Effects of short term exposure of eggs to magnetic field before incubation on hatchability and post-hatch performance of meat chickens.

The effects of exposing meat-type breeder eggs to magnetic field (MF) before incubation on hatchability traits (percents of hatchability and hatchability failures of eggs), chick weight at hatch, and post-hatch performance (weight gain, feed intake, and feed conversion ratio (FCR)) from 1 to 39 d of age were investigated. Eggs from a Ross flock at 38 weeks of age were exposed to MF of 18 Gauss (1.8 mT) at 50 Hz for 0, 15, 30, 45, 60, and 75 min (MF0, MF15, MF30, MF45, MF60, and MF75) before incubation. Exposing eggs to MF did not influence hatchability of eggs and chick weight at hatch. However, chickens of MF60 and MF75 treatments had lower weight gain and feed intake than those of the non-exposed treatment at 39 d of age. MF exposure of eggs did not influence FCR of chickens between 1 and 21 d of age, but tended to increase FCR, albeit non-significantly, between 22 and 39 d of age. It is concluded that exposing meat-type breeder eggs to MF of 18 Gauss (1.8 mT) at 50 Hz for up to 75 min did not influence hatchability traits and chick weight at hatch. However, MF exposure of eggs for 60 and 75 min reduced body weight gain and feed intake of chickens over the 39-d experimental period.

Effects of in ovo administration of L-carnitine on hatchability performance, glycogen status and insulin-like growth factor-1 of broiler chickens.

1. Eggs from a meat-type breeder flock (Ross) were used in two trials to study the effects of in ovo administration of L-carnitine (carnitine) on hatchability traits (hatchability percentage, embryo deaths, pipped with live or dead embryo), chick weight at hatch as an absolute value (CWT) or expressed as a percentage of egg weight (CWT%), hatching period, glycogen status (liver and pectoral muscle) and plasma insulin-like growth factor-1 (IGF-1) of hatched chicks were investigated. There were 9 treatments with three replicates of each. Treatments were non-injected control (negative control), or injection with sterilised saline (09%, positive control), or sterilised saline with carnitine at 25, 50, 100, 200, 300, 400, and 500 microg/egg. 2. In ovo carnitine treatment increased CWT, CWT%, glycogen in the liver and pectoral muscle, glycogen index and plasma IGF-1 of hatched chicks, and did not influence hatchability traits and hatching period. The glycogen index of hatched chicks of the in ovo carnitine treatments with values (500 > 400 = 300 > 200) was higher than that of the control and in ovo carnitine at 25, 50, and 100 microg/egg treatments. The nature of response to carnitine was cubic for CWT and CWT%, and linear for glycogen in the liver and pectoral muscle, glycogen index of hatched chicks when the negative control or positive control treatment was used as base line. 3. It was concluded that in ovo administration of carnitine at 25-500 microg/egg increased chick weight at hatch and IGF-1, and did not influence hatchability traits and hatching period of eggs. The linear relationship between in ovo administration of carnitine and glycogen status of hatched chicks indicated that increasing in ovo doses improved glycogen status of hatched chicks.

Effects of electrical field on hatchability performance of eggs from a layer-type breeder.

1. Eggs from a layer-type breeder flock (Baladi, King Saud University) between 50 and 63 weeks of age were used in three trials to study the effects of electrical field (EF) during incubation on albumen and yolk heights, incubation temperature, egg weight loss and hatchability traits. The effects of egg size and eggshell characteristics on hatchability traits of eggs incubated under EF were investigated. 2. Eggs were weighed and graded into three weight classes (small, medium, and large). The physical dimensions, eggshell characteristics, and conductance of eggs were examined. The incubator was divided into two compartments for the control and EF treatments. Two aluminium plates were fitted on the inside walls of the EF compartment, face to face, and connected to a step up electric transformer. Eggs were exposed constantly to the EF during the first 18 d of incubation at the level of 30 kV/m, 60 Hz. 3. Egg size influenced the physical dimensions and eggshell characteristics of eggs. Large eggs had higher egg weight, egg surface area, egg volume, eggshell conductance, and eggshell weight and lower yolk weight percentage than medium or small size eggs. Small eggs had lower egg length and higher egg density than large or medium size eggs. Large eggs had higher eggshell thickness than small size eggs. 4. EF incubation of eggs raised incubation temperature by 0.06 degrees C, and increased the percentage of egg weight loss, hatchability, and weight of hatching chicks and reduced the early embryo deaths, and length of incubation by approximately 9.8, 19.6, 1.7, 62.1 and 2.1%, respectively. 5. There was no significant difference between the two incubation treatments in the heights of albumen and yolk of incubated eggs, percentages of late embryo deaths, and pips with live and dead embryos. Hatchability traits were not significantly influenced by egg size. 6. It was concluded that EF incubation of eggs increased hatchability, chick-hatching weight, and reduced the length of incubation of Baladi eggs. Differences in the physical dimensions and eggshell characteristics of eggs did not influence hatchability traits of eggs under EF incubation.

Effect of electric field during incubation of eggs on the immune responses of hatched chickens.

The effects of electric field (EF) during incubation of eggs on the immunocompetence of chickens were investigated over a 42-day experimental period. Eggs from a meat-type breeder flock were incubated under EF of 30 kV/m, 60 Hz during the first 18 days of incubation as compared with the control incubation (C). Chickens from the two incubation treatments were fed ad libitum and their immune system were monitored. Measurements were made of body weight (BW), and lymphoid organs weight (thymus, spleen, and bursa of Fabricius (BOF)) of birds at 21 and 42 days of age. Immune systems of birds were tested for specific antibody responses to sheep red blood cell (SRBC) and Newcastle disease vaccine (NDV), in vivo T-lymphocyte proliferation responses to phytohemagglutinin (PHA), and in vitro to concanavalin A (Con-A). EF incubation of eggs did not significantly (P > 0.05) influence BW of bird, absolute weight of lymphoid organs and weight of thymus, and BOF as a percentage of BW of bird (% BW) at 21 and 42 days of age, humoral immune responses as measured by antibody responses to SRBC and NDV, and cell-mediated immune responses as measured by T-lymphocyte proliferation responses to PHA, and Con-A of birds when compared with those of the C treatment. EF incubation of eggs significantly (P < 0.05) increased spleen weight as a % BW at 21 and 42 days of age when compared with those incubated under the C treatment. Birds at 42 days of age had significantly (P < 0.01) higher BW, lymphoid organ weight, and weight of BOF as a % BW, and lower spleen weight as a % BW when compared with those of 21 days of age. It is concluded that the incubation of eggs under EF of 30 kV/m, 60 Hz increased spleen weight as a % BW, without altering cell-mediated and humoral immune responses and, consequently, immunocompetence of meat chickens during the rearing period of 42 days.

Incubation temperature and hemoglobin dielectric of chicken embryos incubated under the influence of electric field.

Eggs from a layer-type breeder flock (Baladi, King Saud University) between 61 and 63 weeks of age were used in 3 trials to study the effects of electric field (EF) during incubation on the internal temperature of incubation, and eggs and hemoglobin (Hb) dielectric of chicken embryos at 18 days of age. Dielectric relative permittivity (epsilon') and conductivity (sigma) of Hb were examined in the range of frequency from 20 to 100 kHz. The values of dielectric increment (Deltaepsilon') and the relaxation times (tau) of Hb molecules were calculated. The internal temperature of eggs was measured in empty (following the removal of egg contents) and fertilized eggs in trials 1 and 2, respectively. The level of the EF was 30 kV/m, 60 Hz. EF incubation of embryos influenced the temperature of incubation and electrical properties of Hb molecules and did not influence the temperature of incubation and internal environment of eggs when empty eggs were incubated. EF incubation of fertilized eggs significantly raised the temperature of incubation, egg air cell, and at the surface of the egg yolk by approximately 0.09, 0.60, and 0.61 degrees F, respectively and Hb epsilon', sigma, Deltaepsilon', and tau as a function of the range of frequency of 20 to 100 kHz when compared with their counterparts of the control group. It was concluded that the exposure of fertilized chicken eggs to EF of 30 kV/m, 60 Hz, during incubation altered dielectric properties of Hb and that probably affected cell to cell communication and created the right environment for enhancing the growing process and heat production of embryos consequently increasing the temperature of the internal environment of the egg, and incubation.

Plasma delipidation process induces rapid regression of atherosclerosis and mobilisation of adipose tissue.

Cholesterol is a major component of atherosclerotic plaques. Cholesterol accumulation within the arterial intima and atherosclerotic plaques is determined by the difference of cellular cholesterol synthesis and/or influx from apo B-containing lipoproteins and cholesterol efflux. In humans, apo A-1 Milano infusion has led to rapid regression of atherosclerosis in coronary arteries. We hypothesised that a multifunctional plasma delipidation process (PDP) would lead to rapid regression of experimental atherosclerosis and probably impact on adipose tissue lipids. In hyperlipidemic animals, the plasma concentrations of cholesterol, triglyceride and phospholipid were, respectively, 6-, 157-, and 18-fold higher than control animals, which consequently resulted in atherosclerosis. PDP consisted of delipidation of plasma with a mixture of butanol-diisopropyl ether (DIPE). PDP removed considerably more lipid from the hyperlipidemic animals than in normolipidemic animals. PDP treatment of hyperlipidemic animals markedly reduced intensity of lipid staining materials in the arterial wall and led to dramatic reduction of lipid in the adipose tissue. Five PDP treatments increased apolipoprotein A1 concentrations in all animals. Biochemical and hematological parameters were unaffected during PDP treatment. These results show that five PDP treatments led to marked reduction in avian atherosclerosis and removal of lipid from adipose tissue. PDP is a highly effective method for rapid regression of atherosclerosis.

Effect of intensity of eggshell pigment and illuminated incubation on hatchability of brown eggs.

The effects of intensity of brown eggshell pigment (light (LBP), medium (MBP) and dark (DBP)) and light intensity during incubation (low and high, 900 to 1380 and 1430 to 2080 lux, respectively) on eggshell characteristics, embryonic growth, hatchability traits, chick hatching weight and hatching time were investigated using eggs from a meat-type breeder (Hybro) flock at 32, 36 and 41 weeks of age in three trials. With eggs of similar weights the intensity of brown pigment was not associated with eggshell weight and thickness, and did not influence embryo weight and egg weight loss during incubation. The shade of brown pigment of eggs laid by young hens influenced the percentage hatchability (HP) of eggs incubated under light. Illuminated incubation improved HP of LBP eggs (compared with MBP and DBP eggs) from 32- and 36-week-old hens, but had no significant effect on HP of eggs from 41-week-old hens. Light intensity during incubation did not influence egg weight loss. High intensity of light during incubation reduced HP and increased early death percentage (EDP) in the LBP and MBP groups, and did not influence HP and EDP in the DBP group. Brown eggshell pigment and intensity of light during incubation did not influence hatching time. It is concluded that the shade of brown pigment, intensity of light during incubation and age of the breeder hens influenced the hatchability performance of embryos from brown eggs. Light during incubation improved the hatchability of embryos in light brown eggs laid by young hens and the shade of brown pigment of eggs laid by older hens did not influence hatchability under illuminated incubation. High intensity of light during incubation reduced hatchability of light and medium brown eggs, but not the dark brown eggs.

Effect of lighted incubation on embryonic growth and hatchability performance of two strains of layer breeder eggs.

1. Eggs from two layer-type breeder flocks (ISA-W vs Leghorn) between 30 and 45 weeks of age were used in 4 trials to study the effects of lighted incubation on embryonic growth from 5 to 18 d of age and hatchability per cent (HP). The physical dimensions, eggshell characteristics and conductance (EC) of eggs of the two strains were compared. 2. Eggs were set in an incubator on trays either in the dark-control or under two tubes of 20-watt white fluorescent light during the first 18 d of incubation. The light intensity ranged from 1230 to 1790 lux at the surface of the eggs. Eggs were transferred to dark hatching compartments at d 19 of incubation. 3. The genetic make-up of birds influenced the physical dimensions and eggshell characteristics of eggs. ISA-W eggs had higher weight, surface area (ESA), volume (EV), width, EC, shell volume and HP, and lower ESA:EV ratio, per cent shell, shell density and dead embryos than those of Leghorn eggs. 4. Lighted incubation increased daily embryonic growth (mg/d) and HP by 3.9 and 5.9%, respectively, when compared with the dark-control incubation. 5. The physical dimensions and eggshell characteristics of eggs influenced the effects of lighted incubation on embryonic growth and HP. Lighted incubation increased embryonic growth and HP of ISA-W eggs. The increase in embryonic growth and HP of the Leghorn eggs was not significant. 6. The genetic make-up of birds influenced the physical dimensions and eggshell characteristics of their eggs and these differences in the characteristics of hatching eggs influenced embryonic growth and HP when incubated under light.

Eggshell conductance, embryonic growth, hatchability and embryonic mortality of broiler breeder eggs dipped into ascorbic acid solution.

1. Eggs from a broiler breeder flock between 25 and 29 weeks of age were dipped into solutions of various concentrations of ascorbic acid (AA) for up to 2 min, in order to evaluate its effects on eggshell conductance (EC), amniotic fluid pH, albumen height and pH, embryonic weight and hatchability. 2. Three experiments were conducted and the following treatments were used: control, non-dipped (CND); control, water-dipped (CWD); 10 g AA/l (AA1); 20 g AA/l (AA2) and 30 g AA/l (AA3). Measurements of EC before and after dipping were made in experiments 1 and 2 in eggs from hens at 25 and 27 weeks of age, respectively. Albumen height and pH were measured after dipping the eggs in experiment 2. In experiment 3, egg weight loss, embryonic weight and amniotic fluid pH at 14 d of age, hatchability percentage (HP), and embryonic mortality were measured in eggs from hens at 29 weeks of age. 3. AA treatment of eggs and dipping period of time (1, 1.5 and 2 min) increased EC of eggs from hens at 25 and 27 weeks of age. 4. AA3 treatment for 2 min reduced albumen height and increased albumen pH of eggs when compared with the CND treatment in eggs from hens at 27 weeks of age. 5. HP of AA1-treated eggs from hens at 29 weeks of age was higher than that of the CND treatment. AA2 and AA3 treatments of eggs reduced HP and increased the percentage of non-pips when compared with any of the other treatments. 6. AA2 and AA3 treatments of eggs increased egg weight loss when compared with the control treatments (CND and CWD). Dipping treatment did not influence amniotic fluid pH or embryo weight expressed as a percentage of initial egg weight. 7. It is concluded that dipping hatching eggs into AA solution increased EC of eggs. Dipping eggs into 10 g AA/l for a period of 2 min increased HP in eggs from hens at 29 weeks of age, although this was not associated with a significant increase in egg weight loss.

Lecithin-cholesterol acyltransferase activity in normocholesterolaemic and hypercholesterolaemic roosters: modulation by lipid apheresis.

Lipid apheresis, a recently described procedure for the elimination of lipid but not apolipoproteins from plasma, was applied to normocholesterolaemic and hypercholesterolaemic roosters. Lipid apheresis resulted in an immediate reduction in plasma unesterified cholesterol concentration, which was sustained for 150 min. The reduction in unesterified cholesterol concentration was higher in the normocholesterolaemic animals than in the hypercholesterolaemic animals. Lipid apheresis induced changes in the ratio of plasma unesterified to total cholesterol in normocholesterolamic animals but not in hypercholesterolaemic animals. In hypercholesterolaemic animals, lecithin-cholesterol acyltransferase (LCAT) activity was not affected by lipid apheresis, whereas in normocholesterolaemic animals LCAT activity was acutely reduced for 150 min after lipid apheresis. Saturated LCAT kinetics occurred in the hypercholesterolaemic animals but not in the normocholesterolaemic animals. LCAT obeyed Michaelis-Menten kinetics. After lipid apheresis, there was a pool of unesterified cholesterol that was available as substrate for LCAT to a greater extent in hypercholesterolaemic animals than in normocholesterolaemic animals. These observations may have important implications for lipid apheresis as a treatment for atherosclerosis.

Lipid apheresis in an animal model causes in vivo changes in lipoprotein electrophoretic patterns.

Lipid apheresis, a new extracorporeal procedure based on plasma delipidation and showing promise as a possible treatment for atherosclerosis, was recently reported for the first time from this laboratory [Cham et al., J Clin Apheresis 10:61-69, 1995]. In the present study lipid apheresis was applied to hypercholesterolemic and normocholesterolemic roosters to examine its effect on plasma lipoprotein particles. This procedure resulted in conspicuous changes in electrophoretic patterns of plasma lipoproteins. The electrophoretic mobilities of all the lipoprotein fractions had changed considerably. Lipid stainable material was present in at least three bands in the alpha-globulin area. In particular, changes in the electrophoretic region of high-density lipoproteins were observed. Lipid apheresis markedly induced the anti-atherogenic pre- beta-high-density lipoproteins. The observed changes induced by lipid apheresis were more pronounced in the hyperlipidemic animals compared with the normocholesterolemic controls. A novel pre-alpha-lipoprotein band was observed soon after lipid apheresis. This lipoprotein band had a density larger than 1.21. At approximately 150 minutes after lipid apheresis, the electrophoretic pattern had almost returned to its original base pattern. Lipid apheresis results in plasma lipoprotein changes which may induce reverse cholesterol transport and shows promise as a possible treatment of atherosclerosis.

Lipid apheresis: an in vivo application of plasma delipidation with organic solvents resulting in acute transient reduction of circulating plasma lipids in animals.

Despite primary and secondary prevention of coronary disease with lowering plasma cholesterol by diet and drug therapy, coronary heart disease remains the major cause of death in Western countries. Low density lipoprotein apheresis had the potential to make a significant impact as it acutely leads to a marked reduction in plasma cholesterol. However, recent preliminary results suggest that low density lipoprotein apheresis may not be more effective in preventing progression of coronary disease than current drug therapy. We have devised a new technique, termed lipid apheresis, which removes cholesterol and triglycerides from plasma but retains the apolipoproteins. This procedure shows great promise in stimulating regression beyond current therapy. Lipid apheresis, a new extracorporeal procedure based on plasma delipidation with the organic solvent mixture butanol-diisopropyl ether, was applied to hypercholesterolemic and normocholesterolemic roosters. Approximately 25% of the calculated blood volume was removed from the animals. The plasma was separated from the blood cells. The plasma was delipidated for 20 min with the organic solvent mixture. The delipidated plasma containing all proteins, including the apolipoproteins and other ionic constituents, was remixed with the blood cells and infused back into the identical donor animals. Analyses of serial blood samples collected from lipid apheresed and sham treated animals up to 16 h after infusion revealed that lipid apheresis caused acute, marked reductions in plasma lipids. The pattern and extent of the plasma levels of cholesterol were different in the hypercholesterolemic animals when compared with normocholesterolemic animals, indicating that a readily extraplasma cholesterol pool in the hypercholesterolemic animals was rapidly mobilized into the plasma pool.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison between wheat, triticale, rye, soyabean oil and strain of laying bird on the production, and cholesterol and fatty acid contents of eggs.

1. The effects of feeding three types of cereal grain (wheat, triticale or rye) and soyabean oil (0 or 20 g/kg) over a 12-week period on the production, yolk cholesterol and yolk fatty acid concentrations of three strains of laying pullets were studied. 2. Pullets fed on wheat- or triticale-based diets had higher body weight gains, egg productions, egg weights, egg mass and lower yolk cholesterol concentrations than pullets fed on rye-based diets. However, there were no significant differences between the cereals in yolk cholesterol content. 3. There were no significant differences between the three cereals in total food consumption of pullets nor of yolk weight nor yolk concentration of palmitic, stearic and oleic acids. 4. Pullets fed on triticale-based diets had higher yolk linoleic acid concentrations and lower yolk oleic acid: linoleic acid ratios than pullets fed on rye- or wheat-based diets. 5. Soyabean oil supplementation increased egg production, egg mass, yolk linoleic concentration and yolk unsaturated to saturated fatty acid ratio, but reduced yolk oleic acid: linoleic acid ratio. 6. There were differences between strains of pullets in weight gain, food consumption, rate of lay, egg weight and yolk cholesterol, but not in yolk fatty acid concentrations. 7. It was concluded that wheat- or triticale-based diets gave good production of eggs of lower cholesterol content, that soyabean oil supplementation gave eggs with a high unsaturated to saturated fatty acid ratio and that two strains of layers produced eggs with lower yolk cholesterol concentrations than a third strain.

The effects of dietary concentrations of minerals, source of protein, amino acids and antibiotics on the growth of and digestibility of amino acids by broiler chickens.

1. The effects of dietary calcium, available phosphorus, amino acid and antibiotic supplements on the digestibilities of amino acids and growth of broiler chickens were investigated in two experiments. 2. The performance of chickens fed on diets containing high concentrations of calcium and available phosphorus was poorer with meat meal-based diets than with soyabean-based diets. Methionine supplementation improved the performance of chickens fed meat meal-based diets. 3. A high dietary content of calcium (25.9 vs 11.8 g/kg) reduced chick performance and the digestibility of glutamic acid, leucine and phenylalanine but increased the digestibility of lysine and histidine. 4. High dietary contents of calcium and available phosphorus (24.3 and 13.0 vs 11.8 and 4.0 g/kg) reduced chick performance and the digestibilities of most amino acids. 5. Antibiotic supplementation did not improve the performance of chickens, but increased the digestibilities of most amino acids in chickens fed on diets with a high calcium or high calcium and available phosphorus contents. 6. It was concluded that excess dietary calcium alone, or calcium and phosphorus together, reduced chick performance and the digestibilities of most amino acids. Growing chickens tolerated excess dietary calcium and available phosphorus better in well-balanced amino acid diets, such as soyabean meal or methionine-supplemented meat meal diets, than in poorly balanced amino acid diets, such as unsupplemented meat meal diets.

Effects of dietary calcium and available phosphorus concentration on digesta pH and on the availability of calcium, iron, magnesium and zinc from the intestinal contents of meat chickens.

1. The effects of high calcium intakes on the pH and availability of calcium, iron, magnesium and zinc in the gastrointestinal tract (GIT) contents of meat chickens were studied in two experiments. 2. A high dietary concentration of calcium (25.3 vs 10.7 g/kg) increased the pH of crop and ileum contents, but did not influence the pH of the contents of other segments of the GIT. 3. The solubilities of minerals in GIT contents were reduced and the size of dissolved mineral complexes were increased as the digesta moved from the duodenum and jejunum to the ileum. 4. After feeding diets with calcium and available phosphorus concentrations (15.3 and 4.3 g vs 21.8 and 4.3 g vs 22.6 and 8.3 g/kg), centrifugation of GIT contents showed that most (70-92%) of the calcium, iron, magnesium and zinc was in an insoluble form. High calcium diets reduced the proportion of soluble zinc associated with small complexes, and high calcium and available phosphorus diets reduced the proportions of soluble magnesium and zinc associated with small complexes. 5. These findings explain the mechanism of the reduced availability of zinc and magnesium in high calcium and high available phosphorus diets.

The effects of dietary calcium, phosphorus, and protein on the performance and nutrient utilization of broiler chickens.

The effects of varying dietary Ca, available phosphorus (AP), and protein on 5- to 17-day performance (growth and feed efficiency), Ca and P contents of tibia and plasma, ME, and N utilization of broiler chickens were investigated in three experiments. In Experiment 1, high dietary Ca (24.3 versus 11.8 g/kg) reduced performance, N digestibility, and ME, whereas N retention was not affected. Reducing dietary protein (186 or 203 versus 217 g/kg) reduced performance and N retention but increased ME. In Experiment 2, high dietary Ca (25.3 versus 10.7 g/kg) reduced performance, tibia Ca, and plasma P and increased plasma total Ca; whereas the diet with both high Ca (25.3 g/kg) and high AP (9.8 versus 4.3 g/kg) reduced only performance. Reducing dietary protein from 206 to 166 g/kg diet reduced growth but improved feed efficiency and tibia P content. In Experiment 3, a diet containing 25.6 g of Ca and 4.9 or 10.7 g of AP compared with a diet containing 11.2 g of Ca and 4.9 g of AP/kg of diet reduced performance. Reducing dietary protein from 236 to 215 g/kg of diet decreased performance. It was concluded that high dietary Ca reduced growth performance and feed efficiency and that altering the dietary protein from 166 to 236 g/kg of diet did not overcome the growth depression effect of high Ca or of high Ca and AP diets.

The effect of dietary calcium upon growth rate, food utilisation and plasma constituents in lines of chickens selected for aspects of growth or body composition.

1. The effect of increasing dietary calcium from 10.3 to 20 g/kg on 5- to 17-day growth performance and plasma minerals, electrolytes, total protein, albumin and glucose in chickens from 4 lines selected for: high 8-week body weight (W), low abdominal fat (L), high abdominal fat (F) or at random (C) was studied in two experiments. 2. High dietary calcium significantly reduced weight gain and plasma phosphate and potassium but increased food:gain ratio, plasma total calcium, glucose and albumin. 3. Significant correlations were found between plasma total calcium and plasma phosphate (r = -0.5, P less than 0.01), plasma total calcium and protein (r = 0.4, P less than 0.01) and between plasma total protein and albumin (r = 0.55, P less than 0.01). 4. Genotypes differed in their response to dietary calcium content. There was a substantial response in line F but little effect in line L. 5. In contrast to the three other lines, in line F high dietary calcium significantly increased plasma ionised calcium without altering plasma phosphate or total calcium concentration. 6. It was concluded that genetic selection has produced lines which vary in their tolerance to high dietary concentrations of calcium. Birds selected for increased fatness were less tolerant to high dietary calcium than their lean-selected counterparts.

Effects of dietary calcium, available phosphorus and vitamin D on growth rate, food utilisation, plasma and bone constituents and calcium and phosphorus retention of commercial broiler strains.

1. The effects of different dietary concentrations of calcium (Ca), available phosphorus (AP) and vitamin D (D) on 5- to 16-day growth performance, and aspects of calcium and phosphorus (P) metabolism of chickens from three commercial strains were studied in two experiments. 2. Increasing dietary Ca reduced weight gain, tibia Ca and P content and increased plasma total Ca, Ca consumption and excretion, whilst dietary Ca at 32 g/kg increased tibia Ca:P ratio, plasma ionized calcium and reduced plasma P, tibia ash, P excretion, excreta moisture and Ca retention. 3. Increasing dietary AP reduced plasma total and ionized Ca and excreta moisture and increased P consumption and excretion, plasma P and tibia ash. 4. The addition of vitamin D increased plasma total and ionized Ca, tibia Ca:P ratio and reduced plasma sodium and P concentrations. 5. Strains differed in their tibia contents of Ca and Ca:P ratios, in response to Ca, AP and vitamin D diets whilst they differed in Ca excretion and excreta moisture caused by feeding either dietary Ca or AP. 6. It was concluded that dietary Ca, AP, vitamin D and strain of broiler chickens influenced the metabolism of Ca and P and that, as a consequence, the tolerance to high dietary Ca. A lean strain of chickens tolerated high dietary calcium better than its fat counterparts.