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The inclusion of fibre-rich ingredients in diets is one possible strategy to enhance intestinal fermentation and positively impact gut ecology, barrier and immunity. Nowadays, inulin-type fructans are used as prebiotics in the feed of piglets to manipulate gut ecology for health purposes. Likewise, some by-products could be considered as sustainable and inexpensive ingredients to reduce gut disorders at weaning. In the present study, chicory root and pulp, citrus pulp, rye bran and soya hulls were tested in a three-stepin vitromodel of the piglet’s gastro-intestinal tract combining a pepsin-pancreatin hydrolysis (digestion), a dialysis step using cellulose membranes (absorption) and a colonic batch fermentation (fermentation). The fermentation kinetics, SCFA and microbiota profiles in the fermentation broth were assessed as indicators of prebiotic activity and compared with the ones of inulin. The immunomodulatory effects of fermentation supernatant (FS) were investigated in cultured intestinal porcine epithelial cells (IPEC-J2) by high-throughput quantitative PCR. Chicory root displayed a rapid and extensive fermentation and induced the second highest butyrate ratio after inulin. Citrus pulp demonstrated high acetate ratios and induced elevatedClostridiumclusters IV and XIVa levels. Chicory root and pulp FS promoted the intestinal barrier integrity with up-regulated tight and adherens junction gene expressions in comparison with inulin FS. Chicory pulp FS exerted anti-inflammatory effects in cultured IPEC-J2. The novel approach combining anin vitrofermentation model with IPEC-J2 cells highlighted that both chicory root and pulp appear to be promising ingredients and should be considered to promote intestinal health at weaning.

Background Dietary strategies such as the inclusion of prebiotics have been suggested for modulating intestinal microbiota. In piglets, this strategy could result in a reduction of post-weaning-associated disorders and the use of antibiotics. To date, mainly purified fractions have been tested for their prebiotic effects at weaning while trials of potential health-promoting effects of products and corresponding by-products remain rare. In this study, fructan- and pectin-based ingredients have been tested in a two-step in vitro model for their fermentation kinetics as well as for their short-chain fatty acid production and microbiota profiles in fermentation broth as indicators for their prebiotic activity. Results Chicory root, in contrast to chicory pulp, exhibited an extensive and rapid fermentation similar to inulin and oligofructose, although butyrate levels of root and pulp did not reach those of the purified fractions. Chicory pulp showed higher relative levels of Lactobacillus spp., Bifidobacterium spp., Clostridium cluster IV and butyryl-CoA:acetate-CoA transferase gene abundance compared to chicory root. Sugar beet pulp, orange and citrus by-products displayed extensive gas fermentation patterns, equivalent to those of purified pectin, and revealed an elevated butyrate production compared to purified pectin. Moreover, several orange and citrus by-products displayed significantly higher relative levels of Bifidobacterium spp. in comparison to purified pectin. Conclusions Chicory root and pulp as well as orange and citrus by-products appear to be promising ingredients for piglet diets for modulating intestinal fermentation for health purposes. © 2019 Society of Chemical Industry.

Prebiotics can modulate gut fermentation and improve intestinal barrier function in mammals. First, inulin fermentation profile was tested in a three-step in vitro model of the piglet’s gastro-intestinal tract combining a hydrolysis – dialysis step to a batch fermentation. Then, the differential effects of digested inulin (after the hydrolysis – dialysis steps) or fermented inulin (after the fermentation step) on the expression of gut barrier and immune-related genes of IPEC-J2 cells were investigated by high-throughput qPCR. Inulin was associated with elevated short-chain fatty acids and butyrate levels. Upregulated expressions of tight and adherens junction genes were observed in IPEC-J2 cells supplemented with inulin fermentation supernatant compared to control IPEC-J2 cells and digested inulin. Therefore, metabolites arising from the fermentation process, including butyrate, could be responsible for the reinforcement of the barrier function.

New Findings What is the central question of this study? Prenatal protein undernutrition by albumen removal in an avian model of fetal programming leads to long-term programming effects, but when do these effects first appear and are these programming effects regulated by the same candidate genes as in mammals? What is the main finding and its importance? The present results indicate that prenatal protein undernutrition by albumen removal induces phenotypical and hormonal changes in the early posthatch period, when the mismatch between the prenatal and postnatal environment first arises, but these changes are not accompanied by an altered gene expression of the selected candidate genes. Studies of the chicken offer a unique model for investigation of the direct effects of reduced prenatal protein availability by the partial replacement of albumen with saline in eggs at embryonic day 1 (albumen-deprived group). The results were compared with mock-treated sham chicks and non-treated control chicks. Although no differences in hatch weight were found, body weight and growth were reduced in the albumen-deprived chicks until 3 weeks of age. The feed intake of the albumen-deprived chicks, however, was increased compared with the control (day 13–21) and the sham chicks (day 16–18). In the albumen-deprived chicks, the ratio of thyroxine to 3,5,3′-triiodothyronine in the plasma was increased compared with the control chicks, whereas the plasma corticosterone level was increased only at day 7 compared with both other groups. The plasma glucose concentration and glucose tolerance were not affected by treatment. Several candidate genes previously associated with effects of prenatal protein deprivation in mammals were examined in the liver of newly hatched chicks. Gene expression of glycogen synthase 2, glycogen phosphorylase 1, peroxisome proliferator-activated receptor α and γ and glucocorticoid receptor was not affected by the treatment. In conclusion, reduction of prenatal protein availability led to differences in body weight and influenced hormones involved in metabolism and growth. Gene expression of the selected candidate genes was not altered, in contrast to mammals.

To examine the relationship of insulin and glucose, broiler embryos were subjected to acute or prolonged hypoglycemia during the late embryonic phase by, respectively, injecting once (at embryonic day [ED] 16 or 17) or on 3 consecutive days (ED 16, 17, and 18) with tolbutamide (80 μg/g embryo weight), a substance that stimulates insulin secretion from the pancreas. After 1 tolbutamide injection, a prolonged (32 h) decrease of plasma glucose and a profound acute increase in plasma insulin were observed. The 3 consecutive tolbutamide injections induced hypoglycemia for 4 days (from ED 16 to ED 19). The postnatal performance after 3 consecutive tolbutamide injections in broiler embryos was also investigated. Body weight was lower in tolbutamide-treated chickens from hatch to 42 d compared with sham (P = 0.001) and control (P0.001) chickens. Feed intake was lower in the tolbutamide group from hatch to 42 d as compared with sham (P = 0.007) and control (P = 0.017) animals. In addition, at 42 d, plasma glucose concentrations, after an insulin injection challenge (50 μg/kg body weight), were higher in tolbutamide-treated chickens compared with the sham and the control group as were their basal glucose levels (P value of group effect0.001). In conclusion, tolbutamide treatment during the late embryonic development in broilers resulted in prolonged hypoglycemia in this period and negatively influenced the posthatch performance.

Breeder age and nutrition are amongst the most important factors affecting progeny growth and development. The present experiment was carried out to evaluate the effects of n-3 fatty acid (FA), with special emphasis on the ratio of eicosapentaenoic (EPA, 20:5 n-3) and docosahexaenoic (DHA, 22:6 n-3) acid, provided to the diet of ageing broiler breeder hens at different ratios, on the incubation parameters and the performance of the offspring. Four hundred and eighty Ross-308 broiler breeder hens were fed one of four different diets (120/treatment), with an equal fat content. The control diet was a basal diet, rich in n-6 FAs (CON). Blends of fish oil were used to enrich the three other diets in n-3 FA and to obtain different EPA/DHA ratios of 1/1 (EPA=DHA), 1/2 (DHA) or 2/1 (EPA). Every 5 weeks, incubation parameters were assessed. Every 15 weeks, offspring was reared until slaughter age on a standard diet. Breeder age affected almost all incubation and post-hatch parameters, whereas n-3 FA treatment only lowered egg weight (p < 0.0001) and consequently hatched chick weight (p < 0.0001). Supplementation of EPA resulted in a higher proportional liver weight (p = 0.0219) at hatch, a lower body weight up to 28 days post-hatch (p = 0.0418), a lower daily weight gain (p = 0.0498) and a higher feed conversion ratio (p = 0.0395) during the starter period (p = 0.0498), resulting in a higher overall offspring feed conversion ratio (p = 0.0317) compared to the control diet. DHA supplementation, on the other hand, resulted in a lower residual yolk weight (p = 0.0220) and a higher overall offspring mortality (p = 0.0125). In conclusion, supplementation of n-3 FA could not counter the adverse effect of breeder flock age, but did not harm incubation or improve post-hatch performance, either. EPA and DHA affected offspring development differently during early post-hatch life.

Het doel van dit project is om een “meetlat” te ontwikkelen die de effecten van (voedings)interventies gericht op de verbetering van de immuuncompetentie van varkens, pluimvee en vleeskalveren kan vaststellen. Immuuncompetentie is binnen dit project gedefinieerd als het vermogen van dieren om effectieve responsen van het immuunsysteem te tonen op het moment dat de gezondheid van het dier onder druk wordt gezet. Een meetlat voor immuuncompetentie kan in de toekomst door de diervoedingssector gebruikt worden bij de ontwikkeling en evaluatie van nieuwe voerconcepten, ingrediënten en additieven gericht op de verbetering en ondersteuning van diergezondheid. Het is bekend dat de samenstelling van de voeding van jonge dieren invloed heeft op de functionele ontwikkeling van het maagdarmkanaal en op de samenstelling van de daarin aanwezige microbiota. De interacties tussen de microbiota en de weefsels van het darmkanaal (cross talk) hebben een belangrijke invloed op de ontwikkeling van immuuncompetentie. Daarom wordt in dit project gefocust op de effecten van (voedings)interventies op de microbiota, genexpressie veranderingen in darmweefsel, en morfologische en immunologische veranderen in de darm. De hier gepresenteerde meetlat voor immuuncompetentie is gebaseerd op de resultaten van onderzoek binnen het VDI programma van Feed4Foodure (projecten VDI-11; vleeskuikens, VDI-12; biggen, VDI- 13; gespeende biggen en kalveren) waarin m.b.v. model interventies de effecten van variatie in voersamenstelling op de microbiota samenstelling in het darmkanaal, de biologische responsen van darmweefsel en de zoötechnische dierprestaties zijn onderzocht. In de hier gepresenteerde meetlat worden gemeten effecten in deze studies aan elkaar gerelateerd en functioneel inzichtelijk gemaakt. Dit rapport beschrijft de ontwikkeling en totstandkoming van een eerste versie van de meetlat. Hierbij worden gemaakte keuzes, beperkingen en mogelijkheden van de meetlat bediscussieerd. Tenslotte wordt inzicht gegeven in de mogelijkheden tot verdere verfijningen en de toepasbaarheid van de meetlat.

Within the VDI-programme 8 microbiota datasets were generated, 5 for pigs and 3 for broilers. The aim of this research was to integrate these datasets in order to 1) identify (dis)similarities between samples of multiple pig and broiler microbiota datasets, and to 2) identify the composition of the core-microbiota of pigs and broilers (independent of intervention). The results of this integrated approach could be of relevance for the development of a ‘ruler’ for immune competence. From the results, we concluded that no clear separation was observed between the microbiota composition of pigs and broilers. Furthermore, some microbial phyla and classes were identified that were common in both pigs and broilers.

Depending on the bird species, about 33-86% of the egg content consists of albumen. In eggs from domestic fowl, albumen contains about 10.5% protein and 88.5% of water and may be regarded as the ma...

When added to the feed of broiler breeder hens, dietary polyunsaturated fatty acids (FA) can be incorporated into the yolk and therefore become available to the progeny during their early development. The mechanism involved in lipid metabolism and deposition in the egg may be influenced by breeder age. Before the effect of an elevated concentration of certain polyunsaturated FA on the embryo can be investigated, the effect at breeder level and egg quality must be further assessed. The aim of the present experiment was to evaluate the effects of dietary n-6/n-3 ratios and dietary eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3) ratios, provided to broiler breeder hens, in terms of their zoo technical performance, egg quality, and yolk FA composition. Starting at 6 wk of age, 640 Ross-308 broiler breeder hens were fed 1 of 4 different diets. The control diet was a basal diet, rich in n-6 FA. The 3 other diets were enriched in n-3 FA, formulated to obtain a different EPA/DHA ratio of 1/1 (EPA = DHA), 1/2 (DHA), or 2/1 (EPA). In fact, after analysis the EPA/DHA ratio was 0.8, 0.4, or 2.1, respectively. Dietary EPA and DHA addition did not affect the performance of the breeder hens, except for egg weight. Egg weight was lower (P < 0.001) for all n-3 treatments. Dietary EPA improved number of eggs laid in the first 2 wk of the production cycle (P = 0.029). The absolute and relative yolk weight of eggs laid by EPA = DHA fed hens was lowest (P = 0.004 and P = 0.025, respectively). The EPA and DHA concentrations in the yolk were highly dependent on dietary EPA and DHA concentrations with a regression coefficient equal to 0.89. It can be concluded that dietary EPA and DHA can be incorporated in the breeder egg yolk to become available for the developing embryo, without compromising the performance and egg quality of the flock.

It is not rare that newly hatched chicks remain without feed for about 24 to 48 h before they are placed on farms due to a series of logistic operations. Furthermore, the spread in hatching time can also mount up to 30 to 48 h for late v. early hatchers. In other words, the practice is a complex combination of spread of hatch and delayed feed access. The present study was aimed to investigate the combined effects of hatching time with a delay in feed access of 48 h, starting from their hatch-time (biological age). When chicks had access to feed immediately after hatch, late hatchers had a higher feed intake and relative growth rate up to day 5 compared with their early hatched counterparts. Feed deprivation during the first 48 h resulted in retarded early growth rate, which was further aggravated by an impaired feed intake after refeeding. In addition, the differential effects of hatching time on relative growth rate and feed intake observed in immediately fed chicks were eliminated by the 48 h feed delay. The yolk utilization after hatch was faster for the late hatchers up to biological day 2 regardless of the feeding treatments. Hatching muscle glycogen content was higher in the late hatchers compared with that of their early counterparts at hatch and at biological day 2 independent of feeding treatment. Moreover, the liver glycogen content of the late hatchers was also higher at hatch. For the immediately fed chicks, the proportional breast muscle weight of the late hatchers was higher at biological day 2 and 5. For the starved chicks, on the other hand, this effect was only observed after they had access to feed (biological day 5). The different plasma T3 levels at hatch may have contributed to the different post hatch performance. It is concluded that the spread of hatch influenced post hatch performance, especially appetite and growth at least until day 5. Moreover, the delay in feed access interacted with the hatching time and caused adverse effects on the post hatch performance.

To examine the importance of albumen as a protein source during embryonic development on the posthatch performance of laying hens, 3 mL of the albumen was removed. At hatch, no difference in BW could be observed. Chicks from the albumen-deprived group had a lower residual yolk weight due to higher yolk utilization. During the rearing phase (hatch to 17 wk of age), the BW of the albumen-deprived pullets was lower compared with the control and sham pullets. The feed intake of the albumen-deprived pullets was also lower than the control pullets. However, during the laying phase (18 to 55 wk of age) these hens exceeded the control and sham hens in BW, although this was not accompanied by a higher feed intake. The albumen-deprived hens exhibited a lower egg production capacity as demonstrated by the reduced egg weight, laying rate, and egg mass and increased number of second grade eggs. In addition, the eggs laid by the albumen-deprived hens had a higher proportional yolk and lower proportional albumen weight. In conclusion, prenatal protein deprivation by albumen removal caused a long-lasting programming effect, possibly by differences in energy allocation, in favor of growth and maintenance and impairing reproductive performance.

Previously, long-term effects on body weight and reproductive performance have been demonstrated in the chicken model of prenatal protein undernutrition by albumen removal. Introduction of such persistent alterations in phenotype suggests stable changes in gene expression. Therefore, a genome-wide screening of the hepatic transcriptome by RNA-Seq was performed in adult hens. The albumen-deprived hens were created by partial removal of the albumen from eggs and replacement with saline early during embryonic development. Results were compared to sham-manipulated hens and non-manipulated hens. Grouping of the differentially expressed (DE) genes according to biological functions revealed the involvement of processes such as 'embryonic and organismal development' and 'reproductive system development and function'. Molecular pathways that were altered were 'amino acid metabolism', 'carbohydrate metabolism' and 'protein synthesis'. Three key central genes interacting with many DE genes were identified: UBC, NR3C1, and ELAVL1. The DNA methylation of 9 DE genes and 3 key central genes was examined by MeDIP-qPCR. The DNA methylation of a fragment (UBC_3) of the UBC gene was increased in the albumen-deprived hens compared to the non-manipulated hens. In conclusion, these results demonstrated that prenatal protein undernutrition by albumen removal leads to long-term alterations of the hepatic transcriptome in the chicken. Funding agencies: Fund for Scientific Research Flanders (FWO-Vlaanderen) (FWO) [G.0566.08]; European Research Council

What is the central question of this study? Prenatal protein undernutrition by albumen removal in an avian model of fetal programming leads to long-term programming effects, but when do these effects first appear and are these programming effects regulated by the same candidate genes as in mammals? What is the main finding and its importance? The present results indicate that prenatal protein undernutrition by albumen removal induces phenotypical and hormonal changes in the early posthatch period, when the mismatch between the prenatal and postnatal environment first arises, but these changes are not accompanied by an altered gene expression of the selected candidate genes. Studies of the chicken offer a unique model for investigation of the direct effects of reduced prenatal protein availability by the partial replacement of albumen with saline in eggs at embryonic day 1 (albumen-deprived group). The results were compared with mock-treated sham chicks and non-treated control chicks. Although no differences in hatch weight were found, body weight and growth were reduced in the albumen-deprived chicks until 3 weeks of age. The feed intake of the albumen-deprived chicks, however, was increased compared with the control (day 13-21) and the sham chicks (day 16-18). In the albumen-deprived chicks, the ratio of thyroxine to 3,5,3'-triiodothyronine in the plasma was increased compared with the control chicks, whereas the plasma corticosterone level was increased only at day 7 compared with both other groups. The plasma glucose concentration and glucose tolerance were not affected by treatment. Several candidate genes previously associated with effects of prenatal protein deprivation in mammals were examined in the liver of newly hatched chicks. Gene expression of glycogen synthase 2, glycogen phosphorylase 1, peroxisome proliferator-activated receptor α and γ and glucocorticoid receptor was not affected by the treatment. In conclusion, reduction of prenatal protein availability led to differences in body weight and influenced hormones involved in metabolism and growth. Gene expression of the selected candidate genes was not altered, in contrast to mammals.

In mammalian models of prenatal undernutrition the maternal diet is manipulated, exerting both nutritional and hormonal effects on the offspring. In contrast, in the chicken, strictly nutritional effects can be applied. Prenatal protein undernutrition in chickens was induced by partial replacement of albumen with saline during early embryonic development (albumen-deprived group) and results were compared with a sham-manipulated and a non-manipulated group. Body weight of the albumen-deprived hens was reduced throughout the entire experimental period (0-55 weeks). The reproductive capacity was diminished in the albumen-deprived hens as reflected in the reduced number of eggs and lower egg weight. The plasma triiodothyronine levels were increased in the albumen-deprived group compared with the non-manipulated hens, but not the sham-manipulated hens. An oral glucose tolerance test (OGTT) at 10 weeks of age revealed a decreased glucose tolerance in the albumen-deprived hens. During adulthood, an age-related loss of glucose tolerance was observed in the hens, leading to disappearance of treatment differences in the OGTT. The offspring of the albumen-deprived hens (PA chicks) had reduced body weight until at least 3 weeks of age. In addition, the PA chicks had a decreased relative residual yolk weight at hatching. An insulin tolerance test revealed increased sensitivity to insulin for the PA chicks compared with the offspring of the non-manipulated (PN) and sham-manipulated hens (PS). In conclusion, prenatal protein undernutrition by albumen removal caused long-term effects on body weight, reproductive performance, and physiology. ispartof: Journal of Endocrinology vol:225 issue:2 pages:89-100 ispartof: location:England status: published

The aim of the present study was to evaluate the transfer of maternal dietary fatty acids (FA) from the yolk to the developing offspring, with special emphasis on n-3 FA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Six hundred forty Ross 308 breeders were housed from 6 to 58 wk of age in 16 pens resulting in 4 replicates per dietary treatment. They were fed 1 of 4 diets: a basal diet, rich in n-6 FA (CON), or an n-3 FA enriched diet formulated to obtain an EPA/DHA ratio of 1/1 (EPA = DHA), 1/2 (DHA), or 2/1 (EPA). At 28, 43, and 58 wk of age, 20 eggs per treatment were collected and analyzed for FA composition. At these same breeder ages, 600 fertilized eggs per treatment were incubated. At hatch the residual yolks of 25 chicks per treatment were collected and analyzed for FA composition. At every hatch, 180 chicks per treatment were raised under standard conditions and livers were sampled at d 1, 14, 28, and 38 d for FA analysis. Concentrations of EPA in the yolk and residual yolk of eggs laid by EPA-fed breeders were highest, next-to-highest for EPA = DHA-fed breeders, next-to-lowest for DHA-fed breeders, and lowest in those laid by control hens, reflecting the inclusion levels in the maternal diets. Yolk and residual yolk DHA concentrations, however, were not only elevated due to DHA supplementation, compared with the control diet, but also due to EPA supplementation. Offspring hepatic EPA concentrations were elevated until d 28 in all n-3 enriched groups, whereas hepatic DHA concentrations were only affected by EPA = DHA and DHA supplementation at d 1. No differences were found in hepatic DHA concentrations at later offspring ages. Considering the role of EPA and DHA in early development and growth, the maternal supply of these n-3 FA might improve offspring health and performance.

Chickens have blood glucose concentrations that are twofold higher than those observed in mammals. Moreover, the insulin sensitivity seems to decrease with postnatal age in both broiler and layer chickens. However, little is known about the response of insulin on plasma glucose concentrations and mRNA abundance of hepatic glucose transporters 1, 2, 3, 8, 9 and 12 (GLUT1, 2, 3, 8, 9 and 12) and three regulatory enzymes of the gluconeogenesis, phosphoenolpyruvate carboxykinase 1 and 2 (PCK1 and 2) or fructose-1,6-biphosphatase 1 (FBP1) in chicks during the perinatal period. In the present study, broiler embryos on embryonic day (ED)16, ED18 or newly-hatched broiler chicks were injected intravenously with bovine insulin (1μg/g body weight (BW)) to examine plasma glucose response and changes in hepatic mRNA abundance of the GLUTs, PCK1 and 2 and FBP1. Results were compared with a non-treated control group and a saline-injected sham group. Plasma glucose levels of insulin-treated ED18 embryos recovered faster from their minimum level than those of insulin-treated ED16 embryos or newly-hatched chicks. In addition, at the minimum plasma glucose level seven hours post-injection (PI), hepatic GLUT2, FBP1 and PCK2 mRNA abundance was decreased in insulin-injected embryos, compared to sham and control groups, being most pronounced when insulin injection occurred on ED16.

Different animal models have been used to study the effects of prenatal protein undernutrition and the mechanisms by which these occur. In mammals, the maternal diet is manipulated, exerting both direct nutritional and indirect hormonal effects. Chicken embryos develop independent from the hen in the egg. Therefore, in the chicken, the direct effects of protein deficiency by albumen removal early during incubation can be examined. Prenatal protein undernutrition was established in layer-type eggs by the partial replacement of albumen by saline at embryonic day 1 (albumen-deprived group), compared to a mock-treated sham and a non-treated control group. At hatch, survival of the albumen-deprived group was lower compared to the control and sham group due to increased early mortality by the manipulation. No treatment differences in yolk-free body weight or yolk weight could be detected. The water content of the yolk was reduced, whereas the water content of the carcass was increased in the albumen-deprived group, compared to the control group, indicating less uptake of nutrients from the yolk. At embryonic day 16, 20 and at hatch, plasma triiodothyronine (T3), corticosterone, lactate or glucose concentrations and hepatic glycogen content were not affected by treatment. At embryonic day 20, the plasma thyroxine (T4) concentrations of the albumen-deprived embryos was reduced compared to the control group, indicating a decreased metabolic rate. Screening for differential protein expression in the liver at hatch using two-dimensional difference gel electrophoresis revealed not only changed abundance of proteins important for amino acid metabolism, but also of enzymes related to energy and glucose metabolism. Interestingly, GLUT1, a glucose transporter, and PCK2 and FBP1, two out of three regulatory enzymes of the gluconeogenesis were dysregulated. No parallel differences in gene expressions causing the differences in protein abundance could be detected pointing to post-transcriptional or post-translational regulation of the observed differences. ispartof: PLoS One vol:9 issue:4 pages:1-12 ispartof: location:United States status: published

In contrast to most mammals, chickens have blood glucose concentrations that are twice as high as these in mammals. In addition, they develop a resistance to insulin early in life (Mc Cormick et al., 1978; Seki et al., 2001) So far, the response of insulin to elevated glucose levels in embryonic and neonatal chicks is not well documented and the aim is to explore the glucose metabolism by the injection of insulin in the embryonic and neonatal chick.

Intermittent high (+3°C) and low (-3°C) temperature treatments for 4 h on embryonic day (E) 16, E17, and E18 showed differential effects on embryonic metabolism, without influencing embryonic growth or hatchability. Embryos in the high-temperature group shifted to a more anaerobic metabolism, as indicated by a lower partial pressure of O(2) and a higher partial pressure of CO(2) in the air cell, lower blood pH, and higher lactic acid production. Three hours after the end of the high-temperature treatment, a decrease in metabolism was observed, as indicated by the lower partial pressure of CO(2) and higher partial pressure of O(2) in the air cell and increased plasma triglyceride levels. The embryos in the low-temperature group responded by temporarily slowing down their metabolism, especially the metabolism of carbohydrates and lipids, as indicated by altered air cell gases, a higher relative yolk weight, higher plasma triglyceride level, and higher liver glycogen level. Three hours after the end of the temperature treatment, the metabolism of embryos in the low-temperature treatment had increased to the level of the control temperature group. However, for both temperature treatments, during the hatching process, all the shortages and excesses created were restored to control levels, which would explain the lack of change in embryo growth and hatchability and the slight delay in the hatching process. These mild consequences of the intermittent temperature treatment indicate that the different metabolic shifts made by the embryos seem to be efficient in overcoming the challenges of the intermittent high- or low-temperature treatment during late incubation.

During avian embryonic development, the carbon dioxide tension inside the egg increases as the shell restricts gas exchange with the environment. Acid-base regulation of the avian embryo is a complex process, not only due to the non-function of the lungs and limited functionality of the kidneys but also because the embryo is affected by the inflow of bicarbonates from the shell, when calcium is reabsorbed for calcification. Moreover, interaction occurs between the embryo and the extraembryonic compartments. It has been shown that carbonic anhydrase plays a crucial role in the formation of sub-embryonic fluid and in the chorioallantoic membrane and kidney. This review provides a detailed overview of the acid-base status of the extraembryonic compartments inside chicken eggs, and their interaction in keeping the acid-base status of the embryo balanced. Secondly, experimental acid-base disturbances are summarized. The last part of the review briefly compares embryos of birds and other amniotes (mammals and reptiles) with regard to acid-base regulation.