Post-hatching Day Research Articles

Prenatal thermal stress affects acute-phase proteins, heat shock protein 70, and circulating corticosterone in developing broiler embryos and neonates

Higher or lower incubation temperature may impose some degree of stress on developing poultry embryos. This study was designed to delineate the effects of prenatal thermal stress on serum levels of acute-phase proteins (APPs), namely ceruloplasmin (CPN) and alpha-1-acid glycoprotein (AGP), the regulation of brain mRNA levels of heat shock protein (Hsp) 70, and serum levels of corticosterone (CORT) in embryos and neonatal chicks. Hatching eggs were subjected to three thermal treatments; (i) standard optimum temperature throughout (SS: 37.8 °C and 56 % RH), (ii) heat stress for 12 h daily (HS: 40.0 °C and 56 % RH), and (iii) cold stress for 12 h daily 18 (CS: 30.2 °C and 56 % RH). The heat and cold stress treatments were imposed from the 10th to the 18th day of incubation (ED). Results showed that thermal stress had a negligible effect on hatchability rate and body temperatures of neonatal chicks. The CS treatment was detrimental to embryonic growth. The HS treatment elevated AGP (ED 16, ED 18, and post-hatch day 1), CPN (on post-hatch day 1), and CORT (ED 14). On the contrary, the CS embryos had reduced AGP (ED14, ED16, ED18, and post-hatch day 1), CPN (ED 16), and CORT (ED 14, ED 16, ED 18). The brain mRNA levels of Hsp70 were upregulated throughout the experimental period in both the HS and CS embryos and chicks. Based on these modifications, AGP, together with Hsp70 mRNA expression, could be considered effective biomarkers useful to evaluate the magnitude and the time response of embryos and neonatal chicks to prenatal thermal stress. It is concluded that developing chicken embryos have the ability to evoke APPs, Hsp70 and CORT reactions which are important to cope with thermal stress.

Effect of thermal manipulation during embryogenesis on gene expression of myogenic regulatory factors pre and post hatch in broilers

A total of 1,440 fertile eggs were divided randomly and equally into 5 treatment groups; control (no TM) and 4 treatment groups: TM1, TM2, TM3, and TM4 that were thermally subjected to 39°C for 18 h with 65% relative humidity daily, during embryonic days ED 7–11, ED 11–15, ED 15–18 and ED 7–18, respectively. Out of TM conditions that were investigated, TM1 resulted in a significant improvement in expression of myogenic factor-5 (Myf5), myoblast determination protein (MyoD) and myogenin (MyoG) in pre and post hatch broiler muscle when compared to the control. This study aimed to determine the optimum time for thermal manipulation during embryogenesis that may result in improvement in expression of myogenic regulatory factors (MRFs): Myf5, MyoD, MyoG and myostatin (MSTN) in broiler muscle. Thus, the results of this research may provide a means of improvement of myogenesis of pectoral and thigh muscles of broilers proceeding from early embryogenesis (ED7) through post-hatch day.

Pre-hatch and post-hatch development of the bursa of Fabricius in broiler chicken: a morphological study.

The developmental morphology of the bursa of Fabricius (BF) of broiler chicken was evaluated in this study using gross anatomical, histological, reticulin histo-chemical, and transmission electron microscopic techniques. The result showed that the short plica of the BF at embryonic day (ED) 14 was a mesenchymal tissue that contained cells, including mesenchymal cells and lymphoblasts. The organo-somatic index (OSI) of the BF peaked at ED 17, while the BF of ED 19 showed well delineated follicle-associated and inter-follicular epithelial (IFE) cells. Whereas, the IFE contained apical vacuoles which increased in size with age, the BF contained lymphoid follicles which were first observed at ED 17, and increased steadily in mean diameter from ED 19 to post-hatch day (PD) 28. The framework of the inter-follicular areas and the follicular capsules were composed of collagen type III fibres. Moreover, the cortico-medullary basement membranes were well established with peripheral and cortico-medullary basement capillaries becoming very consistent between PDs 5 and 7. The lymphoid follicle contained lymphocytes with mitotic figures, and plasma cells which showed extensive network of rough endoplasmic reticulum at PD 21, while macrophages contained increasing evidence of phagocytosis from PDs 35 to 56. In conclusion, the morphological features of the BF of broiler chicken in this study reveals that the key function of B-cell maturation within the BF may occur between the first 3 to 4 weeks after hatching, and thereafter, may primarily produce immunoglobulins until involution occurs.

A diagnosis model of parental care: How parents optimize their provisioning strategy in brood reduction?

Altricial birds often display biased preferences in providing parental care for their dependent offspring, especially during food shortages. During this process, such inflexible rules may result in provisioning errors. To demonstrate how parents optimize their provisioning strategies, we proposed a "diagnosis model" of parental care to posit that parents will undergo a diagnosis procedure to test whether selecting against some particular offspring based on phenotype is an optimal strategy. We tested this model in an asynchronous hatching bird, the Azure-winged Magpie Cyanopica cyanus, based on 10 years of data about demography and parental provisioning behaviors. Given their higher daily survival rates, core offspring (those hatched on the first day) merits an investment priority compared with their marginal brood mates (those hatched on later days). However, a marginal offspring also merited a priority if it displayed greater weight gain than the expected value at the early post-hatching days. Parents could detect such a marginal offspring via a diagnosis strategy, in which they provisioned the brood at the diagnosis stage by delivering food to every nestling that begged, then biased food toward high-value nestlings at the subsequent decision stage by making a negative response to the begging of low-value nestlings. In this provisioning strategy, the growth performance of a nestling became a more reliable indicator of its investment value than its hatching order or competitive ability. Our findings provide evidence for this "diagnosis model of parental care" wherein parents use a diagnosis method to optimize their provisioning strategy in brood reduction.

The Effect of Commercial Genetic Selection on Somatotropic Gene Expression in Broilers: A Potential Role for Insulin-Like Growth Factor Binding Proteins in Regulating Broiler Growth and Body Composition.

The somatotropic axis influences growth and metabolism, and many of its effects are a result of insulin-like growth factor (IGF) signaling modulated by IGF-binding proteins (IGFBPs). Modern commercial meat-type (broiler) chickens exhibit rapid and efficient growth and muscle accretion resulting from decades of commercial genetic selection, and it is not known how alterations in the IGF system has contributed to these improvements. To determine the effect of commercial genetic selection on somatotropic axis activity, two experiments were conducted comparing legacy Athens Canadian Random Bred and modern Ross 308 male broiler lines, one between embryonic days 10 and 18 and the second between post-hatch days 10 and 40. Gene expression was evaluated in liver and breast muscle (pectoralis major) and circulating hormone concentrations were measured post-hatch. During embryogenesis, no differences in IGF expression were found that corresponded with difference in body weight between the lines beginning on embryonic day 14. While hepatic IGF expression and circulating IGF did not differ between the lines post-hatch, expression of both IGF1 and IGF2 mRNA was greater in breast muscle of modern broilers. Differential expression of select IGFBPs suggests their action is dependent on developmental stage and site of production. Hepatic IGFBP1 appears to promote embryonic growth but inhibit post-hatch growth at select ages. Results suggest that local IGFBP4 may prevent breast muscle growth during embryogenesis but promote it after hatch. Post-hatch, IGFBP2 produced in liver appears to inhibit body growth, but IGFBP2 produced locally in breast muscle facilitates development of this tissue. The opposite appears true for IGFBP3, which seems to promote overall body growth when produced in liver and restrict breast muscle growth when produced locally. Results presented here suggest that paracrine IGF signaling in breast muscle may contribute to overall growth and muscle accretion in chickens, and that this activity is regulated in developmentally distinct and tissue-specific contexts through combinatorial action of IGFBPs.

Evidence for the Existence of Two Prolactin Isoforms in the Developing Pituitary Gland of the Goose (Anser cygnoides)

Compared to Galliformes such as chicken and turkey, very little is known about the existence and expression of isoforms of prolactin (PRL) in the pituitary glands of Anseriformes. In this study, by generating a rabbit-anti-goose (Anser cygnoides) PRL polyclonal antibody, we analysed the expression patterns of goose PRL isoforms in the embryonic and post-hatch development of the pituitary gland. Our results showed that two immunoreactive bands with molecular weights of about 23 and 26 kDa were detected using the Western blot technique, corresponding to the non-glycosylated (NG-) and the glycosylated (G-) isoform of PRL, respectively. The protein levels of the total PRL in a goose increased gradually from the embryonic day (ED) 22 to the post-hatch day (PD) 28, with a non-significant decrease on PD6. Furthermore, the percentage of G-PRL in the pituitary gland of the goose fluctuated from about 30.3% to 54.7% throughout the embryonic and post-hatch development. At the mRNA level, the expression of PRL increased steadily during the development and reached the highest levels on PD12, but later showed a non-significant decrease on PD28. The inconsistent expression patterns between the PRL mRNA and protein during the stages from PD6 to PD28 indicated that the PRL gene expression involves both transcriptional and post-translational regulation. Taken together, our data unequivocally demonstrated the existence of NG- and G-PRL in the pituitary gland of a goose and that the expression of the total PRL as well as the percentage of G-PRL significantly changed during embryonic and post-hatch development, indicating that the versatile biological functions of PRL during the ontogenesis of a goose could be closely related to changes in both its total expression and the degree of glycosylation in the pituitary gland.

Evaluation of Auditory Brainstem Response in Chicken Hatchlings.

The auditory brainstem response (ABR) is an invaluable assay in clinical audiology, non-human animals, and human research. Despite the widespread use of ABRs in measuring auditory neural synchrony and estimating hearing sensitivity in other vertebrate model systems, methods for recording ABRs in the chicken have not been reported in nearly four decades. Chickens provide a robust animal research model because their auditory system is near functional maturation during late embryonic and early hatchling stages. We have demonstrated methods used to elicit one or two-channel ABR recordings using subdermal needle electrode arrays in chicken hatchlings. Regardless of electrode recording configuration (i.e., montage), ABR recordings included 3-4 positive-going peak waveforms within the first 6 ms of a suprathreshold click stimulus. Peak-to-trough waveform amplitudes ranged from 2-11 µV at high-intensity levels, with positive peaks exhibiting expected latency-intensity functions (i.e., increase in latency as a function of decreased intensity). Standardized earphone position was critical for optimal recordings as loose skin can occlude the ear canal, and animal movement can dislodge the stimulus transducer. Peak amplitudes were smaller, and latencies were longer as animal body temperature lowered, supporting the need for maintaining physiological body temperature. For young hatchlings (<3 h post-hatch day 1), thresholds were elevated by ~5 dB, peak latencies increased ~1-2 ms, and peak to trough amplitudes were decreased ~1 µV compared to older hatchlings. This suggests a potential conductive-related issue (i.e., fluid in the middle ear cavity) and should be considered for young hatchlings. Overall, the ABR methods outlined here permit accurate and reproducible recording of in-vivo auditory function in chicken hatchlings that could be applied to different stages of development. Such findings are easily compared to human and mammalian models of hearing loss, aging, or other auditory-related manipulations.

Evaluation of Auditory Brainstem Response in Chicken Hatchlings

The auditory brainstem response (ABR) is an invaluable assay in clinical audiology, non-human animals, and human research. Despite the widespread use of ABRs in measuring auditory neural synchrony and estimating hearing sensitivity in other vertebrate model systems, methods for recording ABRs in the chicken have not been reported in nearly four decades. Chickens provide a robust animal research model because their auditory system is near functional maturation during late embryonic and early hatchling stages. We have demonstrated methods used to elicit one or two-channel ABR recordings using subdermal needle electrode arrays in chicken hatchlings. Regardless of electrode recording configuration (i.e., montage), ABR recordings included 3-4 positive-going peak waveforms within the first 6 ms of a suprathreshold click stimulus. Peak-to-trough waveform amplitudes ranged from 2-11 µV at high-intensity levels, with positive peaks exhibiting expected latency-intensity functions (i.e., increase in latency as a function of decreased intensity). Standardized earphone position was critical for optimal recordings as loose skin can occlude the ear canal, and animal movement can dislodge the stimulus transducer. Peak amplitudes were smaller, and latencies were longer as animal body temperature lowered, supporting the need for maintaining physiological body temperature. For young hatchlings (<3 h post-hatch day 1), thresholds were elevated by ~5 dB, peak latencies increased ~1-2 ms, and peak to trough amplitudes were decreased ~1 µV compared to older hatchlings. This suggests a potential conductive-related issue (i.e., fluid in the middle ear cavity) and should be considered for young hatchlings. Overall, the ABR methods outlined here permit accurate and reproducible recording of in-vivo auditory function in chicken hatchlings that could be applied to different stages of development. Such findings are easily compared to human and mammalian models of hearing loss, aging, or other auditory-related manipulations.

Imprintability of Newly Hatched Domestic Chicks on an Artificial Object: A Novel High Time-Resolution Apparatus Based on a Running Disc.

In filial imprinting, newly hatched chicks repeatedly approach a conspicuous object nearby and memorize it, even though it is an artificial object instead of their mother hen. Imprinting on an artificial object in a laboratory setting has a clear sensitive period from post hatch days 1–3 in the case of domestic chicks. However, the establishment of imprintability are difficult to investigate because of the limitations of the behavioral apparatus. In this study, we developed a novel behavioral apparatus, based on a running disc, to investigate the learning processes of imprinting in newly hatched domestic chicks. In the apparatus, the chick repeatedly approaches the imprinting object on the disc. The apparatus sends a transistor-transistor-logic signal every 1/10 turn of the disc to a personal computer through a data acquisition system following the chick’s approach to the imprinting object on the monitor. The imprinting training and tests were designed to define the three learning processes in imprinting. The first process is the one in which chicks spontaneously approach the moving object. The second is an acquired process in which chicks approach an object even when it is static. In the third process, chicks discriminate between the differently colored imprinting object and the control object in the preference test. Using the apparatus, the difference in the chicks’ behavior during or after the sensitive period was examined. During the sensitive period, the chicks at post hatch hour 12 and 18 developed the first imprinting training process. The chicks at post hatch hour 24 maintained learning until the second process. The chicks at post hatch hour 30 reached the discrimination process in the test. After the sensitive period, the chicks reared in darkness until post hatch day 4 exhibited poor first learning process in the training. Thus, this apparatus will be useful for the detection of behavioral changes during neuronal development and learning processes.

Inhibition of miR-128 Enhances Vocal Sequence Organization in Juvenile Songbirds.

The molecular mechanisms underlying learned vocal communication are not well characterized. This is a major barrier for developing treatments for conditions affecting social communication, such as autism spectrum disorder (ASD). Our group previously generated an activity-dependent gene expression network in the striatopallidal song control nucleus, Area X, in adult zebra finches to identify master regulators of learned vocal behavior. This dataset revealed that the two host genes for microRNA-128, ARPP21 and R3HDM1, are among the top genes whose expression correlates to how much birds sing. Here we examined whether miR-128 itself is behaviorally regulated in Area X and found that its levels decline with singing. We hypothesized that reducing miR-128 during the critical period for vocal plasticity would enhance vocal learning. To test this, we bilaterally injected an antisense miR-128 construct (AS miR-128) or a control scrambled sequence into Area X at post-hatch day 30 (30 d) using sibling-matched experimental and control pupils. The juveniles were then returned to their home cage and raised with their tutors. Strikingly, inhibition of miR-128 in young birds enhanced the organization of learned vocal sequences. Tutor and pupil stereotypy scores were positively correlated, though the correlation was stronger between tutors and control pupils compared to tutors and AS miR-128 pupils. This difference was driven by AS miR-128 pupils achieving higher stereotypy scores despite their tutors’ lower syntax scores. AS miR-128 birds with tutors on the higher end of the stereotypy spectrum were more likely to produce songs with faster tempos relative to sibling controls. Our results suggest that low levels of miR-128 facilitate vocal sequence stereotypy. By analogy, reducing miR-128 could enhance the capacity to learn to speak in patients with non-verbal ASD. To our knowledge, this study is the first to directly link miR-128 to learned vocal communication and provides support for miR-128 as a potential therapeutic target for ASD.

Molecular Investigations of the Effect of Thermal Manipulation During Embryogenesis on the Enzymatic Activity of Creatine Kinase and Lactate Dehydrogenase in Broiler Muscle

Incubating temperature and timing or duration is critical to determine the optimum protocol of thermal manipulation (TM), which underlines muscle growth improvement. Therefore, the aim of the present study is to determine the optimum period of embryonic TM that may result in the improvement of pectoral and thigh muscle myogenesis. This is done by investigating the level of mRNA expression of creatine kinase (CK) and lactate dehydrogenase (LDH). An additional goal is measuring the blood levels of CK and LDH as a biomarker of muscle injury due to the experimental thermal challenge on post-hatch day 35. The study was conducted on 1,440 fertile eggs (Ross broilers) that were divided randomly and equally into a control group and four treatment groups (TM1, TM2, TM3, and TM4). The treatment groups were daily subjected to TM at 39 ºC for 18h with 65% relative humidity (RH) during embryonic days (EDs) 7-11, 11-15, 15-18, and 7-18, respectively. Among the thermally manipulated groups that were investigated, TM1 (ED 7-11) resulted in significant improvement of mRNA expression and enzymatic concentration of CK and LDH in muscle during embryogenesis, as compared to the control. Six hours of TC showed the highest significant CK and LDH expression and concentration levels in the control as compared to TM groups. Thus, the results of this study indicate that TM during ED 7-11 improves pectoral and thigh muscles’ response to heat stress without adversely affecting their performance. This finding could be used by commercial breeders to enhance local broiler production.

Light and transmission electron microscopic evaluation of the lamina epithelialis mucosae in the ileum of pre- and post-hatch broiler chicken.

Morphological development of the lamina epithelialis mucosae (LEM) of the ileum of broiler chicken was evaluated using light and transmission electron microscopic techniques. Ileal sections were collected on embryonic days (ED) 14, 17 and 19, as well as post-hatch days (PD) 1, 3, 5, 7, 14, 21, 28, 35, 42 and 56. The result showed that the ileal LEM, which were poorly defined at embryonic days 14 and 17, consisted of enterocytes and some atypically shaped goblet cells. Apico-lateral tight junctions and irregularly shaped microvilli were associated with the enterocytes at ED 14 and 17. The enterocyte microvilli were more uniform in shape and distribution at ED 19. The embryonic goblet cells were varied in shape and possessed basally displaced, star-shaped nuclei and small apical cytoplasmic vacuoles. During the post-hatch ages, the LEM was a typical epithelium with a single layer of columnar-shaped enterocytes that became highly elongated at post-hatch day (PD) 7. The goblet cells were characteristically 'wine-glass' shaped. Follicle-associated epithelium (FAE) showing numerous lymphocytes among the enterocytes occurred in the post-hatch LEM. The intra-epithelial lymphocytes (IEL) were first encountered at PD 1, but increased several folds within the first two weeks post-hatch. Entero-endocrine cells were observed in the epithelium from PD 21. Finally, from this study, it is obvious that enterocytes and small atypically shaped goblet cells occur in the ileal LEM during the pre-hatch period, but these cells assume adult morphological characteristics after hatch. Thus, the cells of the ileal LEM play strategic absorptive, secretory and protective roles in the gut.

Expression of oxytocin receptors in the zebra finch brain during vocal development.

Like human language, song in songbirds is learned during an early sensitive period and is facilitated by motivation to seek out social interactions with vocalizing adults. Songbirds are therefore powerful models with which to understand the neural underpinnings of vocal learning. Social motivation and early social orienting are thought to be mediated by the oxytocin system; however, the developmental trajectory of oxytocin receptors in songbirds, particularly as it relates to song learning, is currently unknown. This gap in knowledge has hindered the development of songbirds as a model of the role of social orienting in vocal learning. In this study, we used quantitative PCR to measure oxytocin receptor expression during the sensitive period of song learning in zebra finches (Taeniopygia guttata). We focused on brain regions important for social motivation, attachment, song recognition, and song learning. We detected expression in these regions in both sexes from posthatch day 5 to adulthood, encompassing the entire period of song learning. In this species, only males sing; we found that in regions implicated in song learning specifically, oxytocin receptor mRNA expression was higher in males than females. These sex differences were largest during the developmental phase when males attend to and memorize tutor song, suggesting a functional role of expression in learning. Our results show that oxytocin receptors are expressed in relevant brain regions during song learning, and thus provide a foundation for developing the zebra finch as a model for understanding the mechanisms underlying the role of social motivation in vocal development.

Histological description of the early gonadal development of Arapaima gigas, paiche

AbstractArapaima gigas, paiche, is the largest freshwater fish species in the South American Amazon. Despite the importance of an accurate understanding of the species' gonadal sexual differentiation mechanisms, the gonadogenesis process is still not well studied. The aim of this study was to determine the histological characteristics of the early gonadal development of paiche fry, belonging to the same “levante” (“levante” is the word used to describe the removal of fry from the male paiche). The fry was sampled during the month of September 2016; from the 5‐day post “levante” (dpl) to the 51 dpl with a minimum size of 2.7 cm and a maximum size of 16.0 cm in total length. The histology showed a large concentration of cells in the dorsal part of the abdominal cavity in 5 dpl fry, being greater in the left side. In addition, the gonadal ridges appeared at 6 dpl and the gonadal primordia appeared at 7 dpl. The two gonadal primordia were observed with different sizes, where the left primordia were larger and more basophilic than the right primordia. Finally, gonad differentiation between presumable females and males were observed with some structural differentiation between presumable females and presumable males since 43 post hatching day.

Perinatal exposure to antibiotics reduces affiliative behavior after post-weaning in zebra finches (Taeniopygia guttata)

Social behavior is influenced by a host of factors, including the immune system; for example, song quality in male starlings predicts immunocompetence suggesting the development of the immune system is interconnected with aspects social development (Duffy and Ball, 2002). Treating birds with antibiotics during the perinatal period may alter this development, and thereby, social behaviors beyond song. We asked if antibiotic exposure during the perinatal period effected parenting and offspring social behavior (e.g. aggressive and affiliative behaviors) in zebra finches? We treated the drinking water of zebra finch parents and hatchlings from post-hatch day 5–14 with azithromycin or a vehicle control and monitored parenting/social behavior. After weaning, we transferred offspring from the breeding cage to group housing and monitored social behavior and integration into the colony by measuring aggressive and affiliative behaviors. For all treatments we saw a reduction in the number of songs performed by fathers, however, specifically for antibiotic treated offspring there was a reduction in affiliative behaviors relative to vehicle treated controls suggesting the immune system, perhaps via the guts microbiome, influences certain aspects of social behaviors in birds.

Histological Analysis and Gene Expression of Satellite Cell Markers in the Pectoralis Major Muscle in Broiler Lines Divergently Selected for Percent 4-Day Breast Yield.

Muscle development during embryonic and early post-hatch growth is primarily through hyperplastic growth and accumulation of nuclei through satellite cell contribution. Post-hatch, muscle development transitions from hyperplasia to hypertrophic growth of muscle fibers. Commercial selection for breast yield traditionally occurs at ages targeting hypertrophic rather than hyperplastic growth. This has resulted in the production of giant fibers and concomitant challenges with regard to muscle myopathies. The current study investigates the impact of selection during the period of hyperplastic growth. It is hypothesized that selection for percentage breast yield during hyperplasia will result in an increased number of muscle cells at hatch and potentially impact muscle fiber characteristics at processing. This study characterizes the breast muscle histology of three broiler lines at various ages in the growth period. The lines include a random bred control (RAN) as well as lines which have been selected from RAN for high (HBY4) and low (LBY4) percentage 4-day breast yield. Post-rigor pectoralis major samples from six males of each line and age were collected and stored in formalin. The sample ages included embryonic day 18 (E18), post-hatch day 4 (d4), and day 56 (d56). The samples were processed using a Leica tissue processor, embedded in paraffin wax, sectioned, and placed on slides. Slides were stained using hematoxylin and eosin. E18 and d4 post-hatch analysis showed advanced muscle fiber formation for HBY4 and immature muscle development for LBY4 as compared to RAN. Post-hatch d56 samples were analyzed for fiber number, fiber diameter, endomysium, and perimysium spacing. Line HBY4 had the largest muscle fiber diameter (54.2 ± 0.96 μm) when compared to LBY4 (45.4 ± 0.96 μm). There was no line difference in endomysium spacing while perimysium spacing was higher for HBY4 males. Selection for percentage 4-day breast yield has impacted the rate and extent of muscle fiber formation in both the LBY4 and HBY4 lines with no negative impact on fiber spacing. The shift in processing age to later ages has exposed issues associated with muscle fiber viability. Selection during the period of muscle hyperplasia may impact growth rate; however, the potential benefits of additional satellite cells are still unclear.

Spinal lumbar dI2 interneurons contribute to stability of bipedal stepping.

Peripheral and intraspinal feedback is required to shape and update the output of spinal networks that execute motor behavior. We report that lumbar dI2 spinal interneurons in chicks receive synaptic input from afferents and premotor neurons. These interneurons innervate contralateral premotor networks in the lumbar and brachial spinal cord, and their ascending projections innervate the cerebellum. These findings suggest that dI2 neurons function as interneurons in local lumbar circuits, are involved in lumbo-brachial coupling, and that part of them deliver peripheral and intraspinal feedback to the cerebellum. Silencing of dI2 neurons leads to destabilized stepping in posthatching day 8 hatchlings, with occasional collapses, variable step profiles, and a wide-base walking gait, suggesting that dI2 neurons may contribute to the stabilization of the bipedal gait.

Exploring the effectiveness of in ovo feeding of vitamin C based on the embryonic vitamin C synthesis and absorption in broiler chickens

BackgroundMany researches about in ovo feeding (IOF) of vitamin C (VC) are gradually carried out to explore physiological development in chicken, but little studies focus on VC synthesis capacity of the embryo itself, the selection of injection site and the effectiveness of IOF of VC. This study aims to explore the above problems.ResultsKidney and yolk sac were the main organs for VC synthesis and L-gulonolactone oxidase (GLO) expression was lower during pre-hatch development than that during post-hatch development. Sodium-dependent vitamin C transporter 1 (SVCT1) expression was increased continuously in yolk sac from embryonic age 19 (E19) to post-hatch day 1 (D1) and in intestine (duodenum, jejunum and ileum) from E17 to D1. Plasma VC content was higher at D1 than that at D21 and D42. IOF of VC significantly reduced GLO expression in liver, kidney and yolk sac as well as SVCT1 expression in duodenum, jejunum and ileum, but increased the VC content in plasma, brain, kidney and liver. In addition, IOF of VC obviously reduced the embryonic morality and increased the hatchability under heat stress.ConclusionsThis study suggested that IOF of VC at E11 in yolk was effective for embryonic VC supplementation. These findings provide a theoretical reference about the method of embryonic VC supplementation and effective methodology on embryonic VC nutrition in broiler chickens.

Effects of genetic selection on activity of corticotropic and thyrotropic axes in modern broiler chickens

Commercial selection for meat-type (broiler) chickens has produced economically valuable birds with fast growth rates, enhanced muscle mass, and highly efficient feed utilization. The physiological changes that account for this improvement and unintended consequences associated with them remain largely unexplored, despite their potential to guide further advancements in broiler production efficiency. To identify effects of genetic selection on hormonal signaling in the adrenocorticotropic and thyrotropic axes, gene expression in muscle and liver and post-hatch circulating hormone concentrations were measured in legacy [Athens Canadian Random Bred (ACRB)] and modern (Ross 308) male broilers between embryonic days (e) 10 and e18 and post-hatch days (d) 10 and d40. No interactive effects or main effects of line were observed for adrenocorticotropic gene expression during either developmental period, although age effects appeared for corticosteroid-binding globulin in liver during embryogenesis and post-hatch and glucocorticoid receptor in both tissues post-hatch. There was a main line effect for circulating corticosterone, with levels in ACRB greater than those in Ross. Several thyrotropic genes exhibited line-by-age interactions during embryonic or post-hatch development. In liver, embryonic expression of thyroid hormone receptor beta was greater in ACRB on e12, and deiodinase 3 (DIO3) levels were greater in Ross on e14 and e16. In juvenile liver, deiodinase 2 (DIO2) expression was greater in ACRB on d10 but greater in Ross on d20, while DIO3 was higher in ACRB on d30 and d40. Levels of thyroid hormone receptor alpha mRNA exhibited a main line effect, with levels greater in ACRB juvenile breast muscle. Several thyrotropic genes exhibited main age effects, including DIO2 and DIO3 in embryonic breast muscle, thyroid hormone receptor alpha and thyroid hormone receptor beta in post-hatch liver, and DIO2 in post-hatch breast muscle. Circulating triiodothyronine displayed a main line effect, with levels in Ross significantly reduced as compared to ACRB. These findings suggest that in modern broilers, a decrease in levels of hormones that control basal metabolism triiodothyronine and the stress response circulating corticosterone, as well as altered expression of genes regulating thyroid hormone activity, could contribute to lower heat production, reduced stress response, and altered nutrient partitioning, leading to more efficient feed utilization and faster, more productive growth.

Integrated mRNA and miRNA transcriptome analysis provides novel insights into the molecular mechanisms underlying goose pituitary development during the embryo-to-hatchling transition

It is well established that the endocrine system plays a pivotal role in preparing the avian embryos for the abrupt switch from chorioallantoic to pulmonary respiration during the critical embryo-to-hatchling transition. However, as the master gland of the endocrine system, there has been little research focusing on the molecular mechanisms controlling the development and function of the pituitary gland during the peri-hatch period in birds. In the present study, we aimed to determine the genome-wide mRNA and miRNA transcriptome profiles of the pituitary during the embryo-to-hatchling transition period from embryonic day 22 (E22) to post-hatching day 6 (P6) in the goose (Anser cygnoides). Of note, expression of Anser_cygnoides_newGene_32456 and LOC106031011 were significantly different among these 4 stages (i.e., E22, E26, P2, and P6). Meanwhile, the neuroactive ligand-receptor interaction pathway was significantly enriched by the DEGs commonly identified among three pairwise comparisons. At the miRNA transcriptome level, there were not commonly identified DE miRNAs among these 4 stages, while the 418 of their predicted target genes were mutually shared. Both the target genes of DE miRNAs in each comparison and these 418 shared target genes were significantly enriched in the ECM-receptor interaction and focal adhesion pathways. In the predicted miRNA-mRNA interaction networks of these 2 pathways, novel_miRNA_467, novel_miRNA_154, and novel_miRNA_340 were the hub miRNAs. In addition, multiple DE miRNAs also showed predicted target relationships with the DEGs associated with extracellular matrix (ECM) components. Among them, expression of novel_miR_120, tgu-miR-92-3p, and novel_miR_398 was significantly negatively correlated with that of LAMC3 (laminin subunit gamma3), suggesting that these miRNAs may regulate pituitary tissue remodeling and functional changes through targeting LAMC3 during development. These identified DE mRNAs and miRNAs as well as their predicted interaction networks involved in regulation of tissue remodeling and cellular functions were most likely to play critical roles in facilitating the embryo-to-hatchling transition. These results provide novel insights into the early developmental process of avian pituitary gland and will help better understand the underlying molecular mechanisms.