Calcium and phosphorus requirements of the laying hen

Unique Calcium Metabolism in Zoologic Companion Animal Species

Regardless of species, calcium, vitamin D, and parathyroid hormone physiology are intricately linked. However, there are many unique differences between taxa that may affect husbandry recommendations, common disease processes, and effective treatment. This article aims to provide a basic overview of calcium metabolism and physiology then specifically delve into unique attributes of calcium homeostasis in common zoologic companion animal species.

Bone Health or Performance? Adaptation Response of Genetically Divergent Chicken Layer Lines to a Nutritive Calcium Depletion

In modern laying hybrids, calcium (Ca) homeostasis is immensely challenged by daily eggshell calcification. However, excessive mobilization of Ca from bones may lead to osteoporosis, which then manifests in a high incidence of poor bone quality. The aim of this study was to characterize the hens' adaptation response to an alternating dietary Ca restriction. The animal model consisted of four purebred layer lines, differing in laying performance (high vs. moderately performing lines) and phylogenetic origin (white- vs. brown-egg lines). According to the resource allocation theory, hens selected for high egg production were assumed to show a different response pattern to cope with this nutritive challenge compared to moderately performing lines. Data collected included egg number, egg quality traits, body weight and bone characteristics. The Ca depletion led to a temporary drop in egg production and shell quality and a loss of bone stability due to Ca mobilization. The white-egg lines response was more pronounced, whereas the brown-egg lines were less sensitive towards reduced Ca supply. Our study shows that the hens' responsiveness to coping with a nutritive Ca depletion is not ultimately linked to genetic selection for increased egg production but rather to phylogenetic origin.

Opportunities for exercise during pullet rearing, Part II: Long-term effects on bone characteristics of adult laying hens at the end-of-lay

Osteoporosis in laying hens has been a production and welfare concern for several decades. The objective of this study was to determine whether differing opportunities for exercise during pullet rearing influences long-term bone quality characteristics in end-of-lay hens. A secondary objective was to assess whether differing opportunities for exercise in adult housing systems alters bone quality characteristics in end-of-lay hens. Four flock replicates of 588 Lohmann Selected Leghorn-Lite pullets were reared in either conventional cages (Conv) or an aviary rearing system (Avi) and placed into conventional cages (CC), 30-bird furnished cages (FC-S), or 60-bird furnished cages (FC-L) for adult housing. Wing and leg bones were collected at the end-of-lay to quantify bone composition and strength using quantitative computed tomography and bone breaking strength (BBS). At the end-of-lay, Avi hens had greater total and cortical cross-sectional area (P < 0.05) for the radius and tibia, greater total bone mineral content of the radius (P < 0.001), and greater tibial cortical bone mineral content (P = 0.029) than the Conv hens; however, total bone mineral density of the radius (P < 0.001) and cortical bone mineral density of the radius and tibia (P < 0.001) were greater in the Conv hens. Hens in the FC-L had greater total bone mineral density for the radius and tibia (P < 0.05) and greater trabecular bone mineral density for the radius (P = 0.027), compared to hens in the FC-S and CC. Total bone mineral content of the tibia (P = 0.030) and cortical bone mineral content of the radius (P = 0.030) and tibia (P = 0.013) were greater in the FC-L compared to the CC. The humerus of Conv hens had greater BBS than the Avi hens (P < 0.001), and the tibiae of FC-L and FC-S hens had greater BBS than CC hens (P = 0.006). Increased opportunities for exercise offered by the aviary rearing system provided improved bone quality characteristics lasting through to the end-of-lay.

Effect of L-carnitine supplementation on growth performance, nutrient utilization, and nitrogen balance of broilers fed with animal fat

Aim:

This experiment was conducted to evaluate the effect of L-carnitine supplementation on growth performance, nutrient utilization and nitrogen balance in broilers fed with animal fat.

Materials and Methods:

80 day-old Cobb commercial broiler chicks were randomly assigned into two dietary treatment groups with four replicates of ten chicks each. The diets were isonitrogenous and isocaloric. The birds in both the control (T₁) and treatment group (T₂) were fed with a diet having 5% animal fat, while the treatment group (T₂) was supplemented with 900 mg of L-carnitine. The birds were fed with standard broiler starter ration up to 4 weeks of age and finisher ration up to 6 weeks of age.

Results:

The average body weight (g), cumulative feed intake (g) and cumulative feed conversion ratio belonging to groups T₁ and T₂ at 6^th week of age were 2091.25 and 2151.11, 3976.49 and 4171.68, 1.97 and 1.96 respectively. The percentage availability of the nutrients of two experimental rations T₁ and T₂ was 68.23 and 68.00 for dry matter, 58.72 and 55.98 for crude protein, 73.85 and 71.35 for ether extract, 34.19 and 33.86 for crude fiber, 79.18 and 79.59 for nitrogen free extract, 70.24 and 70.03 for energy efficiency and nitrogen balance (g/day) were 2.35 and 2.39, respectively.

Conclusion:

This study suggests that the supplementation of 900 mg L-carnitine in diet with added animal fat had no effect on growth performance, nutrient utilization, and nitrogen balance of broilers.

Effects of Feeding Grains Naturally Contaminated with Fusarium Mycotoxins on Performance and Metabolism of Broiler Breeders

A study was conducted to investigate the effects of feeding grains naturally contaminated with Fusarium mycotoxins on performance and metabolism of broiler breeders. Forty-two 26-wk-old broiler breeder hens and nine 26-wk-old roosters were fed the following diets: (1) control, (2) contaminated grains, and (3) contaminated grains + 0.2% polymeric glucomannan mycotoxin adsorbent (GMA) for 12 wk. The major contaminant was deoxynivalenol (12.6 mg/kg of feed), with lesser amounts of zearalenone and 15-acetyl-deoxynivalenol. Feed consumption and BW were not affected by diet. The feeding of contaminated grains did not significantly affect egg production. Decreased eggshell thickness was seen, however, at the end of wk 4, and dietary supplementation with GMA prevented this effect. There was no effect of diet on other egg parameters measured. There was a significant increase in early (1 to 7 d) embryonic mortality in eggs from birds fed contaminated grains at wk 4, but mid- (8 to 14 d) and late- (15 to 21 d) embryonic mortalities were not affected by diet. There were no differences in newly hatched chick weights or viability. The ratio of chick weight to egg weight was not affected by the feeding of contaminated grains. Weight gains of chicks fed a standard broiler starter diet at 7, 14, and 21 d of age were not significantly affected by previous dietary treatments for the dam. It was found that rooster semen volume and sperm concentration, viability, and motility were not affected by the feeding of contaminated diets. There was no effect of diet on the relative weights of liver, spleen, kidney, and testes. The feeding of contaminated grains decreased antibody titers against infectious bronchitis virus at the end of wk 12, and this was prevented by dietary supplementation with GMA. There was no effect of the diet on serum antibody titers against Newcastle disease virus. It was concluded that the feeding of blends of grains contaminated with Fusarium mycotoxins could affect performance and immunity in broiler breeder hens.

Effects of feeding blends of grains naturally contaminated with Fusarium mycotoxins on performance and metabolism of laying hens

An experiment was conducted to evaluate the effects of feeding laying hens grains naturally contaminated with a combination of Fusarium mycotoxins. Parameters measured included performance, organ weights, and plasma chemistry. One hundred and forty-four, 45-wk-old laying hens were fed diets including: (1) control, (2) contaminated grains, and (3) contaminated grains + 0.2% polymeric glucomannan mycotoxin adsorbent (GMA) for a 12-wk period. The feeding of contaminated grains decreased feed consumption compared with controls in the first 4 wk. Feed consumption increased, however, from 4 to 8 wk and from 8 to 12 wk. The efficiency of feed utilization (feed consumption/egg mass) decreased compared with controls in the periods from 4 to 8 and from 8 to 12 wk when birds were fed contaminated grains. Supplementation with GMA decreased feed consumption and increased the efficiency of feed utilization in the period from 8 to 12 wk. Egg production and egg mass decreased in wk 4 and 8 compared with controls when contaminated grains were fed, whereas egg and eggshell weights decreased in the fourth wk. Plasma uric acid concentrations increased throughout the experiment and relative kidney weights increased at the end of the experiment compared with controls when birds were fed contaminated grains. The feeding of GMA prevented the elevation in uric acid concentrations and relative kidney weights. It was concluded that layer performance and metabolism were adversely affected by chronic feeding of a combination of Fusarium mycotoxins, and that GMA prevented many of these effects.

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.

Effects of dietary 1,4-diaminobutane (putrescine) on eggshell quality and laying performance of hens laying thin-shelled eggs

Experiments were conducted to evaluate the potential for dietary 1,4-diaminobutane (putrescine) to influence eggshell quality and overall laying performance in hens. Forty-eight, 60-wk-old White Leghorn hens laying thin-shelled eggs were fed a corn and soybean meal-based diet supplemented with 0.00 (control), 0.05, 0.10, or 0.15% putrescine for 4 wk. Twelve hens that laid thick-shelled eggs were also fed the control diet. The feeding of supplemental putrescine decreased feed consumption; however, egg weight decreased only at higher levels of supplementation. Increasing dietary levels of putrescine responded quadratically in eggshell deformation, eggshell weight, and eggshell weight as a percentage of egg weight (P < 0.05). There were no significant differences in shell deformation, shell thickness, or shell weight when comparing hens laying thick-shelled eggs and those laying thin-shelled eggs that were fed 0.05% supplemental putrescine. Calcium intake, calcium retention, and calcium balance decreased linearly (P < 0.05) with increasing levels of dietary putrescine. Pancreatic putrescine concentrations were significantly higher (P < 0.05) in hens laying thick-shelled eggs compared with hens laying thin-shelled eggs. It appeared that pancreatic cells synthesized more polyamines in hens laying thick-shelled eggs. This increase in polyamines might have caused improved eggshell quality by increasing calcium transport. It was concluded that 0.05% supplemental putrescine improved eggshell quality; however, higher levels proved to be toxic.

Effects of added dietary fat and phosphorus on the performance and egg quality of laying hens subjected to a constant high environmental temperature

Two experiments were conducted to study the combined effect of nonphytate P (NPP), fat, and temperature on the performance and egg quality of hens pre- and postpeak. In Experiment 1, 192 Single Comb White Leghorn layers, aged 22 wk, were individually housed in cages under ambient (AT) and constant high temperature (CHT) of 33 +/- 1 C. In Experiment 2, 28-wk-old birds were used with a CHT of 35 +/- 1 C. Diets contained 0 and 4% added vegetable fat with four dietary NPP levels, ranging from 0.20 to 0.50% in Experiment 1 and from 0.15 to 0.45% in Experiment 2, at increments of 0.1%. These diets were fed to hens for 84 d. Performance and egg quality criteria were measured in both experiments, whereas serum and tibia Ca and P were determined in Experiment 2. Results showed that there was no significant interaction among NPP, fat, and temperature, for any criteria measured. The CHT significantly reduced BW, feed intake, egg production, egg weight, egg mass, and shell thickness. Moreover, it decreased (P < 0.05) serum Ca, P, tibia ash, and tibia P. The lowest NPP levels resulted in the greatest shell thickness (P < 0.05), which decreased with increasing NPP levels in both trials. In the postpeak experiment, the feed intake was significantly reduced by 0.15 and 0.25% NPP. Moreover, 0.15% NPP significantly reduced egg production as compared to 0.35 and 0.45% NPP diets. Levels between 0.25 and 0.45% significantly improved the serum phosphorus content as compared to 0.15%. Added fat improved only serum P level (P < 0.05). The beneficial effect of supplemental fat on hen performance was evident in Experiment 1 but not in Experiment 2, indicating that nutrients were oriented more toward supporting egg production rather than maintaining the BW at the postpeak stage.

Effects of dietary 1, 4-diaminobutane (putrescine) on eggshell quality and laying performance of older hens

We conducted an experiment to evaluate the potential for dietary 1,4-diaminobutane (putrescine) to promote eggshell quality and overall laying hen performance. A total of 128, 60-wk-old Barred Rock hens were fed a corn and soybean meal-based layer diet supplemented with 0.0 (control), 0.2, 0.4, and 0.6% free base 1,4-diaminobutane for 4 wk. The feeding of supplemental putrescine decreased feed consumption (P < or = 0.05) and egg mass (P < or = 0.05) and tended to decrease egg production (P < 0.08). Albumen quality was not significantly affected (P < 0.09) by the end of the experiment, as determined by Haugh units. Eggshell thickness was not significantly improved with lower levels of dietary putrescine (P < 0.08). Although dietary putrescine did not have any effect on the relative weights of duodenum, jejunum + ileum, or pancreas, there was a linear increase in putrescine concentrations in tissues (P < or = 0.05). Supplementation of dietary putrescine also resulted in increased putrescine and spermidine concentrations in egg (P < or = 0.05). Egg weight and eggshell deformation increased over time; however, eggshell weight, eggshell weight as percentage of egg weight, and eggshell thickness decreased (P < or = 0.05). It appeared that eggshell quality declined regardless of diet over the 4-wk experimental period. It was concluded that the lack of effect of dietary putrescine on egg parameters, with the exception of albumen quality and eggshell thickness, was due to putrescine toxicity. Hens transferred excess dietary putrescine and metabolites to eggs.

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.

Layer performance of four strains of Leghorn pullets subjected to various rearing programs

Two experiments were conducted using four strains of Leghorn pullets, namely Babcock, DeKalb, H & N, and Shaver. Pullets were grown on conventional or low protein diets fortified with additional amino acids. At 18 wk of age, 64 pullets from each strain and diet treatment were transferred to individual laying cages, using eight replicate groups of four adjacently caged birds. In a second experiment, pullets from the four strains were selected based on body weight at 18 wk of age (approximately 1,270 vs 1,650 g). Each weight group and strain was again represented by eight replicate groups of four birds. In Experiment 1, there were no strain or rearing diet effects on egg production (P > 0.05). Rearing diet had little long-term effect on any adult characteristics. There were significant (P < 0.01) strain effects on body weight, feed intake, and egg weight, although these were independent of rearing diet. In Experiment 2, regardless of bird strain, the pullets with smaller body weight matured more slowly (P < 0.01) and produced less total egg mass to 70 wk age (P < 0.05). These smaller birds ate less feed and produced smaller eggs (P < 0.01). There were strain effects, independent of 18-wk body weight, for egg weight and eggshell quality (P < 0.01). It is concluded that minor strain differences exist with respect to response to juvenile nutrition, although such effects are only evident in early lay. All strains of bird remain small, 18-wk body weight is reduced, and these birds subsequently eat less feed and produce smaller eggs.

Calcium and phosphorus metabolism and eggshell thickness in laying hens producing thick or thin shells

Two experiments were carried out to investigate the Ca and P metabolism of hens laying thick- (THK) or thin-shelled (THN) eggs on shell-forming days (SF) and days on which shell formation does not occur (NSF). In Experiment 1, 10 hens identified as producing THK or 10 hens producing THN eggs were offered a diet containing 3.5% Ca and .4% available P. Feed consumption, egg production, egg weight, egg deformation, and shell weight were recorded over 8 days. Shells and excreta were collected daily for Ca and P analysis. Feed, Ca, and P intake did not differ significantly (P greater than 0.5) between the two groups of hens, however, feed intake and Ca retention increased significantly (P less than .05) on SF compared with NSF days. The THK hens retained significantly (P less than .05) more Ca compared with THN hens. No differences (P greater than .05) were recorded for egg production, although there were differences (P less than .05) in egg weight and shell deformation between the two groups of hens. Increased egg weight did not account for differences (P less than .05) in eggshell deformation. Although percentage shell Ca was not significantly different (P greater than .05), total shell Ca was different (P less than .05) between the two groups. In Experiment 2, both groups of birds (THK and THN) were allowed simultaneous access to two different diets, a high-energy, high-protein diet low in Ca and P, and a low-energy, low-protein diet high in Ca and P.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Comparison of behavior and performance of laying hens housed in battery cages and an aviary

Experiments were carried out to study the behavior and production performance of hens housed in battery cages (3 birds x 112 cages) and an aviary (437 birds). Direct visual observations and videotapings of hen behavior were collected at 24 to 25, 36 to 37, 49 to 50, and 61 to 62 wk of age. Production data were collected daily. Stereotyped behaviors were much more frequent (P less than .01) in the battery cages (7.0 to 24.7%) than in the aviary (1.0 to 2.7%). Comfort behaviors were performed by aviary birds (3.9 to 5.5%) much more frequently (P less than .01) than by the caged birds (.7 to .9%). The birds were more active during a few hours before dark and just after light in both cages and the aviary. In both groups, the production performance of hens was similar and relatively high. The results of the current study indicate that aviaries provide a more comfortable environment for birds and almost the same productivity per bird as battery cages.

Response of laying hens to supplemental niacin

Two experiments were conducted to investigate the effect of supplemental niacin on laying hen performance and liver fat and egg cholesterol content. In Experiment 1, 16 replicate groups of four adjacently caged birds were fed corn and soybean meal diets calculated to contain 22, 44, 66, or 132 mg supplemental niacin/kg (23.2, 38.7, 57.0, and 143 mg/kg niacin by analysis). Egg production, egg weight, feed intake, and eggshell quality were assessed each 28 days through a 364-day trial period. After 280 days, cholesterol content on three eggs per replicate was measured. At the end of the study, one bird per replicate was killed for subjective scoring of liver fat content. In Experiment 2, 24 birds from the control treatment (22 mg/kg supplemental niacin) of Experiment 1 were retained and fed for a subsequent 28-day period. Over this time, eight birds were each fed diets containing 22, 522, or 1,022 mg/kg supplemental niacin. Egg cholesterol content was measured in eggs collected on the last 3 days of the study. In Experiment 1, birds fed 66 or 132 mg/kg supplemental niacin/kg produced more eggs (P less than .05) than birds fed 22mg/kg. Niacin supplementation affected shell quality (P less than .05). Dietary niacin level had no effect on egg cholesterol content of liver lipid evaluation. In Experiment 2, supplementary niacin levels up to 1,022 mg/kg, which more closely stimulates therapeutic levels used for humans, again failed to affect egg cholesterol content.

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)

Significance of growing photoperiod and light stimulation at various ages for Leghorn pullets subjected to regular or ahemeral photoperiods

Leghorn pullets were cage reared to 15 or 19 wk of age in environmentally controlled rooms that provided either 8 h or 14 h of light per day. In Experiment 1, birds were moved to laying cages at 15 wk of age and subjected to either 14 h light (L): 10 h (D) dark or ahemeral 14L:14D photoperiods. Feed intake, egg weight, shell quality, and egg production were monitored to 67 wk of age. In Experiment 2, pullets were moved at 19 wk of age and subjected to 14L:10D or 17L:7D light programs. Production parameters were measured as previously described. No significant (P greater than 0.5) interactions were observed between rearing and laying photoperiods, suggesting that increase in the length of photoperiod around time of maturity is not essential for adequate performance. In Experiment 1, ahemeral lighting resulting in reduced egg production, whereas egg shell quality and egg weight were improved (P less than .05). In both experiments, the 14-h rearing program resulted in improved egg size together with improved eggshell quality (P less than .05). Whereas increased egg size may relate to body weight, no explanation is apparent for the consistent pattern with respect to shell quality. In Experiment 2, poorer shell quality was observed with 17 vs. 14 h light per day. It is concluded that light stimulation at maturity has little effect on overall egg production. Improved shell quality observed with birds reared under 14 h light vs. those reared under 8 h per day may relate to a less rapid attainment of peak egg production.

Effect of immature body weight on laying performance

Two trials were conducted to note the effect of immature body size of leghorn pullets on subsequent laying performance, and in particular, egg size. In Trial 1, birds were classified as small, medium or heavy at 15 wk of age (997, 1,100, and 1,226 g, respectively). In Trial 2, segregation at 19 wk resulted in groups with mean weights of 1308, 1411, and 1564 g, respectively. In each trial, weight groups were represented by 40 replicate groups of four individually caged birds. Original weight groupings were maintained throughout the trials (P less than .05). In both trials, immature weight classification had a consistent effect on both feed intake and egg weight (P less than .05); larger birds consumed more feed while producing larger size eggs. In Trial 1, medium weight birds produced more eggs over the 52 wk. Similarly, smaller weight birds produced more eggs than did heavy birds (P less than .05). In Trial 2, weight grouping had no overall effect on egg production, although during the 19 to 23-wk period, heavy birds produced more eggs (P less than .05). It is concluded that immature body weight (15 to 19 wk age) can influence egg weight and that this relationship is linked to levels of nutrient intake. Each 100-g increase in body weight was associated with approximately 3.5 g increase in feed intake and 1.2 g increase in egg weight.

Effects of calcium and phase-feeding phosphorus on production traits and phosphorus retention in two strains of laying hens

Three levels of dietary Ca (3.0, 3.5, or 4.0%) were fed throughout a 336-day experiment to two strains of Single Comb White Leghorn hens in a factorial arrangement with three P feeding programs: .64% P fed continuously; .56, .49, and .39% P; or .64, .54, and .44% P fed when hens were 24 to 36, 36 to 52, and 52 to 72 weeks, respectively. In addition to production traits, measurements of P retention were made at 34, 42, 50, 62, and 72 weeks of age. No dietary effects were observed on production traits. Average P retention over the entire experiment was 104, 148, and 178 mg/day when hens were fed 3.0, 3.5, and 4.0% Ca, respectively. Most of the favorable effect of Ca on P retention occurred after 50 weeks of age. However, increasing dietary Ca had an adverse influence on P retention at 42 weeks, when ambient temperature was unusually hot and feed intake decreased markedly. Significant P effects were observed when hens were 42 and 72 weeks of age. At these times, hens fed .64% P retained the most P while those phase fed .56, .49, and .39% P retained at least. Retention of P tended to decline with increasing age of the hens. Overall, the hens were in a state of marginal to negative P balance at 42, 62, and 72 weeks of age even when P deposited in eggs was considered.

Effects of dietary fat level on laying hens fed various concentrations of calcium

The effects of supplementing laying hen diets with 0, 5, or 10% fat in the presence of 3.0, 3.6, or 4.2% dietary calcium was investigated using laying hens over a 7-week period. There was no significant effect of the fat or calcium treatments on laying hen performance as judged by feed intake, weight gain, egg production, egg weight, and egg shell deformation. Although there was an increase in fat retention with an increase in dietary fat level (P less than .01), a larger proportion (P less than .05) of unabsorbed fat was present as soap in the excreta of birds on these diets relative to those fed the control diet. There was evidence to indicate that most of the soap observed in the excreta of laying hens was formed in postabsorptive areas of the gut, thereby explaining why the detrimental effects of soap formation were not seen in the laying hen. Increasing the dietary calcium level reduced both percentage calcium (P less than .01) and magnesium (P less than .05) retention. There were no significant effects of the treatments on nitrogen and phosphorus retention. There were also no significant effects of the treatments on shell ash, shell calcium, magnesium, and phosphorus content. Increasing the dietary calcium level increased bone ash (P less than .05) while reducing bone magnesium content (P less than .05). There were no significant effects of the fat and calcium treatments on bone calcium and phosphorus content.

Response of laying hens to dietary saturated and unsaturated fatty acids in the presence of varying dietary calcium levels

The response of 33-week-old White Leghorn laying hens to dietary palmitic, oleic, or a 50/50 mixture of oleic and palmitic acids at an 8% inclusion level in the presence of 3, 3.6, or 4.2% dietary calcium was investigated over a 7-week period. There was no significant effect of treatments on egg production and egg weight. Although birds on diets supplemented with oleic acid consumed less feed (P less than .01) than those on diets supplemented with palmitic acid (102 g vs. 114 g), they gained more weight (P less than .01) than birds on diets supplemented with palmitic acid (+105 g vs. -32 g) over the 7-week period. There was no significant effect of the fatty acid treatment on shell quality as estimated by shell deformation. However, increasing the calcium content of the diets reduced feed intake and weight gain (P less than .05) and improved egg shell quality (P less than .05). The fat content of diets supplemented with oleic acid was better utilized than that from diets with an oleic/palmitic mixture, which, in turn, was better utilized than fat from diets supplemented with palmitic acid (P less than .01). Metabolizable energy values of diets followed a trend similar to fat retention and were independent of dietary calcium levels. There were no significant effects of fatty acid supplementation on calcium and magnesium retention, although increasing the calcium content of the diet resulted in a decreased (P less than .01) percentage of calcium retention.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary phosphorus level and source on productive performance and egg quality of two commercial strains of laying hens

An experiment was conducted to study the influence of dietary total phosphorus (TP) level and source on the performance of two strains of commercial layers for two consecutive production years (26 to 68 and 76 to 116 weeks of age, respectively). Diet 1 contained .4% TP; Diets 2, 3 and 4 contained .5, .6, and .7% TP with supplemental P from dicalcium phosphate (DCP); Diets 5 and 6 contained .5 and .6% TP, respectively, with supplemental P from a sample of raw rock phosphate (RRP-1); Diets 7 and 8 contained .5 and .6% TP, respectively, with supplemental P from a second sample of raw rock phosphate (RRP-2). Calcium level was 2.75% in all diets, and crushed oyster shell provided ad libitum to all birds increased the total calcium to about 3.00%. Diet 1 was inferior to the average of all supplemented diets relative to feed consumption rate (P less than .005) and egg weight (P less than .005) during the first year. Diet 1 was also inferior relative to egg production rate (P less than .01), feed consumption rate (P less than .005), and egg weight (P less than .005) during the second year, whereas it was superior in shell quality (P less than .05) during the first year. Increasing TP from DCP resulted in a significant linear increase in feed consumption (P less than .05), feed conversion ratio, and Haugh units (P less than .005). Increasing TP from DCP also resulted in a significant linear decrease in shell quality (P less than .05) and significant linear and quadratic decreases in egg weight (P less than .005) during the first year. During the second year, increasing TP from DCP resulted in a significant linear decrease in egg production rate (P less than .005) and feed efficiency but significant linear (P less than .01) and quadratic (P less than .05) increases in feed consumption, and significant linear and quadratic increases (P less than .005) in Haugh units. Hens receiving RRP diets responded differently during the first and second years. The DCP supported greater egg weight than the RRP during the second year and permitted better feed conversion during both years. Strain A produced larger eggs than Strain B regardless of treatment (P less than .005). When egg production rate and most other response criteria were considered, .5% TP with DCP as the supplemental source gave the best results in both production years. A TP of .6% from RRP-2 gave similar results in both years.

Egg Shell Quality, Medullary Bone Ash, Intestinal Calcium and Phosphorus Absorption, and Calcium-Binding Protein in Phosphorus-Deficient Hens

The effect of dietary phosphorus deficiency on the performance and on various parameters of calcium, phosphorus, and vitamin D metabolism was studied in laying hens. Phosphorus deficiency resulted in a decline in rate of production and egg weight, probably through appetite depression. The latter, or any secondary calcium deficiency, does not appear to cause the observed reduction in shell quality due to the deficiency. Similar to the response in the chick, phosphorus deficiency resulted in an increase in calcium-binding protein in intestine and kidney, there was no change in the activity of kidney 25-hydroxy-vitamin D3-1-hydroxylase. Percentages of calcium and phosphorus absorption were also higher during phosphorus deficiency. Medullary bone ash, decreased during phosphorus deficiency, was probably due to a reduction in the rate of bone formation.

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.

Effects of cage density and diet energy concentration on the performance of growing Leghorn pullets subjected to early induced maturity

Leghorn pullets of a commercial strain were cage-reared at densities of 293 or 586 cm2/bird. Diet treatments consisted of a control step-down protein program, a reverse-protein program, and two treatments involving 18% crude protein throughout rearing with modification of texture and energy concentration according to bird age. Thus, one treatment involved a crumbled low-energy diet to 10 weeks, followed by a crumbled high-energy diet to 16 weeks, while the alternate series involved a mash low-energy diet to 10 weeks followed by the crumbled high-energy diet to 16 weeks. Birds were weighed periodically throughout rearing and, when they were subsequently moved to laying cages, light was immediately increased from 8 to 14 hr. Irrespective of diet treatment, the more liberal density of 586 cm2/bird resulted in a 5 to 8% increase in feed intake (P less than .01). However, this increased intake was not associated with increased body weight (P greater than .05), and as confirmed by carcass analysis, it is assumed that this increased nutrient intake relates to increased maintenance requirement associated with bird activity. Birds offered the crumbled vs. mash high-energy diet to 10 weeks of age, consumed more feed (P less than .01), although change of diet texture from mash to crumble at 10 weeks failed to stimulate appetite. Also, birds reared on either the step-up energy programs were similar in weight to control-reared birds at 16 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of heat stress and diet composition on performance of White Leghorn hens

A total of 192 Single Comb White Leghorn pullets were divided into three groups to study the effect of heat stress and diet composition on feed intake and laying performance at 21, 25, and 33 weeks of age. For each age group all birds were fed a control diet [17.1% crude protein (CP), 2770 kcal metabolizable energy (ME)/kg] for a 7-day period. During this time they were kept at a temperature of 18 C. The temperature was then immediately increased to 35 C, and groups of 16 birds offered either the control diet, a high protein diet (43.5% CP), a high energy diet (3371 kcal ME/kg), or a diet of high nutrient density (28.3% CP, 2842 kcal ME/kg, and 6.5% Ca) for a 3-day period. After the 3-day test period, temperature was returned to 18 C, although birds were still offered the experimental diets for an additional 4 days prior to returning to the control diet. Production parameters were measured for individual birds. Feed consumption, egg production (except for the 21-week-old birds), egg weight, and egg shell thickness decreased (P less than .05) with heat stress. Increases in energy and calcium intake helped partially to maintain normal egg production, egg weight, and egg shell deformation. Egg weight and egg shell deformation returned to pretest levels within an 8-week postexperimental period. With the exception of those birds receiving the control and high nutrient density diets at 21 weeks of age, data collected over the test periods showed that heat stress caused a significant reduction (P less than .05) in liveweight birds.

Influence of increasing dietary calcium and magnesium levels on performance, mineral metabolism, and egg mineral content of laying hens

The effects of increasing dietary magnesium level from .17 to .77% and calcium level from 3 to 4.2% for laying hens over a 7-week period was investigated. Increasing either dietary magnesium or calcium level had no significant effect (P greater than .05) on feed consumption, egg production, egg weight, or egg shell deformation. Increasing dietary magnesium level had no significant effect on calcium retention, although there was a significant (P less than .01) reduction in the percentage of magnesium retained. Egg shell calcium content was significantly (P less than .01) reduced and shell magnesium significantly (P less than .05) increased in response to increase in dietary magnesium content. Increasing dietary magnesium level also significantly (P less than .01) reduced bone calcium and zinc contents while concomitantly increasing bone magnesium levels. Bone ash and calcium were significantly (P less than .05) increased and bone magnesium reduced when the calcium content of the diet was increased. Plasma calcium was significantly (P less than .01) increased in dietary calcium level and significantly decreased with increased dietary magnesium. The converse was true for plasma magnesium in response to increases in dietary calcium and magnesium. Significant positive correlations were observed between mineral contents of diet and bone, bone and plasma, and plasma and shell. A negative correlation was observed between shell magnesium level and egg shell quality as assessed by deformation. An antagonistic relationship seems to exist between calcium and magnesium, and this is discussed in relation to skeletal integrity and egg shell quality.

Dietary and plasma phosphorus in hens with fatty liver syndrome

Plasma inorganic phosphorus was determined in two experiments in hens that had fatty liver syndrome. In Experiment 1, plasma inorganic phosphorus was determined in twelve strains of hens all fed the same diet. Plasma inorganic phosphorus immediately following oviposition was elevated in all strains. The two strains in the first experiment with the highest as well as the two strains with the lowest plasma inorganic phosphorus were used in the second experiment. Each of the four strains were subdivided into three groups of 60 hens each and fed a practical layer diet containing either .30, .75, or 1.40% total phosphorus and 3.4% calcium. Significant differences were found in plasma inorganic phosphorus between strains fed the three dietary phosphorus levels. Results indicated that plasma inorganic phosphorus is related to dietary phosphorus in hens with an elevated plasma inorganic phosphorus level associated with fatty liver syndrome.

Use of single-stage low protein diets for growing Leghorn pullets

Two experiments were conducted in which growing White Leghorn pullets were fed single-stage 14% CP diets from 0 to 19 weeks. In the first trial, diet treatments were 1) conventional step-down protein, 2) reverse-protein, 3) 14% CP single-stage with methionine and lysine adjusted to 2 and 5% of CP, respectively, 4) as per 3 to 12 weeks followed by 14% CP with no amino acid constraints to 19 weeks. Each treatment was tested with 14 replicated cages each of 11 commercial strain Leghorn pullets. Single-stage 14% CP diets reduced pullet weight to 16 weeks relative to conventionalLy fed birds, although after this time no significant (P greater than .05) effect was observed. Pullets fed the reverse-protein diets were significantly (P less than .01) smaller than birds from all other treatments. During a subsequent 52-week laying period, rearing treatment had no significant effect on egg production, egg weight, shell deformation, feed intake, or Haugh units. A second trial was conducted to note the effect of energy level on the birds' response to low-protein diets. Diets of 14.4% CP were formulated to provide either 2610 or 3164-kcal ME/kg. A third treatment allowed for self-selection of two diets providing concentrated sources fo protein or energy. Each treatment was tested with nine replicate cages of 10 commercial strain White Leghorn pullets. Dietary energy had little effect on pullet development. Although birds offered the low-energy diets consistently consumed more protein, diet had no effect on body weight or carcass composition at 18 weeks. The data indicate that single-stage low-protein diets are suitable for growing pullets to maturity. Compared to a conventional step-down protein program, the single-stage 14% CP diet does not control body weight but does give comparable laying performance, albeit at reduced protein intake during rearing. The simplicity of the program is discussed relative to industry needs.

Performance of laying hens subjected to intermittent lighting initiated at 24 weeks of age

Leghorn pullets of a commercial strain were subjected to a conventional light program of constant photoperiod or an intermittent programming involving, during the house of conventional "lights-on", 45 min light (L): 15 min dark (D) from 24 to 27 weeks of age; 30 min L:30 min D from 28 to 35 weeks; and 14 min L:45 min D from 36 weeks to the duration of the trial. Each light treatment was tested with 12 replicate groups of 14 individually caged birds housed in adjacent rooms, with all birds fed a standard 15% crude protein, 2750 kcal ME/kg diet. Intermittent lighting resulted in a significant (P less than .05) reduction in feed intake and a consistent but nonsignificant (P less than .05) reduction in egg production. Egg size, egg shell quality, and albumen quality, as assessed by Haugh units, were not affected by light treatment. Due to the effect on egg production, it is concluded that intermittent lighting programs should not be initiated close to time of peak egg production.