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.

Effect of anti-fibroblast growth factor receptor 1 antibodies on phosphorus metabolism in laying hens and their progeny chicks

Targeting fibroblast growth factor 23 (FGF-23) signaling pathway is of interest in controlling body phosphate metabolism. This study investigated the effect of anti-fibroblast growth factor receptor 1 (FGFR1, major FGF-23 receptor in the kidney) antibodies on phosphate metabolism. White Leghorn laying hens (65-wk-old) were vaccinated with either a FGFR1 peptide vaccine (five 8-amino-acid peptides were selected, CrZ-1:LPEDPRWE, CrZ-2:LDKDKPNR, CrZ-3:RRPPGMEY, CrZ-4:GSPYPGVP, and CrZ-5:RMDKPSNC) or adjuvant control. At peak antibody titer, hens were artificially inseminated. Chicks from control-vaccinated hens were fed either a non-phytate phosphorus (nPP) sufficient (nPP = 0.45%, positive control) or deficient (nPP = 0.20%, negative control) diet, while chicks from each of the FGFR1 peptide vaccinated hens were fed with the above nPP-deficient diet, for 14 D. When compared to control hens, plasma phosphate in CrZ-1, CrZ-2, CrZ-3, CrZ-4, and CrZ-5 vaccinated hens were decreased by 33, 30, 24, 20, and 26%, respectively (P < 0.05); egg weight in CrZ-2 and CrZ-5 vaccinated hens were increased by 6 and 7%, respectively (P < 0.05); egg production in CrZ-3, CrZ-4, and CrZ-5 vaccinated hens tended to decrease (P = 0.085; decreased by 14, 15, and 13%, respectively). When compared to positive control, chicks from all other groups had decreased body weight gain (BWG) and feed intake (FI) during 1 to 14 D, and had decreased plasma phosphate, tibiotarsus ash, and 24-h phosphorus excretion on day 14. When compared to negative control, BWG of CrZ-1, CrZ-2, CrZ-3, and CrZ-4 antibody chicks were decreased by 23, 28, 26, and 20%, respectively (P < 0.05); FI of CrZ-1, CrZ-2, and CrZ-3 antibody chicks were decreased by 15, 15, and 18%, respectively (P < 0.05); plasma phosphate of CrZ-5 antibody chicks were decreased by 26% (P < 0.05); plasma FGF-23 levels of CrZ-4 antibody chicks were increased by 18% (P < 0.05); tibiotarsus ash content of CrZ-2, CrZ-3, and CrZ-4 antibody chicks were decreased by 20, 20, and 21%, respectively (P < 0.05). In conclusion, anti-FGFR1 peptide antibodies decreased egg production of hens and growth performance of their progeny chicks probably by activating FGF-23 signaling and stimulating FGF-23 production.

Effects of Dietary Calcium Levels on Productive Performance, Eggshell Quality and Overall Calcium Status in Aged Laying Hens

This study was conducted to investigate the effects of diets with varying levels of calcium on egg production, shell quality and overall calcium status in aged laying hens. A total of five hundred 70-wk-old Hy-Line Brown layers were divided five groups and fed one of the five experimental diets with 3.5%, 3.8%, 4.1%, 4.4%, or 4.7% Ca, for 10 weeks. There were no significant differences in feed intake, egg production and egg weight among groups. The cracked eggs were linearly reduced as dietary Ca levels increased to 4.7% (p<0.01). A significant linear improvement for eggshell strength and thickness were determined with increasing dietary Ca levels (p<0.01). The contents of serum Ca and phosphorus were not affected by dietary Ca levels. With increase in dietary Ca levels, the tibial breaking strength slightly increased. There were no significant differences in the tibial contents of ash, Ca and phosphorus among groups. In conclusion, eggshell quality, as measured by appearance, strength and thickness of eggshell, were influenced by dietary Ca content as expected (p<0.05). These results suggested that aged laying hens require relatively higher level of Ca than required levels from current Korean feeding standards for poultry.

Effects of reducing dietary protein, methionine, choline, folic acid, and vitamin B12 during the late stages of the egg production cycle on performance and eggshell quality

A series of four experiments was conducted to determine whether-shell quality during the late stages of egg production can be improved by using diets that are effective in reducing egg size. The experiments involved dietary manipulation of protein, methionine, choline, folic acid, and vitamin B12. In experiment 1, reducing dietary protein in combination of reducing the dietary methionine and choline or this diet without supplemental folic acid and vitamin B12 resulted in reduced egg weight and improved shell quality. However, egg production also was drastically reduced. In experiment 2, reducing the dietary level of methionine, without adding supplemental choline, folic acid, and vitamin B12 reduced egg size and improved shell quality, but egg production was reduced as well. In this experiment reducing the dietary methionine without supplemental folic acid and vitamin B12 reduced egg size and improved shell quality with no adverse effect on egg production. In experiment 3, reducing the dietary level of methionine and choline or reducing the dietary level of choline, folic acid, and vitamin B12 reduced egg size and improved shell quality without adverse effects on egg production. On the other hand, reducing dietary methionine, folic acid, vitamin B12, and supplemental choline reduced egg weight and improved shell quality but lowered egg production. In experiment 4, reducing dietary methionine together with reducing choline and vitamin B12 reduced egg size and improved shell quality with no adverse effect on egg production. The results of this series of experiments generally indicate that certain manipulations of the combination of methionine, choline, folic acid, and vitamin B12 have the potential to reduce egg weight and improve shell quality without affecting egg production during the latter stages of the egg production cycle.

The effect of different levels of nonphytate phosphorus with and without phytase on the performance of four strains of laying hens

A 4 x 7 factorial experiment was conducted to determine the effect of different nonphytate phosphorus (NPP) regimens with and without phytase on performance of four strains of laying hens. The strains used were Babcock B300, DeKalb Delta White, Hy-Line W36, and ISA-White. The birds of T1 (Treatment 1), control diet, were fed a diet with 0.45% NPP for the entire experiment (20 to 63 wk of age). The birds of T2 were fed a NPP regimen of 0.25% for Phase 1 (20 to 35 wk of age), 0.2% for Phase 2 (36 to 51 wk of age), and 0.15% for Phase 3 (52 to 63 wk of age). The birds of T3 and T4 were fed a NPP regimen similar to T2 plus 150 or 300 units phytase/kg diet, respectively. The birds of T5 were fed a NPP regimen of 0.2, 0.1, and 0.1% for Phases 1, 2, and 3, respectively. The birds on T6 and T7 were fed a NPP regimen similar to T5, with 150 and 300 units phytase/kg diet, respectively. The criteria for evaluating the effect of dietary treatments were production performance, shell quality, bone ash, and total P excretion. Production traits were drastically reduced and mortality was drastically increased when the birds of T5 were fed a diet with 0.1% NPP during Phase 2 (36 to 51 wk of age). Increasing the NPP level of this treatment from 0.1 to 0.45% during Phase 3 restored the production traits almost to the control level during this phase of the experiment. The NPP regimen of 0.2-0.1-0.1% plus either level of phytase (T6 and T7) restored most of the traits for the entire experiment to the control level (T1), except egg production (EP) and the nonprolapse mortality. Bone ash also remained significantly lower than the control group with this NPP regimen plus the higher level of phytase (T7). Production traits were reduced, and nonprolapse mortality was increased due to the use of a NPP regimen of 0.25-0.2-0.15% without phytase (T2) for the entire experiment. The NPP regimen of 0.25-0.2-0.15% plus the lower level of phytase (T3) restored all the traits except EP to the control level for the entire experiment. The only treatment that maintained performance of all the strains comparable to their controls for the entire experiment was a NPP regimen of 0.25-0.2-0.15% plus the higher level of phytase (T4). Total P excretion of birds fed this NPP regimen was reduced by 55.6% as compared to the control group. The data generally indicated that the higher level of phytase was more effective than the lower level in restoring the performance of birds fed the low-P diets to the control level. Numerous interactions existed among strain x diet for various traits throughout the experiment, indicating the NPP requirement for maintaining production performance may be different among strains.

Dietary interaction of 1,4-diaminobutane (putrescine) and calcium on eggshell quality and performance in laying hens

An experiment was conducted to evaluate the potential dietary interaction between 1,4-diaminobutane (putrescine) and calcium on eggshell quality and overall laying performance. One hundred ninety-two 30-wk-old White Leghorn hens were fed a corn-and soybean-meal-based diet supplemented with 0.00, 0.05, 0.10, or 0.15% putrescine and 2.5, 3.0, 3.5, or 4.0% calcium in a factorial design (12 birds per diet) for 4 wk. The percentage of egg production increased linearly (P < 0.05) with increasing levels of dietary calcium. Significant interactions (P < 0.05) were observed between dietary putrescine and calcium for eggshell thickness, eggshell deformation, percentage of eggshell, calcium intake, total calcium retention, total eggshell calcium, and percentage of eggshell calcium. Interactions were due to quadratic effects of putrescine or calcium on these parameters. Eggshell thickness and percent eggshell increased when hens were fed 3.5% calcium in combination with 0.1% putrescine; however, calcium intake and calcium retention were significantly lower (P < 0.05). Eggshell quality improved with increasing dietary levels of calcium due to increased calcium retention and calcium balance. Increasing levels of dietary putrescine did not have a negative effect on eggshell quality; however, calcium intake was lower at higher-supplemented levels of putrescine. It was observed that dietary calcium in excess of requirements resulted in increased egg production and eggshell quality. Eggshell quality improved when hens were fed 3.5% calcium diet in combination with 0.10% putrescine. It was concluded that small supplements of dietary putrescine may improve eggshell quality, depending on dietary calcium concentration.

Nonphytate phosphorus requirement of laying hens with and without phytase on a phase feeding program

An experiment was conducted to reevaluate the nonphytate P (NPP) requirement of laying hens with and without phytase. The experiment involved 12 treatments in a 6 x 2 factorial design. The hens of the control group (T1) were fed a sequence of 0.40-0.35-0.30% NPP during 30 to 42, 42 to 54, and 54 to 66 wk, respectively. The NPP was reduced in increments of 0.05% in T2 to T6. The hens of T7 to T12 were fed NPP regimens similar to T1 to T6 but with 300 units phytase/kg diet. Two digestion trials were conducted during 42 and 66 wk, and nitrogen, phytate, and total P retention were determined. In the absence of phytase, production traits were not different for hens fed a NPP regimen of 0.25-0.20-0.15% than for the unsupplemented phytase control group for the entire experiment (P > 0.05). However, production traits were inferior for hens fed the lower NPP regimens (P < 0.05). In the presence of phytase, production traits were not different for hens fed the lowest NPP regimen (0.15-0.10-0.10%) than for the unsupplemented phytase control for the entire experiment (P > 0.05). The overall effect of NPP regimens and phytase on specific gravity for the entire experiment was significant. Specific gravity was greater for hens fed the regimens with less NPP than for hens fed regimens with greater NPP, and phytase had an adverse effect on specific gravity. However, specific gravity of hens fed the lowest NPP regimen with phytase was not significantly different from the unsupplemented phytase control group. The overall effect of phytase on phytate P retention was significant during digestion trials; phytase increased phytate P retention by about 15%. Daily total P excretion was 34 to 47% less for hens fed the lowest NPP regimen with phytase than for the unsupplemented phytase control group. Significant interactions existed for a number of traits and are discussed in the text.

Investigation on the possibility of reducing protein, phosphorus, and calcium requirements of laying hens by manipulation of time of access to these nutrients

Experiments (Exp.) were conducted to determine whether the daily requirement of laying hens for protein, P, and Ca can be reduced by providing the hens with adequate levels of these nutrients only during those hours of the day that the physiological need for these nutrients for formation of various components of eggs are increasing. In Exp. 1, birds of the positive control were fed a 16% protein diet and birds of the negative control were fed a 13% protein diet continuously during the light period (0500 to 2100 h). The other groups were fed the 16% protein diet during the morning (0500 to 1300 h) and the 13% protein diet during the afternoon (1300 to 2100 h) or vice versa. The design of Exp. 2 was similar to Exp. 1. The birds of the positive control were fed a 0.4% available P (AP) and the birds of the negative control were fed a 0.2% AP diet, with other groups receiving the high-low AP or the low-high AP diets during the morning and the afternoon, respectively. The birds of the negative controls in these Exp. had almost comparable performance to those fed the other dietary treatments. As a result, these Exp. did not have negative controls for comparison of different dietary treatments. Additionally, regardless of dietary treatments, birds consumed about 40% of their daily feed intake during the morning and about 60% during the afternoon in these Exp. Due to these two shortcomings, it was not possible to reach to a decisive conclusion pertaining to the objectives of the Exp. The results of Exp. 3 indicated that the above pattern of daily feed intake was not due to an increased appetite for Ca during the afternoon hours for shell formation. Various indices of shell quality were not improved when most parts of the daily Ca need was fed during the afternoon and evening and were not reduced when most parts of the daily Ca need was fed during the morning.

Effect of dietary calcium and phosphorus concentrations on retention of these nutrients by caged layers

1. A 5 x 3 factorial experiment was carried out with caged White Leghorn hens with 5 concentrations of calcium (26.0, 29.0, 32.5, 36.0, 39.0 g/kg) and 3 concentrations of phosphorus (4.3, 5.0 and 6.0 g/kg) for 120 d. Variables observed were hen day egg production, food consumption, shell weight, shell weight per unit surface area (SWUSA) and egg content. 2. 36.0 g calcium (Ca) and 4.3 g phosphorus (P) kg were found to be the dietary concentrations that resulted in optimal hen day egg production, shell weight, SWUSA and egg content. 3. Lack of a significant interaction between the effects of calcium and phosphorus on production parameters showed that the dietary Ca:P ratio is not of great importance for the laying hen. 4. Absolute retentions of Ca and P were inversely related to percentage retentions. 5. A balance study of calcium and phosphorus also showed optima at 36.0 g Ca and 4.3 g P per kg. 6. It was inferred that 36.0 g Ca and 5.0 g total P per kg are the optimal concentrations in diets for caged layers in a tropical climate.

Influence of supplemental phytase on calcium and phosphorus utilization in laying hens

A 6-wk study was conducted to determine the influence of supplemental phytase on Ca and P utilization in commercial laying hens. Diets were arranged factorially with three levels of dietary Ca (2.5, 2.8, and 3.1%), fed at two levels of nonphytate P (0.1 and 0.3% NPP) with and without supplemental phytase. Each diet was replicated eight times, with 16 hens per replicate. Criteria evaluated included egg specific gravity, feed consumption, egg production, egg weight, eggshell weight, bone quality, and body weight. Increasing dietary Ca significantly improved shell quality within 1 wk. A significant improvement in shell quality due to phytase supplementation was also observed during the 1st wk. Increasing NPP from 0.1 to 0.3% had not effect on egg specific gravity until Week 3, suggesting that the phytase benefit during Weeks 1 and 2 was related to improved Ca utilization. From Weeks 3 to 6, a significant P by phytase interaction was observed in which the magnitude of shell quality improvement was greatest when the 0.1% NPP diet was supplemented with phytase. This interaction was also observed from Weeks 3 to 6 for feed consumption and egg production and during Weeks 4 and 6 for egg weights. Phytase supplementation completely overcame the adverse effects associated with low dietary P and significantly reduced the impact of low dietary Ca on hen performance.

The effect of different levels of vitamin C and cholecalciferol with adequate or marginal levels of dietary calcium on performance and eggshell quality of laying hens

Three experiments were conducted to determine whether shell quality, bone mineralization, and other production traits could be improved by adding vitamin C (ascorbic acid) to laying hen diets. The period of each experiment was 12 wk. Experiment 1 consisted of a 2 x 2 x 3 factorial design with two levels of Ca (2.8 and 3.8%), two levels of cholecalciferol (vitamin D3; 2,200 and 4,400 IU/kg diet), and three levels of vitamin C (0, 125, and 250 ppm). Experiment 2 consisted of a 2 x 3 x 2 factorial design with two levels of Ca (2.8 and 3.8%), three levels of vitamin D3 (250, 500, and 2,000 IU/kg diet), and two levels of vitamin C (0 and 250 ppm). Experiment 3 consisted of a 2 x 4 factorial design with two sources of vitamin D3 (12.5 micrograms vitamin D3/kg diet or 12.5 micrograms 25-OH-D3/kg diet) and four levels of vitamin C (0, 250, 500, and 1,000 ppm). Calcium level was kept constant at 3.5% for all the diets in Experiment 3. Production performance was not influenced by dietary treatments in Experiment 1. In Experiment 2, feed conversion was improved (P < 0.05) due to increasing the dietary Ca, and egg weight and egg size were increased (P < 0.05) due to adding 250 ppm vitamin C to the diet. In experiment 3, albumen quality was increased by the addition of 1,000 ppm vitamin C to the diet. Egg specific gravity was increased in Experiments 1 and 2 only, due to increasing the Ca level (P < 0.05). In Experiment 2, increasing the Ca level and increasing the vitamin D3 level from 250 to 2,000 ppm reduced (P < 0.05) the number of cracked eggs, but incidence of cracked eggs was increased with the addition of 250 ppm vitamin C to the diet. In Experiment 1, plasma level of 1,25(OH)2D3 was greater (P < 0.05) for hens fed 2.8 than 3.8% Ca, but blood acidbase balance was not influenced by dietary regimens. Bone ash was not influenced by dietary treatments in any of the experiments. The data indicated that a supplemental level of vitamin C had no beneficial effects on shell quality and bone mineralization under the conditions of the current experiments.

Duodenal calcium uptake, femur ash, and eggshell quality decline with age and increase following molt

An experiment was conducted to test the hypothesis that the decline in eggshell quality over time during egg production, and its improvement after molting, paralleled the rate of calcium uptake by the duodenum of the laying hen. In vitro duodenal calcium uptake rate and femur ash (percentage of femur weight) were determined at 37, 45, 51, 58, 68, and 72 wk of age. Percentage shell and shell thickness (millimeters) were determined at 22, 29, 36, 44, 50, 57, and 71 wk of age. Molt was induced at 63 wk of age. Three commercial strains DeKalb XL-Link, ISA/Babcock B-300V, and Hy-Line W-36 were compared. There were no differences in duodenal calcium uptake rate among strains. There was a significant decline (P < .01) in duodenal calcium uptake from 408 pmol/mg tissue per min at 37 wk of age to 329 pmol/mg per min at 58 wk of age. Femur ash decreased (P < .01) from 50.8% at 37 wk of age to 47.6% at 58 wk of age. Percentage shell and shell thickness declined (P < .01) from 9.79% and .403 mm at 22 wk of age to 8.88% and .373 mm at 57 wk of age, respectively. After the induced molt, duodenal calcium uptake increased (P < .01) to 402 pmol/mg tissue per min, and percentage shell and shell thickness increased (P < .01) to 10.23% and .389 mm, respectively. Duodenal calcium uptake increased immediately postmolt, whereas femur ash did not increase until 72 wk of age (P < .01).

Calcium and phosphorus metabolism and eggshell formation of hens fed different amounts of calcium

Twenty-seven 42-wk-old Single Comb White Leghorn hens housed in separate cages were fed either 2.5, 3.5, or 4.5% Ca diets, each providing .45% available P. Birds were allowed a 7-day adaption period followed by an 8-day collection period. Feed and water were available for ad libitum consumption with feed intake recorded daily. Eggs and excreta were collected daily for mineral analysis. Feed, Ca, and P intake of hens increased significantly (P less than .05) on shell-forming (SF) days compared with days on which shell formation did not take place (NSF). Dietary Ca level had a significant (P less than .05) effect on feed and Ca intake of hens. On SF days, hens retained more dietary Ca, both as a percentage and per gram Ca basis, compared with NSF days. As dietary Ca increased, the percentage Ca retained decreased (P less than .05) and per gram Ca retained increased (P less than .05). Dietary Ca had no effect (P greater than .05) on egg weight or egg production. Increasing dietary Ca significantly (P less than .05) decreased shell deformation and increased (P less than .05) shell weight and grams of shell Ca, although there was no significant (P greater than .05) effect on percentage shell Ca. Calcium retention increased linearly (P less than .05) as Ca intake increased, and shell weight increased quadratically (P less than .05). There was a diminishing response of shell weight to Ca intake at higher levels.

Evaluation of the dietary interaction of calcium and phosphorus in the high producing laying hen

1. In a 6 x 7 factorial experiment using 2688 22-week-old laying hens of the Lohmann-SL strain kept in cages (4 birds/cage), diets containing six calcium (20, 25, 30, 35, 40, 45 g calcium/kg) and seven phosphorus concentrations (3.2, 4.2, 5.2, 6.2, 7.2, 8.2, 16.2 g total phosphorus/kg (Pt)) were combined orthogonally. The resulting 42 treatments were replicated 8 times so that a replicate consisted of a double cage of 2 x 4 hens. The experiment lasted 40 weeks (10 x 28 days). 2. The experimental diets, based on maize and soyabean meals contained 11.5 MJ metabolisable energy/kg and 175 g/kg protein. Different dietary calcium and phosphorus contents were obtained by substituting oat hulls with limestone and dicalcium phosphate. 3. Mortality, egg production, egg weight, egg mass, food intake and food conversion efficiency were determined as well as the breaking strength, thickness of shells and the percentage of eggs with defective shells. 4. All responses measured were significantly influenced by the variance sources (calcium, phosphorus, interaction). Most of the production traits responded asymptotically to increasing dietary phosphorus concentration, the greatest increases or decreases generally being seen between 3.2 and 5.2 g Pt/kg. Further but weaker increases were seen between 5.2 and 8.2 or 16.2 g Pt/kg. 5. Increases in dietary calcium content always resulted in curvilinear responses. In all cases optimal effects were obtained with diets containing 25 g calcium/kg and the worst values at 45 g calcium/kg. The interaction between calcium and phosphorus was recognised by strong performance depressions and a high mortality at combinations of the lowest phosphorus concentration (3.2 g/kg) with high calcium contents (35 to 45 g/kg). These were largely offset by increasing dietary phosphorus. Thus, between 7.2 and 16.2 g Pt/kg and 25 and 45 g Ca/kg a plateau was formed where only small differences in egg production were observed. 6. From the three egg shell characteristics measured, breaking strength and shell thickness responded differently to the percentage of eggs with defective shells. While breaking strength and shell thickness were respectively negatively and positively influenced by increasing dietary phosphorus and calcium contents, both elements affected the proportion of eggs with defective shells.(ABSTRACT TRUNCATED AT 400 WORDS)

Modelling the relationships of egg weight, specific gravity, shell calcium and shell thickness

1. The relationships between egg weight, egg specific gravity, shell weight, shell calcium and shell thickness of 800 eggs from 8 treatments were expressed using mathematical models. 2. The equations describing the relationships were on the basis of any two independent variables predicting the remainder. 3. Of 10 possible models, 4 had high co-efficients of determination (R2 greater than 0.80) for each predicted dependent variable. 4. The two independent variables in each of these 4 models were, in turn, egg weight and specific gravity, egg weight and shell weight, egg weight and shell thickness, and specific gravity and shell weight. 5. The best model was that having egg weight and specific gravity as independent variables, with R2 values of 0.94, 0.88, and 0.85 for predicted shell weight, shell calcium, and shell thickness, respectively. Moreover, egg characteristics can be measured non-destructively by this model, whereas the other three require destruction of the egg.

Shell quality: potential for improvement by dietary means and relationship with egg size

Three experiments were conducted by sampling a total of 15,705 eggs from Leghorn hens fed diets varying in methionine, Na, and Ca content. In Experiment 1, birds of four different ages were housed in a common environment and fed diets containing between .233 and .383% methionine. In Experiment 2, birds of five different ages were housed in a common environment and fed diets containing .15, .30, and .45% Na and .25, .45, and .65% nonphytate phosphorus (NPP). In Experiment 3, eggs were sampled from 42 to 62 wk of age in 4-wk intervals from hens fed diets containing from 3 to 9% Ca in increments of 1.5%. Feeding lower levels of methionine (.233%) produced significantly lower egg weights and greater shell strength but at the expense of a decline in egg production at early ages. Reducing the NPP level from .65 to .25% produced lower egg weights and greater shell strength. A corresponding drop in production was not observed except at the .45%-Na level. No significant effects of Na on shell strength were observed. Higher Ca levels produced greater shell strength and had variable effects on egg weight. Increasing the Ca level beyond 6% resulted in a significant decline in production. Regression analyses indicated that within a population, the relationship between egg weight and shell strength is positive. In some instances, the relationship was curvilinear, where the positive association between egg weight and shell strength decreased with increasing egg weights.

The effect of marginal levels of calcium, fish meal, torula yeast and alfalfa meal on feed intake, hepatic lipid accumulation, plasma estradiol, and egg shell quality among laying hens

In two 2 X 3 factorial-design experiments, Single Comb White Leghorn (SCWL) laying hens were fed either a corn-soy (CS) diet or one containing 5% each of fish meal, alfalfa meal, and torula yeast (FAY), each with 2.0, 2.75, or 3.5% calcium in Experiment 1 and 2.5, 3.5, or 4.5% in Experiment 2. Duration of the experiments were 6 and 8 weeks, respectively. Low dietary calcium resulted in decreased efficiency of energy utilization in both experiments and significantly elevated energy consumption in Experiment 2. Liver lipids and body weight were unaffected by dietary calcium level, and declines in both egg production and shell quality were observed in both studies. In Experiment 1, overall plasma estradiol and tibial bone ash were significantly reduced with lowered dietary calcium, but this was not observed in Experiment 2. Egg weight was significantly increased by decreased dietary calcium in Experiment 1. Plasma calcium was not affected by dietary calcium in either trial. Feeding FAY resulted in significantly lower liver lipid than feeding CS in both experiments, and similar but nonsignificant trends were realized for plasma estradiol. Tibial bone ash and egg-breaking strength were significantly higher for hens fed FAY in Experiment 1. In Experiment 2, plasma total calcium was lower and the percent shell was higher in hens fed FAY with 3.5% calcium than in hens fed CS with 3.5% calcium. No differences were observed between CS and FAY in feed consumption, body weight, or egg production. These studies indicate that feeding a more complex diet to laying hens may change calcium metabolism and improve shell quality at marginal levels of calcium compared with feeding a simplified CS diet.

Interrelationship between phosphorus, sodium, and chloride in the diet of laying hens

Two experiments were conducted with commercial egg production type hens to determine the effects of dietary phosphorus, sodium, and chloride levels as related to levels of plasma calcium and phosphorus, blood acid-base balance, and production characteristics. Sodium and chloride were supplied to the diet as sodium bicarbonate and hydrochloric acid, respectively. In Experiment 1, five treatment groups were fed diets ad libitum containing .2, .6, 1.0, 1.4, and 1.8% total phosphorus. The remaining treatment group was fed a diet containing .4% total phosphorus from 1400 to 2030 hr and 1.4% total phosphorus from 600 to 1100 hr. In Experiment 2, a 3 X 4 factorial arrangement of treatments was used that consisted of three levels of total phosphorus (.2, .6, and 1.4%) and four levels of added sodium (0, .06, .22, and .45%) provided by sodium bicarbonate. Three other treatment groups were fed diets containing .36% supplemental chloride supplied by hydrochloric acid and either .2, .6, or 1.4% total phosphorus. Egg production was decreased in hens fed diets containing 1.8% total phosphorus. Egg specific gravity was decreased by both low and high phosphorus levels. Hens fed .4% total phosphorus in the afternoon produced eggs with higher specific gravity as compared with hens fed 1.4% total phosphorus during the entire experiment. At 1.4% dietary phosphorus, a significant increase in specific gravity was observed when .2 or .8% sodium bicarbonate was added to the diet. Increasing dietary phosphorus resulted in elevated plasma phosphorus and calcium concentration. Plasma phosphorus of hens fed .2 through 1.8% total phosphorus declined slowly from oviposition until 6 hr after oviposition and then reached a peak at 21 hr after oviposition.(ABSTRACT TRUNCATED AT 250 WORDS)