Egg yolk plasma can replace egg yolk in stallion freezing extenders.

Hen egg yolk is normally used as a cryoprotective agent in semen freezing extenders, but its use has sanitary and practical disadvantages. Moreover the protection afforded by egg yolk has not yet been completely elucidated. The objective of this study was to compare the egg yolk plasma fraction to whole egg yolk in stallion freezing extender. Plasma contains mainly Low Density Lipoproteins (LDL), which are widely presumed to be the cryoprotective agent in egg yolk. Plasma can be produced on an industrial scale, sterilised by gamma-irradiation and incorporated in a ready-to-use extender (our ultimate objective). Plasma samples were subjected to different doses of gamma-irradiation (3, 5, 10 kGy) without dramatic chemical changes that may affect their cryoprotective properties. Stallion semen was frozen with whole egg yolk as a control and with sterilised egg yolk plasma. A fertility trial was conducted on a total of 70 mares' cycles. Fertility per cycle was 60% after insemination of semen frozen in our control extender containing egg yolk (EY), compared to 69% for the extender containing sterilised egg yolk plasma (EYP) (P > 0.05). Post-thaw motility and membrane integrity of spermatozoa were also analysed. Motility parameters were not significantly different between extenders except for the variable VAP (for EY versus EYP, VAP: 63 µm.s(-1) versus 59 µm.s(-1), a, b: P < 0.001; PROG: 41% versus 39%, RAP30: 56% versus 54%; RAP40: 51% versus 48%, P > 0.05). Membrane integrity was better preserved in EY than in EYP but the difference between extenders was small (P < 0.05). Our results demonstrated that sterilised egg yolk plasma has the potential to replace egg yolk in stallion freezing extender. This experiment led to the development of a ready-to-use extender called INRA-Freeze(®) (IMV-Technologies, France).

Protein components of low-density lipoproteins purified from hen egg yolk.

To identify apoproteins present in purified low-density lipoproteins from hen egg yolk in relation with their emulsifying properties, they have been separated by SDS-PAGE. We identified two different proteins by liquid chromatography-tandem mass spectrometry analysis of the peptides obtained by the trypsin digestion of protein gel bands. Apovitellenin I was identified as a monomer and a dimer. Its amino acid sequence was totally confirmed, and molecular mass determination by liquid chromatography-mass spectrometry showed that it did not present post-translational modifications but only a slight heterogeneity by the loss of one or two amino acids at the C-terminal part of the protein. Apolipoprotein B was identified into seven bands corresponding to fragments resulting of a processing of the hen blood apo-B protein. The identity of the fragments was determined by the observation of the sequence coverage by trypsin peptides and the sequence alignment with homologous human blood apolipoprotein B-100.

Filler effects of oil droplets on the rheology of heat-set emulsion gels prepared with egg yolk and egg yolk fractions.

Hen egg yolk is a traditional ingredient used in a wide variety of food emulsions, especially fluid sauces. Industrial processing of these sauces generally involves heat treatments in order to pasteurise or sterilise them. These heat treatments may cause undesired gelation of the emulsion, because egg yolk proteins are particularly thermosensitive. Heat gelation of oil-in-water emulsions prepared with egg yolk may differ from that of egg yolk solutions, because of the influence of oil droplets on network formation. In this study, we investigated the influence of oil droplets on the gelation of oil-in-water emulsions made with yolk. We studied three pH values: 3.0, 5.0 and 7.0 with a constant NaCl concentration: 0.55 M. Oil droplet size was controlled after emulsification, gelation of solutions and emulsions was monitored in situ by coupling heating with recording viscoelastic properties, and transmission electron microscopy was conducted in heat-set emulsion gels. In an attempt to target the proteins that impose the kinetic of gelation of egg yolk, we repeated the experiment with plasma and granules, the main fractions of yolk. In situ rheology showed that, in our experimental conditions [especially oil volume fraction (0.3) and oil droplet size (d3.2=1 &mgr;m)], emulsions made with yolk and plasma have a similar gelation process with oil droplets acting as inactive fillers. Furthermore, transmission electron microscopy showed similar network characteristics between heated emulsions made with yolk and plasma. Moreover, we demonstrated that acidic conditions provided the fastest gelation of yolk solutions and emulsions. On the other hand, in emulsions prepared with granules, oil droplets behaved as active filler particles and reinforced the gel strength.

Changes in the concentrations of glucose, non-esterified fatty acids, urea, insulin, cortisol and some mineral elements in the plasma of the primiparous sow before, during and after induced parturition.

The concentrations of selected metabolites, minerals and hormones relative to parturition were studied in 12 primiparous sows. Blood sampling was performed on day -5, 0 and +5 relative to the farrowing day. On the day of parturition (d 0), samples were taken every hour from 07.00 to 24.00 hours. All sows had an indwelling catheter in the jugular vein, and the evolution of glucose, insulin, urea, non-esterified fatty acids (UEFA), calcium (Ca), phosphorus (P), magnesium (Mg) and cortisol were studied. The concentrations of NEFA, cortisol and P were significantly higher at d 0 than at d -5 or d +5, whereas the Mg level was lower. During the expulsion of foetuses, NEFA and cortisol levels increased (+18 and +30%, respectively), and they decreased immediately after the birth of the last piglet, to reach the initial levels observed before farrowing (around 700 microEq.L-1 and 110 ng.mL-1, respectively). Glucose and insulin levels remained unchanged during the expulsion of the piglets (105 ng.dL-1 and 5 microIU.mL-1, respectively), but they both increased immediately after the birth of the last animal. During the expulsion of the foetuses, the Ca concentration remained unchanged (93 mg.L-1), whereas the P level increased (+9%) and the Mg concentration decreased (-7.4%). These data suggested that parturition induces large variations in the concentrations of plasma metabolites that may affect its normal process.

Effect of the feeding level during rearing on performance of Large White gilts. Part 1: Growth, reproductive performance and feed intake during the first lactation.

Fifty pure-bred Large White gilts were allocated to two feeding levels from 28 kg until service. They were fed a standard growing diet (13.4 MJ digestible energy (DE) per kg; 18.1% crude protein, CP; 0.96% lysine) either to appetite (AP) or at 80% of the AP level (R). Growth rate was reduced by about 20% in R gilts, whereas feed conversion ratio was unaffected by rearing treatment. First oestrus was detected earlier in AP gilts (234 versus 247 d of age). At service, AP females had larger body weight (190 versus 150 kg) and thicker backfat (20.9 versus 13.4 mm). After service, the reproductive performances of 30 of these gilts were studied during the first reproductive cycle. All gilts received 2.6 kg/d of a standard diet (12.6 MJ DE/kg; 13.9% CP; 0.59% lysine) during pregnancy and were fed ad libitum a commercial lactation diet (13.1 MJ DE/kg; 17.1% CP; 0.90% lysine) from day five after farrowing. At farrowing, AP females were larger (257 versus 225 kg) and had more backfat (23.7 versus 17.4 mm) than R ones. Reproductive performance during the first lactation was not affected by rearing treatment, and weaning to oestrus interval was similar in both groups (4.8 d, on average). During lactation, R sows consumed significantly more feed (+650 g/d) and lost less backfat depth (1.5 versus 3.8 mm) than AP ones.

Effect of the feeding level during rearing on performance of Large White gilts. Part 2: Effect on metabolite profiles during gestation and lactation, and on glucose tolerance.

Eighteen primiparous Large White sows were selected on d 104 of gestation. Animals had either high (AP) or reduced (R) level of body fatness, as a result of different feeding levels during rearing. A jugular catheter was surgically implanted under general anaesthesia and regular blood sampling, glucose tolerance and meal tests were performed. Plasma concentrations of insulin, glucose, urea, non-esterified fatty acids (NEFA), phosphorus and calcium were determined by radio-immune assay or enzymatic assay. Plasma concentration of urea increased with the progress of lactation, whereas NEFA decreased. Results of glucose tolerance and test meals suggested that animals with greater body reserves at farrowing were less tolerant to glucose than the lean ones. In addition, the higher NEFA level observed in AP animals also suggested that the level of body fatness at farrowing might be involved in the regulation of feed intake during lactation and could partially explain the lower spontaneous feed intake observed in these animals.