FMO3 deficiency of duck leads to decreased lipid deposition and increased antibacterial activity.

BACKGROUND: Most duck eggs possess a fishy odor, indicating that ducks generally exhibit impaired trimethylamine (TMA) metabolism. TMA accumulation is responsible for this unpleasant odor, and TMA metabolism plays an essential role in trimethylaminuria (TMAU), also known as fish odor syndrome. In this study, we focused on the unusual TMA metabolism mechanism in ducks, and further explored the unclear reasons leading to the debilitating TMA metabolism. METHODS: To achieve this, transcriptome, proteome, and metagenome analyses were first integrated based on the constructed duck populations with high and low TMA metabolism abilities. Additionally, further experiments were conducted to validate the hypothesis regarding the limited flavin-containing monooxygenase 3 (FMO3) metabolism ability of ducks. RESULTS: The study demonstrated that liver FMO3 and cecal microbes, including Akkermansia and Mucispirillum, participated in TMA metabolism in ducks. The limited oxidation ability of FMO3 explains the weakening of TMA metabolism in ducks. Nevertheless, it decreases lipid deposition and increases antibacterial activity, contributing to its survival and reproduction during the evolutionary adaptation process. CONCLUSIONS: This study demonstrated the function of FMO3 and intestinal microbes in regulating TMA metabolism and illustrated the biological significance of FMO3 impairment in ducks.

Effects of different duck rearing systems on egg flavor and quality and microbial diversity.

The fishy odor of duck eggs has restricted their consumption and industrial development, a problem that producers need to address. We estimated the effects of cage, floor, and pond rearing systems on duck egg flavor, egg quality, and microbial diversity by evaluating yolk trimethylamine (TMA) content, egg quality, and the differences between duck cecum (cage cecum, CC; floor cecum, FC; pond cecum, PC) and the environment (cage environment, CE; floor environment, FE; pond environment, PE). The results show that the yolk TMA content of the floor-rearing and pond-rearing systems was significantly higher than that of the cage-rearing system (P < 0.001), with no difference between the floor and pond-rearing systems. No significant differences were detected in egg quality among the rearing systems. Firmicutes, Actinobacteria, and Bacteroidetes were the dominant phyla in the cecum, and in the rearing environment, Firmicutes, Actinobacteria, Bacteroidetes, and Proteobacteria were the dominant phyla. The results of α and ß diversity analyses show that changes in the rearing system affected the composition and diversity of duck cecal microbes. In addition, we screened several genera that may be related to the production of TMA in duck cecum under different rearing systems using LEfSe analysis; for example, Subdoligranulum in the CC group; Romboutsia in the FC group; and Lactobacillus, Clostridium, and Streptococcus in the PC group. In conclusion, the rearing system affects the cecal microbes of ducks, which in turn affect the deposition of TMA in duck eggs but have no adverse effect on egg quality. This study provides a basis for the development of rearing strategies to reduce the fishy odor of egg yolk in the duck industry.

Associations of the T329S Polymorphism in Flavin-Containing Monooxygenase 3 With Atherosclerosis and Fatty Liver Syndrome in 90-Week-Old Hens.

This study aimed to evaluate the effects of the spontaneous genetic mutation T329S in flavin-containing monooxygenase 3 (FMO3) on atherosclerosis (AS), fatty liver syndrome (FLS), and adiposity in 90-week-old layers. At 90 weeks of age, 27 FMO3 genotyped Rhode Island White chickens (consisting of nine AA hens, nine AT hens, and nine TT hens) with normal laying performance were selected. The AS lesions, incidence of FLS, fat deposition, metabolic characteristics, and production performance of these egg-layers with different FMO3 genotypes were assessed. The T329S mutation in TT hens reduced the AS lesions (P < 0.01) and altered the plasma metabolic indices more than it did in the AA and AT hens. Furthermore, it reduced the incidence of FLS, hepatic triglyceride deposition (P < 0.05), liver indices (P < 0.05), and fat deposition (P < 0.05) in the subcutis and abdomen of TT hens compared to those of AA and AT hens. Moreover, as an effect of T329S, TT hens laid a higher than average number of eggs and maintained a higher egg-laying rate from 68 to 90 weeks than AA and AT hens. Our study confirmed that the T329S mutation in FMO3 could reduce the development of AS lesions, the incidence of FLS, and fat deposition, which are associated with changes in plasma and hepatic metabolic indices and improvements in the laying performance of older layers. Our results may provide a new strategy for using the T329S mutation to improve the health status and production performance of layers during the late laying period.

Choline diet improves serum lipid parameters and alters egg composition in breeder ducks.

BACKGROUND: Choline is an important nutrient, playing key roles in numerous metabolic pathways relevant to animal health. OBJECTIVES: The objective of this study was to evaluate the effect of dietary choline on the lipid parameters, cardiovascular health (CVH), and levels of egg trimethylamine (TMA) and cholesterol in breeder ducks during the late laying period. METHODS: A total of 60 Jingjiang ducks were randomly separated into six replicates of 10 ducks each. After peak production until 65 weeks of age, the birds were fed a control basal diet. The same ducks served as the control group until 65 weeks of age, when the same ducks served as the choline-supplemented group, after 15 days of dietary choline supplementation at 2955 mg/kg choline above and over the basal diet initially provided. The 15 days of choline supplementation included an initial 5-day acclimatisation period. RESULTS: Dietary choline supplementation increased serum TMA (p < 0.01), high-density lipoprotein cholesterol, very low-density lipoprotein, and triglyceride levels in older breeder ducks. However, it did not change the levels of trimethylamine N-oxide but decreased the atherosclerosis index compared with those of the control group (p < 0.01). Moreover, it increased (p < 0.01) the egg yolk TMA levels but did not change the concentrations of cholesterol in egg yolk. CONCLUSIONS: Dietary choline supplementation had a beneficial effect on lipid parameters and CVH in older breeder ducks, although it increased the serum and egg yolk TMA levels.

Antibacterial Properties of TMA against Escherichia coli and Effect of Temperature and Storage Duration on TMA Content, Lysozyme Activity and Content in Eggs.

Studies on trimethylamine (TMA) in egg yolk have focused on how it impacts the flavor of eggs, but there has been little focus on its other functions. We designed an in vitro antibacterial test of TMA according to TMA concentrations that covered the TMA contents typically found in egg yolk. The change in TMA content in yolk was analyzed at different storage temperatures and for different storage durations. The known antibacterial components of eggs, including the cuticle quality of the eggshell and the lysozyme activity and content in egg white, were also assessed. The total bacterial count (TBC) of different parts of eggs were detected. The results showed that the inhibitory effect of TMA on Escherichia coli (E. coli) growth increased with increasing TMA concentration, and the yolk TMA content significantly increased with storage duration (p < 0.05). The cuticle quality and lysozyme content and activity significantly decreased with storage time and increasing temperature, accompanied by a significant increase in the TBC on the eggshell surface and in the egg white (p < 0.05). This work reveals a new role for trace TMA in yolks because it reduces the risk of bacterial colonization, especially when the antibacterial function of eggs is gradually weakened during storage.

Cuticle deposition duration in the uterus is correlated with eggshell cuticle quality in White Leghorn laying hens.

The cuticle formed in the uterus is the outermost layer as the first defense line of eggshell against microbial invasions in most avian species, and analyzing its genetic regulation and influencing factors are of great importance to egg biosecurity in poultry production worldwide. The current study compared the uterine transcriptome and proteome of laying hens producing eggs with good and poor cuticle quality (GC and PC, the top and tail of the cuticle quality distribution), and identified several genes involved with eggshell cuticle quality (ESCQ). Overall, transcriptomic analysis identified 53 differentially expressed genes (DEGs) between PC versus GC group hens, among which 25 were up-regulated and 28 were down-regulated. No differences were found in the uterine proteome. Several DEGs, including PTGDS, PLCG2, ADM and PRLR related to uterine functions and reproductive hormones, were validated by qPCR analysis. Egg quality measurements between GC and PC hens showed GC hens had longer laying interval between two consecutive ovipositions (25.64 ± 1.23 vs 24.94 ± 1.12 h) and thicker eggshell thickness (352.01 ± 23.04 vs 316.20 ± 30.58 µm) (P < 0.05). Apart from eggshell traits, other egg quality traits didn't differ. The result demonstrated eggshell and cuticle deposition duration in the uterus is one of the major factors affecting ESCQ in laying hens. PTGDS, PLCG2, ADM and PRLR genes were discovered and might play crucial roles in cuticle deposition by regulating the uterine muscular activities and secretion function. The findings in the present study provide new insights into the genetic regulation of cuticle deposition in laying hens and establish a foundation for further investigations.

T329S Mutation in the FMO3 Gene Alleviates Lipid Metabolic Diseases in Chickens in the Late Laying Period.

The T329S mutation in flavin-containing monooxygenase 3 (FMO3) impairs the trimethylamine (TMA) metabolism in laying hens. The TMA metabolic pathway is closely linked to lipid metabolic diseases, such as atherosclerosis and fatty liver disease. We aimed to evaluate the effects of the T329S mutation in FMO3 on lipid metabolism in chickens during the late laying period. We selected 18 FMO3 genotyped individuals (consisting of six AA, six AT, and six TT hens) with similar body weight and production performance. The lipid metabolism and deposition characteristics of the laying hens with different genotypes were compared. The T329S mutation moderated the serum-lipid parameters in TT hens compared to those in AA and AT hens from 49 to 62 weeks. Furthermore, it reduced the serum trimethylamine N-oxide concentrations and increased the serum total bile acid (p < 0.05) and related lipid transporter levels in TT hens. Moreover, it significantly (p < 0.01) decreased atherosclerotic lesions and hepatic steatosis in TT hens compared to those in the AA and AT hens. Our findings may help improve the health status in laying hens during the late laying period.

Analysis of fishy taint in duck eggs reveals the causative constituent of the fishy odor and factors affecting the perception ability of this odor.

Fresh duck eggs normally have an unpleasant fishy odor when compared with eggs from other poultry. However, the cause of this unpleasant smell remains unknown. Besides, we have limited knowledge regarding the perception ability of this odor. Therefore, we aimed to identify the causative substances responsible for the fishy odor in duck eggs, and further evaluate the factors affecting the perception ability of this odor. We detected and quantified the volatile substances in the yolks of Jingjiang duck and Beijing duck eggs using headspace gas chromatography, and evaluated the fishy odor rating scores. We performed association studies on the relationship between the relative content of volatile substances and fishy odor rating scores. The fishy odor of egg yolks from different species/breeds was also characterized. Furthermore, we assessed the species/breeds of poultry eggs and the effects of gender and region of the evaluators on the fishy odor rating score by using an ordinal logistic regression model. Results showed that trimethylamine (TMA) is responsible for the fishy odor of duck eggs, which was confirmed with subsequent verification (P < 0.001). The fishy odor of duck eggs was stronger than that of chicken eggs; the fishy odor of Jingjiang duck eggs was the strongest. Results also indicated that the fishy odor perception ability was affected by the gender and region of the evaluators (P < 0.001). Overall, these data clarified that TMA imparted the fishy odor to duck eggs; factors such as gender and region may affect the fishy odor perception ability.

Impact of cuticle quality and eggshell thickness on egg antibacterial efficiency.

The cuticle is the first barrier against bacterial trans-shell penetration. To evaluate the cuticle quality among different colored eggshells, an efficient and reliable method is proposed in this paper on the basis of the opacity theory. It is shown that the Spearman's rank correlation coefficients between the proposed opacity method and the reported reflectance and ΔE*ab methods are all more than 0.90 in measuring the cuticle deposition for the same breed eggs, indicating that the result measured by the opacity method is credible. In addition, the validity of opacity method is also verified by the Escherichia coli penetration experiments performed on the eggs of Dwarf Layer (tinted-shelled), Hy-Line Brown (brown-shelled), and White Leghorn (white-shelled) birds. Results show that the Dwarf Layer eggs, with the thickest cuticle deposition, have the lowest bacterial penetration ratio than the eggs of the other 2 investigated breeds. We found that eggshell thickness is another important factor influencing bacterial penetration apart from the cuticle. Therefore, enhancing cuticle deposition and eggshell thickness would significantly improve the eggs' antibacterial efficiency. It is found that the antibacterial efficiency will reach as high as 98% in such a case where the cuticle opacity is over 27.5% and the eggshell is thicker than 340 µm. No significant difference was found in pore density between the penetrated and non-penetrated eggs. Moreover, according to the data for 3 regions of the penetrated eggs, we found that the sharp end shows the highest proportion of bacterial contamination compared with the blunt end and equator. The cuticle quality at equator shows a strong positive correlation between the blunt and sharp end (r2 = 0.8 and 0.7, respectively, P < 0.05). The cuticle at the equator can be selected as an indicator for cuticle breeding to improve the cuticle quality at the blunt and sharp end simultaneously. These results are of significance for the improvement of egg quality and safety in modern commercial breeding.