Influence of dietary phosphorus on shell quality1

Performance, egg quality traits, and serum metabolite concentrations of laying hens affected by dietary supplemental chromium picolinate and vitamin C under a heat-stress condition

A 3 × 2 factorial experiment consisting three levels (0, 200, and 400 μg/kg) of chromium (chromium picolinate) and two levels (0 and 250 mg/kg) of vitamin C was employed to evaluate the effects of these dietary supplements on performance, egg quality traits, and serum biochemical parameters of heat-stressed laying hens (Lohmann LSL-Lite) from 66 to 74 weeks of age. Feed intake increased when birds were given either 400 μg/kg chromium or 250 mg/kg vitamin C (P < 0.05), but the birds that received both chromium and vitamin C consumed feed similar to those that received only chromium. Dietary treatments had no effect on egg production, egg mass, egg volume, feed conversion ratio, and body mass (P > 0.05). The birds that fed on diet with chromium or vitamin C produced eggs with higher shell mass and thickness compared to the control. Both eggshell mass and thickness decreased when vitamin C and chromium were supplemented simultaneously, and birds given the diet supplemented with 400 μg/kg chromium and 250 mg/kg vitamin C had eggshell mass and thickness similar to those of the control group. The serum concentration of chromium increased due to increasing level of dietary chromium (P < 0.05). The birds that received diet with chromium and vitamin C had higher serum concentrations of chromium compared to those that received only chromium (P < 0.05). Similarly, the hens that received chromium and vitamin C had higher serum concentrations of calcium and phosphorus compared to the hens fed with other treatments (P < 0.05). The birds given with supplemental chromium exhibited lower serum glucose, total cholesterol, and triglycerides concentrations but higher serum albumin and total protein concentrations compared to the other groups (P < 0.05).

Maternal health status correlates with nest success of leatherback sea turtles (Dermochelys coriacea) from Florida

Of the seven sea turtle species, the critically endangered leatherback sea turtle (Dermochelys coriacea) exhibits the lowest and most variable nest success (i.e., hatching success and emergence success) for reasons that remain largely unknown. In an attempt to identify or rule out causes of low reproductive success in this species, we established the largest sample size (n = 60-70 for most values) of baseline blood parameters (protein electrophoresis, hematology, plasma biochemistry) for this species to date. Hematologic, protein electrophoretic and biochemical values are important tools that can provide information regarding the physiological condition of an individual and population health as a whole. It has been proposed that the health of nesting individuals affects their reproductive output. In order to establish correlations with low reproductive success in leatherback sea turtles from Florida, we compared maternal health indices to hatching success and emergence success of their nests. As expected, hatching success (median = 57.4%) and emergence success (median = 49.1%) in Floridian leatherbacks were low during the study period (2007-2008 nesting seasons), a trend common in most nesting leatherback populations (average global hatching success = ∼50%). One protein electrophoretic value (gamma globulin protein) and one hematologic value (red blood cell count) significantly correlated with hatching success and emergence success. Several maternal biochemical parameters correlated with hatching success and/or emergence success including alkaline phosphatase activity, blood urea nitrogen, calcium, calcium:phosphorus ratio, carbon dioxide, cholesterol, creatinine, and phosphorus. Our results suggest that in leatherbacks, physiological parameters correlate with hatching success and emergence success of their nests. We conclude that long-term and comparative studies are needed to determine if certain individuals produce nests with lower hatching success and emergence success than others, and if those individuals with evidence of chronic suboptimal health have lower reproductive success.

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.

Influence of cage density and prior dietary phosphorus level on phosphorus requirement of commercial leghorns

Two studies were conducted to determine whether cage density and prior dietary nonphytate P (NPP) level affect hens' P requirements. In Experiment 1, hens were housed at three cage densities (300, 400, and 600 cm2 or 46.5, 62.0, and 93.0 inches2/hen) and fed four levels of NPP (0.15, 0.25, 0.35, and 0.40%) for 6 wk to determine the effect of cage density on the P requirement. Egg production (EP), feed consumption (FC), egg weight (EW), and egg specific gravity (ESG) were measured to evaluate performance. Cage density influenced EP within Week 1 (P < 0.01), and during Weeks 5 and 6, there was a cage density x NPP-level interaction (P < 0.05). At 300 cm2, EP was more severely affected by 0.15 and 0.25% NPP than at 400 and 600 cm2. A linear decrease (P < 0.001) in FC was observed because of decreased NPP. Hens at 300 cm2 consumed 4 g less feed/hen per d than hens at 400 cm2. A linear decrease in EW was observed as the NPP level decreased (P < 0.01) from 0.25 to 0.15%, and there was no effect of cage density. Experiment 2 was conducted to determine the effect of prior dietary P levels on time required to create a P deficiency. Hens fed 0.4% NPP were divided into two groups and fed 0.25 and 0.4% NPP for 4 wk. At the end of 4 wk, hens fed 0.25% NPP were further divided into three groups and were fed diets containing 0.09, 0.25, and 0.30% NPP for an additional 6 wk. Hens fed 0.4% NPP were divided into three groups and fed diets containing 0.09, 0.4, and 0.45% NPP. Reduction of NPP from 0.4 and 0.25% to 0.09% reduced EP by 8.5 and 6.8%, respectively, within 3 wk. Prior NPP levels had no influence on time required to create a P deficiency in terms of EP. Reduction of NPP from 0.4 and 0.25% to 0.09% reduced (P < 0.05) FC. A decline in FC occurred 2 wk earlier in hens previously fed 0.4% than those fed 0.25% NPP. This result indicates that hens fed 0.4% NPP became P deficient more quickly than hens fed 0.25%. We concluded that cage density and prior NPP level affect the hen P requirements or time required to create a P deficiency.

Dietary phosphorus supply, egg-shell deposition and plasma inorganic phosphorus in laying hens

1. In 2 experiments the effects of dietary phosphorus on relationships between plasma inorganic phosphorus concentration (Pi), shell and egg production and depletion states were measured in brown laying hens. 2. In a 12-week experiment dietary phosphorus concentrations from conventionally deficient (1.6 g non-phytate-phosphorus (PNP)/kg) to moderate excess (3.9 g PNP/kg) had little effect on egg and shell production, although there was evidence that plasma Pi concentration, when not influenced strongly by shell formation, reflected dietary phosphorus content. 3. Among birds at each dietary phosphorus concentration there was a negative linear relationship between shell weight of early eggs in the sequence and plasma Pi concentration. The relationship was apparently not affected by dietary phosphorus concentration. 4. Continued feeding of the deficient diet to 61 weeks of age did not have effects on body weight, egg and shell production, other than those associated with age, but plasma Pi and bone measurements indicated marginal phosphorus depletion. 5. In another experiment excessive dietary phosphorus (11.9 g PNP/kg) fed in a cross-over design caused small adverse effects on shell production, increased food intake and body weight and increased plasma Pi content, while there was no relationship between shell weight and plasma Pi concentration. 6. The results are consistent with an indirect effect of plasma phosphorus accumulation on shell formation, probably via an inhibitory effect on skeletal calcium release, in addition to any effect of excess dietary phosphorus on intestinal calcium availability. 7. Phosphorus requirement and status in the laying hen are complicated by the failure to recognise the contribution of digestible phytate-phosphorus to the available phosphorus supply.

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.

Egg-shell deposition and blood plasma inorganic phosphorus concentration in individual laying hens

1. The relationship between plasma inorganic phosphorus measured at the end of the dark period and the weight of the next egg shell produced was investigated in 30 Hisex Brown hens. 2. Hens received an adequate conventional layers' diet and the lighting pattern was conventional (17 L: 7 D). Observations were made early (31 to 40 weeks) and late (62 to 68 weeks of age) in the laying period. 3. Eggs were classified by position in the clutch sequence and significant negative correlations were found between shell weights of early eggs in the sequence and plasma phosphate at the end of the dark period. 4. No significant trends were found in plasma total calcium. 5. No significant differences were found in bone compositions of birds producing consistently more or less than average shell weight during the laying period. 6. The negative correlations between plasma phosphate and shell weight are consistent with the observations of Sauveur and Mongin (1983) and show that impairment of shell deposition is associated with skeletal mobilisation as indicated by increase in plasma phosphate. This is consistent with the observations on bone composition and indicates that selection for shell quality will tend to select birds which are not dependent on excessive skeletal mobilisation during shell formation.

Relationship of plasma calcium and phosphorus to the shell quality of laying hens receiving saline drinking water

1. From 36 to 43 weeks of age 210 White Leghorn laying hens were used to study the relationship of plasma calcium and phosphorus concentrations to egg-shell quality when saline drinking water was given. 2. Seven experimental treatments in which different amounts of sodium chloride were supplied by the food and/or the drinking water were compared. 3. Increasing salt intake through the drinking water or the food reduced shell thickness and shell calcium, and increased the numbers of damaged eggs. Sodium chloride given in the drinking water was more effective in reducing shell quality and increasing plasma calcium and phosphorus than sodium chloride given in the food.

Laying hens respond differently to high dietary levels of phosphorus in monobasic and dibasic calcium phosphate

A series of experiments were conducted to determine the relative acidogenicities of dietary chloride, phosphorus, and sulfate and their effects on shell quality. Calcium salts of these anions were added to a corn-soybean meal diet to provide supplemental levels of 150 to 450 meq/kg diet chloride, 150 to 600 meq/kg diet monobasic phosphate, 150 to 1,200 meq/kg diet dibasic phosphate, and 150 to 1,200 meq/kg diet sulfate. The results indicated that laying hens can safely tolerate up to 200 meq/kg diet supplemental chloride (.95% total chloride in the diet) and up to 450 to 600 meq/kg diet supplemental sulfate (2.16 to 2.88% added sulfate). Levels higher than these adversely affected shell quality and altered blood acid-base balance. Laying hens responded quite differently to phosphorus when it was supplied as monobasic or dibasic phosphate. Supplemental levels of 900 to 1,200 meq/kg diet dibasic phosphate (1.95 to 2.41% total phosphorus) did not have an adverse effect on performance and up to a supplemental level of 450 meq/kg diet (1.25% total phosphorus) did not affect shell quality. In contrast, performance was seriously impaired by a supplemental level of 150 meq/kg diet monobasic phosphate (1.02% total phosphorus in the diet). The results further indicated that phosphate in monobasic (but not in dibasic) form is a strong acidogenic anion and that most of its adverse effect on performance and shell quality can be ameliorated by alkaline salts of sodium or potassium bicarbonate. The relative acidogenicities of calcium salts of these acidic anions were as follows: phosphate (monobasic) > chloride > sulfate > phosphate (dibasic).

The influence of various calcium and phosphorus levels on tibia strength and eggshell quality of pullets during peak production

One thousand and eighty DeKalb XL pullets were randomly allocated to nine treatments and arranged in a 3 x 3 factorial to determine the effects of three levels of dietary calcium (2.75, 3.75, and 4.25%) and three levels of dietary available phosphorus (.30, .40, and .50%) on eggshell quality and tibia weight, tibia breaking strength, tibia ash, and bone mineral content of pullets during peak production. Feed consumption increased as dietary calcium or phosphorus increased. Increasing dietary calcium caused a significant linear increase in egg specific gravity, but dietary phosphorus had no significant effect on egg specific gravity. Calcium and phosphorus levels did not significantly affect egg production, body weight, plasma chloride, or phosphorus. Ionized calcium increased significantly as dietary calcium increased. Tibia breaking strength, tibia weight, tibia ash, and bone mineral content increased significantly with increasing dietary calcium. Dietary phosphorus had no significant effect on these parameters. However, when 2.75% calcium was fed, reducing dietary phosphorus significantly decreased tibia weight, tibia ash, and bone mineral content.

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.

Influence of phase feeding available phosphorus on egg production characteristics, carcass phosphorus content, and serum inorganic phosphorus levels of three commercial layer strains

An experiment was conducted to obtain information on the concept of progressively decreasing dietary phosphorus levels (phase feeding) on the performance of three different commercial layer strains. Dietary available phosphorus (AP) levels of .15, .30, or .45% were fed continuously from 22 to 70 weeks of age. Concurrently, a diet containing .35, .25, and .15% AP was phase-fed during age intervals of 22 to 34, 34 to 50, and 50 to 70 weeks, respectively. Dietary AP levels did not significantly affect egg production except the .15% AP level, which significantly reduced egg production when compared with the other three dietary AP treatments. Efficiency of feed utilization was significantly superior for hens phase-fed AP compared with hens fed the other AP treatments. There were no differences in egg weight or mortality due to dietary AP. Eggshells were significantly thicker when hens received .15% AP. The .15% AP and phase-fed regimen resulted in hens with significantly lower body weights at the end of the experiment. Hens fed .30% AP and phase-fed AP had significantly lower carcass ash and phosphorus levels. Serum phosphorus levels corresponded directly to dietary AP levels. There were no significant differences in egg production due to strain nor were there any strain by dietary treatment interactions that influenced production traits. Significant strain differences were noted in feed efficiency, egg weight, carcass ash, and carcass phosphorus.

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)

Plasma phosphorus at 0, 6, and 21 hours postoviposition in hens laying in the morning or afternoon

Two experiments were conducted using White Leghorn hens. Blood samples were collected immediately following oviposition (0 hr) or 6 or 21 hr postoviposition from hens laying in the morning or afternoon. Plasma phosphorus was determined at each time period. In Experiment 1, plasma phosphorus at oviposition was essentially the same for hens laying in the morning or afternoon (3.95 and 4.10 mg/dl, respectively). At 6 hr postoviposition plasma phosphorus was lower than that observed at 0 hr (3.22 and 3.15 mg/dl, respectively). When comparing plasma phosphorus levels at 21 hr postoviposition of hens laying in the morning or afternoon a higher (P less than or equal to .05) phosphorus level was observed for hens that laid in the morning (5.90 vs. 4.91, respectively). In Experiment 2, plasma phosphorus levels at 0 and 6 hr postoviposition were 3.32 vs. 3.18 and 2.81 vs. 2.74 mg/dl for hens laying in the morning and afternoon, respectively. At 21 hr postoviposition, phosphorus values of 5.30 vs. 3.65 mg/dl were reported for hens laying in the morning and afternoon, respectively. Data also indicated that on the day a hen does not lay an egg, plasma phosphorus does not rise. An hypothesis is offered to explain the difference in egg shell quality between eggs laid in the morning or afternoon.

Interrelationship between sodium chloride, sodium bicarbonate, calcium, and phosphorus in laying hen diets

Three experiments were conducted with Hy-Line W-36 laying hens housed in individual wire cages in open type houses. The first and second experiments were designed to investigate the effects of sodium chloride and sodium bicarbonate fed at two levels of dietary total phosphorus (.30 and .60%). The third experiment was designed to study the interrelationships between age and sodium source. Supplementing sodium chloride at two levels (.37 and 1.11%) did not effect hen performance, except that egg production was better at the lower NaCl. Egg production was greater when .60 rather than .30% dietary phosphorus was fed. Egg specific gravity and egg weight were decreased at the lower dietary phosphorus. The addition of 1.6% sodium bicarbonate in the sodium chloride-free diets was deleterious to hen performance in all experiments. High mortality was observed in both experiments in which hens were fed diets containing high sodium and low chloride. Plasma calcium and phosphorus levels were significantly depressed in hens fed diets containing the lower phosphorus. Blood pH, base excess, bicarbonate, and total carbon dioxide were significantly increased by sodium bicarbonate supplementation, and these values were found to be inversely related to dietary phosphorus levels.

Effects of different short-term dietary phosphorus levels on egg specific gravity and blood phosphorus of hens

In the first 2 experiments, laying hens were fed a diet containing .30% phosphorus for a preliminary period of 3 days. At the beginning of the experimental period, hens were fed .30, .75, or 1.40% phosphorus with 3.50% calcium. Another group of hens was fed .75% phosphorus and 1.40% calcium. Specific gravity of the eggs and blood serum inorganic phosphorus were determined and compared with those from control hens continuously fed a diet containing .75% phosphorus and 3.50% calcium. Both high phosphorus and/or low calcium decreased the specific gravity of eggs and increased the serum phosphorus level. In experiment 2, hens were fed different levels of phosphorus at different times of the day. Birds receiving 1.40% phosphorus between 0700 and 0930 hr and .30% phosphorus between 0930 and 2000 hr (Treatment 2) laid eggs with higher specific gravity than hens fed .30% phosphorus between 0700 and 0930 hr and 1.40% phosphorus between 0930 and 2000 hr (Treatment 3). there was no further improvement in egg shell quality over that from hens fed .75% phosphorus for both time periods (0700 to 2000 hr). In both experiments it was apparent that the dietary phosphorus level affected egg shell quality.

Influence of dietary calcium and phosphorus on metabolism and production in laying hens

1. The effects of different dietary concentrations of calcium (24 to 56-9 g/kg) and phosphorus (4-5 to 14-2 g/kg) on production and some aspects of metabolism were studied in laying hens. 2. Treatments did not affect egg numbers, food consumption, conversion efficiency of food to egg, bodyweight gain or mortality. 3. Increasing dietary calcium (Ca) significantly increased plasma Ca and inorganic phosphorus (P), breaking strength at the radius and egg specific gravity and significantly decreased plasma alkaline phosphatase and egg weight. 4. Increasing dietary phosphorus increased plasma P and decreased egg specific gravity significantly. 5. Plasma Ca, P and alkaline phosphatase and radius breaking strength were suitable indices of the Ca status of the hens.

The ability of hens to regulate phosphorus intake when offered diets containing different levels of phosphorus

Two experiments were conducted to determine the extent and ability of laying hens to regulate their phosphorus (P) intake when offered a choice of diets containing different levels of phosphorus. In the first experiment, Babcock B-300 hens, 72 weeks old, received a choice of diets offered in each of two plastic cups. The dietary choices of P levels included: 0.75 percent P vs. 0.75 percent P diet (control), 0.19 percent vs. 0.46 percent P, 1.00 percent vs. 2.43 percent P and 0.19 percent vs. 2.43 percent P diet. The cups were weighed and replenished every three days. After one month, the calcium level in all diets was increased from 3.00 to 6.00 percent calcium and the experiment continued for a second month. The second experiment involved the same dietary choices of P with a constant level of 3.00 percent calcium. Hens in this experiment were 48 weeks old. In both Experiments 1 and 2 the daily feed consumption was determined by weighing all cups at two hour intervals for two days. This procedure was performed after hens had been on the experimental regime for one month. Hens in both experiments clearly regulated their intake of P when offered the above choices. Hens avoided the consumption of the 2.43 percent P diet in favor of the diet containing less P. Consumption of the 2.43 percent P diet, even when avoided to a large extent, reduced both egg production and egg specific gravity. Increased calcium levels in the diets resulted in an increase in consumption of the 2.43 percent P diet. Young hens demonstrated a significant increase in consumption of the 0.46 percent P diet over the 0.19 percent P diet. Both old and young hens in the 0.46 percent P vs. 0.19 percent P group in both experiments maintained egg specific gravity, egg weight and egg production at levels comparable to controls. Results of the two hour feed weighings showed that laying hens in the 0.19% vs. 2.43% P group exhibited a noon-time peak in preferential consumption of P, followed by a marked afternoon-evening decline. This decline occurs both for relative and absolute P intake.

Calcium and phosphorus requirements of the laying hen

Three experiments were conducted; the first studied the influence of pre-laying dietary calcium levels on subsequent hen performance, while in the second and third the influence of various levels of dietary calcium and phosphorus on performance, egg shell quality and calcium and phosphorus retention were investigated. Pre-dietary calcium levels (0.5 and 1.5%) resulted in a significant strain X diet interaction for weight gain up to commencement of lay but did not influence production, feed intake, egg size or sheel quality. Dietary calcium levels varying from 2.5 to 4.0% did not significantly alter the avove parameters during a 140 day laying test. Compared to a non-pelleted control diet, steam pelleting resulted in a significant enhancement in phosphorus availability is judged by higher levels of performance. Percent calcium retention varied with the level of dietary calcium and there was an indication that level of dietary phosphorus influenced calcium retention. Lower levels of dietary phosphorus resulted in egg shells with slightly lower deformation values. Regardless of dietary phosphorus, retention values were quite low. Changing the level of dietary calcium and phosphorus had little or no effect on the retention of phosphorus thus suggesting a relatively constant and low requirement for this nutrient.

Effects of short term phosphorus deprivation on laying hens

An experiment was conducted to determine the effects on laying hens of ingestion of a phosphorus deficient diet for 6, 9, or 21 days. Four experimental groups consisting of 3 replicates of 5 Leghorn pullets averaging 90 percent egg production were maintained in individual cages. A diet containing corn, soy, and meat and bone meal was formulated to contain 0.39 percent total P on a 90 percent dry matter basis (LP). A normal P diet (NP), 0.64 percent total P, was obtained by supplementation with an inorganic P source. Group 1 (Control) was fed the NP diet for 21 days. Groups 2, 3 and 4 were fed the LP diet for 6, 9, and 21 days respectively. Groups 2 and 3 resumed consumption of NP diet after 6 and 9 days. Individual egg production and egg weight were recorded daily. Individual hen determinations of serum P, g. shell/cm.2 surface area, and feed consumption by replicate were made at 3 or 4 day intervals. The serum P of Group 1 averaged 5.01 +/- 0.31 mg./100 ml. over the 21 days. Serum P was significantly reduced after 3 days of consuming the LP diet. Serum phosphorus of Groups 2,3, and 4 were 2.95 +/- 0.18, 3.03 +/- 0.24, 3.13 +/- 0.32 mg./100 ml. respectively after 6, 9, and 21 days of consuming the LP diet. Serum P returned to control levels within 4 days after resumption of the NP diet by Groups 2 and 3. There were no differences in feed consumption, egg production nor any detrimental effects on egg weight or shell calcification despite the low serum P. Body weight gain of the hens fed the phosphorus deficient diet for 21 days was significantly reduced. At the end of the experiment femur density was determined; the hens which had consumed the phosphorus deficient diet for 21 days had reduced femur density (osteoporous) compared to the control group or the hens fed the phosphorus deficient diet for only 9 days. It is concluded that pullets in 90 percent production can tolerate this low P diet for at least 9 days without apparent detrimental effects.

INORGANIC PHOSPHORUS, ORGANIC PHOSPHORUS, AND INORGANIC CALCIUM IN BLOOD PLASMA FROM TWO BREEDS OF CHICKENS FED VARIOUS LEVELS OF DIETARY CALCIUM AND PHOSPHORUS

Male crossbred broiler-type and Single Comb White Leghorn (SCWL) chickens were fed graded levels of dietary calcium (0.0, 0.3, 0.6, 0.9, 1.2, and 1.5% added) and phosphorus (0.18 and 0.36% added) from hatching to 4 wk of age. Inorganic phosphorus (PPi), inorganic calcium (PCai), and organic phosphorus (PPo) were determined on blood plasma obtained when the chickens were 4 wk old. PCai was influenced by breed, phosphorus, calcium, breed × calcium, and phosphorus × calcium. PPi was influenced by the dietary level of phosphorus and calcium and a significant (P < 0.01) phosphorus × calcium interaction occurred. The dietary calcium level had a significant (P < 0.05) effect on PPo and there was a highly significant (P < 0.01) breed × calcium interaction. Regression coefficients were determined for PCai on PPi, PCai on PPo, and PPi on PPo using individual data from the 24 groups and by dietary calcium levels (six groups). Few significant regressions were obtained using the individual data from the 24 groups or the data pooled by calcium levels (six groups). The most important significant regression appeared to be between PCai and PPi at the lowest dietary calcium level.