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.     

An Escherichia coli phytase expressed in yeast effectively replaces inorganic phosphorus for finishing pigs and laying hens

Two experiments determined the efficacy of an Escherichia coli phytase (ECP) added to P-deficient, corn-soybean meal diets fed to finishing pigs and second-cycle laying hens. Sixty finishing pigs (49 +/- 0.9 kg) were formed into blocks within sex based on weight and ancestry and allotted to a P-deficient diet unsupplemented or supplemented with 0.10% inorganic P (iP) from KH2PO4 or ECP at 250, 500, 1,000, or 10,000 phytase units (FTU)/kg. Individually fed pigs were allowed ad libitum access to the experimental diets until a BW of 120 +/- 3 kg was achieved, at which time the pigs were euthanized and the left fibula and fourth metatarsal were excised for determination of bone ash. Pigs were fed a 2-phase diet program for early- and late-finishing pigs; available P in the basal diets was set 0.10% below the requirement. Dietary supplementation of iP or ECP increased weight gain (P < 0.10) and G:F (P < 0.01); performance was not different (P > 0.13) among the phytase-supplemented groups. Fibula ash was greatest (P < 0.01) for pigs fed diets containing 10,000 FTU of ECP/kg. Two hundred forty second-cycle hens were allotted to a P-deficient diet or a P-deficient diet supplemented with 0.10% iP or ECP at 150, 300, or 10,000 FTU/kg for a 12-wk experiment. The basal diet was a corn-soybean meal diet with no added iP (17% CP, 3.8% Ca, 0.10% available P). Hens fed the P-deficient diet were removed from the experiment after 4 wk due to poor egg production. Supplementation of iP or ECP resulted in increased (P < 0.01) feed intake, egg weight, and egg production during the first 4 wk. During the entire 12-wk period, there were no differences (P > 0.28) between the iP- and ECP-supplemented groups in feed intake, egg weight, or egg production. These experiments reveal that ECP was as efficacious as supplemental iP and that supplementation of an excess dose of ECP was efficacious and without negative effects in finishing pigs and laying hens.     

The effects of phytase and root hydroalcoholic extract of Withania somnifera on productive performance and bone mineralisation of laying hens in the late phase of production

1. A 6-week study was conducted to investigate the effects of phytase and hydroalcoholic extract of Withania somnifera root (WS) on productive performance and bone mineralisation of laying hens in the late phase of production.

2. Diets were arranged factorially (3?×?2?×?2) and consisted of a positive control with adequate Ca (4·37%) and nonphytate P (NPP; 0·39%) and a negative control diet with Ca (4·06%) and NPP (0·36 %); three concentrations of Withania somnifera (0, 65 and 130?mg/kg diet); and two concentrations of microbial phytase (0 and 300 U/kg diet).

3. A total of 144 72-week-old Hy-Line W36 laying hens were randomly assigned to the 12 treatment groups. Each treatment was replicated 4 times (4 x 3 hens). Egg production and egg weight were recorded daily, while feed intake and egg quality traits were recorded every two weeks. Bone quality traits were evaluated at the end of experiment.

4. Withania somnifera supplementation increased egg production and lowered egg weight only in the second two weeks of the experiment. Addition of phytase significantly depressed specific gravity of the eggs for the entire experiment period. No dietary treatment effects were observed on egg shell thickness and yolk weight.

5. Withania somnifera at 130?mg/kg did not affect feed intake. The hens fed on the positive control diet had higher albumen weight than the negative control diet in the second two-week period. Supplementation of the positive control diet with 65?mg/kg Withania somnifera in the absence of phytase significantly improved shell weight compared with the negative control (5·779 vs. 5·273?g respectively).

6. Supplementing Withania somnifera significantly improved Ca and P retention in tibia bone. In addition, an increase in tibia bone P was observed with phytase supplementation. There were significant interactions between Withania somnifera content and phytase for tibia bone Ca and P.

7. The results of this experiment indicated that dietary Withania somnifera has beneficial effects on tibia bone Ca and P content, and phytase improved tibia bone P retention without adverse effects on productive performance.     

植酸酶对产蛋鸡生产性能和代谢的影响

磷酸氢钙是饲料中最主要的磷来源之一 ,无机磷资源不仅在我国 ,就是在全世界范围内 ,已经处于匮乏状态 ,磷资源的匮乏使饲用磷产品价格上升 ,增加了饲料成本。植物性饲料中有 65 %～86 %的磷以植酸磷的形式存在 ,这些磷源不仅不能为单胃动物有效利用 ,而且会对环境造成严重的污染。如果能将植酸磷中的磷释放出来供动物利用 ,减少磷酸氢钙的用量 ,可缓解供求矛盾 ,并减轻粪磷污染。本试验旨在应用植酸酶迈特 -5 0 0 0以减少产蛋鸡日粮中的磷酸氢钙用量 ,观察其对产蛋鸡生产性能和代谢的影响。1　材料与方法试验在南京市青龙山养鸡场进行 ,选…     

The effect of dietary supplementation with phytase transgenic maize and different concentrations of non-phytate phosphorus on the performance of laying hens

1. The objective of this study was to evaluate the effects of dietary supplementation with phytase transgenic corn (maize) (PTC) which has a phytase activity of 21 000 units (U) phytase per kg of maize on productive performance, egg quality, tibia bone quality and phosphorus (P) excretion in laying hens.

2. In the experiment, 1800 44-week-old Hy-line brown laying hens were divided into 5 groups with 6 replicates per group and 60 hens per replicate. The experiment lasted for 12 weeks. The layers in the control group (control) were given a basal diet with 0.36% non-phytate P (NPP), while the treatment groups received diets containing 360 U of exogenous phytase/kg with 0.26% NPP (EP) or 360 phytase U of PTC/kg diet with 0.26% (PTC1), 0.21% (PTC2) or 0.16% (PTC3) NPP.

3. The results showed that there was no significant difference in egg production, average daily feed intake, feed efficiency, rate of broken or soft-shell egg production or egg mass among the treatments. There was no significant difference in eggshell thickness or eggshell strength. On the other hand, no differences in any of the bone variables were found between treatments. The faecal P percentage content in EP, PTC1, PTC2 and PTC3 groups was significantly lower than the control group.

4. In summary, the PTC could be used in the feed of laying hens instead of EP to reduce P excretion without effecting production and bone mineralisation.     

合生素对蛋鸡生产性能的影响

选择49周龄海兰褐蛋鸡1275只,随机分成5组,设3个正对照组、1个负对照组和1个试验组。试验组饲喂负对照组日粮（未加微生态制剂）基础中添加0．05％合生素,3个正对照组分别饲喂负对照组日粮基础中依次添加其他微生态产品M100、NW和GEK（营养标准相对负对照组低6％蛋白）的日粮。预试期30d,试验期30d,考察不同添加剂产品对蛋鸡生产性能的影响。结果表明,合生素添加组与M100添加组、负对照组、NW添加组和GEK添加组的生产性能相比．产蛋率分别提高4．82％、1．01％、1．78％和5．55％;蛋质量分别提高2．79％、3．77％、2．61％和3．82％。统计上均差异显著。合生素添加组和正负对照组的料蛋比分别是2．331、2．471、2．369、2、400和2．441。鸡蛋的平均合格率统计上均无显著差异。这表明,饲料中添加0．05％合生素可达到较理想的效果。     

The effects of phytase and xylanase supplementation on performance and egg quality in laying hens

ABSTRACT

1. The aim of this study was to evaluate the effects of phytase and xylanase and their interaction on laying hen performance, egg quality, phosphorus (P) digestibility, phytate breakdown, volatile fatty acid (VFA) production and peptide YY concentration.

2. Two hundred and forty hens were allocated to cages at 22 weeks of age based on a 3 × 2 arrangement with phytase (0, 300 or 1500 FTU/kg) and xylanase (0 or 12 000 BXU/kg) as factors.

3. Phytase increased hen-day production (P < 0.05), daily egg mass (P < 0.05) and P digestibility with increasing levels of phytase (P < 0.001). Phytase fed at 1500 FTU/kg reduced IP6 and IP5 and increased myo-inositol concentration in gizzard digesta (P < 0.05). Phytase fed at 300 FTU/kg reduced IP6 in ileal digesta (P < 0.05); however, IP6 and IP5 were further reduced and myo-inositol increased when phytase was added at 1500 FTU/kg (P < 0.05).

4. Xylanase improved feed efficiency when phytase was fed at 300 FTU/kg (P < 0.05). In the absence of phytase, xylanase reduced dry matter and Ca digestibilities (P < 0.05).

5. Neither phytase nor xylanase had an effect on peptide YY or caecal VFA concentrations.     

Effects of an experimental phytase on performance, egg quality, tibia ash content and phosphorus bioavailability in laying hens fed on maize- or barley-based diets

A 24-week performance trial was conducted to evaluate the efficacy of an experimental phytase on performance, egg quality, tibia ash content and phosphorus excretion in laying hens fed on either a maize- or a barley-based diet. At the end of the trial, an ileal absorption assay was conducted in order to determine the influence of phytase supplementation on the apparent absorption of calcium and total phosphorus (P). Each experimental diet was formulated either as a positive control containing 3.2 g/kg non-phytate phosphorus (NPP), with the addition of dicalcium phosphate (DCP), or as a low P one, without DCP addition. Both low P diets (containing 1.3 or 1.1 g/kg NPP) were supplemented with microbial phytase at 0, 150, 300 and 450 U/kg. The birds were housed in cages, allocating two hens per cage as the experimental unit. Each of 10 dietary treatments was assigned to 16 replicates. Low dietary NPP (below 1.3 g/kg) was not able to support optimum performance of hens during the laying cycle (from 22 to 46 weeks of age), either in maize or barley diets. Rate of lay, daily egg mass output, feed consumption, tibia ash percentage and weight gain were reduced in hens fed low NPP diets. The adverse effects of a low P diet were more severe in hens on a maize diet than in those on a barley diet. Low dietary NPP reduced egg production, weight gain, feed consumption and tibia ash content and microbial phytase supplementation improved these parameters. Hens given low NPP diets supplemented with phytase performed as well as the hens on positive control diets containing 3.2 g/kg of NPP. A 49% reduction of excreta P content was achieved by feeding hens on low NPP diets supplemented with phytase, without compromising performance. Phytase addition to low NPP diets increased total phosphorus absorption at the ileal level, from 0.25 to 0.51 in the maize diet and from 0.34 to 0.58 in the barley diet. Phosphorus absorption increased linearly with increasing levels of dietary phytase. Mean phosphorus absorption was higher in barley diets than in maize diets (0.49 vs 0.39).     

Effects of dietary metabolisable energy, calcium and phosphorus on bone mineralisation, leg weakness and performance of broiler chickens

1. Performance, gait score (GS), tibial dyschondroplasia (TD), and tibia bone mineralisation and breaking strength were determined in 2880 male and female Ross 208 broilers fed on diets with two different concentrations of dietary metabolisable energy (ME) (11.00 or 12.00 MJ/kg) and 4 different concentrations of available phosphorus (aP) adjusted for dietary ME content (4.0, 4.5, 5.0 or 5.5 g/kg aP in starter and 3.5, 4.0, 4.5 or 5.0 g/kg aP in finisher diets containing 12.00 MJ/kg). 2. Tibia ash, calcium (Ca) and phosphorus (P) contents in broilers given diets with low ME (11.00 MJ/kg) were greater than those of broilers given diets with higher ME (12.00 MJ/kg). Tibia ash, Ca and P contents increased curvilinearly with increasing dietary aP content. The dietary aP level had no effect on GS. 3. Dietary concentration of ME or aP had no effect on tibia breaking strength. 4. Walking ability, as measured by GS, was negatively correlated with the body weight (BW) of tested birds at 23 and 35 d of age, but the dietary ME content or aP level had no significant effect on GS at 35 d of age. 5. The results indicated that bone mineral content had no clear correlation with the walking ability of broilers.     

Effect of dietary nonphytate phosphorus on laying performance and small intestinal epithelial phosphate transporter expression in Dwarf pink-shell laying hens

This study examined the effects of various levels of dietary nonphytate phosphorus on laying performance and the expression patterns of phosphorus metabolism related genes in Dwarf pink-shell Jaying hens. A total of 405 28-week-old Dwarf pink-shell laying hens were fed the same corn-soybean basal meals but containing 0.20%, 0.25%, 0.30%, 0.35% or 0.40% nonphytate phosphorus. The results showed that feed intake, egg production, and average egg weights were quadratically correlated with dietary nonphytate phosphorus content （P 〈 0.05）, and the highest egg production, feed intake and average egg weights were achieved when dietary nonphytate phosphorus was at 0.3% （P 〈 0.05）. mRNA expression of intestinal sodium phosphorus co-transporter linearly decreased when dietary nonphytate phosphorus increased, mRNA and protein expression of intestinal calbindin and vitamin D receptor correlated quadratically with dietary nonphytate phosphorus, and the highest expression was found when dietary available phosphorus was at 0.2,5% to 0.3%. In conclusion, the ideal phosphorus requirement for Dwarf pink-shell layer hens is estimated to be 0.3% in a corn-soybean diet. With this level of phosphorus supplementation, calbindin and vitamin D receptor reached their highest expression.     

甪里艾叶粉对蛋鸡产蛋性能与蛋品质的影响

为了研究甪里艾叶粉对蛋鸡产蛋性能与蛋品质的影响,试验选用50周龄健康状况良好、生产性能相近的海兰褐蛋鸡288只,随机分为四组,一个对照组,三个试验组,各组甪里艾叶粉分别添加0、1%、2%、3%,每组6个重复,每个重复12只鸡,预试期为7 d,试验时间为42 d。结果显示:(1)甪里艾叶粉对产蛋性能的影响:试验各组的平均日产蛋重均高于对照组(P0.05),分别提高了2.62%、3.58%、2.41%;随着艾叶粉添加量的增加,平均日采食量显著减少(P0.05),分别减少了2.76%、3.29%、3.62%;试验各组料重比均显著低于对照组(P0.05),分别降低了5.10%、6.63%、5.61%;随着甪里艾叶粉添加量的增加,产蛋率分别提高了2.85%(P0.05)、3.99%(P0.01)、5.93%(P0.01)。试验各组的蛋重与对照组均无显著差异(P0.05)。(2)甪里艾叶粉对蛋品质的影响:甪里艾叶粉可显著提高蛋的比重(P0.05),其中添加量为2%时差异极显著(P0.01)。各组间的蛋形指数、哈氏单位、蛋黄颜色差异均不显著(P0.05)。但试验各组的蛋白高度分别提高了8.92%(P0.05)、11.29%(P0.05)、10.21%(P0.05),哈氏单位则相应提高了4.51%、5.67%、5.69%。各组间的蛋壳指标差异不显著(P0.05)。试验各组的蛋白比率、蛋黄比率差异不显著(P0.05),随着甪里艾叶粉添加量的增加,蛋壳比率逐渐降低,其中添加2%和3%的甪里艾叶粉可显著降低蛋壳比率(P0.05)。甪里艾叶粉可以改善海兰褐蛋鸡的产蛋性能,蛋的比重和蛋白高度显著提高,蛋壳比率呈降低的趋势。     

有机源锌和锰对蛋鸡生产性能、蛋壳和骨质量的影响

文章旨在研究日粮添加有机源锌和锰替代无机锌和无机锰对蛋鸡生产性能、蛋壳和骨骼质量的影响。试验选择31周龄产蛋性能接近的罗曼粉壳蛋鸡616只,随机分为7组,每组4个重复,每个重复22只。基础日粮锌和锰含量分别为50和30 mg/kg,对照组饲喂基础日粮,分别添加氧化锌和硫酸锰(锌40 mg/kg,锰60 mg/kg)。处理组分别在基础日粮中添加20 mg/kg有机锌,30 mg/kg有机锰、20 mg/kg有机锌+30 mg/kg有机锰、40 mg/kg有机锌、60 mg/kg有机锰、40 mg/kg有机锌+60 mg/kg有机锰,上述含量均以相应元素计。试验共进行7周。结果显示:日粮用有机锌或锰替代50%或100%无机锌、锰对蛋鸡生产性能相关参数均无显著影响(P> 0.05)。对照组相比,有机锌或锰替代无机锌或锰的比例对32、46、60和74周龄蛋鸡蛋壳相对重量、蛋壳密度和蛋壳厚度均无显著影响(P> 0.05)。与对照组相比,30 mg/kg有机锰、20 mg/kg有机锌+30 mg/kg有机锰组的蛋壳强度显著提高(P <0.05)。40 mg/kg有机锌+60 mg/kg有机锰组较无机锌、锰组显著提高了60、74周龄及全期蛋壳强度(P <0.05)。日粮添加有机锌或锰对胫骨物理参数及胫骨和趾骨灰分含量均无显著影响。结论 :日粮添加有机锌、锰替代无机锌锰对蛋鸡产蛋性能和骨质量无影响,但可以降低蛋鸡由于年龄升高对蛋壳强度的负面影响。     

低磷日粮中添加植酸酶对蛋鸡肠道形态结构的影响

试验旨在研究在低磷的玉米-豆粕型日粮中添加植酸酶对蛋鸡肠道形态结构的影响。选用18周龄体重、产蛋周龄相近的伊莎褐蛋鸡840羽,随机分成7组:正、负对照组及在负对照组基础上分别添加300、1000和10000U/kg的包衣状植酸酶、300U/kg的粉状及300U/kg的微丸状植酸酶(试验Ⅲ、Ⅳ、Ⅴ、Ⅵ和Ⅶ组)。结果表明:与负对照组相比,Ⅳ组的空肠绒毛高度得到了显著提高(P<0.05),Ⅲ、Ⅴ、Ⅵ和Ⅶ组与之相比无显著差异(P>0.05),但分别提高了16.49%、21.80%、15.73%以及17.29%;隐窝深度、绒毛高度/隐窝深度、黏膜厚度与之相比差异不显著(P>0.05)。各试验组间以及试验组与正对照组之间亦无显著差异(P>0.05)。因此,在低磷日粮中添加植酸酶对蛋鸡肠道结构具有一定的改善作用。     

海藻饲料添加剂对蛋鸡产蛋性能、血清抗氧化性及生长的影响

试验研究了在蛋鸡饲粮中添加不同剂量的海藻饲料添加剂对蛋鸡产蛋性能、血清抗氧化性、生长及营养物质消化率等的影响。选取360只26周龄体重相近的海兰褐蛋鸡,随机分为6组(每组3个重复,每个重复20只鸡),1组为空白对照组,饲喂基础饲粮;2组为抗生素对照组,在基础饲粮中添加0.005%的杆菌肽锌;3~6组为试验组,分别在基础饲粮中添加0.02%、0.04%、0.06%、0.08%的菊粉,0.025%、0.050%、0.100%、0.150%的大西洋海藻粉及相同剂量的铜藻粉(以下简称低、中、较高、高剂量海藻复合物),预试期7 d,正式试验期63 d。结果表明:海藻饲料添加剂对蛋鸡的产蛋性能有明显的剂量-效应关系,添加量为中等剂量海藻复合物(4组)时最佳且差异显著(P<0.05)。此添加量下,蛋鸡血清中超氧化物歧化酶活性最高(P<0.05)。试验中粗纤维的表观消化率随添加剂量的增加而增加(P<0.05)。低剂量试验组体重增长最多且差异显著(P<0.05)。试验结果表明,基础饲粮中添加中剂量海藻复合物作为蛋鸡饲料添加剂,能够显著提升蛋鸡产蛋性能及血清抗氧化性。     

Effect of dietary fibre on the performance of laying hens

1. In tests to determine whether gizzard weight could be influenced by dietary fibre concentrations, caged layers were fed on diets containing 15, 30 or 60 g pine shavings/kg diet.

2. As dietary fibre content increased, gizzard weight increased, but there was no effect on body weight, hen‐day production, egg weight, efficiency of food conversion, mortality, percentage of liver ether extract or egg shell breaking strength. Percentage of body ether extract tended to be lower when pine shavings were fed.     

脂肪粉对蛋鸡生产性能及相关理化指标的影响

为探讨饲料中添加脂肪对蛋鸡生产性能的影响,选择300日龄褐壳蛋鸡720只,随机分为3个处理,每个处理分为6个重复;试验组分别添加1％、2％脂肪粉,观测其对蛋鸡生产性能、生理变化及经济效益的影响。结果表明：添加脂肪,可以明显提高（P〈0．05）蛋鸡产蛋率（3．51～5．23％）和蛋重（6．03～8．69％）,降低采食量（3．63～3．67％）,改善饲料报酬（13．08～16．03％）;生理指标检测结果显示,试验组血清T3、T4含量显著提高（P〈0．05）,并且有提高GH、IGF－1含量趋势（P〉0．05）;综合经济效益分析,添加脂肪可以提高蛋鸡养殖效益（16．67～26．98％）。因此,杂粕型蛋鸡饲料中添加脂肪有实际意义。     

酵母培养物对蛋鸡生产性能及免疫性能的影响

为研究酵母培养物对蛋鸡生产性能及免疫性能的影响,本试验选用健康、体重相近的23周龄海兰褐蛋鸡120只,随机分成2个组,每组设3个重复,每个重复20只鸡。其中一组为对照组,饲喂基础日粮;另外一组为试验组,饲喂基础日粮中添加0.3%酵母培养物日粮,其他条件均保持一致,试验期共6周。试验结果表明:(1)在基础日粮中添加0.3%的酵母培养物可极显著提高4 ~ 6周的蛋重(P < 0.01),试验组比对照组提高了2.33%;但对蛋鸡的平均日采食量、产蛋率和料蛋比无显著影响(P > 0.05)。(2)添加0.3%酵母培养物可极显著提高第3周末血清中IgG含量(P < 0.01),提高了21.74%;并且可极显著提高第6周末血清中IgM和IgG的含量(P < 0.01),分别提高了10.69%和16.15%;对IgA有提高的趋势,但是差异不显著(P > 0.05)。由此试验表明添加0.3%酵母培养物可有效提高鸡蛋蛋重,并且可以极显著提高蛋鸡的免疫性能。     

不同添加量植酸酶对蛋鸡生产性能的影响

选择42周龄海兰褐蛋鸡1200只,随机分成5组,设正对照组、负对照组和3个试验组。3个试验组分别饲喂负对照组日粮基础上含不同添加量植酸酶(150、300、600U/kg)的日粮(营养标准相对正对照组低0.12%有效磷)。试验期60d,考察不同添加量的植酸酶对蛋鸡生产性能的影响。试验结果表明:150U/kg添加组与正对照组生产性能相比,产蛋率提高0.22%,蛋重、采食量、料蛋比分别降低0.16%、0.42%和0.47%,统计上均无显著差异(P>0.05);150U/kg添加组与300、600U/kg添加组相比统计上也无显著差异(P>0.05)。这表明饲料中使用150U/kg该植酸酶可达到与目前市场上普遍使用300U/kg植酸酶的效果,也能满足蛋鸡营养(磷)需要。     

The calcium and phosphorus requirements of laying hens

Two experiments were carried out with a modern hybrid laying strain to establish the calcium requirement for maximum egg production. The first experiment, with three calcium concentrations of 1.7, 2.8 and 3.9 per cent indicated that with 0.55 Per cent dietary phosphorus the requirement for calcium was between 1.7 per cent and 2.8 per cent. Dietary phosphorus supplements added to the mixed cereal diets containing 0.55 per cent phosphorus were without effect on production or the conclusions reached. In a subsequent experiment with four dietary calcium concentrations between 2.3 and 3.3 per cent there was no significant improvement in egg production above 2.6 per cent calcium.

In both experiments the lower production at the lower levels of calcium concentration was associated with reduced food intake. Measurements made in the first experiment showed an increasing shell thickness round the equator of the egg with increasing dietary calcium. In this experiment also a small practical test concerned with cracking of the egg shell in boiling water, indicated that incidence of cracks did not alter as the laying cycle progressed and that resistance to cracking was greatest at the highest dietary calcium concentration.