Cholesterol metabolism in the laying fowl

Dietary crude palm oil supplementation improves egg quality and modulates tissue and yolk vitamin E concentrations of laying hen

Crude palm oil (CPO) is a valuable energy supplement for poultry diets and a rich source of vitamin A and E. Data on the effect of vitamin E tocotrienol in CPO on laying hen metabolism are limited. The present study examined the effects of dietary CPO supplementation on the performance and tissue distribution of vitamin E in laying hens and on egg quality. In total, 144 49-week old Hysex Brown hens were allocated randomly into four groups (36 per group), in single cages, and received corn–soybean basal diet supplemented with either lard at 20 g/kg (control), or CPO at 20 (CPO1), 30 (CPO2) or 40 g/kg (CPO3). Egg quality, hen performance, egg yolk cholesterol and hen tissue concentrations of vitamin E were examined. Dietary supplementation with CPO increased the egg yolk colour, egg and yolk weight compared with the control group, but not specific gravity, albumen quality, albumen weight and shell weight. Importantly, CPO supplementation significantly decreased egg yolk cholesterol concentrations (lowest level in the CPO3 group) and enhanced (P < 0.05) the total vitamin E tocopherols in CPO1 and total tocotrienols in CPO2 and CPO3. Hens fed on CPO3 had the lowest total tocopherol concentrations in their egg yolk and adipose tissue, but the highest tocotrienol in their plasma, egg yolk and adipose tissue. In addition, dietary CPO supplementation resulted in the highest deposition of tocotrienol in the hen’s adipose tissue compared with in the egg yolk, or hen’s liver and plasma. In conclusion, dietary supplementation with CPO improved the egg yolk weight and yolk colour, while it reduced the total cholesterol concentration and resulted in more vitamin E in the egg and hen’s adipose tissue, with increased concentrations of α-tocopherol, α-tocotrienol and γ-tocotrienol.

Does dietary vitamin E or C decrease egg yolk cholesterol?

An experiment was conducted to determine the effect of dietary vitamin E and C on serum metabolites, yolk cholesterol, egg quality, and performance of layer hens. One hundred sixty-eight commercial Hy-Line W-36 layer hens were randomly divided into seven groups and six replicates with four hens in each. Dietary treatments were introduced after the pre-experimental period (10 days) to adjust egg production. Treatments were levels of vitamin E or C (100, 200, and 400 mg/kg diet) supplementation to the basal diet for 4 weeks, whereas the control group received no supplementation. Egg production, egg weight, and feed consumption were recorded during the study. Shell thickness, Haugh unit score, yolk color, yolk weight, yolk cholesterol, and blood parameters were measured at the end of experiment. There was no significant effect of dietary vitamin E or C on hen performance. Egg yolk cholesterol concentrations decreased linearly by antioxidant vitamin supplementation (P < 0.01). Egg yolk cholesterol reduction did not have any negative effect on egg production rate. Antioxidants, especially vitamin C, increased serum glucose concentration (P < 0.05). Serum total cholesterol content did not change by vitamin supplementation but cholesterol in high-density lipoprotein (HDL-C) decreased and cholesterol in low-density lipoprotein (LDL-C) increased (P < 0.05), as dietary vitamin E or C supplementation increased in diets. These results are in conflict with the previous hypothesis that antioxidants have a role in LDL-C removal from the blood or increasing HDL-C. Vitamin E was more effective than vitamin C in this case and if these results are confirmed by further studies, they may result to revision in researchers' point of view about antioxidant especially in human medicine.

Correlations between breeder age, egg cholesterol content, blood cholesterol level and hatchability of broiler breeders

1. The research was carried out to investigate correlations between breeder age, egg cholesterol content, blood cholesterol level and hatchability of broiler breeders. 2. Egg cholesterol content increased with increased breeder age. The mean yolk cholesterol contents (mg per g yolk) were 10.47+/-0.28, 15.34+/-0.65 and 15.64+/-0.71 mg/g at 28, 45 and 65 weeks of age, respectively. 3. There were positive correlations between yolk weight and yolk cholesterol content (mg/g yolk) (r=01.941; P<0.01) and egg cholesterol content (mg/egg) (r=0.980; P<0.01). 4. Negative correlations were found between egg yolk cholesterol content and hatchability of fertile eggs (r=-0.345; P<0.05), fertility ratio (r=-0.609; P<0.01) and hatchability of total eggs (r=-0.574; P<0.01). 5. The mean blood cholesterol levels were 165.1+/-11.04, 166.5+/-11.97 and 179.5+/-11.33 mg/dl at 28, 45 and 65 weeks of age, respectively.

Effect of probiotic supplementation on laying hen diets on yield performance and serum and egg yolk cholesterol

The effects of dietary supplementation of a commercial probiotic (BioPlus 2B) on daily feed consumption, egg yield, egg weight, specific gravity, body weight, feed conversion ratio, serum and egg yolk cholesterol, and serum trigylceride in layer hens were investigated. In 12 replicates, 480 27-week-old Brown-Nick layers were fed with diets containing 0, 250, 500 or 750 mg kg(-1) probiotic for 90 days. When compared with the controls, supplementation of 250, 500 and 750 mg kg(-1) probiotic increased egg production, but decreased the damaged egg ratio (p < 0.05), egg yolk cholesterol and serum cholesterol (p < 0.001) levels. In addition, serum triglyceride levels were reduced by using 500 and 750 mg kg(-1) probiotic supplementation (p < 0.001). Feed conversion ratios were positively affected by supplementation of 250 and 500 mg kg(-1) probiotic compared with controls (p < 0.05). There was no statistically significant difference between the control and all treatment groups on feed consumption, egg weight, specific gravity, body weight, and egg yolk weight.

Oral administration of pravastatin reduces egg cholesterol but not plasma cholesterol in laying hens

The effect of different 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGR)-inhibitors (statins) on plasma and egg cholesterol in laying hens was investigated. Forty-four ISA brown layers were fed lovastatin, simvastatin, or pravastatin at 0.03 or 0.06% for 4 wk. Cholesterol levels in plasma, liver, and egg yolk as well as hen laying performance were studied. Egg weight was significantly lowered with all statin treatments, although egg production was relatively unaffected. Total plasma cholesterol was significantly reduced by 0.06% lovastatin, 0.03% simvastatin, and 0.06% simvastatin, in agreement with previous reports, whereas pravastatin had no effect. In contrast, liver cholesterol concentrations showed a significant decrease in response to 0.03 and 0.06% pravastatin, implying selective regulation of liver cholesterol synthesis. Furthermore, oral administration with 0.06% pravastatin reduced egg cholesterol levels by almost 20% compared with the control diet. This suggests that pravastatin, unlike other classes of statin, may be a good candidate for commercial production of low cholesterol eggs with limited impact on hen physiology and egg production.

Effect of red mold rice supplements on serum and egg yolk cholesterol levels of laying hens

Monacolin K is a secondary metabolite of Monascus species and reduces cholesterol levels. This research focuses on the effect of adding red mold rice to hens' diet on cholesterol level in egg yolk and on cholesterol, triglyceride, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) levels in serum. Forty-eight Hy-line laying hens of 48 weeks of age were studied by dividing them into four groups. Except for the control group, the feed for three other groups contained 2.0, 5.0, and 8.0% red mold rice (monacolin K concentrations were 0.0145, 0.035, and 0.056%, respectively). The experiment lasted 6 weeks. During this period, egg weight and egg production were recorded every day, and cholesterol, triglyceride, HDL, and LDL in serum were measured weekly as well. The result showed that the cholesterol in eggs produced by experimental groups was lower than that of the control group (0%, 194.14 +/- 8.30; 2%, 167.17 +/- 4.34; 5%, 168.93 +/- 9.38; 8%, 183.02 +/- 7.63 mg/egg; p < 0.05), and the triglyceride (0%, 1494 +/- 178; 2%, 1280 +/- 174; 5%, 1189 +/- 248; 8%, 1381 +/- 218 mg/dL; p < 0.05) and LDL levels (0%, 36.81 +/- 5.53; 2%, 32.25 +/- 7.93; 5%, 30.06 +/- 4.39; 8%, 28.81 +/- 4.16 mg/dL; p < 0.05) were also significantly lowered in the experimental groups. However, the HDL level did not show significant change for either control or experimental groups (0%, 36.06 +/- 3.96; 2%, 36.25 +/- 5.39; 5%, 33.13 +/- 3.68; 8%, 31.44 +/- 4.29 mg/dL; p > 0.05). Besides, the addition of red mold rice also helps to inhibit production of malondialdehyde (MDA) in serum lipid oxidation (0%, 27.42 +/- 0.53; 2%, 25.62 +/- 0.76; 5%, 24.35 +/- 0.59; 8%, 23.63 +/- 0.48 microM; p < 0.05).

Select 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors vary in their ability to reduce egg yolk cholesterol levels in laying hens through alteration of hepatic cholesterol biosynthesis and plasma VLDL composition

The inability to markedly attenuate cholesterol levels in chicken eggs has led to speculation that cholesterol is essential for yolk formation and that egg production would cease when yolk cholesterol deposition was inadequate for embryonic survival. However, this critical level hypothesis remains unproven. Here, we determine the relative responsiveness of laying hens to three select inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), the rate-limiting enzyme of cholesterol biosynthesis. A control diet, either alone or supplemented with one of two dietary levels (0.03 or 0.06%) of atorvastatin, lovastatin, or simvastatin, was fed to White Leghorn hens for 5 wk. Liver cholesterol concentrations (mg/g tissue) were decreased (P </= 0.05) by each HMGR inhibitor; however, total liver cholesterol (mg) did not differ among treatments. Microsomal hepatic HMGR activities were increased one- to twofold in all HMGR inhibitor-treated groups, while HMGR mRNA levels were unaffected. Diameters of plasma VLDL particles, the main cholesterol-carrying yolk precursor macromolecules, were reduced (P </= 0.05) only in hens fed 0.06% atorvastatin, and the particles contained 38% less total cholesterol (P </= 0.05) than controls. Plasma total cholesterol concentrations were lowered (P </= 0.05) by both doses of atorvastatin (-56, -63%) and simvastatin (-36,-45%). Egg cholesterol contents were maximally reduced by 46% (P </= 0.05), 7% (P > 0.05), and 22% (P </= 0.05) in hens fed the 0.06% level of atorvastatin, lovastatin, and simvastatin, respectively, while overall egg production [-19% (P </= 0.05), +4% (P > 0.05), and -3% (P > 0.05)], was much less affected. We concluded that cholesterol per se may not be an obligatory component for yolk formation in chickens and, as such, may be amenable to further pharmacological manipulation

Evaluation of two novel biochemicals on plasma and egg yolk lipid composition and laying hen performance

PD132301-2, an inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT; EC 2.3.1.26), and 1-stearylboronic acid (SBA), a fatty acid analogue, were orally administered to White Leghorn hens in separate experiments to evaluate their effects on layer performance and plasma and egg yolk lipids. Five 60-wk-old hens each were fed either a corn-soybean meal basal layer ration, or the basal diet supplemented with .0121, .0363, or .1089% PD132301-2. In a second experiment, 12 37-wk-old hens each were fed either a basal layer ration, or the basal diet supplemented with .20 or .40% SBA. The duration of the experiments were 21 and 16 days, respectively. Neither compound significantly affected hen-day production, egg weight, yolk weight, BW gain, feed consumption, feed efficiency, plasma total cholesterol and triglyceride concentrations, or egg yolk cholesterol content. PD132301-2 had no effect on yolk fatty acid profiles, and C22:6n3 was the only fatty acid altered by SBA. Although 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors have been successful in reducing egg cholesterol, ACAT inhibitors and fatty acid analogues apparently hold little promise in this regard. The results of the present work also support the concept that, in order to pharmacologically alter the cholesterol content of eggs, direct inhibition of key enzymes in the cholesterol biosynthetic pathway is necessary.

In vivo clearance of low-density lipoproteins and beta-very-low-density lipoproteins in normal and hypercholesterolemic White Carneau pigeons

Low-density lipoproteins (hLDL) and beta-migrating-very-low-density lipoproteins (beta-VLDL) were isolated from the plasma of cholesterol-fed White Carneau (WC) pigeons and low-density lipoproteins (nLDL) were isolated from the plasma of grain-fed WC pigeons. The lipoproteins were radiolabeled with 125I or 131I and injected into normocholesterolemic or hypercholesterolemic WC pigeons to determine their rate of clearance from the plasma. The fractional catabolic rate (FCR) of nLDL and hLDL in normocholesterolemic pigeons averaged 0.202 and 0.206 pools/h.respectively. beta-VLDL was cleared at a significantly slower rate of 0.155 pools/h. The FCR of the same lipoproteins injected into hypercholesterolemic pigeons was reduced by 17% for nLDL, 50% for hLDL and 57% for beta-VLDL, indicating that the effect of hypercholesterolemia on clearance in vivo was different for the three lipoproteins. The FCR of reductively methylated pigeon LDL (MeLDL), which gives a measure of receptor-independent clearance of LDL, was shown previously to be 0.037 pools/h. These studies suggest therefore that LDL and beta-VLDL are cleared from the plasma of normocholesterolemic and hypercholesterolemic pigeons at a rate substantially greater than that predicted for non-specific processes. Despite the reduction in the clearance rate of hLDL and beta-VLDL due to cholesterol feeding, the absolute amount of cholesterol that was cleared from the plasma by these lipoproteins was increased from approx. 200 mg/kg body weight per day in the normocholesterolemic pigeons to greater than 1000 mg/kg body weight per day in the hypercholesterolemic pigeons. This is due principally to the enrichment in cholesterol relative to protein of the lipoproteins isolated from cholesterol-fed pigeons and the failure of hypercholesterolemia to completely inhibit receptor-dependent clearance of LDL and beta-VLDL. The lower rate of clearance of beta-VLDL relative to LDL is in marked contrast to mammalian beta-VLDL, which is cleared much faster than LDL, but is consistent with the lack of apo E on pigeon lipoproteins. Apo E is the apoprotein that is thought to be responsible for the rapid clearance of beta-VLDL in normocholesterolemic mammals. The low rate of beta-VLDL clearance in pigeons also suggests that pigeons lack an apolipoprotein that function like mammalian apo E.

[The effect of increasing additions of low-esterified pectins in the diet on the metabolism of laying hens--tested by pair-feeding studies]

A series of trials was carried out with 32 laying hens in order to study metabolism after addition of low methylated citrus pectin in levels of 2% and 6%. The following results should be pointed out: Addition of pectic substances reduced feed-intake and stimulated water intake. The limited tolerance for pectins resulted in an increasing water-content of the excreta with a rise of the concentration of volatile fatty acids and an alteration of their spectrum. In consequence of supplementation with pectins a considerable loss of body weight could be established, which exceeded the expected effects of reduced energy-intake. The egg production was impaired by addition of pectin. In the serum the level of total lipids, cholesterol, triglycerides, phospholipids, furthermore of bile acids diminished. These effects exceeded remarkably those induced solely by reduced feed-intake. The level of volatile fatty acids in the serum was elevated as result of the supplementation with pectic substances.

The effect of feeding di-(2-ethylhexyl) phthalate and related compounds on lipids in the laying hen

Di-(2-ethylhexyl) phthalate (DEHP) and three structurally related side-chain analogs were fed to laying hens to determine relationships of structure to effects on lipid metabolism. Hubbard broiler breeder hens were fed either a standard laying mash control diet or the control diet containing DEHP, 2-ethylhexanol (2-EH), 2-ethylhexanal (2-EHALD), or 2-ethylhexanoic acid (2-EHA). Experimental treatments lowered feed consumption, body weight, and egg production. The DEHP and side-chain analog diets lowered plasma total lipids. DEHP, 2% 2-EH, and 1% 2-EHA diets lowered plasma free cholesterol. Liver weights were not significantly changed, but liver fat was reduced. Lipid classes were measured by quantitative thin layer chromatography densitometry. The decreases observed in plasma lipids occurred primarily in the triglyceride fraction. Liver lipid decreases occurred mainly in triglyceride and free fatty acid classes. Hen egg yolk percent fat, lipid classes, and free and total cholesterol were unaffected by any DEHP or side-chain analog diets. Plasma and liver hypolipidemic effects were observed with all of the oxidation state structural analogs of DEHP's side chain, but 2% 2-EH was the most effective treatment. These results suggest that the active portion of DEHP may be the metabolite, 2-EH, formed in vivo by hydrolysis of DEHP's ester bond.

Effect of dietary factors on serum and egg yolk cholesterol levels of laying hens

Effects of dietary lipid factors (saturated and unsaturated oil, cholesterol and plant sterols) on the serum and egg yolk cholesterol levels of the laying hen were investigated. Single Comb White Leghorn laying hens, at thirty weeks of age, were used in two trials by feeding two basal diets containing 8.0% hydrogenated coconut oil or safflower oil, with or without supplemental cholesterol (1.0%), soysterols (2.0%) or combinations of both. Safflower oil, per se, had a superior property to hydrogenated coconut oil in suppressing cholesterol levels, in both serum and egg yolk. Cholesterol supplementation to the safflower oil basal diet resulted in a significant (P less than 0.01) elevation of serum and egg yolk cholesterol levels, whereas cholesterol in combination with hydrogenated coconut oil did not change the serum level. Cholesterol lowering effect of soysterols was clearly demonstrated in both serum and egg yolk by feeding soysterols alone as well as by feeding soysterols in combination with cholesterol.