Integral apolipoproteins increase surface-located triacylglycerol in intact native apoB-100-containing lipoproteins

High-resolution NMR was used to measure the presence and quantity of triacylglycerol (TAG) in the surface of intact native apolipoprotein B-100-containing lipoprotein particles that are made by chickens in response to estrogen treatment and that in hens are deposited in yolk follicles (VLDLy). Integration of 13C NMR resonances shows that intact VLDLy particles contain more surface TAG (5.1 +/- 0.6 mol%, 6.7 +/- 0.8 weight %) than predicted by apolipoprotein-free models using similarly acyl-heterogenous TAG. Change in downfield chemical shift values of surface to core TAG in VLDLy was 0.8 ppm compared with 1.3 ppm in vesicles prepared with purified egg phosphatidylcholine and TAG isolated from the VLDLy, indicating that reduced surface TAG hydration may contribute to the resistance to lipase hydrolysis characteristic of this lipoprotein species. Apolipoprotein-mediated changes in surface lipid composition and lipid hydration provide possible general mechanisms for selectivity in lipoprotein substrate characteristics.     

Effect of melengestrol acetate as an alternative to induce molting in hens on the expression of yolk proteins and turnover of oviductal epithelium

Inducing hens to molt increases egg quality, egg production and extends the productive life of hens. It has been previously demonstrated that melengestrol acetate (MGA), an orally active progestin, decreased gonadotropic support for the ovary, which decreased the steroidogenic support for the oviduct and resulted in the cessation of lay. Estradiol produced by the theca cells of small follicles stimulates the production of the yolk proteins vitellogenin II and apolipoprotein II by the liver and supports the oviductal epithelial cells. The objective of the present experiment was to determine gene expression for yolk proteins and oviductal epithelial cell turn-over in response to a MGA-induced molt. Hy-Line W-36 laying hens were fed either 0 or 8mg MGA per day for 28 days in a balanced diet and then returned to a standard layer ration until day 36. Four birds per treatment on days 1, 8, 16, 28 and 36 were euthanized and the liver was removed and snap frozen in liquid nitrogen until RNA was extracted. Expression of vitellogenin II and apolipoprotein II genes was determined using real-time RT-PCR. A portion of the magnum was removed to determine proliferation and programmed cell death for secretory and ciliated luminal epithelium. Vitellogenin II and apolipoprotein II gene expression was reduced in hens fed 8mg MGA compared to those fed 0mg MGA. There was no effect of day on gene expression of either yolk protein. Cell proliferation was increased in the ciliated epithelial cells of the oviduct in hens receiving 8mg MGA compared to those receiving 0mg. However, programmed cell death of the ciliated epithelial cells was not different between controls and MGA treatment. Programmed cell death and proliferation increased in the secretory epithelial cells in hens receiving 8mg MGA compared to controls. Therefore, utilizing MGA as an alternative method to induce molt results in some, but not all, of the physiological changes previously described for hens molted by feed withdrawal. These findings lead us to suggest that some of the observed physiological changes resulting from feed withdrawal are required to increase egg quality and egg production following molt and other changes are not necessary, but are just a result of nutrient deprivation.     

Production and fates of unique organelles (transosomes) in ovarian follicles of Gallus domesticus under various conditions. II

Production and fates of transosomes (sacs of ribosomes made in the follicular cells of an ovarian follicle and subsequently passed to the cytoplasms of the oocyte) have been studied by electron microscopy in ovaries of young chicks, a testosterone-treated hen, aged hens which had ceased laying eggs and a "non-layer" mutant. Study was also made of "primitive yolk" (vacuoles present in both follicular cells and ooplasms of small follicles of normally laying hens). It was found that both transosomes and vacuoles of primitive yolk were present in small oocytes of young chicks, and "non-layer" mutants. However, the transosomes deep within the ooplasms were present within lysosomal vesicles in both of these instances and the vacuoles containing primitive yolk were patently abnormal in the "non-layer" mutant. Very few transosomes or primitive yolk vacuoles were present within the ooplasms of follicles from a testosterone-treated hen or from those of aged hens which were no longer laying. In both of these latter cases such bodies were present in the follicular cells. However, many transosomes were seen to be in the process of being lysed within the cytoplasms of these follicular cells.     

Lipoproteins from the blood and egg yolk of the hen. The transfer of very-low-density lipoprotein to egg yolk and possible changes to apoprotein B

As part of a study of the transfer of proteins and lipids from avian blood to egg yolk, some properties of lipoproteins from the blood of laying hens were compared with those of the low-density lipoprotein (YLP) from egg yolk of the same hens. Although it is known from previous work that particles of the very-low-density lipoprotein (VLDL) of blood are the most likely precursors of YLP, their apoprotein patterns are different, according to electrophoresis and chromatography, with only one protein in common. YLP has the more complicated pattern which does not, however, include apoprotein B (ApoB) the main apoprotein of VLDL. It is suggested that during the transfer of VLDL to yolk, ApoB is cleaved to give smaller yolk apoproteins, especially apovitellenins IV and VI. Some evidence for this suggestion from the similarity of protein digests is presented.     

Apolipoprotein VLDL-II inhibits lipolysis of triglyceride-rich lipoproteins in the laying hen

In the laying hen, very low density lipoprotein (VLDL) particles contain large amounts of apolipoprotein (apo)-VLDL-II in addition to apoB. These triglyceride-rich lipoproteins are transported from the liver primarily to growing oocytes. Since no appreciable hydrolysis of triglyceride occurs during this transport, we have investigated the possibility that apoVLDL-II functions as an inhibitor of lipoprotein lipase (LPL). The presence of LPL in chicken follicular granulosa cells was demonstrated by immunoblotting, and LPL activity with the usual in vitro characteristics could be measured in cultured granulosa cell extracts. ApoVLDL-II inhibited LPL activity in these extracts as well as in the post-heparin medium of rat cardiac myocytes. Half-maximal inhibition in both systems occurred at 40 micrograms/ml, a concentration that is one-tenth of the circulating apoVLDL-II in the laying hen. Much less inhibition was observed with reduced and alkylated apoVLDL-II and with apoA-I. We conclude that the presence of apoVLDL-II on laying hen VLDL ensures efficient delivery of triglyceride to the oocyte for subsequent use as energy source by the embryo.     

Influence of high vitamin E dosages on retinol and carotinoid concentration in body tissues and eggs of laying hens

The aim of the study was to contribute to the discussion of overdosing vitamin E in laying hens. A total of 45 laying hens, divided into 5 groups were fed diets supplemented with either 0; 100; 1000; 10 000 or 20 000 mg dl‐α‐tocopheryl acetate/kg diet over a period of 10 weeks. Concentrations of vitamins A and E were measured in plasma, various tissues and egg yolk. Furthermore egg yolk colour and some carotinoids were measured in egg yolks. None of the vitamin E doses significantly influenced performance of the hens. As expected, vitamin E concentration in plasma, all tissue samples and egg yolk was significantly increased with increasing tocopherol content in the diet. The egg yolk showed the highest vitamin E concentration, followed by liver and muscles. Feeding 1000 mg α‐tocopheryl acetate per kg diet resulted in an increase of vitamin A concentration in the liver. Very high doses (10 000 and 20 000 mg/kg diet) significantly decreased retinol concentration in the liver and egg yolk, as well as carotinoid concentration in the egg yolk. The lower carotinoid concentration in egg yolk resulted in a decreased intensity of egg yolk colour. A prooxidative and/or competitive effect of very high doses of vitamin E with other fat soluble substances has been discussed.     

The impact of incorporation of n-3 fatty acids into eggs on ovarian follicular development, immune response, antioxidative status and tibial bone characteristics in aged laying hens

The objectives of this study were to investigate the effects of different dietary sources of unsaturated fatty acids (fish oil (FO) and/or linseed oil (LO)) on laying performance, egg yolk fatty acid composition, ovarian follicular development, antioxidative properties, immune response and tibial bone characteristics in aged laying hens. A total of 100 Hisex Brown hens at 56 weeks of age were housed individually in laying cages in an open-sided building under a 16 h light:8 h dark lighting schedule. Hens were randomly divided into four experimental treatments (n=25 each). Birds were fed ad libitum diets containing 2.5% vegetable oil (C, control), 2.5% FO, 2.5% LO and a mixture of 1.25% LO+1.25% FO (LO+FO) from 56 to 68 weeks of age. Egg production, egg quality characteristics and yolk lipid profile were analyzed. At 68 weeks of age, ovarian follicles were classified and tibial bone characteristics were determined. Serum thiobarbituric acid reactive substance (TBARS), glutathione peroxidase (GSH-Px) activity and total antioxidant capacity were measured. Incorporation of n-3 polyunsaturated fatty acids (n-3PUFA) into the egg yolks has been successful by using dietary FO and/or LO. There were no significant effects of treatments on hen-day egg production, feed intake, egg weight, egg shape index, albumen height, Haugh units and yolk height. However, dietary FO and/or LO supplementation had a significantly positive effect on eggshell percentage, eggshell thickness and yolk color. At 68 weeks of age, there was no significant difference among dietary treatments for tibial bone measurements. Also, no negative effects were detected in ovarian follicular development and weights of the ovary and oviduct, expressed in both absolute terms and relative to body weight. Dietary 2.5% LO, 2.5% FO and a mixture of 1.25% FO+1.25% LO enhanced GSH-Px activity, total antioxidant capacity and antibody titers significantly in comparison with control. It could be concluded that inclusion of mixed sources of n-3PUFA in diets at moderate levels (2.5%) increased the n-3PUFA content and decreased the n-6/n-3 ratio content in the yolk, improved the antioxidative status, reduced lipid peroxidation, enhanced the antibody response and did not have any negative influence on ovarian follicular development and tibial bone characteristics in aged laying hens.     

The composition of triglycerides from liver, egg yolk and adipose tissue of the laying hen

The composition of the triglycerides of liver, egg yolk and adipose tissue of laying hens fed on a standard diet were investigated by using argentation thin-layer chromatography to separate the triglycerides according to their degree of unsaturation. About 40% of liver triglycerides consisted of one saturated and two monoenoic fatty acids. Triglycerides containing linoleate were more abundant in adipose tissue than in either yolk or liver. Hydrolysis by pancreatic lipase of the tissue triglycerides and fractions obtained from these triglycerides showed that the triglycerides of adipose tissue had a less ordered arrangement of fatty acids at the 2-position than did either yolk or liver triglycerides. The labelling patterns of triglycerides formed in liver slices incubated in the presence of [1-(3)¹⁴C]glycerol indicated that triglycerides containing four or more double bonds are formed to a greater extent than are other triglyceride fractions. This is evidence for the concept that the type of triglyceride formed depends on the availability of fatty acids to the liver cells.     

Follicular development and plasma yolk precursor dynamics through the laying cycle in the European starling (Sturnus vulgaris)

We investigated the quantitative matching of plasma yolk precursor supply (the plasma pool) to follicle demand during yolk formation in European starlings (Sturnus vulgaris). Plasma concentrations of the two yolk precursors, vitellogenin (VTG) and very low density lipoprotein (VLDL), were only elevated coincident with rapid yolk development (RYD) and matched variation in total yolky follicle mass. VTG and VLDL were low (<0.4 microg/mL and <4.2 mg/mL, respectively) in nonbreeders and prebreeders with no yolky follicles, and at clutch completion. They increased to 4.02 microg/mL and 19.4 mg/mL in birds with a full follicle hierarchy (F1-F4), and concentrations then remained high and actually increased up to the point where only a single, yolky (F1) follicle remained. However, there was some evidence for mismatching of supply and demand: (a) precursor concentrations increased throughout the laying cycle even though the number of developing follicles decreased. We suggest that this is because of a requirement to maintain a large precursor pool to maintain high uptake rates; and (b) in birds with a full follicle hierarchy, precursor concentrations were negatively correlated with total follicle mass. This suggests that high uptake rates in large follicles can actually deplete circulating precursor concentrations. Plasma concentrations of both yolk precursors increased rapidly in the early morning with (predicted) time after ovulation, consistent with a lack of fine control of precursor concentrations. However, mean plasma VTG concentrations did not differ between morning or evening samples. In contrast, plasma VLDL concentrations were lower in the morning (16.8 mg/mL) than in the evening (22.9 mg/mL). Although there is marked individual variation in plasma VTG and VLDL (four- to eightfold), both precursors were repeatable in the short term (24 h), and plasma VTG was repeatable over a 14-d interval between successive breeding attempts.     

Chicken oocyte growth: receptor-mediated yolk deposition

During the rapid final stage of growth, chicken oocytes take up massive amounts of plasma components and convert them to yolk. The oocyte expresses a receptor that binds both major yolk lipoprotein precursors, vitellogenin (VTG) and very low density lipoprotein (VLDL). In the present study, in vivo transport tracing methodology, isolation of coated vesicles, ligand- and immuno-blotting, and ultrastructural immunocytochemistry were used for the analysis of receptor-mediated yolk formation. The VTG/VLDL receptor was identified in coated profiles in the oocyte periphery, in isolated coated vesicles, and within vesicular compartments both outside and inside membrane-bounded yolk storage organelles (yolk spheres). VLDL particles colocalized with the receptor, as demonstrated by ultrastructural visualization of VLDL-gold following intravenous administration, as well as by immunocytochemical analysis with antibodies to VLDL. Lipoprotein particles were shown to reach the oocyte surface by passage across the basement membrane, which possibly plays an active and selective role in yolk precursor accessibility to the oocyte surface, and through gaps between the follicular granulosa cells. Following delivery of ligands from the plasma membrane into yolk spheres, proteolytic processing of VTG and VLDL by cathepsin D appears to correlate with segregation of receptors and ligands which enter disparate sub-compartments within the yolk spheres. In small, quiescent oocytes, the VTG/VLDL receptor was localized to the central portion of the cell. At onset of the rapid growth phase, it appears that this pre-existing pool of receptors redistributes to the peripheral region, thereby initiating yolk formation. Such a redistribution mechanism would obliterate the need for de novo synthesis of receptors when the oocyte's energy expenditure is to be utilized for plasma membrane synthesis, establishment and maintenance of intracellular topography and yolk formation, and preparation for ovulation.     

Leptin receptor in the chicken ovary: potential involvement in ovarian dysfunction of ad libitum-fed broiler breeder hens

In hens, the ovarian follicles committed to ovulation are arranged in an ordered follicular hierarchy. In standard broiler breeders hens genetically selected for high growth rate the reproductive function is clearly dysfunctional. Feed restriction is needed during reproductive development to limit the formation of excessive numbers of ovarian yellow follicles arranged in multiple hierarchies. To determine whether leptin is involved in the nutritional and reproductive interactions controlling follicular hierarchy in hens, blood leptin levels and ovarian expression of the leptin receptor mRNA were determined during follicle maturation in three chicken lines; a slow growing broiler "Label" genotype without reproductive dysfunction, a fast growing "Standard" genotype fed ad libitum or restricted and a fast growing "Experimental" line with intermediate reproductive performance levels. Whereas expression of the leptin receptor mRNA did not change in the theca, it clearly decreased with follicular differentiation in the granulosa of slow growing hens. In fast growing standard hens fed ad libitum and presenting significant reproductive dysfunction, the decrease was disrupted and dramatic up-regulation of granulosa cell expression of the leptin receptor was observed. On the other hand, feed restriction decreased the overall level of expression of the leptin receptor mRNA and restored the decrease with follicular growth. The level of expression of the leptin receptor probably modulates the action of leptin on follicular differentiation. Since blood leptin and other metabolic factors were not affected by the genotype or by nutritional state, the factors involved in the regulation of leptin receptor gene expression remain to be determined. This study demonstrates the involvement of leptin in the nutritional control of reproduction in birds. Leptin action on the ovary probably controls follicular hierarchy through the regulation of steroidogenesis.     

Apolipoprotein B-related gene expression and ultrastructural characteristics of lipoprotein secretion in mouse yolk sac during embryonic development.

In mice, the yolk sac appears to play a crucial role in nourishing the developing embryo, especially during embryonic days (E) 7;-10. Lipoprotein synthesis and secretion may be essential for this function: embryos lacking apolipoprotein (apo) B or microsomal triglyceride transfer protein (MTP), both of which participate in the assembly of triglyceride-rich lipoproteins, are apparently defective in their ability to export lipoproteins from yolk sac endoderm cells and die during mid-gestation. We therefore analyzed the embryonic expression of apoB, MTP, and alpha-tocopherol transfer protein (alpha-TTP), which have been associated with the assembly and secretion of apoB-containing lipoproteins in the adult liver, at different developmental time points. MTP expression or activity was found in the yolk sac and fetal liver, and low levels of activity were detected in E18.5 placentas. alpha-TTP mRNA and protein were detectable in the fetal liver, but not in the yolk sac or placenta. Ultrastructural analysis of yolk sac visceral endoderm cells demonstrated nascent VLDL within the luminal spaces of the rough endoplasmic reticulum and Golgi apparatus at E7.5 and E8.5. The particles were reduced in diameter at E13.5 and reduced in number at E18.5;-19.The data support the hypothesis that the yolk sac plays a vital role in providing lipids and lipid-soluble nutrients to embryos during the early phases (E7;-10) of mouse development. secretion in mouse yolk sac during embryonic development.     

The effect of replacing soya bean oil with glycerol in diets on performance,egg quality and egg fatty acid composition in laying hens

The objective of this experiment was to replace soya bean oil with glycerol in laying hen diets and assess the change’s effect on performance, parameters of egg quality and the egg fatty acid profile. A total of 60 44-week-old Hy-Line W36 laying hens were distributed according to a completely randomised experimental design into four treatments consisting of glycerol substitutions for soya bean oil dietary at varying inclusion levels (0%, 25%, 50% and 75%), with five replicates of three birds each. Dietary treatments had no significant effect on BW change, egg production, feed intake, feed conversion ratio, egg weight and egg mass of laying hens. The inclusion of glycerol in the diet of laying hens had no significant effect on egg specific gravity, eggshell breaking strength, eggshell weight, eggshell thickness, egg shape index, albumen index, yolk index, haugh unit, albumen pH, yolk pH and egg yolk colour values. The inclusion of glycerol in the diet of laying hens had no significant effect on palmitic, palmitoleic, stearic, oleic and linolenic acid contents of the egg yolk. The linoleic acid and polyunsaturated fatty acid contents of the egg yolk significantly decreased with the higher levels of dietary glycerol supplementation (P<0.05). The results of this study show that it is possible to replace 75% of soya bean oil (4.5% in diet) with glycerol.     

Ovarian follicular development, lipid peroxidation, antioxidative status and immune response in laying hens fed fish oil-supplemented diets to produce n-3-enriched eggs

The objective of the present study was to research the effect of feeding laying hens fish oil-supplemented diets to produce n-3-enriched eggs on their ovarian follicular development, serum lipid peroxidation, antioxidative status and immune response. A total of 105 white Bovens hens at 24 weeks of age were housed in cages in an open-sided building under a 16 h light : 8 h dark lighting schedule. Birds were randomly divided into five treatments and were fed, ad libitum, diets containing 0% (control), 1.25%, 2.5%, 3.5% or 5.0% fish oil from 24 to 36 weeks of age. Egg production and weight were recorded. By weeks 35 and 36 of age 15 eggs were taken at random from each treatment to determine the yolk lipid profile and cholesterol content. At the end of the experimental period, 10 females from each treatment were randomly chosen, anaesthetised and killed by decapitation. Ovary and oviduct samples were immediately weighted and ovarian follicles were classified. Serum thiobarbituric acid-reactive substance (TBARS), hepatic TBARS and hepatic glutathione peroxidase (GSH-Px) activity were measured. No clear trend was observed concerning egg production and egg yolk cholesterol. As dietary fish oil levels increased, n-3-polyunsaturated fatty acids (n-3 PUFA) increased, whereas n-6 PUFA tended to decrease in yolk lipids. No negative effects were detected in ovary and oviduct weights, expressed in both absolute terms and relative to body weight. The numbers and total weights of large yellow follicles (LYF) in the ovary were not significantly affected by fish oil supplementation. Low levels (1.25% to 2.5%) of fish oil reduced both plasma and hepatic TBARS and enhanced GSH-Px activity. It is also interesting to note that inclusion of 2.5% fish oil in laying hen diets enhanced the antibody titre in laying hens. Therefore, it could be concluded that inclusion of fish oil in laying hen diets at moderate levels increased the n-3 fatty acids content in eggs, improved antioxidative status, enhanced the antibody response and did not have a negative influence on the different reproductive morphology parameters in laying hens.     

Lipid transport in the developing bovine follicle: messenger RNA expression increases for selective uptake receptors and decreases for endocytosis receptors

Differences in rates of steroid production and secretion will, eventually, determine the developmental rates of ovarian follicles. The major supply of cholesterol, the precursor for steroid and androgen biosynthesis, to ovarian cells is from circulating lipoproteins via membrane receptors from the low density lipoprotein receptor (LDL) superfamily. This occurs by either endocytosis, which has been described for very low density lipoprotein receptors (VLDLr), for LDL receptors (LDLr), and by the selective uptake pathway described for the scavenger receptor class B type 1 receptor (SRB1) and the recently described ovarian receptor, lipoprotein receptor-related protein 8 (LRP8). In this study, the mRNA expression of these four cholesterol receptors in bovine ovarian cells was determined at different stages of follicular development. In small antral follicles, mRNA expression of the endocytosis receptors was higher than in large antral follicles. Expression of LRP8 mRNA increased linearly with follicular size together with an increase in LDL, VLDL, and cholesterol concentrations in the follicular fluid. SRB1 mRNA expression tended to increase with follicular diameter. Because different mRNA expression patterns were found for the two types of receptor, this may imply different regulation of cholesterol supply at different stages of follicular development. Accumulation of LDL and VLDL particles in the follicular fluid of large antral follicles may enhance cholesterol availability for the intense steroidogenic activity that is essential at these stages.     

Effects of fasting on serum lipids and lipoprotein profiles in the egg-laying hen (Gallus domesticus)

The effects of a 24-h fast on serum lipids and lipoprotein profiles in commercial laying hens were investigated. Blood was analyzed at 34 and 46 weeks of age from Single Comb White Leghorn hens that had been either fed ad libitum or had been fasted for 24 h prior to collection. At 12 weeks, birds were divided into 16 biological isolation units, with 8 replicate units assigned to each treatment group. Four birds out of 10 in each unit were tagged for bleeding. Parameters evaluated included total serum cholesterol and triglycerides, mean diameters of very low density lipoproteins (VLDLs) for the 10th, 50th, and 90th percentiles of serum total VLDL, mean total population VLDL particle diameter (MPD), and percentage serum cholesterol recovered in VLDL, low density lipoprotein (LDL), and high density lipoprotein (HDL) fractions. Fasting led to decreases in total serum cholesterol and triglycerides, and a decrease in mean serum VLDL particle diameter in the 90th population percentile. At Week 34, percentage serum cholesterol recovered from LDL was increased, whereas percentage serum cholesterol recovered from HDL was decreased due to fasting. At Week 46, MPD and percentage serum cholesterol recovered from VLDL were decreased, whereas percentage serum cholesterol recovered from HDL was increased due to fasting. It was concluded that a 24-h fast decreased serum lipids (cholesterol and triglycerides) and the size of VLDL particles in the 90th population percentile in commercial laying hens. Furthermore, bird age influenced the effects of a 24-h fast on MPD and the redistribution of serum cholesterol among VLDL, LDL, and HDL particles.     

Effects of early prenatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on postnatal reproduction in the laying hen (Gallus gallus)

This study demonstrates the long-term effects of very early embryonic exposure to a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0, 10 and 20 ng/egg), administered before the beginning of embryonic development, on growth and reproductive performance in laying hens. Hatchability and body weight gain from 11 weeks onwards were significantly depressed in 20 ng treated hens. All hens started laying egg at around the same age and the laying performance of TCDD-treated hens was normal. No disturbances in the age-related pattern and concentrations of oestradiol, LH or FSH in plasma could be found but mean progesterone concentrations were significantly lower in 20 ng treated hens. Moreover, follicular distribution was changed with less small white follicles and smaller yellow follicles, which probably resulted in the lower egg weight of the 20 ng treated hens. At 43 weeks of age, hens treated in ovo with TCDD showed a retained right oviduct, mostly filled with clear fluid. From these results, it seems that in ovo exposure to TCDD interferes in the right oviduct regression during embryonic development and induces some changes in follicular distribution but without impairment of reproductive performance in the adult laying hen.     

Flaxseed and dried tomato waste used together in laying hens diet

The aim of this study was to investigate the effects of simultaneous supplementation of laying hens with dietary sources of n-3 polyunsaturated fatty acids (PUFA) and carotenoids on egg quality, fatty acids and carotenoid profile of the egg yolk and on feed and yolk lipid peroxidation. A 6-week experiment was carried out with 53-week old laying hens (96 Tetra SL) assigned to a control and three treatment groups supplemented with 5% flaxseeds and different levels of dried tomato waste (DTW, 2.5%, 5.0% and 10.0%). Hens from the groups supplemented with 5% and 7.5% DTW had a significantly lower average daily feed intake and laying percentage as compared to the control. Increased doses of dietary DTW enhanced yolk Roche colour score in direct correlation with the enrichment of egg yolk in carotenoids but decreased their transfer efficiency from feed to egg. After 4 weeks, egg yolk from hens fed with 5% flaxseeds and 7.5% DTW had increased lutein and zeaxanthin levels (by 29% and 24%, respectively) and the colour score was 3.5 fold higher compared to the control group. As a result of the dietary supplementation with flaxseed, the n-3 fatty acid content was 3.1–3.7-fold higher in egg yolk compared with the control and the n-6/n-3 ratio decreased from 18.3 (control) to 4.1–5.4 in supplemented diets. Dietary supplementation with 5% DTW effectively prevented lipid oxidation of eggs enriched with n-3 PUFA, but the increase in DTW content depressed the absorption and deposition of n-3 PUFA in egg yolk.     

Proteolysis of apoprotein B during the transfer of very low density lipoprotein from hens' blood to egg yolk

We report an example of the enzymic cleavage of an apoprotein B (apoB), the main apoprotein in the very low density lipoprotein (VLDL) of laying hens' blood, in a normal biological process, the formation of egg yolk. Plasma VLDL was labeled in vivo with 3H-amino acids, isolated by centrifuging, and injected into another laying hen. Yolk VLDL was isolated and its apoproteins were separated. ApoB was not detected in this lipoprotein. Most of the label originally in apoB was distributed among four smaller yolk apoproteins, apovitellenins III to VI, which are a large proportion of the apoproteins of VLDL in yolk. This distribution of 3H suggested that 80% of apoB was cleaved at three places. One yolk apoprotein, apovitellenin II, was not labeled, indicating that it did not originate from an apoprotein in plasma VLDL. The site for cleavage of apoB in the ovarian tissue has not been determined, but cleavage may occur during receptor-mediated endocytosis. The pattern of cleavage of apoB during transfer to yolk was not imitated by some known proteolytic enzymes.     

Potential of alfalfa as an alternative molt induction diet for laying hens: egg quality and consumer acceptability

Dietary molt induction to initiate additional egg laying cycles in commercial laying hen flocks is a wide spread practice in the United States. Feed deprivation is the most commonly used method but this practice has generated several concerns which has lead to research for viable alternative approaches. From a management standpoint a single ingredient molting diet consisting of high fiber-low energy represents an easily adaptable diet for large laying hen production units. Alfalfa meal is readily available in most commercial locations and possesses many of the desirable properties of an ideal laying hen molt diet. In the current study hens at a commercial laying facility were molted by both alfalfa and feed deprivation. After the hens had reentered post-molt commercial egg production, eggs were examined for egg quality performance. Egg shell strength, albumen height, yolk height, weight, length, and yolk color were all tested using various mechanical techniques. The eggs were also sampled for testing by consumer sensory panels that assessed the desirability of the eggs' color and flavor/texture. Eggs laid by hens molted by alfalfa had a significantly lower (p<0.05) "a*" level of colorimetry. Eggs laid by hens molted with alfalfa also exhibited significantly higher (p<0.05) egg weights and length. In the consumer sensory test, there was no significant difference (p>0.05) in color or flavor/texture scores in eggs from either feed deprived or alfalfa molted hens. The consumer sensory and mechanical quality attributes indicates that alfalfa shows promise as an alternative molt induction diet by providing a single diet option for extending egg production into a second egg laying cycle.