Dynamics of bone mineralization in primiparous sows as a function of dietary phosphorus and calcium during lactation.

To maximize the efficiency of dietary P utilization in swine production, understanding the mechanisms of P utilization in lactating sows is relevant due to their high P requirement and the resulting high inorganic P intake. Gaining a better knowledge of the Ca and P quantities that can be mobilized from bones during lactation, and subsequently replenished during the following gestation, would enable the development of more accurate P requirements incorporating this process of bone dynamics. The objective was to measure the amount of body mineral reserves mobilized during lactation, depending on dietary digestible P and phytase addition and to measure the amount recovered during the following gestation. Body composition of 24 primiparous sows was measured by dual-energy x-ray absorptiometry 2, 14, 26, 70 and 110 days after farrowing. Four lactation diets were formulated to cover nutritional requirements, with the exception of Ca and digestible P: 100% (Lact100; 9.9 g Ca and 3.0 g digestible P/kg), 75% (Lact75), 50% without added phytase (Lact50) and 50% with added phytase (Lact50 + FTU). The gestation diet was formulated to cover the nutritional requirements of Ca and digestible P (8.2 g Ca and 2.6 g digestible P/kg). During the 26 days of lactation, each sow mobilized body mineral reserves. The mean amount of mobilized bone mineral content (BMC) was 664 g, representing 240 g Ca and 113 g P. At weaning, the BMC (g/kg of BW) of Lact50 sows tended to be lower than Lact100 sows (-12.8%, linear Ca and P effect × quadratic time effect) while the BMC of Lact50 + FTU sows remained similar to that of Lact100 sows. During the following gestation, BMC returned to similar values among treatments. Therefore, the sows fed Lact50 could recover from the higher bone mineral mobilization that occurred during lactation. The P excretion was reduced by 40 and 43% in sows fed Lact50 and Lact50 + FTU, respectively, relative to sows fed Lact100. In conclusion, the quantified changes in body composition during the lactation and following gestation of primiparous sows show that bone mineral reserves were mobilized and recovered and that its degree was dependent on the dietary P content and from phytase supplementation during lactation. In the future, considering this potential of the sows' bone mineralization dynamics within the factorial assessment of P requirement and considering the digestible P equivalency of microbial phytase could greatly limit the dietary use of inorganic phosphates and, thus, reduce P excretion.

A first model of the fate of dietary calcium and phosphorus in broiler chickens.

To reduce P excretion and increase the sustainability of poultry farms, one needs to understand the mechanisms surrounding P metabolism and its close link with Ca metabolism to precisely predict the fate of dietary P and Ca and related requirements for birds. This study describes and evaluates a model developed to estimate the fate of Ca and P consumed by broilers. The Ca and P model relies on three modules: (1) digestion of Ca and P; (2) dynamics of Ca and P in soft tissue and feathers; and (3) dynamics of body ash. Exogenous phytase affects the availability of Ca and P; thus, to predict the absorption of those minerals, the model also accounts for the effect of phytase on Ca and P digestibility. We used a database to estimate the consequences of dietary Ca, P, and phytase over feed intake response. This study followed a four-step process: (1) Ca and P model development and its coupling with a growth broiler model; (2) model behavior assessment; (3) sensitivity analysis to identify the most influential parameters; and (4) external evaluation based on three databases. The proportion of P in body protein and the Ca to P ratio in bone are the most sensitive parameters of P deposition in soft tissue and bone, representing 91 and 99% of the total variation. The external evaluation results indicated that body water and protein had an overall mean square prediction error (rMSPE) of 7.22 and 12.3%, respectively. The prediction of body ash, Ca, and P had an rMSPE of 7.74, 11.0, and 6.56%, respectively, mostly errors of disturbances (72.5, 51.6, and 90.7%, respectively). The rMSPE for P balance was 13.3, 18.4, and 22.8%, respectively, for P retention, excretion, and retention coefficient, with respective errors due to disturbances of 69.1, 99.9, and 51.3%. We demonstrated a mechanistic model approach to predict the dietary effects of Ca and P on broiler chicken responses with low error, including detailed simulations to show the confidence level expected from the model outputs. Overall, this model predicts broilers' response to dietary Ca and P. The model could aid calculations to minimize P excretion and reduce the impact of broiler production on the environment. A model inversion is ongoing that will enable the calculation of Ca and P dietary quantities for a specific objective. This will simplify the use of the model and the feed formulation process.

Effect of phytase and limestone particle size on mineral digestibility, performance, eggshell quality, and bone mineralization in laying hens.

The effect of microbial phytase and limestone particle size (LmPS) was assessed in Lohmann Tradition laying hens from 31 to 35 wk of age. Seventy-two hens were used in a completely randomized trial according to a 2 × 2 factorial arrangement with 2 levels of phytase/basal available P (aP); 0 FTU/kg with 0.30% aP or 300 FTU/kg with 0.15% aP, and 2 limestone particle sizes; fine particles (FL, <0.5 mm) or a mix (MIX) of 75% coarse limestone (CL, 2-4 mm) and 25% FL. Diets contained equivalent levels of Ca (3.5%), phytic P (PP; 0.18%), and aP (0.30%) considering the P equivalency of phytase. Thus, dietary treatments were FL0 and MIX0 without phytase, and FL300 and MIX300 with 300 FTU/kg phytase. Performance were recorded daily and eggshell quality (eggshell weight proportion, weight, thickness, and breaking strength) was measured weekly. At the end of the trial, bone parameters (tibia breaking strength, elasticity, and ash) and the apparent precaecal digestibility (APCD) of P and Ca were determined. No differences were observed between treatments in feed intake, FCR and bone parameters. Addition of MIX increased the eggshell proportion, weight and thickness in groups receiving no phytase (+6.5, +6.9, and +4.5%, respectively) while no effect was observed in groups receiving phytase (Phytase × LmPS, P < 0.05). In hens receiving FL, the APCD of P was lower in diets supplemented with phytase (-14 percentage points; Phytase × LmPS, P < 0.001). A higher phytate disappearance was observed in hens fed diets with phytase in combination with MIX (Phytase × LmPS, P = 0.005). Phytase and MIX together increased the APCD of Ca by 7.3 percentage points (Phytase × LmPS, P < 0.001). In conclusion, addition of CL could limit the formation of Ca-phytate complex thus improving the response of the birds to phytase compared to FL.

Development of bone mineralization and body composition of replacement gilts fed a calcium and phosphorus depletion and repletion strategy.

This study investigated the ability of replacement gilts to adapt their calcium and phosphorus utilization and their kinetics in bone mineralization to compensate for modified intake of these nutrients by applying a novel Ca and P depletion and repletion strategy. A total of 24 gilts were fed according to a two-phase feeding program. In the first phase, gilts (60-95 kg BW) were fed ad libitum a depletion diet providing either 60% (D60; 1.2 g digestible P/kg) or 100% (D100; 2.1 g digestible P/kg) of the estimated P requirement. In the second phase, gilts (95-140 kg BW) were fed restrictively (aim: 700-750 g/d BW gain) a repletion diet. Half of the gilts from each depletion diet were randomly assigned to either a control diet or a high-P diet (R100 and R160; with 2.1 and 3.5 g digestible P/kg, respectively) according to a 2 × 2 factorial design, resulting in four treatments: D60-R100, D60-R160, D100-R100 and D100-R160. Dual-energy X-ray absorptiometry was used to measure whole-body bone mineral content (BMC), bone mineral density (BMD) and lean and fat tissue mass on each gilt at 2-week intervals. The depletion and repletion diets, fed for 5 and 8 weeks, respectively, did not influence growth performance. The D60 gilts had a reduced BMC and BMD from the second week onwards and ended (95 kg BW) with 9% lower values than D100 gilts (P < 0.001). During repletion, D60 gilts completely recovered the deficit in bone mineralization from the second and fourth week onwards, when fed R160 (D60-R160 vs D100-R160) or R100 (D60-R100 vs D100-R100) diets, respectively (treatment × time interaction, P < 0.001); thus, the depletion diets did not affect these values at 140 kg BW. These results illustrate the rapid homeostatic counter-regulation capacity of dietary Ca and P, and they show the high potential to limit dietary digestible P concentration by completely excluding the use of mineral phosphates during the depletion phase, representative of the fattening period, without causing any detrimental effects to gilts at mating. The gilts were able to recover their BMC deficit between their selection at 95 kg BW and first mating at 140 kg BW by increasing their dietary Ca and P efficiency. Finally, excess dietary digestible P, requiring increased amounts of mineral phosphates, further increased the gilts' BMC.

Effect of low-protein corn and soybean meal-based diets on nitrogen utilization, litter quality, and water consumption in broiler chicken production: insight from meta-analysis.

The growing demand for high-value animal protein must be met using sustainable means that optimize the utilization of nutrients, especially nitrogen (N) so that excreta do not over-fertilize fields and end up causing soil acidification, waterway eutrophication and greenhouse gas emissions. Malodorous N compounds can cause respiratory diseases and poor growth in livestock. The increasing availability of feed-grade amino acids makes it possible to formulate low-protein diets for broilers and thereby reduce N excretion. However, published studies of the effects of such diets on broiler growth performance have been based on reducing CP contents gradually in a variety of ways that have given inconsistent results. Since the amount of published data is now large, a meta-analysis was performed in order to categorize diet formulation strategies and quantify their impact on N balance, water consumption, litter moisture, plasma uric acid. This showed that lowering the CP content of broiler diets generally means replacing some soybean meal with corn and hence increasing the starch content. However, since soybean meal is also a source of potassium, this reduces electrolyte balance. Lowering the CP content from 19% to 17% is associated with a 29% reduction of N excretion in broilers aged 0-21 d, and a 7% increase in N efficiency (N retention/N intake). Reducing the CP content from 19% to 17% decreases daily water consumption by 20.6 mL/bird, litter moisture by 2.2% and plasma uric acid by 0.56 mg/dL. This meta-analysis improves our understanding of the low-protein strategy and allows us to quantify its impact on N balance, litter quality and uric acid. It shows that managing N excretion is wholly beneficial and reduces litter wetness.

Effects of Bacillus subtilis, butyrate, mannan-oligosaccharide, and naked oat (ß-glucans) on growth performance, serum parameters, and gut health of broiler chickens.

Four nonantibiotic alternative growth promoters for broiler chickens were evaluated. Ross 308 chicks were fed a control diet (mainly corn and soybean meal) or a diet supplemented with a probiotic (Bacillus subtilis Gallipro DSM 17299), encapsulated butyric acid (Novyrate C), mannan-oligosaccharide (Actigen MOS) or formulated with 20% naked oat (starter diet) and 30% naked oat (grower and finisher). The study was carried out as a complete random blocked design with 10 pens for each diet, 45 birds per pen. Compared to the control, the naked oat diet improved the average daily gain by 16% during the starter phase (up to d 10). The probiotic did so during the grower phase as did butyric acid in the finisher phase (up to d 34). For the experiment overall, the probiotic decreased average daily gain slightly. The best improvement in feed conversion ratio was obtained in the butyrate group (5%). No significant treatment effect on crop pH or on mortality was observed. The naked oat diet gave a slightly lower cecum pH on d 34. The MOS supplement decreased jejunal mass on d 34 and increased villus length (34%) and villus height/crypt depth ratio (32%) measured on d 10. Naked oat, butyric acid and MOS diets all reduced serum endotoxin levels. The probiotic increased serum C-reactive protein. All noncontrol diets reduced serum malondialdehyde. The naked oat diet reduced d 34 litter pH by about 0.3. Some effects of the proposed non-antibiotic growth promoters have been observed and could contribute to livestock performance. Their exact modes of action remained to be defined.

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 500TM 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.

Phosphorus and calcium requirements for bone mineralisation of growing pigs predicted by mechanistic modelling.

Phosphorus (P) is an essential nutrient in livestock feed but can pollute waterways. In order for pig production to become less of a threat to the environment, excreta must contain as little P as possible or be efficiently used by plants. This must be achieved without decreasing the livestock performance. Phosphorus and calcium (Ca) deposition in the bones of growing pigs must be optimised without affecting the muscle gain. This requires precision feeding based on cutting-edge techniques of diet formulation throughout the animal growth phase. Modelling and data mining have become important tools in this quest. In this study, a mechanistic model taking into account the distribution of P between bone and soft tissues was compared to the established factorial models (INRA (Jondreville and Dourmad, 2005) and NRC (National Research Council, 2012)) that predict P (apparent total tract digestible, ATTD-P; or standardised total tract digestible, STTD-P) and Ca (total and STTD) requirements as a function of BW and protein deposition. The requirements for different bone mineralisation scenarios, namely, 100% and 85% of the genetic potential, were compared with these two models. Sobol indices were used to estimate the relative impact of growth-related parameters on mineral requirements at 30, 60 and 120 kg of BW. The INRA showed the highest value of ATTD-P requirement between 29 and 103 kg of BW (6%) and lower for lighter and higher BW. Similarly, the model for 85% bone mineralisation showed lower STTD-P requirement than NRC between 29 and 93 kg of BW (7%) and higher for lighter and higher BW. Contrary to other models, the Ca requirement of the proposed model is not fixed in relation to P. It increases from 95 kg of BW while the others decrease. The INRA showed the highest Ca requirements. The model Ca requirements for 100% bone mineralisation are higher than NRC from 20 to 38 kg of BW similar until 70 kg of BW and then higher again. For 85% objective, the model showed lower Ca requirements from 25 to 82 kg of BW and higher for lighter and higher BW. The potential Ca deposition in bones is the most sensitive parameter (84% to 100% of the variance) of both ATTD-P and Ca at 30, 60 and 120 kg. The second most sensitive parameter is the protein deposition, explaining 1% to 15% of the ATTD-P variance. Studies such as this one will help to usher in a new era of sustainable and eco-friendly livestock production.

Effects of dietary calcium and phosphorus deficiency and subsequent recovery on broiler chicken growth performance and bone characteristics.

The ability of birds to modify dietary phosphorus utilisation when fed with low-phosphorus and calcium (Ca) diets was studied using different sequences of dietary phosphorus and Ca restriction (depletion) and recovery (repletion) during the grower and the finisher phases. A total of 3600 Ross 708 broilers were randomly divided into 10 replicate pens per treatment (60 per pen, six pens per block). Chicks were fed a common starter diet from days 0 to 10, then a grower control diet (C: 0.90% Ca, 0.39% non-phytate phosphorus, nPP), mid-level diet (M: 0.71% Ca, 0.35% nPP) or low Ca and nPP diet (L: 0.60% Ca, 0.30% nPP) from days 11 to 21, followed by a finisher diet C, M or L containing, respectively, 0.85%, 0.57% or 0.48% Ca and 0.35%, 0.29% or 0.24% nPP from days 22 to 37. Six treatment sequences were tested: CC, MM, LL, ML, LC and LM. Bone mineral content by dual-energy X-ray, tibia ash, toe ash weight and tibia breaking strength were measured on days 21 and 37. No significant effect was observed on growth performance throughout the experiment. Diet L reduced bone mineral content, breaking strength, tibia and toe ash by 9%, 13%, 11% and 10%, respectively, on day 21 (compared with diet C, for linear effect, P<0.05). On day 37, bone mineral content, breaking strength, tibia and toe ash remained lower compared with control values (CC v. MM v. LL, P<0.05 for linear and quadratic effects). Mineral depletion duration (ML v. LL) did not affect bone mineral status. Replenishing with the C diet during the finisher phase (LC) restored bone mineral content, tibia ash and toe ash weight better than the M diet did, but not to control levels (CC v. LC v. LM, for linear effect, P<0.05). These results confirm that dietary Ca and nPP may be reduced in the grower phase without affecting final growth performance or breaking strength as long as the finisher diet contains sufficient Ca and nPP. The practical applications of this strategy require further study in order to optimise the depletion and repletion steps.

Consequences of dietary calcium and phosphorus depletion and repletion feeding sequences on growth performance and body composition of growing pigs.

The effect of a calcium (Ca) and phosphorus (P) depletion and repletion strategy was studied in four consecutive feeding phases of 28 days each. In all, 60 castrated male pigs (14±1.6 kg initial BW) received 60% (low (L) diet; depletion) or 100% (control (C) diet; repletion) of their Ca and digestible P requirements according to six feeding sequences (CCCC, CCCL, CLCC, CCLC, LCLC and LLLL; subsequent letters indicate the diet received in phases 1, 2, 3 and 4, respectively). Pigs bone mineral content in whole-body (BMCb) and lumbar vertebrae L2 to L4 (BMCv) was measured in every feeding phase by dual-energy X-ray absorptiometry. Growth performance was slightly (<10%) affected by depletion, however, dietary treatments did not affect overall growth. Compared with control pigs, depletion reduced BMCb (34%, 38%, 33% and 22%) and BMCv (46%, 54%, 38% and 26%) in phases 1 to 4, respectively. Depletion increased however digestible P retention efficiency from the second to the fourth phases allowing LLLL pigs to present no differences in BMCb and BMCv gain compared with CCCC pigs in phase 4. Growth performance in repleted compared with control pigs was lower in phase 2, was no different in phase 3 and was lower in CLCC pigs in phase 4. Repletion increased body P and Ca retention efficiency when compared with control pigs (respectively, 8% and 10% for LC v. CC, P<0.01; 8% and 10% for CLC v. CCC, P<0.10; 18% and 25% for CLCC, CCLC, LCLC v. CCCC, P<0.001). Moreover, BMCv gain was higher in CLC pigs (P<0.001) and gains of body P, Ca, BMCb and BMCv in phase 4 were also higher in repleted than in CCCC pigs (respectively, 14%, 20%, 20% and 52%; P⩽0.02). Repletion reduced body P, Ca, BMCb and BMCv masses in phase 2 but no differences were found in phase 4 compared with control pigs. Lumbar vertebrae L2 to L4 bone mineral content was more sensitive to depletion and repletion sequences than BMCb especially in the first phase probably due to a higher proportion of metabolically active trabecular bone in vertebrae than in the whole skeleton. Dietary Ca was, however, oversupply in L compared with C diets (3.1 v. 2.5 Ca:digestible P ratio, respectively) suggesting that P has probably driven the regulations. Phosphorus and Ca depletion and repletion increases dietary P utilization efficiency and can help to reduce dietary P supply, but the underlying mechanisms need elucidation before its practical application.

Effect of dietary flax seed and oil on milk yield, gross composition, and fatty acid profile in dairy cows: A meta-analysis and meta-regression.

Several experiments were conducted over the past few years to evaluate the feeding value of flax seed and oil in dairy cow diets. The current meta-analysis and meta-regression was undertaken to assess the overall effect of different forms of flax, as a source of trienoic (cis-9,cis-12,cis-15 18:3) fatty acids (FA), on lactation performance and on transfer efficiency of its constituent n-3 FA from diet to milk fat. Comparisons were first conducted with nonsupplemented controls or with diets containing either saturated (mainly 16:0 or 18:0 or both), monoenoic (mainly cis-9 18:1), or dienoic (mainly cis-9,cis-12 18:2) FA. Results indicate that supplementing flax seed and oil decreased dry matter intake, as well as actual and energy-corrected milk yield without affecting the efficiency of utilization of dietary dry matter or energy as compared with nonsupplemented iso-energetic controls. When compared with the other 3 types of dietary fat evaluated, flax rich in trienoic FA supported a yield of energy-corrected milk similar to supplements rich in saturated, monoenoic, or dienoic FA. Greater milk fat concentration and feed efficiency were observed with saturated supplements. However, milk fat concentration and yield were lower with dienoic FA than with flax supplements. Further analyses were conducted to compare the effect of different forms of flax oil, seed, or fractions of seed. Among the 6 categories evaluated, mechanically processed whole seed (rolled or ground) allowed the greatest yield of energy-corrected milk and the best feed efficiency when compared with free oil, intact or extruded whole seed, protected flax, and flax hulls. Feeding protected flax and flax hulls allowed the greatest milk fat concentration of cis-9,cis-12,cis-15 18:3. Moreover, the greatest transfer efficiencies of this fatty acid from diet to milk were recorded with the same 2 treatments, plus the mechanically processed whole seed. These results make this last category the most suitable treatment, among the 6 flax forms evaluated, to combine optimum lactation performance and protection of flax constituent cis-9,cis-12,cis-15 18:3.

Meta-analysis of the amino acid digestibility of oilseed meal in growing pigs.

Oilseed meal is an important source of essential amino acids (EAA) for livestock production. It is the second most important ingredient in pig feed after grains. Optimal use of these ingredients requires precise knowledge of amino acid standardized ileal digestibility (SID), which may vary depending on several factors including botanical variety or processing treatments. A meta-analysis was performed in order to derive models for predicting the SID of soybean, cotton and rapeseed meal EAA, based on chemical composition data such as CP, total concentration of each EAA and fibre (crude fibre, ADF and NDF) content. A database of 47 references (224 experimental treatments) was built. A model incorporating processing method of the meals (e.g. cold pressed, expeller pressed, solvent extracted), experimental surgical procedure (T-cannula, re-entrant cannula, post valve T-cannula and ileo-rectal anastomosis) and pig growth stage (BW⩽ or ⩾25 kg) was tested. Results indicated that neither processing nor BW affected EAA SID. NDF was the best predictor of SID (R 2=0.944, 0.836, 0.779, 0.899 and 0.814, respectively, for Lys, Met, Thr, Trp and Val). The total EAA content was the best predictor of digestible content (g/kg diet) for each EAA (R 2=0.990, 0.985, 0.977, 0.985 and 0.978, respectively, for Lys, Met, Thr, Trp and Val). This study shows that routine chemical analyses may be used to predict EAA digestibility with satisfactory accuracy.

Modeling the metabolic fate of dietary phosphorus and calcium and the dynamics of body ash content in growing pigs.

A better understanding of the fate of dietary P use by growing pigs will allow an optimization of P use and enhance sustainable practices. The optimization of P utilization is complicated by the multiple criteria, such as growth performance, bone mineralization, and manure P used for assessment of needs. Mathematical modeling is a useful tool to describe relevant biological mechanisms and predict relationships that describe the whole system behavior. Modeling allows development of robust multicriteria approaches to optimize P utilization, feeding cost, and manure application cost. This paper describes and evaluates a model developed to simulate the fate of dietary P, that is, to simulate its digestive and metabolic utilization through digestion, soft tissue, and ash modules. The digestion module takes into account the varied sources of dietary minerals including responses to microbial and plant phytase and Ca and P interactions and predicts absorption and fecal excretion. The soft tissue module simulates the growth of the protein and is based on InraPorc model principles. The ash module simulates the partitioning of absorbed Ca and P into the bone, protein, and lipid compartments as well as urinary excretion. Model behavior showed that the model was able to accurately represent the impact of Lys deficiency on P retention, of Ca and P imbalances, and of Ca and P depletion and repletion sequences. The model's prediction capabilities in simulating whole-body protein, Ca, P, and ash based on published data showed high accuracy, with a slope and intercept that did not differ from 1 and 0, respectively, and an error due to disturbance (ED; variance not accounted for by regression of observed on predicted values). The model's prediction capabilities in simulating balance trial data showed good accuracy for apparent total tract digestibility (ATTD) of P (observed = -0.77 + 1.06 predicted) and P retention coefficient (observed = -4.5 + 1.15 predicted) with an ED of 89% for both criteria. The model's prediction capabilities in simulating Ca ATTD and Ca retention coefficient are lower (ED of 88 and 28%, respectively). This model simulates body ash independently of body protein and accounts for the impact of past and current dietary Ca and P supply. That ability is essential for the real-time adaptation of mineral supplies to suit individual production objectives, which would contribute to the overall success of pig production.

Apparent total tract digestibility of dietary calcium and phosphorus and their efficiency in bone mineral retention are affected by body mineral status in growing pigs.

Improving dietary P utilization without modifying pig performance is crucial for production sustainability. A feeding program comprising three 28-d phases (20 to 40, 40 to 70, and 70 to 100 kg) was used to feed 72 pigs with an initial BW of 20 kg. The ability of the pigs to modify the digestive and metabolic utilization of P when fed either a control (CON) diet or a low-P (LOW) diet providing 40% less digestible P with a constant Ca:digestible P was studied using different sequences of dietary P and Ca restriction (i.e., depletion [LOW]) and recovery (i.e., repletion [CON]), namely CON-CON-CON, CON-CON-LOW, CON-LOW-LOW, LOW-CON-CON, LOW-LOW-CON, and LOW-LOW-LOW. Bone mineral content (BMC) was measured in the lumbar region (L2-L4) by dual-energy X-ray absorptiometry at the beginning and end of each feeding phase. Total feces and urine were collected during phases 2 and 3. At the end of phase 1, BMC was lower in the LOW pigs than in the C pigs (29%; P < 0.001). During phase 2, the BMC gain was greater in the LOW-CON pigs than in the CON-CON pigs (16%; P < 0.001). During phase 3, the LOW-LOW-CON pigs absorbed 26% more Ca (P < 0.001) and retained 56% more BMC (P < 0.001) than the CON-CON-CON pigs did. Digestive and metabolic adaptations allowed the LOW-LOW-CON and LOW-CON-CON pigs to reach BMC similar to that of the CON-CON-CON pigs. These metabolic adaptations are promising, but practical applications of these results requires a better understanding of the underlying mechanisms to fine-tune the degree of depletion, pig age, and the duration of P and Ca depletion and repletion periods.

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.

Effect of reduced dietary calcium concentration and phytase supplementation on calcium and phosphorus utilization in weanling pigs with modified mineral status.

The present study was conducted to assess the effect of 2 dietary Ca concentrations on P and Ca digestive and metabolic utilization in weanling pigs fed diets providing practical concentrations of P, with or without phytase. The responses of pigs fed diets adequate or moderately deficient in Ca and P postweaning were compared. A total of 60 pigs weaned at 28 d of age were used. Two groups of 30 pigs with differing mineral status resulted from a 10-d depletion period, during which the animals received depletion diets (DD) that consisted of corn-soybean meal with either 1.42% Ca and 0.80% P (DD+) or 0.67% Ca and 0.43% P (DD-), designed to achieve the same Ca:digestible P ratio. At the end of the depletion period, a plasma sample was taken from each pig and 12 pigs (6 from each group) were slaughtered for bone assessment to establish the baseline mineral status. The animals fed the DD- diet had signs of P deficiency with reduced plasma P (13%; P < 0.01) and femur ash concentration (8%; P < 0.05), and increased plasma Ca (9%; P < 0.05) and alkaline phosphatase activity (31%; P < 0.01). For the subsequent 25-d period, the remaining 24 pigs from each group were fed 1 of 4 repletion diets: 1) 0.56% P, 1.06% Ca; 2) 0.56% P, 0.67% Ca; 3) diet 1 + 1,000 phytase units (FTU) of Natuphos phytase/kg; and 4) diet 2 + 1,000 FTU of Natuphos phytase/kg. Total feces and urine were collected from d 5 to 11, and a blood sample was taken from each pig at d 11 and 25. The initial moderate P deficiency (DD-) stimulated Ca absorption (5%; P < 0.01), irrespective of the repletion diet, and stimulated P absorption (5%; DD x phytase, P < 0.05), only when the diets contained phytase. At the end of the repletion period, because of these compensatory phenomena, the depleted pigs achieved full recovery of femur DM and ash weight when they received phytase, whereas ash concentration tended to remain reduced by 3% (P = 0.08). Phosphorus digestibility was improved in the diets supplemented with phytase (73.0 vs. 56.0%; P < 0.001), whereas an increase in dietary Ca decreased P digestibility (65.6 vs. 63.4%; P < 0.05). Those 2 effects were independent, indicating that dietary Ca reduced equally P digestibility with and without phytase and did not influence the efficiency of phytase in releasing P in the digestive tract. In pigs fed diets with phytase, however, the reduction of Ca (Ca:P from 1.9 to 1.3) increased urinary P losses 5-fold. Those extra losses were due to a lack of Ca for skeleton ash deposition, resulting in a 4% reduction in femur ash concentration. In the end, reducing the dietary Ca:P from 1.9 to 1.3 in a practical diet containing 0.56% P did not improve the efficiency of phytase in releasing P. Moreover, the reduction in dietary Ca (Ca:P) caused an imbalance between Ca and P that impaired bone mineralization.

Effects of reduced dietary calcium and phytase supplementation on calcium and phosphorus utilisation in broilers with modified mineral status.

1. The impact of modified mineral status and dietary Ca:P ratio on Ca and P utilisation was measured in chicks with or without phytase supplementation. 2. In a preliminary study, 4 diets were given to chicks from 3 to 15 d of age: D1 (6.5 g P/kg and Ca:P = 1.5) and D2, D3 and D4 (6.0, 5.4 and 5.0 g P/kg, respectively, and Ca:P = 1.2). Growth performance was similar across diets. Tibia ash was similar in chicks given D1 and D2, but was gradually depressed from D2 to D4 (-22%). 3. In the depletion period, two groups of chicks, with similar performance, but with different mineral status were achieved by feeding them, from 5 to 15 d of age, diets with a similar Ca:P ratio of 1.2, but containing 6.3 or 5.2 g P/kg. 4. During the subsequent 11 d of the repletion period, chicks from each of the two previous groups were given one of the 4 diets containing 5.7 g P/kg, but differing in their Ca (8.3 and 5.3 g Ca/kg) and microbial phytase (0 or 1000 FTU, Natuphos levels in a 2 x 2 x 2 factorial arrangement. 5. At the end of the repletion period, the initially depleted chicks could not be differentiated from the non-depleted chicks, indicating the capacity of chicks to compensate for their initial depleted mineral status. 6. Interaction between dietary Ca and phytase levels was not significant. Phytase improved growth performance and bone characteristics. Reduced dietary Ca enhanced feed intake and growth rate, but depressed bone dry matter and ash weight. 7. At the end, diets supplemented with phytase maximised bone ash weight when chicks were fed with a Ca:P ratio of 1.5 but elicited the highest growth rate when chicks were fed with a Ca:P ratio of 0.9.