Phosphorus. 1. Effect of breed and strain on utilization of suboptimal levels of phosphorus in the ration

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.

Phosphorus Availability in Laying Hens Given Non-phytate Phosphorus Deficient Diets Containing Buckwheat

To date, the effect of buckwheat phytase on laying hens has not yet been investigated. Thus, this study was conducted to compare the production performance, egg quality, and phosphorus (P) balance of laying hens given nonphytate P deficient diets supplemented with non-germinated buckwheat (BU) or germinated buckwheat (GBU). Experimental diets (17.8% CP, 2,988 kcal/kg ME) consisted of two control diets, the positive control (PC), satisfying all nutrient requirements and negative control (NC) containing 0.16% less non-phytate P than that in the PC diet, and six experimental diets (containing 10%, 15%, 20% BU or GBU), prepared by replacing maize with BU or GBU, along with the raw materials of NC diet. Fifty-six laying hens (46 week of age) were allocated to eight dietary groups (seven hens each) and experimental diets were given for a period of six weeks (week one was employed for acclimatization, and the subsequent five weeks for data collection). Deteriorated production performance (hen-day egg production, feed intake, egg weight and egg mass) and eggshell quality (shell breaking strength, shell weight and shell thickness) in laying hens given a non-phytate P deficient NC diet was restored by the addition of at least 15% BU and 10% GBU to the NC diet. Total P retention significantly increased in 20% BU, 15% GBU and 20% GBU groups as excretion decreased considerably in these groups than the NC group. Considering the hen-day egg production as an economically important parameter, we found that a 340 phytase unit (PU)/kg diet of buckwheat phytase was equivalent to 0.10% non-phytate P in laying hens. These results suggested that the addition of buckwheat in non-phytate P deficient diets can alleviate the deficiency and improve P availability in laying hens.

The effects of broiler chicken growth rate on valgus, varus, and tibial dyschondroplasia

An experiment was conducted to test the hypothesis that the growth rate of broilers influences their susceptibilities to bone abnormalities, causing major leg problems. Leg angulations, described in the twisted legs syndrome as valgus and bilateral or unilateral varus, were investigated in 2 subpopulations of mixed-sex Arkansas randombred broilers. Valgus angulation was classified as mild (tibia-metatarsus angle between 10 and 25°), intermediate (25-45°), or severe (> 45°). Body weight was measured at hatch and weekly until 6 wk of age. There were 8 different settings of approximately 450 eggs each. Two subpopulations, slow growing (bottom quarter, n = 581) and fast growing (top quarter, n = 585), were created from a randombred population based on their growth rate from hatch until 6 wk of age. At 6 wk of age, tibial dyschondroplasia incidences were determined by making a longitudinal cut across the right tibia. The tibial dyschondroplasia bone lesion is characterized by an abnormal white, opaque, unmineralized, and unvascularized mass of cartilage occurring in the proximal end of the tibia. It was scored from 1 (mild) to 3 (severe) depending on the cartilage plug abnormality size. Mean lesion scores of left and right valgus and tibial dyschondroplasia (0.40, 0.38, and 0.06) of fast-growing broilers were higher than those (0.26, 0.28, and 0.02) of slow-growing broilers (P = 0.0002, 0.0037, and 0.0269), respectively. Growth rate was negatively associated with the twisted legs syndrome and a bone abnormality (tibial dyschondroplasia) in this randombred population.

Genetic interrelationships among phosphorus, nitrogen, calcium, and energy bioavailability in a growing chicken population

A random-mating population was used to study the genetic interrelationship between phytate P (PPB), Ca (CaB), N (NB), and energy bioavailability (EB), BW at 4 wk of age, relative growth (RG), and feed conversion ratio (FCR). Heritability estimates for PPB, CaB, NB, and EB were 0.09, 0.13, 0.16, and 0.10, respectively, and those of BW, RG, and FCR were 0.66, 0.15, and 0.10, respectively. Genetic correlations between PPB and BW, and FCR were moderate and negative, suggesting that improvement in PPB will impair growth. The genetic correlations between PPB and CaB, and EB and RG were positive and moderate, indicating that improvement in PPB would also lead to improved CaB, EB, and RG. Energy bioavailability was positively correlated with CaB, NB, PPB, and BW. Even though the genetic correlation between EB and the other traits measured, except RG and FCR, ranged from low to moderate, improving the ability of birds to utilize caloric energy in the feed would consequently improve PPB as well as growth. Improving PPB would reduce the amount of P in excreta and provide an additional savings if exogenous phytase were not added to poultry feed. The genetic correlation between PPB and NB was low but positive, whereas NB had a positive genetic correlation with BW. Therefore, selecting on NB will result in positive correlated responses in BW and PPB. Improving PPB and NB will not only improve productivity, but also reduce the polluting effects of P and N on the environment.

Non-phytate phosphorus requirements and efficacy of a genetically engineered yeast phytase in male Lingnan Yellow broilers from 1 to 21 days of age

This experiment was conducted to investigate the requirement of non-phytate phosphorus (nPP) and efficacy of a genetically engineered yeast phytase in performance and tibia characteristics by male Lingnan Yellow broilers from 1 to 21 days of age. A total of 2640 1-day-old male chicks were randomly allotted to one of 11 dietary treatments, which consisted of six replicate floor pens with 40 birds per pen. All treatments had the same levels of all nutrients except for phosphorus and phytase. The control group (treatment 1) was fed the basal diet without dicalcium phosphate or phytase supplementation. Dietary concentrations of nPP were 0.11%, 0.19%, 0.27%, 0.35%, 0.43%, 0.51% and 0.59% respectively for treatments 1, 2, 3, 4, 5, 6 and 7, through addition of dicalcium phosphate (chemistry grade) to the basal diet. Diets 8-11 were supplemented with a genetically engineered yeast phytase 250, 500, 750 U/kg and a commercial phytase product 500 U/kg in basal diet respectively. The results showed that 0.46% and 0.51% nPP were required for maximum body-weight gain and optimum tibia development indicators respectively. However, 0.59% nPP had a negative effect on bird growth. The equivalency value of the genetically engineered yeast phytase was estimated to be 874 U/kg to liberate 0.1% nPP.

Effects of calcium and nonphytate phosphorus concentrations on phytase efficacy in broiler chicks

Phytase supplementation over a range of different levels of dietary Ca and nonphytate phosphorus (NPP) was investigated by comparing surface response curves from regression equations generated with (experiment 1) and without (experiment 2) phytase using various performance and bone quality parameters. Cobb x Cobb broiler chicks were raised from 0 to 16 d in 2 experiments using corn-soybean meal based diets. Experiment 1 used a 4 x 4 factorial arrangement with diets formulated to contain combinations of 4 levels of Ca: 0.38, 0.58, 0.78, and 0.98% and 4 levels of NPP: 0.2, 0.3, 0.4, and 0.5%. Experiment 2 used a composite rotatable design in which rations were formulated to contain dietary Ca levels of 0.38, 0.47, 0.68, 0.89, and 0.98% and NPP levels of 0.20, 0.24, 0.35, 0.46, and 0.50%. An extra point was included in the design to contain the lowest Ca and lowest NPP levels (0.38% Ca and 0.20% NPP). All combinations of Ca and NPP were fed with 657 phytase units/kg Natuphos 5000 phytase, plus 4 combinations (0.38% Ca and 0.20% NPP, 0.47% Ca and 0.24% NPP, 0.68% Ca and 0.35% NPP, and 0.89% Ca and 0.46% NPP) were fed without phytase to determine the suitability of comparing multiple regression response surfaces for particular variables among experiments. Comparison of surfaces, with and without phytase, showed that growth and bone quality responses to phytase were greatest at low NPP levels and high Ca levels, and these decreased when the Ca level was reduced or when the NPP level was increased. A third experiment confirmed that phytase elicits a greater response at higher Ca levels and lower NPP levels (0.86% Ca and 0.20% NPP) versus low Ca levels and low NPP levels (0.47% Ca and 0.24% NPP). The data demonstrated why it is impossible to determine a single NPP equivalency value for phytase supplements.

Correlated responses to divergent selection for phytate phosphorus bioavailability in a randombred chicken population

The current study was undertaken to evaluate the correlated responses to 3 generations of divergent selection for phytate phosphorus bioavailability (PBA) in the Athens-Canadian randombred chicken population. The traits studied were BW at 4 wk of age, BW gain (BWG), feed consumption (FC), and feed conversion ratio (FCR) during a period of 3 d. The first evaluation criterion was the cumulated divergent correlated response (CR(C)), which was calculated as the line difference of the least square means of phenotypic values for each trait at a given generation after adjustment for sex and hatch effects. The results showed a consistent correlated response in BW across generations. The CR(C) at generation G3 was 26.8 g (P < 0.01). The chickens in the low PBA line (L line) had higher BW than the high PBA line (H line). The CR(C) for BWG, FC, and FCR were significant (P < 0.05) only at G3. The second evaluation criterion was the average best linear unbiased prediction estimated breeding value (EBV). The results showed asymmetric genetic trends in BW, BWG, and FC, and the correlated responses were mainly due to the genetic changes that occurred in H line because little genetic change occurred in L line across generations. At G3, the line differences of EBV were close to the CR(C) values for all the traits except FCR. This suggested that CR(C) and EBV criteria would tend to be consistent with the increase across generations. However, at G1 and G2, the line differences of the EBV actually deviated from the CR(C) values for BWG and FC. The inconsistency could be attributed to experimental errors and genetic drift that were not accounted by the fixed model for obtaining CR(C).

Modeling of Parameters Affecting Phytate Phosphorus Bioavailability in Growing Birds

The current study was undertaken to establish a population from an unselected random-mating chicken population for the development of a model to predict factors that affect phytate P utilization in growing birds. A population was established from a mating of 40 male and 200 female chickens from the Athens Canadian randombred population. At 4 wk of age, birds were housed in individual metabolic cages and fed a diet containing 1.06% Ca, 0.35% total P, and 0.03% available P. After 3 d of acclimatization, feed consumption (FC) was measured and excreta produced in 3 consecutive d were collected. Individual 4-wk BW, BW gain (BWG), phytate P intake (PPI), inorganic P intake (IPI), Ca intake (CaI), N intake (NI), and energy intake (EI) during the 3 d excreta collection period were also measured. Feed conversion ratios (FCR) and relative growth rate were calculated. Phytate P bioavailability (PPB), Ca bioavailability (CaB), and N bioavailability (NB) were estimated from the disappearance of the nutrients during the passage of feed through the gastrointestinal tract. Energy bioavailability (EB) was measured by bomb calorimetry as the difference in the gross energy of the feed and the energy of the excreta. The major factors affecting PPB were CaB and EB for both sexes. In the males, BW contributed significantly to PPB. However, in the females, NB also contributed significantly to PPB. Faster growing birds tended to have a reduced retention time of feed compared with slow growing birds, and as a result utilized phytate P less. Birds that are able to utilize phytate P better are putatively able to release P for energy utilization. Therefore, the birds that were able to utilize phytate P better were also better energy utilizers.

Genetics of phytate phosphorus bioavailability: heritability and genetic correlations with growth and feed utilization traits in a randombred chicken population

The current study was undertaken to estimate variance components for phytate P bioavailability (PBA) and the genetic correlations among PBA with growth and feed utilization (or intake) traits in an unselected random mating chicken population. Pedigreed data from 901 Athens-Canadian randombred chickens hatched from 26 sires, 71 dams, and 105 grandparents were used for estimation of genetic parameters. Birds were individually housed in metabolic cages at 4 wk of age and fed a 0.35% P diet. After 3 d of acclimatization, excreta produced for 3 consecutive d were collected and feed consumed (FC) was measured. Individual 4-wk BW and BW gain (BWG) during the 3-d excreta collection period were also measured. Feed conversion ratios (FCR) were calculated. Phytate P bioavailability was estimated from the disappearance of phytate during the passage of feed through the gastrointestinal tract. The restricted maximum likelihood method with the average information matrix algorithm was used for the estimation of variance components. The heritability estimate for PBA was about 0.10. Genetic correlations between PBA and BW, BWG, and FC were moderate and negative, indicating that improving PBA utilization would moderately affect growth. The genetic correlation between PBA and FCR was negligible and suggested that selection for PBA will not adversely affect FCR. The economic implications of genetically modifying poultry to improving phytate P utilization and the subsequent elimination or reduction of the amount of phytase used in poultry diets are yet to be determined.

A bioassay to determine the effect of phytase on phytate phosphorus hydrolysis and total phosphorus retention of feed ingredients as determined with broilers and laying hens

In order to accurately formulate diets for broilers and laying hens to meet phosphorus requirements without overfeeding, precise knowledge of an individual feed ingredient's contribution to the retainable phosphorus is needed. Seven feed ingredients, included as the sole source of phosphorus, were tested with and without the addition of 600 phytase units (FTU) phytase/kg diet, in a 5-d bioassay with 10 22-d-old male broilers. Without addition of phytase, the amounts of phytate phosphorus hydrolyzed in corn, soybean meal, wheat, wheat midds, barley, defatted rice bran, and canola were 30.8, 34.9, 30.7, 29.1, 32.2, 33.2, and 36.7%, respectively. The addition of phytase increased (P < or = 0.05) each value to 59.0, 72.4, 46.8, 52.2, 71.3, 48.0, and 55.8%, respectively. The addition of phytase increased total phosphorus retention from 34.8, 27.0, 16.0, 31.9, 40.3, 15.5, and 39.4% to 40.9, 58.0, 33.8, 43.4, 55.5, 26.5, and 45.7%, respectively. A similar bioassay was conducted with laying hens fed corn, soybean meal, and defatted rice bran. Without phytase addition, phytate phosphorus hydrolyzed in soybean meal, corn, and rice bran was determined to be 25.7, 23.0, and 36.1%, respectively, and was increased (P < or = 0.05) to 62.4, 52.0, and 50.9%, respectively, with the addition of 300 FTU phytase/kg feed. Total phosphorus retention of soybean meal, corn, and rice bran increased from 36.8, 28.6, and 35.9% to 53.4, 44.7, and 43.0%, respectively, with the addition of phytase.

Influence of supplemental phytase on performance of broilers four to six weeks of age

The influence of dietary phytase on phytate P availability was investigated using Ross x Hubbard male broiler chicks. A randomized complete block design with a factorial arrangement of 2 x 3 was used with eight replicates (n = 2,400; 50 chicks per replicate) per treatment. Diets were formulated to contain two levels of nonphytate P (NPP; 0.225 and 0.325%) and three levels of phytase [0, 300, and 600 phytase units (FTU)/kg] with 0.75% Ca. An additional diet with 0.425% NPP and 0.85% Ca was used as a positive control (n = 400). Prior to assigning treatments, all chicks were fed a commercial starter mash adequate in all nutrients until 3 wk of age. Neither performance nor bone strength was significantly influenced by a reduction of NPP to 0.325% and Ca to 0.75% as compared to the positive control. However, when NPP was reduced to 0.225% and Ca to 0.75%, significant negative impacts on body weight, feed consumption, feed efficiency, and bone strength were observed. Phytase significantly increased BW at the lower NPP level but not at the higher NPP level. A significant NPP by phytase interaction occurred in bone criteria and livability. Phytase (300 FTU/kg) had greater influence on bone mineral content, bone density, bone breaking strength, and livability in broilers fed 0.225% NPP than in broilers fed 0.325% NPP. This study indicates that supplementing phytase in grower diets containing reduced levels of NPP and Ca significantly improved performance and bone strength of broilers. In diets containing marginal to deficient levels of either NPP or Ca or both, the addition of microbial phytase at 300 to 600 FTU/kg feed prevents P deficiency symptoms. Increasing phytase levels from 300 to 600 FTU/kg feed provided no additional benefit.

The effects of 1,25-dihydroxycholecalciferol and phytase on the natural phytate phosphorus utilization by laying hens

Two experiments were conducted to investigate the effects of supplementing a corn-soybean layer diet with either phytase, 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], or their combination. The basal diet was formulated to contain 3.00% Ca and 0.33% total P. In Experiment 1, 160, 56-wk-old laying hens were randomly assigned to treatment groups fed either the basal diet alone or diets supplemented with either 600 phytase units (FTU) per kilogram feed, 5 microg 1,25-(OH)2D3/kg feed, or their combination for an experimental period of 9 wk. Experiment 2 had the same design and treatment groups except that laying hens 24 wk of age were used for 8 wk. In both experiments, phytase had a positive effect on BW and increased plasma dialyzable P, tibia bone ash, and phytate P retention. In the first experiment, the addition of phytase, 1,25-(OH)2D3, or their combination prevented a rapid decrease in egg production due to a Mycoplasma gallisepticum infection observed in hens fed the basal diet. However, no benefit in egg production was obtained in the second experiment. No effects on egg weight and egg specific gravity were observed in both experiments. These results clearly indicate that phytase, and to a lesser extent 1,25-(OH)2D3, can be used to increase the utilization of phytate P by laying hens.

Phytase activity in the small intestinal brush border membrane of the chicken

The kinetics, mineral dependency, and pH dependency of phytate hydrolysis by preparations of chicken small intestinal brush border membrane vesicles were determined. Substantial phytate hydrolysis occurred over the pH range from 5 to 6.5 with a maximum hydrolysis at pH of 6. Inclusion of 25 mM MgCl2 in the media doubled the rate of phytate hydrolysis. The brush border was shown to have no nonspecific acid phosphatase activity and excess phytate had no effect on alkaline phosphatase activity at pH 11. Under optimal conditions of pH 6 plus 25 mM MgCl2, a kinetic model of a single Michaelis-Menten type of enzymatic activity with a Km of 0.160 +/- 0.008 mM and a Vmax of 42.5 +/- 1.0 nmol/mg vesicle protein per min plus a small unsaturable component converged to the data (P < 0.05). The specific and total activities of intestinal brush border phytase were highest in the duodenum (P < 0.05) and decreased progressively down the length of the gut. Intestinal brush border vesicles prepared from broiler chicks and mature laying hens had comparable specific phytase activity. However, the total activity of brush border phytase was 35% higher in the small intestine of laying hens (P < 0.05). Intestinal brush border phytase could contribute to phytate-phosphorus digestibility and may be subject to regulation in response to the dietary phosphorus and vitamin D status of the chicken.

Calcium and phosphorus requirements of the very young turkey as determined by response surface analysis

The first experiment was a central composite rotatable design with calculated calcium levels of 6.2, 7.0, 9.0, 11.0, and 11.8 g/kg diet and total phosphorus levels of 5.2, 6.0, 8.0, 10.0, and 10.8 g/kg diet (2.8 g phytin-P/kg by analysis). This design involved three replicates for each rotatable point and fifteen replicates of the central point. The second experiment was a 4 x 4 factorial design with calculated Ca levels of 8.0, 10.0, 12.0, and 14.0 g/kg diet and calculated total P levels of 7.0, 9.0, 11.0, and 13.0 g/kg diet (2.5 g phytin-P/kg by analysis). There were four replicates for each treatment. In both 16 d experiments maize-soya-bean diets were used and each replicate consisted of one pen containing 10-d-old broad-breasted, white tom turkeys. The Ca and total P requirements for optimum growth were estimated to be 12.5 and 10.0 g/kg diet respectively. Bone ash was adequate at these levels of Ca and total P, but maximum bone ash was not achieved until much higher levels of Ca and total P were employed. At the required levels of Ca and total P for growth the incidences of Ca- and P-deficiency rickets were very low. There were no treatment effects on feed efficiency. Increasing dietary Ca decreased the incidence of the Ca-deficiency lesion. There was a quadratic response due to dietary total P on both P-deficiency rickets and plasma dialysable P; intermediate levels of dietary P resulted in low incidence of the P-deficiency lesion and high levels of plasma dialysable P. There was a strong negative correlation between the incidence of P-deficiency rickets and plasma dialysable P. Percentage retention was very low at high levels of dietary P and low levels of Ca which corresponded with slightly higher P-deficiency rickets and low plasma dialysable P. No such obvious relationships existed between Ca retention, incidence of Ca-deficiency rickets, and plasma Ca. The incidence of tibial dyschondroplasia was very low in the present study. There were pronounced dietary treatment effects on phytin-P retention; at 14 d percentage phytin-P retention treatment means ranged from 18 to 46 in Expt 1 and from 0 to 40 in Expt 2 with the highest retention of phytin-P at low levels at both Ca and total P.