In contrast, NPt2a expression increased steadily with age and decreased at 80 wk (P < 0.0001). In conclusion, the expressions of intestinal calcium and phosphorus transporters were changed by age, intestinal CaBP-D28k and renal NPt2a showed a dramatic increase after maturity, which coincide with the increased calcium and phosphorus requirement for egg production.

Mechanisms of Epidermal Growth Factor Effect on Animal Intestinal Phosphate Absorption: A Review

Phosphorus is one of the essential mineral elements of animals that plays an important role in animal growth and development, bone formation, energy metabolism, nucleic acid synthesis, cell signal transduction, and blood acid–base balance. It has been established that the Type IIb sodium-dependent phosphate cotransporters (NaPi-IIb) protein is the major sodium-dependent phosphate (Pi) transporter, which plays an important role in Pi uptake across the apical membrane of epithelial cells in the small intestine. Previous studies have demonstrated that epidermal growth factor (EGF) is involved in regulating intestinal Pi absorption. Here we summarize the effects of EGF on active Pi transport of NaPi-IIb under different conditions. Under normal conditions, EGF inhibits the active transport of Pi by inhibiting the expression of NaPi-IIb, while, under intestinal injury condition, EGF promotes the active absorption of Pi through upregulating the expression of NaPi-IIb. This review provides a reference for information about EGF-regulatory functions in Pi absorption in the animal intestine.

Prolonged scotophase within a 24 hour light regime improves eggshell quality by enhancing calcium deposition in laying hens

Calcium (Ca) and phosphorus (P) transporters are responsible for their absorption and transport in small intestine and kidney, contributing to eggshell formation. The light-dark cycle is a primary cue in the reproduction of laying hen. In this study, we investigated the effect of different light-dark programs on eggshell quality and the expression of genes related to Ca and P transportation in laying hens. Seventy-two 56-week-old laying hens were randomly divided into two groups and reared at 16-h light and 8-h dark (control) or 9-h light and 15-h dark regime (long dark phase, LDP). The expressions of calcium transporter calbindin-D28k (CaBP-D28k), plasma membrane Ca ATPase 1b (PMCA1b), and phosphorus transporter NaPi-IIb (NPt2b) and NaPi-IIa (NPt2a) were measured in the small intestine, kidney, and eggshell gland. The results showed that feed intake (P < 0.001) and egg weight (P = 0.05) were decreased by LDP treatment. Compared with control, the eggshell hardness was increased (P = 0.011) by LDP treatment, but the eggshell thickness and the percentage of eggshell were not changed. The Ca and P contents in eggshell were increased by LDP treatment. During the scotophase, LDP-hens showed higher serum Ca (P = 0.0056) and P levels (P = 0.079) but lower alkaline phosphatase (ALP) activity than that of control hens. In the duodenum, the relative higher expression of CaBP-D28k and PMCA1b in scotophase compared to photophase was masked by LDP treatment. The expression of CaBP-D28k and osteopontin (OPN) in the eggshell gland were increased by LDP treatment, compared to control hens. In the jejunum, the protein expression levels of CaBP-D28k and PMCA1b decreased during photophase in LDP-hens. The result indicates that the increased blood Ca and P concentration during scotophase by LPD treatment is beneficial to the deposition of Ca and P in the eggshell. The result offers an alternative strategy for managing laying hens with poor eggshell quality.

Changes in duodenal and nephritic Ca and P absorption in hens during different egg-laying periods

Ca and P metabolic disorders during the egg-laying period can reduce egg production, impair eggshell quality, and even cause bone problems in hens; however, little is known regarding the capacity of duodenal and nephritic Ca and P absorption. Here, the levels of serum Ca and P metabolic indices and the expression of duodenal and renal Ca and P transporter genes were measured in hens at different egg-laying stages. The Ca, 25-(OH)-VD3, and 1,25-(OH)2-VD3 content increased during the peak (43 weeks of age) and late (72 weeks of age) egg-laying periods compared to that during the early (23 weeks of age) egg-laying period; however, there were no differences in Pi levels among the three egg-laying periods. Moreover, duodenal VDR and CaBP-D28k mRNA expression was markedly higher but NPt2b mRNA expression was markedly lower during the peak and late egg-laying periods than during the early egg-laying period. Furthermore, nephritic CaBP-D28k, PMCA1b, and FGFR1 mRNA expression was markedly higher but NPt2a and Cyp24a1 mRNA expression was markedly lower during the peak and late egg-laying periods than during the early egg-laying period. In conclusion, the present study indicated that the increased duodenal and nephritic Ca absorption during the peak and late egg-laying periods may be associated with the VD-VDR pathway, while the decreased P absorption despite relatively stable serum P levels in all three egg-laying stages may associated with osteolysis.

Early-life conditioning strategies to reduce dietary phosphorus in broilers: underlying mechanisms

Chickens adapt to P and Ca restriction during the very first days of life by improving P utilisation efficiency. The present study was built to identify the mechanisms underlying this adaptive capacity, and to identify the optimal window of application of the restriction (depletion). A total of 1600 Cobb 500^TM male broilers were used. During each phase (from age 0 to 4 d, 5 to 8 d, 9 to 18 d and 19 to 33 d), the animals received either a control diet (H) or a restricted diet (L) with reduced levels of non-phytate P (nPP) and Ca (between −14 and −25 % for both) with four dietary sequences: HHHH, HLHL, LHHL and LLHL. None of the feeding strategies affected growth. Tibia ash content at day 4 and 8 was impaired when the L diet was fed from 0 to 4 and 5 to 8 d, respectively (P = 0⋅038 and P = 0⋅005). Whatever the early restriction period or length between 0 and 8 d of age, the mineralisation delay was compensated by day 18. This was accompanied by an increased mRNA expression of the Ca transporter, CALB1, and an increased apparent ileal digestibility of Ca at day 8 (P < 0⋅001). This adaptation was limited to the starter phase in restricted birds. No effect was seen on P transporters mRNA or protein expression. In conclusion, birds adapted to mineral restriction by increasing Ca and nPP utilisation efficiencies. Depletion−repletion strategies are promising in improving the sustainability of broiler production but need to be validated in phytase-supplemented diets.

Effect of inorganic phosphate supplementation on egg production in Hy-Line Brown layers fed 2000 FTU/kg phytase

Phytase has long been used to decrease the inorganic phosphorus (Pi) input in poultry diet. The current study was conducted to investigate the effects of Pi supplementation on laying performance, egg quality and phosphate-calcium metabolism in Hy-Line Brown laying hens fed phytase. Layers (n = 504, 29 weeks old) were randomly assigned to seven treatments with six replicates of 12 birds. The corn-soybean meal-based diet contained 0.12% non-phytate phosphorus (nPP), 3.8% calcium, 2415 IU/kg vitamin D3 and 2000 FTU/kg phytase. Inorganic phosphorus (in the form of mono-dicalcium phosphate) was added into the basal diet to construct seven experimental diets; the final dietary nPP levels were 0.12%, 0.17%, 0.22%, 0.27%, 0.32%, 0.37% and 0.42%. The feeding trial lasted 12 weeks (hens from 29 to 40 weeks of age). Laying performance (housed laying rate, egg weight, egg mass, daily feed intake and feed conversion ratio) was weekly calculated. Egg quality (egg shape index, shell strength, shell thickness, albumen height, yolk colour and Haugh units), serum parameters (calcium, phosphorus, parathyroid hormone, calcitonin and 1,25-dihydroxyvitamin D), tibia quality (breaking strength, and calcium, phosphorus and ash contents), intestinal gene expression (type IIb sodium-dependent phosphate cotransporter, NaPi-IIb) and phosphorus excretion were determined at the end of the trial. No differences were observed on laying performance, egg quality, serum parameters and tibia quality. Hens fed 0.17% nPP had increased (P < 0.01) duodenum NaPi-IIb expression compared to all other treatments. Phosphorus excretion linearly increased with an increase in dietary nPP (phosphorus excretion = 1.7916 × nPP + 0.2157; R2 = 0.9609, P = 0.001). In conclusion, corn-soybean meal-based diets containing 0.12% nPP, 3.8% calcium, 2415 IU/kg vitamin D3 and 2000 FTU/kg phytase would meet the requirements for egg production in Hy-Line Brown laying hens (29 to 40 weeks of age).

Effects of available phosphorus source and concentration on performance and expression of sodium phosphate type IIb cotransporter, vitamin D-1α-hydroxylase, and vitamin D-24-hydroxylase mRNA in broiler chicks

This experiment was conducted to examine the effect of 2 phosphorus (P) sources on broiler performance to day 14. The P bioavailability was estimated using bird performance and tibia ash measurements, whereas P digestibility, intestinal P transporter, kidney vitamin D-1α-hydroxylase, and vitamin D-24-hydroxylase mRNA abundances were also determined. Slope regression analysis was used to determine the bioavailability of dicalcium phosphate (Dical P) and nanocalcium phosphate (Nano P) with dietary available P (AvP) set to 0.20% P (control) using AvP from the major ingredients and Dical P. The experimental treatments were achieved by supplementation with either Dical P or Nano P to generate 0.24, 0.28, 0.32, and 0.36% AvP. A total of 648-day-old unsexed broiler chicks were divided into 72 birds per treatment (8 replicate cages of 9 birds). Slope regression analysis showed positive linear relationships between BW, feed intake (FI), tibia ash weight (TAW), and tibia ash percentage (TAP) with dietary Dical P and Nano P levels. Comparisons between regression slopes for Dical P and Nano P fed birds were not significantly different for BW, feed intake, tibia ash weight, and tibia ash percentage, indicating similar P bioavailability from Dical P and Nano P. There were interactions between P source and AvP for feed efficiency (FE) and apparent ileal P digestibility (AIPD). Dicalcium phosphate had greater FE than Nano P at 0.28% AvP and greater AIPD than Nano P at 0.24% AvP. The addition of AvP from Dical P and Nano P resulted in reduced sodium phosphate cotransporter mRNA abundance in the duodenum in a dose–dependent response. In the kidney, vitamin D-1α-hydroxylase mRNA abundance was greater at 0.36% Nano P compared with control, but there was no difference with Dical P. There was no difference in vitamin D-24-hydroxylase mRNA abundance between control and supplementation with Nano P or Dical P. In conclusion, Nano P and Dical P had the same bioavailability but had different effects on gene expression.

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.

Optimal Dietary Levels of 1α-Hydroxycholecalciferol in Broiler Chickens from 1 to 42 Days of Age

1α-Hydroxycholecalciferol (1α-OH-D₃) is an active vitamin D derivative. In this study, three experiments were conducted to evaluate the optimal dietary levels of 1α-OH-D₃ in broiler chickens from 1 to 42 days of age. 1α-OH-D₃ levels used were 0, 1.25, 2.5, 5, and 10 µg/kg in experiment 1, 0.625, 1.25, 2.5, 5, 7.5, and 10 µg/kg in experiment 2, and 2, 2.5, 3, 3.5, 4, 4.5, and 5 µg/kg in experiment 3. In experiment 1, the addition of 0 to 10 µg/kg of 1α-OH-D₃ quadratically improved growth performance, tibia development, and mRNA expression levels of nuclear vitamin D receptor (nVDR), membrane vitamin D receptor (mVDR), and type IIb sodium-phosphate cotransporter (NaPi-IIb) in the duodenum of broiler chickens from 1 to 12 days of age. Body weight gain (BWG), the weight and ash weight of the tibia, and mRNA expression levels of mVDR and NaPi-IIb of broilers fed with 0 and 10 µg/kg of 1α-OH-D₃ were lower than those of birds fed with 2.5 µg/kg of 1α-OH-D₃. In experiment 2, 1α-OH-D₃ levels were quadratically related to BWG and to weight and ash weight of the femur and the tibia of broiler chickens at 42 days of age. The highest values of growth performance and bone mineralization were recorded in broilers fed with 2.5 to 5 µg/kg of 1α-OH-D₃. In experiment 3, there was no difference observed in BWG and the weight and ash weight of the femur and the tibia of the 42-day-old broilers fed with 2 to 5 µg/kg of 1α-OH-D₃. These data suggest that the optimal dietary levels of 1α-OH-D₃ were 2 to 5 µg/kg for broiler chickens from 1 to 42 days of age.

Restriction of dietary non-phytate phosphorus on growth performance and expression of intestinal phosphate cotransporter genes in broilers

Effects of dietary non-phytate phosphorus (nPP) restriction on growth and duodenal type IIb sodium-dependent phosphate cotransporter (NaPi-IIb) genes were observed. A total of 432 one-day old Cobb500 male broiler chickens in 36 cage pens were divided into 6 groups with each group containing 6 pens. Each group was treated with one of the diets containing 0.33, 0.37, 0.41, 0.45, 0.49, and 0.53% of nPP up to 14 D. During 15 to 31 D, birds were treated with one of the diets containing 0.23, 0.27, 0.31, 0.35, 0.39, and 0.43% of nPP. Level of Ca was kept the same across all treatments. Dietary nPP level influenced (P < 0.001) weight gain and feed intake in both growth phases, whereas effect on feed per gain ratio was seen only in the second phase. Toe ash, tibia ash, and tibia breaking strength responded to treatments (P < 0.01) at 14 D. Only tibia ash content was significantly improved (P < 0.001) at 31 D. Growth and bone parameters linearly improved with an increase in dietary nPP content (P < 0.05). Above dietary nPP 0.41% and 0.31% for first phase and second phase, respectively, no significant improvement was seen. Duodenal NaPi-IIb mRNA overexpressed with a decrease in dietary nPP in both phases (P < 0.05). Relative expression of NaPi-IIb in lowest nPP group were 2.2 folds higher in the first phase and 3.6 folds higher in the second phase compared to respective highest nPP groups of each phase. No significant change in NaPi-IIb expression was seen above 0.37% of dietary nPP for 14 D and 0.31% of dietary nPP for 31 D. Dietary requirements of nPP 0.41% for 0 to 14 D and 0.31% for 15 to 31 D were adequate for optimal growth and bone parameters. This study fills the gap in understanding of intestinal NaPi-IIb expression in response to dietary nPP restriction in broilers older than 21 D of age.

Dietary phosphorus deficiency impaired growth, intestinal digestion and absorption function of meat ducks

Objective

An experiment was conducted to investigate the effects of dietary non-phytate phosphorus (nPP) deficiency on intestinal pH value, digestive enzyme activity, morphology, nutrient utilization, and gene expression of NaPi-IIb in meat ducks from 1 to 21 d of age.

Methods

A total of 525 one-d-old Cherry Valley ducklings were fed diets (with 7 pens of 15 ducklings, or 105 total ducklings, on each diet) with five levels of nPP (0.22%, 0.34%, 0.40%, 0.46%, or 0.58%) for 21 d in a completely randomized design. Five experimental diets contained a constant calcium (Ca) content of approximately 0.9%. Body weight (BW), body weight gain (BWG), feed intake (FI), and feed to gain ratio (F:G) were measured at 14 and 21 d of age. Ducks were sampled for duodenum and jejunum digestion and absorption function on 14 and 21 d. Nutrient utilization was assessed using 25- to 27-d-old ducks.

Results

The results showed ducks fed 0.22% nPP had lower (p<0.05) growth performance and nutrient utilization and higher (p<0.05) serum Ca content and alkaline phosphatase (ALP) activity. When dietary nPP levels were increased, BW (d 14 and 21), BWG and FI (all intervals), and the serum phosphorus (P) content linearly and quadratically increased (p<0.05); and the jejunal pH value (d 14), duodenal muscle layer thickness (d 14), excreta dry matter, crude protein, energy, Ca and total P utilization linearly increased (p<0.05); however, the serum ALP activity, jejunal Na⁺-K⁺-ATPase activity, and duodenal NaPi-IIb mRNA level (d 21) linearly decreased (p<0.05).

Conclusion

The results indicated that ducks aged from 1 to 21 d fed diets with 0.22% nPP had poor growth performance related to poor intestinal digestion and absorption ability; but when fed diets with 0.40%, 0.46%, and 0.58% nPP, ducks presented a better growth performance, intestinal digestion and absorption function.

Phosphorus absorption and gene expression levels of related transporters in the small intestine of broilers

To investigate the P absorption and gene expression levels of related co-transporters, type IIb sodium-dependent phosphate co-transporter (NaPi-IIb), inorganic phosphate transporter 1 (PiT-1) and inorganic phosphate transporter 2 (PiT-2) in the small intestine of broilers, 450 1-d-old Arbor Acres male broilers were randomly allocated to one of three treatments with ten replicate cages of fifteen birds per cage for each treatment in a completely randomised design. Chickens were fed a diet with no added inorganic P (containing 0·06 % non-phytate P (NPP)) or with either 0·21 or 0·44 % NPP for 21 d. Plasma P concentration in the hepatic portal vein, mRNA and protein expression levels of NaPi-IIb, PiT-1 and PiT-2 were determined at 7, 14 and 21 d of age. The results showed that the concentration of P in plasma in the hepatic portal vein increased as dietary NPP increased (P<0·0001). At 14 and 21 d of age, the increase in dietary NPP inhibited (P<0·003) NaPi-IIb mRNA expression level in the duodenum, as well as PiT-1 mRNA and protein expression levels in the ileum, but promoted NaPi-IIb protein expression level (P<0·002) and PiT-2 mRNA and protein expression levels (P<0·04) in the duodenum. These results suggest that NaPi-IIb, PiT-1 and PiT-2 might be important P transporters in the small intestine of broilers. Higher intestinal P absorption may be achieved by up-regulating the protein expression levels of NaPi-IIb and PiT-2 and down-regulating the protein expression of PiT-1.

Lack of a relationship between plasma fibroblast growth factor-23 and phosphate utilization in young chicks

Fibroblast growth factor 23 (FGF-23) is proposed to be the hormone that controls phosphate (P) homeostasis in chickens. This study was initiated to investigate the effect of feeding young chicks diets that were either adequate (0.45%) or marginal (0.25%) in available P content on plasma FGF-23 levels. The dietary level of available P significantly (P ≤ 0.05) affected bone mineralization and bone length, but was without effect (P > 0.05) on growth rate and circulating FGF-23 concentrations. Substantial individual variation in bone mineralization and plasma FGF-23 levels was observed, and the correlation between these two variables was non-significant (P > 0.05). This suggested that there was no alteration in FGF-23 activity in response to suboptimal dietary P intake. The relationship of these observations to studies on the immunosuppression of FGF-23 activity is subsequentlydiscussed.

Dietary supplemental vitamin D3enhances phosphorus absorption and utilisation by regulating gene expression of related phosphate transporters in the small intestine of broilers

The present study was carried out to evaluate the effect of dietary supplemental vitamin D3(VD3) on P absorption and utilisation as well as its related mechanisms in the small intestine of broilers. A total of 384 1-d-old Arbor Acres male broilers were assigned randomly into four treatments following a completely randomised design with a 2 (dietary non-phytate P (NPP) contents: 0·43 and 0·22 %)×2 (dietary VD3supplemental levels: 0 and 87·5 μg/kg) factorial arrangement. The experiment lasted for 22 d. The results showed that P contents in serum from the hepatic portal vein and tibia ash of broilers were higher (P<0·05) for 0·43 % NPP than for 0·22 % NPP. The type IIb Na-dependent phosphate cotransporter (NaP-IIb) protein expressions in the duodenum and ileum were higher (P<0·05) also for 0·43 % NPP than 0·22 % NPP. Supplementation of VD3enhanced (P<0·05) tibia P retention rate and type III Na-dependent phosphate cotransporter (PiT)-1 protein expression in the duodenum of all broilers. Moreover, VD3supplementation decreased (P<0·002) mortality and increased (P<0·02) serum P content from the hepatic portal vein after 4 h of feeding, tibia ash content, tibia ash P content and protein expressions of NaP-IIb and PiT-1 in the jejunum of broilers fed diet with 0·22 % NPP. Thus, dietary supplemental VD3promoted intestinal P absorption and bone P utilisation, and this effect might be associated with enhanced PiT-1 levels in the duodenum and PiT-1 and NaP-IIb levels in the jejunum respectively when dietary NPP is limiting.

Effects of Dietary Phosphorus Level on the Expression of Calcium and Phosphorus Transporters in Laying Hens

The transport of calcium and phosphorus is mainly relied on their corresponding transporters. The aim of this study was to determine the effect of dietary phosphorus level on the expression of the relevant calcium and phosphorus transporters in laying hens, which has a large amount of calcium and phosphorus input from intestine and output from kidney and eggshell gland. Thirty-six 25-week-old Hy-line Brown hens were fed diets with different available phosphorus level (AP, 0.15, 0.41, and 0.82%), respectively. The expression of phosphorus transporters type IIa and type IIb Na/Pi co-transporter (NPt2a, NPt2b), calcium transporter calbindin-D28k (CaBP-D28k), and plasma membrane Ca ATPase 1b (PMCA1b) were measured in small intestine, kidney, and eggshell gland by RT-PCR and western blot. The results showed that serum calcitriol and PTH concentrations were not affected (P > 0.05) by dietary AP levels. Duodenum had the highest mRNA and protein expression level of NPt2b than jejunum and ileum (P < 0.05). The protein expression abundance of CaBP-D28k and PMCA1b were higher in duodenum than that in jejunum and ileum (P < 0.05). 0.15%-AP diet upregulated the ileal mRNA expression level of NPt2b and renal mRNA expression level of NPt2a (P < 0.05), while downregulated the protein abundance of NPt2b and CaBP-D28k mRNA expression in shell gland (P < 0.05). In conclusion, both the Ca and P transporters were highly expressed in duodenum. Low AP diet decreased protein expression abundance of NPt2b in duodenum while upregulated the mRNA expression level of NPt2a in kidney. The result suggests that both the phosphorus absorption in proximal intestine and its reabsorption in kidney are involved in the adaption to low AP diet.

1α-Hydroxycholecalciferol improves the growth performance and up-regulates the mRNA expression of vitamin D receptor in the small intestine and kidney of broiler chickens

1α-Hydroxycholecalciferol (1α-OH-D3) is a vitamin D derivative. The objective of this study was to evaluate the effects of 1α-OH-D3 on the growth and the mRNA expression of vitamin D receptor (VDR) in the small intestine and kidney of chickens. A total of 240 males of one-day-old Ross 308 broilers was randomly assigned to 4 treatments with 5 replicates of 12 birds per replicate. Three levels of 1α-OH-D3 (1.25, 2.5, and 5 μg/kg) were added to a basal diet containing 0.50% calcium (Ca), 0.25% non-phytate phosphorus (NPP), and without supplemental cholecalciferol (vitamin D3). The control diet contained 1.00% Ca, 0.45% NPP, and 25 μg/kg cholecalciferol. Dietary 1α-OH-D3 levels linearly improved the average daily feed intake (ADFI), average daily gain (ADG), femur and tibia mineralization, and plasma Ca concentration, and retained Ca and total phosphorus (tP) amounts in broilers from 1 to 21 d of age (P < 0.05). In addition, 1α-OH-D3 also linearly up-regulated the mRNA expression levels of VDR in the duodenum as well as those of VDR and sodium-phosphate cotransporter NaPi-IIa and NaPi-IIc in the kidney of broilers (P < 0.05). However, 1α-OH-D3 did not affect the mRNA levels of 25-hydroxylase in the liver or NaPi-IIb in the duodenum (P > 0.05). No differences were observed in the ADFI, ADG, bone length, plasma mineral concentration, retained tP amount, or the mRNA levels of the above genes (except for VDR in the kidney) between the birds fed the diet with 5 μg/kg 1α-OH-D3 and the birds fed the control diet (P > 0.05). By contrast, the weight, ash weight, ash percentage, and Ca percentage of the bone, retained Ca amount, and the mRNA level of VDR in the kidney were lower in the birds fed the diet with 5 μg/kg 1α-OH-D3 than in the birds fed the control diet (P < 0.05). These data indicate that 1α-OH-D3 up-regulates the gene expression of VDR in the small intestine and kidney at the transcriptional level, thereby improving the growth performance and bone mineralization of broiler chickens from 1 to 21 d of age.

Pathophysiology of avian intestinal ion transport

The gut has great importance for the commercial success of poultry production. Numerous ion transporters, exchangers, and channels are present on both the apical and the basolateral membrane of intestinal epithelial cells, and their differential expression along the crypt-villus axis within the various intestinal segments ensures efficient intestinal absorption and effective barrier function. Recent studies have shown that intensive production systems, microbial exposure, and nutritional management significantly affect intestinal physiology and intestinal ion transport. Dysregulation of normal intestinal ion transport is manifested as diarrhoea, malabsorption, and intestinal inflammation resulting into poor production efficiency. This review discusses the basic mechanisms involved in avian intestinal ion transport and the impact of development during growth, nutritional and environmental alterations, and intestinal microbial infections on it. The effect of intestinal microbial infections on avian intestinal ion transport depends on factors such as host immunity, pathogen virulence, and the mucosal organisation of the particular intestinal segment.

Effects of age on intestinal phosphate transport and biochemical values of broiler chickens

OBJECTIVE

The objective of this experiment was to characterize the mRNA expression profile of type IIb sodium-inorganic phosphate cotransporter (NaPi-IIb) and the biochemical values of serum alkaline phosphatase (AKP), calcium, inorganic phosphorus, tibial ash and minerals of broiler chickens with aging.

METHODS

A total of 56 one-day-old Arbor Acres male broiler chickens were used. Broiler chickens were weighed and samples were collected weekly from day 1.

RESULTS

The result showed that before the growth inflection point, ash, calcium, and phosphorus content in the tibia of broiler chickens increased with growth (before 3 weeks of age), although there were no significant differences in chicks at different ages in the later period of the experiment and weight gain rate was relatively slow at this stage (4 to 6 weeks). NaPi-IIb gene expression in the small intestine in the early growth stage was higher than that in the later growth stage. Expression of calbindin and the vitamin D receptor protein in the intestinal mucosa increased with age in the duodenum and jejunum. Serum AKP activity first increased and subsequently decreased after peaking at 1 week of age, but there was no significant difference after 3 weeks of age.

CONCLUSION

These results show that compared with the early growth stage, the weight-gain rate of broiler chickens in the late growth stage gradually decreased with gradual tibia maturation, along with weaker positive transport of phosphorus in the intestine and reinforced re-absorption of phosphorus in the kidney, which might be the reason that phosphorus requirement in the late growth stage was decreased.

Characterizing and evaluating the expression of the type IIb sodium-dependent phosphate cotransporter (slc34a2) gene and its potential influence on phosphorus utilization efficiency in yellow catfish (Pelteobagrus fulvidraco)

A sodium-dependent phosphate cotransporter gene, NaPi-IIb (slc34a2), was isolated from yellow catfish (Pelteobagrus fulvidraco) intestine through homology cloning and the rapid amplification of cDNA ends. The full-length cDNA of slc34a2 consisted of 2326 bp with an open reading frame encoding 621 amino acids, a 160-bp 5' untranslated region, and a 300-bp 3' untranslated region. The deduced amino acid sequence showed 79.0 and 70.9% sequence identity to Astyanax mexicanus and Pundamilia nyererei, respectively. The membrane-spanning domains based on the hydrophilic and hydrophobic properties of the deduced amino acids were predicted, and results showed that the putative protein had eight transmembrane domains, with the intracellular NH2 and COOH termini. Two functional regions including first intracellular loop and third extracellular loop as well as the six N-glycosylation sites in second extracellular loop were found. The slc34a2 mRNA in the tested tissues was examined through semiquantitative reverse transcription polymerase chain reaction and quantitative real-time PCR, with the highest level found in the anterior intestine, followed by the posterior and middle intestines. The slc34a2 mRNA expression in the whole intestine under different dietary phosphorus (P) treatments was detected using qPCR. The results showed that the slc34a2 expression levels in the low-P groups (0.33 and 0.56%) were significantly higher (p < 0.05) than levels in the sufficient-P (0.81%) and high-P (1.15, 1.31, and 1.57%) groups. High expression of slc34a2 mRNA in low-P groups stimulated P utilization efficiency, indicating the close relationship between genotype and phenotype in yellow catfish. In contrast with conventional strategies (formula and feeding strategies), this study provided another possible approach by using molecular techniques to increase the P utilization in yellow catfish.

Oral antibodies to human intestinal alkaline phosphatase reduce dietary phytate phosphate bioavailability in the presence of dietary 1α-hydroxycholecalciferol

While it is well established that active vitamin D treatment increases dietary phytate phosphate utilization, the mechanism by which intestinal alkaline phosphatase (IAP) participates in phytate phosphate use is less clear. The ability of human IAP (hIAP) oral antibodies to prevent dietary phytate phosphate utilization in the presence of 1α-hydroxycholecalciferol (1α-(OH) D3) in a chick model was investigated. hIAP specific chicken immunoglobulin Y (IgY) antibodies were generated by inoculating laying hens with 17 synthetic peptides derived from the human IAP amino acid sequence and harvesting egg yolk. Western blot analysis showed all antibodies recognized hIAP and 6 of the 8 antibodies selected showed modest inhibition of hIAP activity in vitro (6 to 33% inhibition). In chicks where dietary phosphate was primarily in the form of phytate, 4 selected hIAP antibodies inhibited 1α-(OH) D3-induced increases in blood phosphate, one of which, generated against selected peptide (MFPMGTPD), was as effective as sevelamer hydrochloride in preventing the 1α-(OH) D3-induced increase in blood phosphate, but ineffective in preventing an increase in body weight gain and bone ash induced by 1α-(OH) D3. These studies demonstrated that orally-delivered antibodies to IAP limit dietary phytate-phosphate utilization in chicks treated with 1α-(OH) D3, and implicate IAP as an important host enzyme in increasing phytate phosphate bioavailability in 1α-(OH) D3 fed chicks.

Age and adaptation to Ca and P deficiencies: 2. Impacts on amino acid digestibility and phytase efficacy in broilers

A total of 1,152 straight-run hatchling Heritage 56M×fast feathering Cobb 500F broiler birds were used to determine Ca, age, and adaptation effects on apparent ileal digestibility of crude protein (AID of CP), amino acids (AID of AA) and phytase efficacy. Twelve treatments with 8 replicates, each were fed from 7 to 9 d (6 birds per replicate), 7 to 21 d (6 birds per replicate) and 19 to 21 d (3 birds per replicate) d of age. Diets were prepared with 3 Ca (0.65, 0.80, and 0.95%) and 2 non-phytate P, (0.20 and 0.40%) concentrations. A 6-phytase was added at 500 or 1,000 FTU/kg to the 0.20% nPP diet at each Ca concentration. The age and adaptation effects were determined by comparing the responses between birds fed from 7 to 9 and 19 to 21 d of age, 19 to 21, and 7 to 21 d of age, respectively. An age effect was observed regardless of Ca, nPP, or phytase concentration, with older birds (19 to 21 d) having greater apparent ileal digestibility (AID) of amino acids (AA) and CP than younger birds (7 to 9 d; P<0.05). Response to adaptation varied depending on Ca, nPP, and phytase concentrations. Constant lower AID of CP and AA was seen in adapted birds (7 to 21 d) compared to unadapted bird (19 to 21 d) when 0.20% nPP diets were fed at 0.95% Ca concentrations (P<0.05). At 0.40% nPP, there was no effect of adaptation on AID of CP and AA at any Ca concentration. Phytase efficacy was significantly lower in younger (7 to 9 d) compared to older birds (19 to 21 d; P<0.05), except at 0.65% Ca. Phytase inclusion increased AID of CP and AA regardless of Ca (P<0.05). In conclusion, the AID of CP and AA can be affected by diet, age, and adaptation.

Modulation of small intestinal phosphate transporter by dietary supplements of mineral phosphorus and phytase in broilers

Dietary phosphorus (P) is known as a main modulator of phosphate (Pi) transporter expression. The effect of supplemented mineral P with or without phytase on protein expression of two sodium-dependent Pi (NaPi) transporters and a calcium channel was studied in the small intestine of broilers. Thirty-six broilers were randomly assigned to six different diets at 15 days of age. Two levels of total P (tP, adjusted by monocalcium phosphate (MCP) supplementation), 0.39% (BD-) and 0.47% (BD+) were fed until day 25; and at each tP level, three levels of phytase were used with 0, 500, and 12,500 FTU/kg of an E. coli phytase. Mucosa samples from jejunum and ileum were taken and apical membranes were isolated by MgCl2 precipitation. Protein expression of NaPi IIb, NaPi type III (PiT1) and the calcium channel TRPV6 were semiquantitatively measured by Western blotting and jejunal mucosal phytase activity by measurement of Pi release. The jejunal NaPi IIb transporter was expressed with two distinct bands, which were modulated differently by diet. NaPi IIb Band1 increased (P < 0.05) and Band2 decreased (P < 0.05) with phytase supplementation but was not affected by MCP supplementation. This inverse modulation of Band1 and Band2 was significantly related to the amount of net absorbed P with higher expression of Band1 at higher amounts of net absorbed P. In addition, a second Pi transporter, PiT1, was detected in which ileal expression decreased (P < 0.05) in response to higher phytase supplementation. The expression of the calcium channel TRPV6 was increased in BD+ groups. A trend for an interaction between MCP and phytase supplementation on mucosal phytase activity was observed (P = 0.079) with a decrease in activity when BD+ with 12,500 FTU/kg phytase was fed. Chicken intestinal epithelial cells responded to dietary supplemented phytase and MCP by changing the Pi transporter expression in apical membranes. In conclusion, availability of Pi is most likely the key modulator of transporter protein expression. However, a contribution of lower inositol phosphates generated by phytases and other phosphatases may also be relevant.

Different phosphate transport in the duodenum and jejunum of chicken response to dietary phosphate adaptation

Intestinal phosphate (Pi) absorption across the apical membrane of small intestinal epithelial cells is mainly mediated by the type IIb Na-coupled phosphate co-transporter (NaPi-IIb), but its expression and regulation in the chicken remain unclear. In the present study, we investigated the mRNA and protein levels of NaPi-IIb in three regions of chicken small intestine, and related their expression levels to the rate of net phosphate absorption. Our results showed that maximal phosphate absorption occurs in the jejunum, however the highest expression levels of NaPi-IIb mRNA and protein occurs in the duodenum. In response to a low-Pi diet (TP 0.2%), there is an adaptive response restricted to the duodenum, with increased brush border membrane (BBM) Na-Pi transport activity and NaPi-IIb protein and mRNA abundance. However, when switched from a low- (TP 0.2%) to a normal diet (TP 0.6%) for 4 h, there is an increase in BBM NaPi-IIb protein abundance in the jejunum, but no changes in BBM NaPi-IIb mRNA. Therefore, our study indicates that Na-Pi transport activity and NaPi-IIb protein expression are differentially regulated in the duodenum vs the jejunum in the chicken.

Phosphorus utilization in finishing broiler chickens: effects of dietary calcium and microbial phytase

A decrease in dietary P, especially in finishing broilers (21 to 38 d old), is a crucial issue in poultry production from an environmental and economic point of view. Nevertheless, P must be considered together with other dietary components such as Ca and microbial phytase. Different corn and soybean meal-based diets varying in Ca [low (LCa) 0.37, medium (MCa) 0.57, and high (HCa) 0.77%], and nonphytate P [nPP; low (LnPP) 0.18 and high (HnPP) 0.32%] content were tested with and without microbial phytase [0 or 500 phytase units (FTU)/kg]. Feed intake, BW gain, bone mineralization, and mineral retention were examined in 144 Ross PM3 broilers (22 to 38 d old) reared in individual cages. Growth performance was not significantly affected by the treatments. Nevertheless, a numerical decrease of ADG and ADFI was observed in HCa-LnPP and LCa-HnPP associated with an increase of feed conversion ratio. Decreased dietary Ca reduced tibia ash content (Ca, linear: P < 0.001; quadratic: P = 0.034) and tibia ash weight for the highest level of nPP (Ca × nPP; P = 0.035). In parallel, increasing dietary Ca reduced the flow of retained P (P = 0.022) but also tibia ash weight in LnPP diets (Ca × nPP; P = 0.035). The responses of the animals in terms of tibia ash content and P retention were improved by the addition of microbial phytase especially for the lowest P diets (nPP × phytase, P = 0.021 and P = 0.009; respectively). Phytase increased dry tibia weight, bone breaking strength, and tibia diameter in broilers fed the highest Ca diets (Ca × phytase; P < 0.05). We conclude that is possible to decrease P levels in finishing broilers, if the Ca content is appropriate. Nevertheless, decreasing the dietary P and Ca cannot allow a maximization of bone mineralization, but the optimal threshold remains to be determined.

Molecular cloning and functional characterization of swine sodium dependent phosphate cotransporter type II b (NaPi-IIb) gene

A sodium-dependent phosphate transporter gene, NaPi-IIb, was isolated from swine small intestine using cDNA library screening method. Sequencing analysis revealed that the NaPi-IIb cDNA sequences was 2,016 bp in length and encoded an open-reading frame consisting of 671 amino acids. The cDNA showed 83.1 % sequences identity to the human NaPi-IIb and 78.7 % sequences identity to the chicken NaPi-IIb. Prediction of membrane spanning domains based on the hydrophilic and hydrophobic properties of the amino acids suggested that a putative protein had nine transmembrane domains, with both the NH(2) and COOH terminal being intracellular. By northern blot, a ~4.2 kb transcript was found to be abundantly expressed in mall intestine, lung, ovary, mammary glands, liver, kidney, salivary glands, placenta and thymus. Microinjection of swine NaPi-IIb cRNA into Xenopus oocytes demonstrated that the NaPi-IIb showed sodium-dependent Pi cotransport activity, and an approximate 31-fold increase of Pi uptake was seen in cRNA injected oocytes. The swine NaPi-IIb transporter expressed in Xenopus oocytes had a Km for Pi of ~79.35 ± 7.2 μM. Furthermore, the pH dependency characterization of swine NaPi-IIb transporter showed activation at extracellular alkaline-pH.

Phosphate transporter expression in Holstein cows

Phosphorus nutrition in cattle is increasingly becoming an important topic because excess dietary P is excreted in manure and can be washed into surface water, causing increased algal growth and eutrophication. However, little is known about the mechanism or regulation of P absorption in dairy cattle. Phosphorus transporters have been characterized in other species and homologous genes have been found to be expressed in bovine cell cultures. However, no other information is available regarding the active transport of phosphate in the digestive tract of cattle. The objective of this study was to determine the patterns of expression of a known phosphate transporter, NaPi-IIb, in 4 sections of the small intestine of Holstein cows. Ribonucleic acid was isolated from the duodenal, proximal jejunal, distal jejunal, and ileal mucosa of 20 Holstein cows. Relative amounts of NaPi-IIb mRNA expression were determined using real-time reverse-transcription PCR. Expression of NaPi-IIb was highest in the 2 distal sections and almost absent in the proximal sections. Expression did not differ between the 2 proximal sections or the 2 distal sections. These data suggest that a Na+-dependent secondary active P transport system is not responsible for P absorption in the proximal portion of the bovine small intestine, whereas it does contribute to the P absorbed in the distal sections of the bovine small intestine.

Transcriptional profiling of cecal gene expression in probiotic- and Salmonella-challenged neonatal chicks

Probiotics are currently used to improve health and reduce enteric pathogens in poultry. However, the mechanisms by which they reduce or prevent disease are not known. Salmonella are intracellular pathogens that cause acute gastroenteritis in humans, and infections by nontyphoid species of Salmonella also can result in diarrhea, dehydration, and depression in poultry. Frequently, however, no clinical signs of infection are apparent in poultry flocks. In this study, day-of-hatch chicks were challenged with Salmonella enterica serovar Enteritidis (SE) and treated 1 h later with a poultry-derived, Lactobacillus-based probiotic culture (FloraMax-B11, Pacific Vet Group USA Inc., Fayetteville, AR). Cecae were collected 12 and 24 h posttreatment for Salmonella detection and RNA isolation for microarray analysis of gene expression. At both 12 and 24 h, SE was significantly reduced in chicks treated with the probiotic as compared with the birds challenged with only SE (P < 0.05). Microarray analysis revealed gene expression differences among all treatment groups. At 12 h, 170 genes were expressed at significantly different levels (P < 0.05), with a minimum difference in expression of 1.2-fold. At 24 h, the number of differentially regulated genes with a minimum 1.2-fold change was 201. Pathway analysis revealed that at both time points, genes associated with the nuclear factor kappa B complex, as well as genes involved in apoptosis, were significantly regulated. Based on this analysis, probiotic-induced differential regulation of the genes growth arrest-specific 2 (GAS2) and cysteine-rich, angiogenic inducer, 61 (CYR61) may result in increased apoptosis in the cecae of chicks. Because Salmonella is an intracellular pathogen, we suggest that increased apoptosis may be a mechanism by which the probiotic culture reduces Salmonella infection.