Effect of Dietary Clostridium butyricum Supplementation on Growth Performance, Intestinal Barrier Function, Immune Function, and Microbiota Diversity of Pekin Ducks

Simple Summary

In poultry farming, the use of prophylactic antibiotics can lead to increased resistance, so probiotics are a good alternative. Clostridium butyricum (C. butyricum) has been widely used to improve the gut health of animals. Therefore, we carried out the current study of Pekin ducks supplemented with C. butyricum for a period of 42 days. Here, we found a clear increase in the growth performance of Pekin ducks supplemented with C. butyricum. Moreover, a high level of secretory IgA, IgM, IgG, IL-4, and IL-10 and comparatively higher short-chain fatty acids (SCFAs) and intestinal tight junction changes were found in Pekin ducks supplemented with C. butyricum. The gut microbial diversity of Pekin ducks supplemented with C. butyricum was clearly different than that of Pekin ducks fed a non-C. butyricum diet. In conclusion, our findings suggest that 400 mg/kg C. butyricum supplementation improved the intestinal health of Pekin ducks by increasing the α-diversity of intestinal microbiota, enhancing the SCFAs contents, and strengthening the intestinal barrier function and immune systems indicating that 400 mg/kg C. butyricum might be a preferable antibiotic alternative for commercial application.

Abstract

Clostridium butyricum (C. butyricum) is increasingly being used to test the promotion of the gut health of animals. However, the modes of action for such applications for waterfowl remain unclear. Thus, we investigated whether or not intestinal barrier function, immune-related gene expression, and the diversity of the intestinal microbiota in Pekin ducks varied under C. butyricum supplementation. A total of 500 ducks were randomly assigned into five treatments supplemented with basal diets containing: either 0 (group Control), 200 (group CB200), 400 (group CB400) and 600 (group CB600) mg/kg C. butyricum or 150 mg/kg aureomycin (group A150) for 42 days. In comparison with the control group, C. butyricum supplementation enhanced the growth performance and intestinal villus height of Pekin ducks at 42 d. Serum immune indexes and fecal short-chain fatty acids (SCFAs) were all improved at both 21 d and 42 d after C. butyricum addition. The mRNA expression levels of Mucin2, Zonula occludens-1 (ZO-1), Caudin-3, and Occludin increased at 21 d and 42 d and the mRNA expression levels of IL-4 and IL-10 only increased at 42 d after C. butyricum addition. Dietary C. butyricum also resulted in an increase in the number of diversities of operational taxonomic units (OTUs), and an increase in the α-diversity of intestinal microbiota. The addition of C. butyricum altered the composition of the intestinal microbiota from 21 d to 42 d. The relative abundance of Firmicutes and Bacteroidetes showed little changes among groups; however, the relative abundance of Firmicutes/Bacteroidetes were found to have been significantly different between the 21 d and 42 d. C. butyricum administration improved the intestinal health of Pekin ducks by increasing the diversity of intestinal microbiota, enhancing the SCFAs contents, and strengthening the intestinal barrier function and immune systems. The optimal dietary supplementation dosage was recommended as 400 mg/kg in the diet.

Genome-wide association study reveals novel loci associated with feeding behavior in Pekin ducks

Background

Feeding behavior traits are an essential part of livestock production. However, the genetic base of feeding behavior traits remains unclear in Pekin ducks. This study aimed to determine novel loci related to feeding behavior in Pekin ducks.

Results

In this study, the feeding information of 540 Pekin ducks was recorded, and individual genotype was evaluated using genotyping-by-sequencing methods. Genome-wide association analysis (GWAS) was conducted for feeding behavior traits. Overall, thirty significant (P-value < 4.74E-06) SNPs for feeding behavior traits were discovered, and four of them reached the genome-wide significance level (P-value < 2.37E-07). One genome-wide significance locus associated with daily meal times was located in a 122.25 Mb region on chromosome 2, which was within the intron of gene ubiquitin-conjugating enzyme E2 E2 (UBE2E2), and could explain 2.64% of the phenotypic variation. This locus was also significantly associated with meal feed intake, and explained 2.72% of this phenotypic variation.

Conclusions

This study is the first GWAS for feeding behavior traits in ducks. Our results provide a list of candidate genes associated with feeding behavior, and also help to better understand the genetic mechanisms of feeding behavior patterns in ducks.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07668-1.

Characterization and Comparative Transcriptomic Analysis of Skeletal Muscle in Pekin Duck at Different Growth Stages Using RNA-Seq

Simple Summary

Skeletal muscle is an important tissue and its development is strictly regulated by genes. In this study, in order to understand the muscle-related gene expression in Pekin duck, RNA-seq was performed to analyze and compare skeletal muscle at different growth stages. Alternative splicing, single nucleotide polymorphisms and insertion–deletions were detected, and 299 novel genes were discovered. MYL4, IGF2BP1, CSRP3, SPP1, KLHL31, LAMB2, LAMA2, ITGB1 and OPN played crucial roles in skeletal muscle development. Oxidative phosphorylation, ECM-receptor interaction, focal adhesion, carbon metabolism, and biosynthesis of amino acids participated in the regulation of skeletal muscle development in Pekin duck. This study provides an important reference for revealing the developmental mechanisms of pectoral and leg muscles in duck.

Abstract

Skeletal muscle, accounting for approximately 50% of body weight, is the largest and most important tissue. In this study, the gene expression profiles and pathways in skeletal muscle of Pekin duck were investigated and compared at embryonic day 17, 21, and 27 and postnatally at 6 months of age. An average of 49,555,936 reads in each sample was obtained from the transcriptome libraries. Over 70.0% of alternative splicing (AS) in each sample was mainly alternative 5′ first exon (transcription start site)—the first exon splicing (TSS) and alternative 3′ last exon (transcription terminal site)—the last exon splicing (TTS), indicating that TSS and TTS were the most common AS event in Pekin ducks, and these AS events were closely related to the regulation of muscle development at different growth stages. The results provided a valuable genomic resource for selective breeding and functional studies of genes. A total of 299 novel genes with ≥2 exons were obtained. There were 294 to 2806 differentially expressed genes (DEGs) in each pairwise comparison of Pekin duck. Notably, 90 DEGs in breast muscle and 9 DEGs in leg muscle were co-expressed at all developmental points. DEGs were validated by qPCR analysis, which confirmed the tendency of the expression. DEGs related to muscle development were involved in biological processes such as “endodermal cell differentiation”, “muscle cell cellular homeostasis”, “skeletal muscle tissue growth” and “skeletal muscle cell differentiation”, and were involved in pathways such as oxidative phosphorylation, ECM-receptor (extracellular matrix receptor) interaction, focal adhesion, carbon metabolism, and biosynthesis of amino acids. Some DEGs, including MYL4, IGF2BP1, CSRP3, SPP1 and KLHL31, as well as LAMB2, LAMA2, ITGB1 and OPN, played crucial roles in muscle growth and development. This study provides valuable information about the expression profile of mRNAs and pathways from duck skeletal muscle at different growth stages, and further functional study of these mRNAs and pathways could provide new ideas for studying the molecular networks of growth and development in duck skeletal muscle.

Effect of Dietary L-Methionine Supplementation on Growth Performance, Carcass Traits, and Plasma Parameters of Starter Pekin Ducks at Different Dietary Energy Levels

Simple Summary

Tremendous improvements have been made in the duck commercial industry, especially in aspects such as the increase of body weight and shortening of the production cycle. Meat duck production has been increasing annually worldwide. Improvements in precise nutrition were crucial for ducks to improve growth efficiency and reduce diet costs. Currently, L-Met, a new methionine (Met) source, has been commercially available for duck diet formulation. The bioavailability of L-Met is greater than DL-Met for growth performance in duck. The present study estimated the Met requirement of starter Pekin ducks from 1 to 21 days of age by supplementing crystal L-Met to formulate the diets at different ME levels. The results suggested that the Met requirement of starter Pekin ducks was affected by dietary ME levels. The data potentially provide theoretical support for the utilization of crystalline L-Met in duck production.

Abstract

A 2 × 6 factorial experiment was conducted to determine the influences of dietary metabolizable energy (ME) and methionine (Met) levels on growth performance, carcass traits, and plasma biochemical parameters of starter Pekin ducks from 1 to 21 days of age. A total of 600 one-day-old male Pekin ducklings were randomly assigned to 12 groups (six replicates each group and eight ducks per replicate) in a 2 × 6 two-factor arrangement. The basal Met levels of two basal diets (11.54 and 12.52 MJ/kg ME) were 0.31 and 0.29%, respectively. The crystalline L-Met was supplemented to yield six diets according to different supplemental levels (0, 0.05, 0.10, 0.15, 0.20, and 0.25%). The results showed that the body weight (BW) and average daily weight gain (ADG) were increased (p < 0.05) with increasing dietary Met levels. Dietary ME levels changed from 11.54 to 12.52 MJ/kg increased the BW and ADG (p < 0.05) as well as decreased the average daily feed intake and feed to gain ratio (p < 0.05). As the dietary Met level increased, leg muscle yield increased (p < 0.05). Conversely, increasing the dietary ME level decreased the leg muscle yield (p = 0.0024) and increased abdominal fat (p < 0.001). Meanwhile, the concentrations of total cholesterol (TCHO), high-density lipoprotein cholesterol (HDLC), and low-density lipoprotein cholesterol (LDLC) in plasma were decreased (p < 0.05) when the ME levels of diets changed from 11.54 to 12.52 MJ/kg. Meanwhile, the plasma TCHO and HDLC concentrations decreased (p < 0.05) as dietary Met levels increased. Based on the linear-broken line model, the dietary Met requirement of starter Pekin ducks from 1 to 21 days of age for optimal ADG were 0.362% (0.052% supplemental L-Met) at 11.54 MJ ME/kg and 0.468% (0.178% supplemental L-Met) at 12.52 MJ ME/kg, respectively, when crystal L-Met was supplemented to formulate the diets. This suggested that the Met requirement of starter Pekin ducks was affected by dietary ME levels. The data potentially provide theoretical support for the utilization of crystalline L-Met in duck production.

Short Beak and Dwarfism Syndrome in Ducks in Poland Caused by Novel Goose Parvovirus

Short beak and dwarfism syndrome (SBDS), which was previously identified only in mule ducks, is now an emerging disease of Pekin ducks in China and Egypt. The disease is caused by the infection of ducks with a genetic variant of goose parvovirus-novel goose parvovirus (nGPV). In 2019, SBDS was observed for the first time in Poland in eight farms of Pekin ducks. Birds in the affected flock were found to show growth retardation and beak atrophy with tongue protrusions. Morbidity ranged between 15% and 40% (in one flock), while the mortality rate was 4-6%. Co-infection with duck circovirus, a known immunosuppressive agent, was observed in 85.7% of ducks. The complete coding regions of four isolates were sequenced and submitted to GenBank. The phylogenetic analysis revealed a close relationship of Polish viral sequences with the Chinese nGPV. Genomic sequence alignments showed 98.57-99.28% identity with the nGPV sequences obtained in China, and 96.42% identity with the classical GPV (cGPV; Derzsy's disease). The rate of amino acid mutations in comparison to cGPV and Chinese nGPV was higher in the Rep protein than in the Vp1 protein. To our knowledge, this is the first report of nGPV infection in Pekin ducks in Poland and Europe. It should be emphasized that monitoring and sequencing of waterfowl parvoviruses is important for tracking the viral genetic changes that enable adaptation to new species of waterbirds.

Dietary resveratrol supplement improves carcass traits and meat quality of Pekin ducks

With the increase of consumer demand for high-quality animal protein, it becomes imperative to improve meat quality through nutritional strategy. Resveratrol is a plant polyphenol that exists in grapes and grape products, and it has been considered as a potential functional feed additive. Here, we aimed to explore the optimal dose of resveratrol in Pekin ducks' diet and its effect on improving meat quality. A total of 432 male Pekin ducks (1-day-old) were selected and randomly allotted to 4 treatment groups, with each group containing 6 replicates. Four different levels of resveratrol were evaluated (0, 150, 300, and 450 mg/kg) for 42 d. The carcass traits, meat quality, and muscle fiber characteristics of Pekin ducks were investigated. Results showed that a∗_24h, b∗_24h, intramuscular fat, crude protein, total flavor amino acid content of duck breast muscle, and a∗_45min of duck leg muscle were increased (P < 0.05) by resveratrol. Resveratrol also reduced abdominal fat deposition, shear force, L∗_45min of breast muscle and drip loss, shear force, and L∗_45min of leg muscle. In addition, the breast muscle fibers of resveratrol-fed ducks had lower diameter and cross-sectional area and higher density (P < 0.05). Overall, we conclude that dietary resveratrol supplement can effectively improve Pekin duck meat quality, the optimal additional range in diet being 300 to 450 mg/kg. Its underlying mechanism might be partly through stimulation of intramuscular fat and flavor amino deposition and alteration of muscle fiber characteristics.

Evaluation of crude protein levels in White Pekin duck diet for 21 days after hatching

In poultry diets, a requirement of crude protein is one of the most important factors in poultry productivity. Besides, the Pekin duck requirement of crude protein is still not clear. This experiment was conducted to determine the crude protein requirement of Pekin duck on diet formulation by investigation of growth performance, carcass trait, and analysis of blood parameter for a hatch to 21-day (d) of age. A total of 432 male White Pekin ducks were randomly allocated to six levels of crude protein (i.e., 15%, 17%, 19%, 21%, 23%, and 25%) to give six replicate pens per treatment with 12 ducklings per each pen. Body weight and feed intake were measured weekly by calculating feed conversion ratio and protein intake. Two ducklings each pen was euthanized via cervical dislocation for analysis of carcass trait and plasma blood on 21-d of age. Data were applied on both prediction linear-plateau and quadratic-plateau models by estimation of the crude protein requirements. Data were applied on both prediction linear-plateau and quadratic-plateau models by estimation of the crude protein requirements. The level of crude protein requirements of Pekin ducks for 21 days after the hatch was estimated to be 20.63% and 23.25% diet for maximum daily gain, and minimum feed conversion ratio, respectively.

Protease supplementation attenuates the intestinal health damage caused by low-protein diets in Pekin ducks

The objective of this study was to investigate the effects of low-protein diets with low digestibility of feed ingredients on intestinal damage and to explore whether the protease supplementation can alleviate the damage in Pekin ducks. A total of 576 Pekin ducklings (6 replicate pens, 16 ducks/pen) were randomly assigned to 6 dietary treatments (3 × 2 factorial arrangement) in a randomized complete block design. Factors were CP levels (13.5%, 15.5%, and 17.5%) and protease (0 or 20,000U/kg). Compared with the diets containing 17.5% CP, low-protein diets (13.5% CP) showed suppressed (P < 0.05) growth performance and feed intake (FI); reduced (P < 0.05) serum-free arginine, isoleucine, leucine, methionine, phenylalanine, valine, and proline as well as the cecal acetate and propionate concentration; increased (P < 0.05) plasma and ileal mucosal tumor necrosis factor-α (TNF-α) concentration; and downregulated (P < 0.05) mRNA expression of TNF-α, nuclear transcription factor-κb, interferon gamma, and Occludin in ileal mucosa. Irrespective of the dietary CP levels, protease supplementation significantly increased (P < 0.05) the serum-free glutamic acid concentration while decreasing (P < 0.05) the plasma endotoxin, IL-6, and the cecal isovalerate concentration. A significant interactive effect was observed between low-protein diets and protease supplementation (P < 0.05) on serum-free arginine concentration, the ratio of ileal villus height to crypt depth, and the IL-6 concentration in ileal mucosa. These results indicated that low-protein diets could damage intestinal integrity to induce systemic inflammation response and at last to suppress growth performance. Protease supplementation could partly attenuate the negative effects on gut health caused by low-protein diets in Pekin ducks.

Selection response and genetic parameter estimation of feeding behavior traits in Pekin ducks

Body weight-related traits and feeding behavior traits are important in poultry breeding and production. To investigate the heritability of feeding behavior and their genetic correlation with body weight-related traits in Pekin ducks, 5,594 Pekin ducks were selected. The information about body weight-related traits and feeding behavior from 3 to 6 wk of age were recorded by automatic electronic feeders. The heritability estimates for body weight, residual feed intake, and feeding behavior traits are relatively high (ranging from 0.29 to 0.65). We observed that total feed intake, meal feed intake, body weight at the age of 3 wk, and daily body weight gain had strong positive genetic correlations with body weight at the age of 6 wk. Moreover, body weight at the age of 3 wk also showed a positive genetic correlation with the feed conversion ratio (0.33). Total feeding time, daily feed intake, and feeding rate had significant positive phenotypic correlations with feed efficiency. However, the average interval between meals, the number of daily visits, and the number of meals all had a low genetic or phenotypic relationship with body weight and feed efficiency. In conclusion, our study revealed that body weight, residual feed intake, and feeding behavior traits were all highly heritable traits, and the selection for certain feeding behaviors could improve feed efficiency in Pekin ducks. This study is the first report about genetic parameter estimates about feeding behaviors in ducks based on large datasets and provides solid data for genetic study in ducks.

On-farm welfare assessment of commercial Pekin ducks: a comparison of methods

Although a number of welfare assessment methods have been developed for poultry, none have been evaluated for use in commercial duck farms. The primary objective of the study was to evaluate the inter-rater reliability and relative accuracy of 4 duck welfare assessment strategies. Over 2 experiments, 12 flocks of commercial meat ducks (5,850 to 6,300 ducks/flock) aged 30 to 34 D were evaluated. During experiment 1, six flocks were evaluated using 2 welfare assessment methods: transect walks (TW) and catch-and-inspect (CAI). During TW, 2 observers walked predetermined transects along the length of the house and recorded the number of ducks per transect that were featherless, were dirty, were lethargic, had bloody feathers, had infected eyes, and/or had plugged nostrils or were found dead. During CAI, a total of 150 ducks per flock were corralled and individually evaluated. The same welfare indicators were assessed using both methods. During experiment 2, six flocks were initially evaluated using CAI, TW, and a distance evaluation (DE; a total of 50 ducks per flock evaluated from a walking distance) and then reassessed within 24 h during the loadout (LO) process. Data were analyzed in SAS (version 9.4) to determine the observer and method effects on the incidence of welfare indicators. Interobserver reliability was high (P > 0.05) across methods for most welfare indicators. The assessment method affected the measured outcome variables in both experiments (P < 0.05). CAI resulted in higher estimated incidences of most welfare indicators than TW (experiment 1 and 2) and LO (experiment 2). DE yielded intermediate results compared with other methods (experiment 2). Results obtained using TW and LO were most similar, the only difference being the number of dead birds observed using each method (P < 0.0001). The average time required for CAI, TW, DE, and LO was 2.40 ± 0.004, 1.12 ± 0.02, 1.54 ± 0.001, 3.56 ± 0.006 h, respectively. Bootstrapping analyses showed that the observed welfare indicator prevalence estimates were affected by the number of transects (TW) and number of birds (CAI) sampled.

Effect of dietary energy levels on growth performance, blood parameter and intestinal morphology of Pekin ducks in low ambient temperature

This study was carried out to investigate the effects of dietary energy levels on growth performance, blood parameter, and intestinal morphology of Pekin ducks in low temperature. A total of 500, 21-d-old Pekin ducks (initial BW = 1,089 ± 5.21 g) were evenly assigned to five dietary treatments (2,950, 3,000, 3,050, 3,100, or 3,150 kcal AME/kg, calculated on an as-is basis) with four replicates (pens) for each treatment (25 ducks per pen). During the experiment, hens were provided with feed and water ad libitum. Overall, increasing dietary energy levels corresponded to an increase of final body weight and body weight gain (linear, p < 0.01). Feed intake decreased (linear, p < 0.01) and feed conversion ratio increased (linear, p < 0.01) with increasing levels of energy. There were no significant differences (p < 0.05) in the level of leukocytes between groups. However, heterophils decreased (quadratic, p < 0.05) and lymphocytes increased (linear, p < 0.01) as inclusion of dietary energy levels increased. The H/L ratio increased (linear, p < 0.01) with increasing dietary energy levels while serum corticosterone levels decreased at overall experimental periods. Triglycerides increased (linear and quadratic, p < 0.05) with increasing dietary energy levels. There were no significant changes in villus height or crypt depth of the jejunum at overall experimental. In conclusion, increasing concentrations of dietary energy levels up to 2,950–3,150 kcal/kg in diet. Additionally, 3,150 kcal/kg dietary energy had been revealed more beneficial and could be practiced as protective management for the Pekin ducks reared under low ambient temperature (8°C to 10°C).

Dynamics of transcriptome changes during subcutaneous preadipocyte differentiation in ducks

BACKGROUND

Pekin duck is an important animal model for its ability for fat synthesis and deposition. However, transcriptional dynamic regulation of adipose differentiation driven by complex signal cascades remains largely unexplored in this model. This study aimed to explore adipogenic transcriptional dynamics before (proliferation) and after (differentiation) initial preadipocyte differentiation in ducks.

RESULTS

Exogenous oleic acid alone successfully induced duck subcutaneous preadipocyte differentiation. We explored 36 mRNA-seq libraries in order to study transcriptome dynamics during proliferation and differentiation processes at 6 time points. Using robust statistical analysis, we identified 845, 652, 359, 2401 and 1933 genes differentially expressed between -48 h and 0 h, 0 h and 12 h, 12 h and 24 h, 24 h and 48 h, 48 h and 72 h, respectively (FDR < 0.05, FC > 1.5). At the proliferation stage, proliferation related pathways and basic cellular and metabolic processes were inhibited, while regulatory factors that initiate differentiation enter the ready-to-activate state, which provides a precondition for initiating adipose differentiation. According to weighted gene co-expression network analysis, pathways positively related to adipogenic differentiation are significantly activated at the differentiation stage, while WNT, FOXO and other pathways that inhibit preadipocyte differentiation are negatively regulated. Moreover, we identified and classified more than 100 transcription factors that showed significant changes during differentiation, and found novel transcription factors that were not reported to be related to preadipoctye differentiation. Finally, we manually assembled a proposed regulation network model of subcutaneous preadipocyte differentiation base on the expression data, and suggested that E2F1 may serve as an important link between the processes of duck subcutaneous preadipocyte proliferation and differentiation.

CONCLUSIONS

For the first time we comprehensively analyzed the transcriptome dynamics of duck subcutaneous preadipocyte proliferation and differentiation. The current study provides a solid basis for understanding the synthesis and deposition of subcutaneous fat in ducks. Furthermore, the information generated will allow future investigations of specific genes involved in particular stages of duck adipogenesis.

Transcriptome Analysis Reveals Differential Expression of Genes Regulating Hepatic Triglyceride Metabolism in Pekin Ducks During Dietary Threonine Deficiency

Dietary threonine (Thr) deficiency increases hepatic triglyceride accumulation in Pekin ducks, which results in fatty liver disease and impairs hepatic function. However, the underlying molecular mechanisms altered by dietary Thr deficiency are still unknown. To identify the underlying molecular changes, 180 one-day-old ducklings were divided into three groups, including Thr deficiency group (Thr-D), Thr sufficiency group (Thr-S), and pair-fed group (Pair-F) that was fed with a Thr-sufficient diet but with reduced daily feed intake. The results showed that feed intake was similar between Thr-D and Pair-F groups, but weight gain rate and final body weight in the Thr-D group were lower than those in the Pair-F group. Feed intake, weight gain, and body weight in Thr-D and Pair-F groups were lower than those in the Thr-S group. The Thr-D diet reduced abdominal fat percentage but increased hepatic triglyceride content when compared with that of the Thr-S and Pair-F groups. The Pair-F reduced hepatic levels of C15:0, C17:0, C18:0, C20:0, C20:4n6, and C22:0 and also reduced total fatty acid, saturated fatty acid, and unsaturated fatty acid content when compared with those of the Thr-D and Thr-S groups. The Thr-D diet increased hepatic content of C6:0, C17:1, C18:3n6, C20:0, C20:1n9, and C22:2, as well as reduced the content of C18:2n6t and C23:0 when compared with those of the Thr-S group. Transcriptome analysis in the liver indicated that the Thr-D diet upregulated genes related to fatty acid and triglyceride synthesis and downregulated genes related to fatty acid oxidation and triglyceride transport. Gene ontology analysis showed that more genes related to lipid metabolism processes and molecular function were differentially expressed in the Thr-D group relative to Thr-S and Pair-F groups than in the Pair-F group relative to the Thr-S group. KEGG pathway analysis showed that differentially expressed genes were enriched in signal transduction, immune, hormone, lipid, and amino acid metabolism pathways. Our findings indicated that the Thr-D diet increased hepatic triglyceride and fatty acid accumulation via increasing fatty acid and triglyceride synthesis and reducing fatty acid oxidation and triglyceride transport. These findings provide novel insights into our understanding of the molecular mechanisms underlying fat accumulation in the liver caused by dietary threonine deficiency.

Molecular cloning, expression and characterization of Pekin duck programmed death-1

Programmed death-1 (PD-1) has a pivotal role in the attenuation of adaptive immune responses and peripheral tolerance. Here we describe the identification of the Pekin duck programmed death-1 orthologue (duPD-1). The duPD-1 cDNA encodes a 283-amino acid polypeptide that has an amino acid identity of 70%, 32% and 31% with chicken, murine and human PD-1, respectively. The duck PD-1 gene shares five conserved exons with chicken, murine and human PD-1 genes. A cluster of putative regulatory elements within the conserved region B (CR-B) of the basal promotor is conserved. Homology modeling was most compatible with the two β-sheet IgV domain structure of murine PD-1. Contact residues, shown to be critical for binding of the respective human and murine PD-1 ligands are mostly conserved between avian and mammalian species, whereas residues that define the cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) and immunoreceptor tyrosine-based switch motif (ITSM) are highly conserved across higher vertebrates and frog. Constitutive expression of duPD-1 transcripts was predominantly found in lymphocyte-rich tissues, and mitogen-stimulation of duck peripheral blood mononuclear cells transiently increased duPD-1 mRNA expression. A soluble duPD-1 protein was expressed and shown to engage the identified duck PD-1 ligands. Our observations show considerable evolutionary conservation between mammalian and avian PD-1 orthologues. This work will facilitate further investigation of the role of PD-1 signaling in adaptive immunity in the Pekin duck, a non-mammalian vertebrate and pathogen host with relevance for human and animal health.

Virulence of three European highly pathogenic H7N1 and H7N7 avian influenza viruses in Pekin and Muscovy ducks

Background

There is paucity of data on the virulence of highly pathogenic (HP) avian influenza viruses (AIV) H7 in ducks compared to HPAIV H5. Here, the virulence of HPAIV H7N1 (designated H7N1-FPV34 and H7N1-It99) and H7N7 (designated H7N7-FPV27) was assessed in Pekin and/or Muscovy ducklings after intrachoanal (IC) or intramuscular (IM) infection.

Results

The morbidity rate ranged from 60 to 100% and mortality rate from 20 to 80% depending on the duck species, virus strain and/or challenge route. All Muscovy ducklings inoculated IC with H7N7-FPV27 or H7N1-FPV34 exhibited mild to severe clinical signs resulting in the death of 2/10 and 8/10 ducklings, respectively. Also, 2/10 and 6/9 of inoculated Muscovy ducklings died after IC or IM infection with H7N1-It99, respectively. Moreover, 5/10 Pekin ducklings inoculated IC or IM with H7N1-It99 died. The level of virus detected in the oropharyngeal swabs was higher than in the cloacal swabs.

Conclusion

Taken together, HPAIV H7 cause mortality and morbidity in Muscovy and Pekin ducklings. The severity of disease in Muscovy ducklings depended on the virus strain and/or route of infection. Preferential replication of the virus in the respiratory tract compared to the gut merits further investigation.

Genome-wide association study of the level of blood components in Pekin ducks

Blood components are considered to reflect nutrient metabolism and immune activity in both humans and animals. In this study, we measured 12 blood components in Pekin ducks and performed genome-wide association analysis to identify the QTLs (quantitative trait locus) using a genotyping-by-sequencing strategy. A total of 54 QTLs were identified for blood components. One genome-wide significant QTL for alkaline phosphatase was identified within the intron-region of the OTOG gene (P = 1.31E-07). Moreover, 21 genome-wide significant SNPs for the level of serum cholinesterase were identified on six different scaffolds. In addition, for serum calcium, one genome-wide significant QTL was identified in the upstream region of gene RAB11B. These results provide new markers for functional studies in Pekin ducks, and several candidate genes were identified, which may provide additional insights into specific mechanisms for blood metabolism in ducks and their potential application for duck breeding programs.

Differences in Pre-Laying Behavior between Floor-Laying and Nest-Laying Pekin Ducks

Simple Summary

Floor-laying is a behavior seen in farmed ducks, where eggs are laid onto the shed floor rather than in the nest boxes provided. This behavior costs producers, due to damaged eggs, and may be a negative experience for those birds performing it. However, factors contributing to floor laying in Pekin ducks are not well understood. We aimed to identify whether behavioral differences exist between floor and nest-laying ducks. We found that some floor-laying ducks never interacted with nest boxes, while other floor-layers used nests in a similar way to nest-laying ducks. Floor-layers that did not interact with nests experienced less aggression than the other two groups. We concluded that competition is a contributing factor to floor-laying in ducks, and it is possible that those ducks not using nests avoid doing so to reduce agonistic encounters. Developing strategies to reduce competition for nest boxes may help improve production efficiency and minimize negative welfare outcomes that might exist for floor-laying ducks.

Abstract

Floor-laying in commercially farmed Pekin ducks is not well understood. This exploratory study aimed to determine if behavioral differences exist between floor-laying and nest-laying ducks. Retrospective analysis of video footage from a small commercial breeding flock (n = 60 birds) was used to quantify the behavior of floor-laying and nest-laying birds (n = 24 events per group) in the hour prior to oviposition site selection. The frequency, percentage of time spent, and duration of bouts were compared for nest box interactions, behaviors inside and outside of boxes and aggressive interactions. Some floor-laying birds did not enter or investigate nest boxes (FL-Out), whilst some floor-layers (FL-In) used nest boxes similarly to nest-laying birds (NL). Nest-building behavior differed only in location, with FL-Out performing the behavior on the shed floor and the other groups performing it primarily in boxes. FL-Out sat more, walked less, and engaged in less aggression (p < 0.05) than FL-In and NL. The occurrence of multiple birds in a nest box was strongly correlated with the number of aggressive interactions that occurred in the box (R = 0.81). Competition appears to contribute to floor-laying in Pekin ducks; FL-Out birds may not engage with nest boxes as a coping strategy to avoid agonistic behavior. These findings indicate that developing practical strategies to reduce nest box competition could help mitigate floor-laying. However, other factors such as nest design may also contribute to FL-Out birds’ reluctance to use nest boxes and require further investigation.

Genome-wide association study reveals novel loci associated with body size and carcass yields in Pekin ducks

Background

Pekin duck products have become popular in Asia over recent decades and account for an increasing market share. However, the genetic mechanisms affecting carcass growth in Pekin ducks remain unknown. This study aimed to identify quantitative trait loci affecting body size and carcass yields in Pekin ducks.

Results

We measured 18 carcass traits in 639 Pekin ducks and performed genotyping using genotyping-by-sequencing (GBS). Loci-based association analysis detected 37 significant loci for the 17 traits. Thirty-seven identified candidate genes were involved in many biological processes. One single nucleotide polymorphism (SNP) (Chr1_140105435 A > T) located in the intron of the ATPase phospholipid transporting 11A gene (ATP11A) attained genome-wide significance associated with five weight traits. Eight SNPs were significantly associated with three body size traits, including the candidate gene plexin domain containing 2 (PLXDC2) associated with breast width and tensin 3 (TNS3) associated with fossil bone length. Only two SNPs were significantly associated with foot weight and four SNPs were significantly associated with heart weight. In the gene-based analysis, three genes (LOC101791418, TUBGCP3 (encoding tubulin gamma complex-associated protein 3), and ATP11A) were associated with four traits (42-day body weight, eviscerated weight, half-eviscerated weight, and leg muscle weight percentage). However, no loci were significantly associated with leg muscle weight in this study.

Conclusions

The novel results of this study improve our understanding of the genetic mechanisms regulating body growth in ducks and thus provide a genetic basis for breeding programs aimed at maximizing the economic potential of Pekin ducks.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5379-1) contains supplementary material, which is available to authorized users.

CT venography and pathological characterization of crus haemorrhage in Pekin ducks

The crus haemorrhage is one of the main causes of carcass defects in Pekin duck processing houses. However, its pathologic features are currently unclear. In order to examine the injury to the hind limb veins and illustrate the pathologic characteristics of crus haemorrhage in Pekin ducks, a total of 68 Pekin ducks with crus haemorrhage (test group) and 10 unaffected ducks (control group) were collected in this study. Five ducks randomly selected from each group were examined by computed tomographic venography with 2.0 mm thickness, 120 kVp, and 90 mA. Pathological changes were observed macroscopically, and under a microscope and electron microscope. The computed tomographic venography results showed no differences in the main hind limb veins between Pekin ducks with crus haemorrhage and the control. Macroscopic results demonstrated that the haemorrhage only occurred in crural muscles, most frequently in musculus gastrocnemius and musculus tibialis cranialis. In severe cases, muscular rupture and multiple intermuscular blood clots could be observed. Histological analysis showed rupture of myofibers and massive red blood cells between muscle bundles. Besides, infiltration of connective tissues and inflammatory lesions could be seen. However, no differences were observed in other organs between these two groups. The main ultrastructural characteristics were myofibrillar rupture and split, accompanied by mitochondrial membrane disintegration and vacuolization. All these results indicate that the haemorrhage in crus is a focal myopathy with the characteristics of bleeding, rupture, and inflammatory lesions. Research highlights CTV was a feasible method to evaluate the hind limb veins in Pekin ducks. The focal myopathy presented here only affected crural muscles. The focal myopathy was characterized by bleeding, rupture and inflammatory lesions.

RNA-Seq transcriptome analysis of breast muscle in Pekin ducks supplemented with the dietary probiotic Clostridium butyricum

BACKGROUND

Increased attention is being paid to breast muscle yield and meat quality in the duck breeding industry. Our previous report has demonstrated that dietary Clostridium butyricum (C. butyricum) can improve meat quality of Pekin ducks. However, the potential biological processes and molecular mechanisms that are modulated by dietary C. butyricum in the breast muscle of Pekin ducks remain unknown.

RESULTS

Supplementation with C. butyricum increased growth performance and meat yield. Therefore, we utilized de novo assembly methods to analyze the RNA-Seq transcriptome profiles in breast muscle to explore the differentially expressed genes between C. butyricum-treated and control Pekin ducks. A total of 1119 differentially expressed candidate genes were found of which 403 genes were significantly up-regulated and 716 genes were significantly down-regulated significantly. qRT-PCR analysis was used to confirm the accuracy of the of RNA-Seq results. GO annotations revealed potential genes, processes and pathways that may participate in meat quality and muscle development. KEGG pathway analysis showed that the differentially expressed genes participated in numerous pathways related to muscle development, including ECM-receptor interaction, the MAPK signaling pathway and the TNF signaling pathway.

CONCLUSIONS

This study suggests that long-time dietary supplementation with C. butyricum can modulate muscle development and meat quality via altering the expression patterns of genes involved in crucial metabolic pathways. The findings presented here provide unique insights into the molecular mechanisms of muscle development in Pekin ducks in response to dietary C. butyricum.

The Pekin duck programmed death ligand-2: cDNA cloning, genomic structure, molecular characterization and expression analysis

Programmed death-1 (PD-1), upon engagement by its ligands, programmed death ligand-1 (PD-L1) and programmed death ligand-2 (PD-L2), provides signals that attenuate adaptive immune responses. Here we describe the identification of the Pekin duck PD-L2 (duPD-L2) and its gene structure. The duPD-L2 cDNA encodes a 321 amino acid protein that has an amino acid identity of 76% and 35% with chicken and human PD-L2, respectively. Mapping of the duPD-L2 cDNA with duck genomic sequences revealed an exonic structure similar to that of the human Pdcd1lg2 gene. Homology modelling of the duPD-L2 protein was compatible with the murine PD-L2 ectodomain structure. Residues known to be important for PD-1 receptor binding of murine PD-L2 were mostly conserved in duPD-L2 within sheets A and G and partially conserved within sheets C and F. DuPD-L2 mRNA was constitutively expressed in all tissues examined with highest expression levels in lung, spleen, cloaca, bursa, cecal tonsil, duodenum and very low levels of expression in muscle, kidney and brain. Lipopolysaccharide treatment of adherent duck PBMC upregulated duPD-L2 mRNA expression. Our work shows evolutionary conservation of the PD-L2 ectodomain structure and residues important for PD-1 binding in vertebrates including fish. The information provided will be useful for further investigation of the role of duPD-L2 in the regulation of duck adaptive immunity and exploration of PD-1-targeted immunotherapies in the duck hepatitis B infection model.

Systematic analysis of feeding behaviors and their effects on feed efficiency in Pekin ducks

Background

Feeding behavior study is important for animal husbandry and production. However, few studies were conducted on the feeding behavior and their relationship with feeding efficiency in Pekin ducks. In order to investigate the feeding behavior and their relationship with feed efficiency and other economic traits in Pekin ducks, we selected 358 male Pekin ducks and recorded feeding information between 3 to 6 wk of age using automatic electronic feeders, and compared the feeding behavior under different residual feed intake (RFI) levels.

Results

We observed that total feed time, daily feed intake and feed intake per meal had strong positive correlations with feed efficiency traits; moreover, strong correlation between feed intake per meal and body weight was found (R=0.32, 0.36). Daily feeding rate meal and meal duration had weak correlations with feed efficiency (R=0.14~0.15). The phenotypic correlation of between-meal pauses, with feed efficiency was not observed. When daily changes were analyzed, high RFI ducks had the highest feed consumption over all times, and obvious differences in daily visits were found among different RFI level animals during the middle period; these differences were magnified with age, but there was no difference in daily meal number. Moreover, our data indicate that high RFI birds mainly take their meals at the edge of the population enclosure, where they are more susceptible to environmental interference.

Conclusions

Overall, this study suggests that the general feeding behaviors can be accurately measured using automatic electronic feeders and certain feeding behaviors in Pekin ducks are associated with improved feed efficiency.

Electronic supplementary material

The online version of this article (10.1186/s40104-017-0212-2) contains supplementary material, which is available to authorized users.

Threonine supplementation reduces dietary protein and improves lipid metabolism in Pekin ducks

1. This study was conducted to investigate the efficiency of threonine (Thr) supplementation on reducing dietary crude protein (CP) content and the effects of Thr on lipid metabolism in Pekin ducks. The effects of dietary CP concentration (160, 190 and 220 g/kg) and Thr supplemental concentration (0, 0.7, 1.4, 2.1 and 2.8 g/kg) on growth performance, carcass, liver lipid and plasma profiles were determined in Pekin ducks from 1-21 d of age. 2. A total of 720-d-old male Pekin ducks were randomly allotted to 1 of 15 dietary treatments with 6 replicate cages of 8 birds per cage for each treatment according to average body weight. 3. Dietary Thr supplementation improved growth performance and breast muscle percentage at all CP diets, and ducks fed Thr-supplemented diets had higher plasma concentrations of some plasma amino acids. Thr supplementation reduced the concentrations of total lipid, triglyceride, cholesterol in liver, and plasma low density lipoprotein cholesterin concentration at 160 and 190 g/kg CP, whereas it increased triglyceride concentration at 160 g/kg CP. 4. Thr requirements based on quadratic broken-line model estimation were 6.6 and 7.0 g/kg for optimal average daily gain (ADG), and 6.7 and 7.3 g/kg for breast muscle percentage of Pekin ducks from 1-21 d of age at 190 and 220 g/kg CP, respectively. The dietary Thr requirements and estimated ADG (55.18 vs. 55.86 g/d/bird) and breast muscle percentage (2.79% vs. 2.75%) of Pekin ducks did not differ between 190 and 220 g/kg CP according to the t-test results. 5. Dietary CP level could be reduced to 190 g/kg in Pekin ducks from 1-21 d of age with Thr supplementation to balance dietary amino acids, and Thr supplementation prevented excess liver lipid deposition in this instance.

Pathogenicity of Pekin duck- and goose-origin parvoviruses in Pekin ducklings

Goose parvovirus (GPV) usually affects goslings and Muscovy ducks but not Pekin ducks. Earlier works showed that a variant GPV can cause short beak and dwarfism syndrome (SBDS) in Pekin ducks. Here, we investigated the pathogenicity of a variant GPV of Pekin duck-origin (JS1) and a classical GPV of goose-origin (H) in Pekin ducklings. Following intramuscular infection at two days of age, both JS1 and H strains influenced weight gain and development of beaks and bones of wings and legs, and caused microscopic lesions of internal organs of ducks. However, the clinical signs typical of SBDS could only be replicated with the JS1 isolate. The findings suggest that both variant and classical GPVs are pathogenic for Pekin ducklings, while the former is more virulent than the latter. Using a quantitative real-time PCR assay, high levels of viral load were detected from bloods, internal organs, leg muscles, and ileac contents in JS1- and H-infected ducks from 6h to 35days postinfection (DPI). Using a GPV VP3-based ELISA, antibodies in sera of JS1- and H-infected ducks were detectable at 1 DPI and then persistently rose during the subsequent five weeks. These results suggest that both variant and classical GPVs can infect Pekin ducklings. The present work contributes to the understanding of pathogenicity of GPV to Pekin ducks and may provide clues to pathogenesis of GPV-related SBDS.

Host Differences Affecting Resistance and Susceptibility of the Second Generation of a Pekin Duck Flock to Duck Hepatitis A Virus Genotype 3

Earlier work suggested the possibility to anti duck hepatitis A virus genotype 3 (DHAV-3) using the resistance breeding strategy. Here, we report the creation of the second generations of a resistant Pekin duck flock (designated Z8R2) and a highly susceptible Pekin duck flock (designated Z8S2) and the investigation of their responses to DHAV-3. Experimental infection with DHAV-3 at 7 days of age resulted in a high mortality (66.3%) in 11 susceptible Z8S2 families and an extremely low mortality rate (2.67%) in 32 Z8R2 families, indicating that Z8R2 exhibits strong resistance to DHAV-3, while Z8S2 is highly susceptible to the virus. Detection of DHAV-3 in the liver between 1 and 60 hours post inoculation (hpi) suggests that DHAV-3 can be replicated rapidly and efficiently in the liver of Z8S2, whereas the replication of the virus in the liver of Z8R2 is suppressed greatly. High levels of serum biochemical markers (e.g., ALT, AST, ALP and GGT) were detected in Z8S2 at 24 hpi, which were significantly higher than those in Z8R2. Analysis of transcripts in the liver revealed that the expression levels of several pattern recognition receptors (PRRs) (e.g., TLR4/7, RIG-1 and MDA5) and cytokines (e.g., IL-2, IL-6, IL-8, IFN-α, and IFN-γ) in Z8S2 were significantly higher than those in Z8R2 at 12 and 24 hpi. Together these findings suggest that Z8R2 and Z8S2 Pekin ducks, which were derived from the same Z8 line, exhibit disparate pathogenic outcomes following DHAV-3 infection. Therefore, it is possible to select a Pekin duck flock resistant to DHAV-3 employing the strategy described here. It is likely that the high viral load and the strong inflammatory response correlate with the high susceptibility of Z8S2 Pekin ducks to DHAV-3.