Effects of Dietary n-6:n-3 PUFA Ratios on Lipid Levels and Fatty Acid

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Effects of dietary n-6:n-3 PUFA ratios on lipid levels and fatty acid profile of Cherry valley ducks at 15–42 days of age mengmeng li, shuangshuang zhai, qiang xie, lu tian, xiaocun li, jiaming zhang, hui ye, yongwen zhu, lin yang, and wence wang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b02918 • Publication Date (Web): 30 Oct 2017 Downloaded from http://pubs.acs.org on November 4, 2017

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Journal of Agricultural and Food Chemistry

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Effects of dietary n-6:n-3 PUFA ratios on lipid levels and fatty acid

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profile of Cherry valley ducks at 15–42 days of age

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Mengmeng Li†, Shuangshuang Zhai†, Qiang Xie†, Lu Tian†, Xiaocun Li‡, Jiaming Zhang‡,

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Hui Ye†, Yongwen Zhu†, Lin Yang†*, Wence Wang†*

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†

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University, Guangzhou 510642, China

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‡

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*

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Phone: +86 20 85285232. Fax: +86 20 85285232.

College of Animal Science & College of Marine Sciences, South China Agricultural

Henan Huaying Agriculture development Co., Ltd, Xinyang 464000, China Correspondence should be addressed to [email protected] and [email protected].

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ACS Paragon Plus Environment


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Abstract

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The objective of this study was to investigate the effects of dietary n-6:n-3 PUFA

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ratio on growth performance, serum and tissue lipid levels, fatty acid profile, and hepatic

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expression of fatty acid synthesis genes in ducks. A total of 3,168 15-day old ducks were

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fed different n-6:n-3 PUFA ratios: 13:1 (control), 10:1, 8:1, 6:1, 4:1, and 2:1. The feeding

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trial lasted four weeks. Our results revealed that dietary n-6:n-3 PUFA ratios had no

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effects on growth performance. The 2:1 group had the highest serum triglyceride levels.

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Serum total cholesterol and HDL levels were higher in the 13:1 and 8:1 groups than in

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the 6:1 and 2:1 groups. The concentration of C18:3n-3 in serum and tissues (liver and

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muscle) increased with decreasing dietary n-6:n-3 PUFA ratios. The hepatic expression of

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FADS2, ELOVL5, FADS1, and ELOVL2 increased on a quadratic function with

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decreasing dietary n-6:n-3 PUFA ratios. These results demonstrate that lower dietary

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n-6:n-3 PUFA ratios had strong effects on the fatty acid profile of edible parts and the

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deposition of n-3 PUFAs in adipose tissue of ducks.

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Keywords: n-6:n-3 PUFA ratio, serum lipid level, fatty acid profile, gene mRNA

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expression, duck

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Introduction

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Based on their chemical structure, essential fatty acids are classified into n-3 and n-6

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polyunsaturated fatty acids (PUFAs). The n-3 and n-6 PUFAs are not inter-convertible

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and have opposite physiological functions1. Specifically, n-3 PUFAs decrease

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inflammatory signaling and fatty acid synthesis and increase lipid oxidation2. Fatty acid

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composition, especially the n-6:n-3 PUFA ratio of cell and organelle membranes, affect

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membrane function and cellular processes such as cell death and survival3. Metabolism

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and organ function are dependent on a balanced concentration of n-6 and n-3 PUFAs4, 5.

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Studies have reported that adequate dietary n-6:n-3 PUFA ratios are 6:1 and 3:1 in geese6

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and 2.5:1 and 5:1 in chickens7. High n-6 PUFA levels and imbalanced n-6:n-3 PUFA

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ratios are associated with the development of fatty acid deposition, adverse sperm quality,

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and disease8, 9.

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Dietary n-6:n-3 PUFA ratios decreased with increasing n-3 PUFA levels in animal

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tissues and products, including eggs, milk, and meat10. There is a large variation in

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n-6:n-3 PUFA ratios among commercial fattening duck feeds11. Conventional diets

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contain high n-6 PUFA levels and low n-3 PUFA levels12. Vegetable and seed oils with

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high levels of alpha-linolenic acid (ALA; C18:3n-3) have been used in livestock feed13.

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Linseed oil, an n-3 PUFA source, increases n-3 PUFA content and decreases n-6:n-3

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PUFA ratios in diets14. Previous studies in poultry and monogastric animals revealed that,

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compared with tallow- and rapeseed-supplemented diets, linseed oil-supplemented diets

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increase n-3 PUFA levels and decrease n-6:n-3 PUFA ratios in muscle of broiler and in



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longissimus dorsi of swine7,

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contributing factors to cardiovascular diseases in humans16. In humans, the optimal

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n-6:n-3 PUFA ratio is < 517, 18. Therefore, increasing public awareness of the health

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benefits of low n-6:n-3 PUFA ratios has prompted researchers to improve the fatty acid

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profile of commonly consumed animal products.

. High n-6:n-3 PUFA ratios in animal products are

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Dietary n-6:n-3 PUFA ratios affect the regulation of genes involved in the

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metabolism of n-3 and n-6 fatty acids19-21. The conversion of ALA into eicosapentaenoic

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(EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) occurs through the sequential

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actions of ∆-6 desaturase (encoded by FADS2), elongases (encoded by ELOVL5 and

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ELOVL2), and ∆-5 desaturase (encoded by FADS1), which are susceptible to the

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nutritional status of the organism22-24. Fatty acid composition analysis have revealed that

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ALA-supplemented diets increased n-3 PUFA levels in broilers and pigs25, 26, but this

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effect is weak in geese6, 27. Therefore, it is important to investigate the effect of dietary

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n-6:n-3 PUFA ratios on gene expression and n-3 PUFA content in duck tissues. In this

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study, we assessed the effect of n-6:n-3 PUFA ratios on the fatty acid composition of

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duck meat and evaluated the feasibility in producing n-3 fatty-acid-enriched ducks.

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Materials and Methods

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Experimental design and diets

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A total of 3,168 15-day old Cherry valley ducks of the commodity generation

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(average weight: 728.56 ± 1.83 g) were randomly divided into six treatment groups. Each

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treatment group had six replicates (males and females), each consisting of 88 ducks. This

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ducks from one batch were fed the same dietary at 1-14 days of age. The six treatment

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groups were fed diets supplemented with linseed oil and containing different n-6:n-3

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PUFA ratios: 13:1 (control), 10:1, 8:1, 6:1, 4:1, and 2:1. The feeding trial lasted four

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weeks. The isonitrogenous and isocaloric experimental diets (dietary ME and CP levels

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were 12.50 MJ/kg and 17%, respectively) were formulated to meet or exceed the nutrient

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requirements of ducks based on NRC (1994) recommendations (Table 1). The nutrient

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levels and fatty acid composition of the experimental diets are presented in Table 1. All

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ducks had ad libitum access to the diets and water.

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Sample collection

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Animal handling and sampling protocols were approved by the Animal Care and

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Use Committee of South China Agricultural University; all efforts were made to

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minimize the suffering of animals according to recommendations proposed by the

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European Commission (1997). The study was performed according to the protocol

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D201611160945519 and conducted in accordance with relevant guidelines. Following a

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12-h fast, body weight (BW) and feed intake of the ducks (42 d of age) were recorded,

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and average daily gain (ADG), average daily feed intake (ADFI), and average feed: gain



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(F/G) were calculated. Six ducks from each replicate were selected and sacrificed at the

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end of the experiment (three male and three female). Blood samples were collected via

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jugular vein puncture, and serum was obtained after centrifugation of blood samples at

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2,000 g for 15 min at 4°C and stored at –20°C. After bleeding, a small portion of the liver

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was collected, immediately placed in liquid N2, and stored at −80°C for hepatic gene

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expression analysis. A large portion of the liver, breast, and thigh muscle were collected

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and stored at −30°C for fatty acid analysis.

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Serum biochemical parameters

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Serum total triglyceride (TG), total cholesterol (TC), low-density lipoprotein

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cholesterol (LDL), and high-density lipoprotein cholesterol (HDL) concentrations were

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determined spectrophotometrically (Bayer Diagnostics Manufacturing Ltd., Dublin,

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Ireland) using commercial kits (Biosino Biotechnology and Science Inc., Beijing, China;

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catalog numbers 0180, 0221, 0215, and 0200 for the analysis of TG, TC, LDL, and HDL,

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respectively). These indicators were determined by Guangzhou LabGene Biotech Co.,

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Ltd. There were six replicates per sample.

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Fatty acid composition

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Fatty acid composition was determined as previously reported28. Briefly, 2 g of

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sample was extracted with chloroform: methanol (2:1; v/v) according to the method by

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Folch29. Total fat was converted into fatty acid methyl esters (FAMEs) using a mixture of

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boron-trifluoride, hexane, and methanol (35:20:45 v/v)30. FAME profiles were

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determined by gas chromatography (GC; Model 7890A, Agilent Technologies, Palo Alto,


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CA) as reported by Sukhija and Palmquist31. The gas chromatograph was equipped with a

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capillary column (60 m × 0.25 mm DB-23, 0.25 film thickness; Agilent Technologies,

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Palo Alto, CA). Nitrogen (1.1 mL/min) was used as the carrier gas, and the split/splitless

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injector was used at a split/splitless ratio of 30:1. Injector and detector temperatures were

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250°C and 300°C, respectively. The column oven temperature was maintained at 140°C

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for 5 min after sample injection and was programmed to increase from 140°C to 220°C at

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5°C/min and kept at 220°C for 16 mins. FAME separation was recorded using the GC

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Chem Station software (Agilent Technologies, Palo Alto, CA). By comparing the FAME

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profile of the samples with those of FAME standards (Supelco, 37 Component FAME

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mix C4-C24, Catalog No. 47885-U, Supelco, Bellefonte, PA), we identified the fatty acids

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in serum and tissues. The results were recorded as percentage of the total fatty acids.

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Real-time PCR

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Total RNA was extracted from the frozen tissues using Trizol reagent (Invitrogen,

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Carlsbad, CA). RNA was digested with DNase I (RNase-Free DNase set; Qiagen)

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(Invitrogen, Carlsbad, CA, USA). First-strand cDNA was synthesized using an equal

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amount of total RNA and High Capacity RNA-to-cDNA Kit (Applied Bio-systems,

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Madrid, Spain). The sequence of primers used in real-time PCR assays are shown in

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Table 2. Real-time PCR was performed in an ABI 7500 (Applied Bio-systems, Foster

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City, CA) using SYBR Green Quantitative PCR kit (TaKaRa). The thermal cycling

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conditions consisted of one cycle at 95°C for 30 s followed by 40 cycles at 95°C for 5 s

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and 60°C for 34 s. The target genes and reference genes (GAPDH and β-actin) were used



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to calculate PCR efficiency. The mRNA expression of each gene was calculated by the

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2−∆∆Ct method32.

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Statistical analysis

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Data were analyzed by one-way ANOVA and Tukey test using SAS for Windows

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version 9.2 (SAS Institute Inc., Cary, NC). Data were expressed as mean ± standard

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deviation. Differences among the groups were considered significant at P < 0.05.

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Results

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Growth performance

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Table 3 shows the growth performance results. Dietary n-6:n-3 PUFA ratios had no

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effects on BW of ducks at 42 d of age. Additionally, dietary n-6:n-3 PUFA ratios had no

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effects on ADG, ADFI, or F/G of ducks at 15–42 d of age (P > 0.05).

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Serum lipid concentrations

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Table 4 shows the serum TC, TG, HDL, and LDL concentrations of ducks at 15–42 d

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of age. Dietary n-6:n-3 PUFA ratios had no effects on serum LDL concentrations (P >

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0.05). The 2:1 treatment group had higher serum TG concentrations than ducks fed the

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other diets (P < 0.05). Serum TC and HDL concentrations were higher in the 13:1 and 8:1

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groups than in the 6:1 and 2:1 groups (P < 0.05). Serum lipid concentrations (TG, TC,

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and HDL) were affected by dietary n-6:n-3 PUFA ratios.

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Tissue fat content

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Dietary n-6:n-3 PUFA ratios had an effect (P < 0.05) on liver, breast, and thigh

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muscle fat of ducks from 15 d to 42 d of age (Table 5). Ducks fed the 6:1 treatment had

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lower liver fat content than ducks fed the 4:1 treatment (P < 0.05). The lowest fat content

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in breast muscle and thigh muscle was observed in the 4:1 (P < 0.05) and 6:1 (P < 0.05)

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groups, respectively.

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Fatty acid composition

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Tables 6–9 show the fatty acid composition of serum, liver, breast, and thigh muscle.

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Serum arachidonic acid (AA; C20:4 n-6) was significantly (P < 0.05) lower in the 4:1 and



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2:1 treatment groups than in the control group (13:1; Table 6). Ducks fed the 13:1 and

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10:1 treatments had higher AA concentrations of liver than birds fed the 6:1, 4:1, or 2:1

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treatments (P < 0.01); the 8:1 group reached a plateau (Table 7). However, dietary

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n-6:n-3 PUFA ratios had no effect on AA concentrations of breast and thigh muscle

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(Tables 8 and 9, P > 0.05). The EPA concentrations in serum and liver of the 2:1

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treatment group were higher (P < 0.01) than those in other groups (Tables 6 and 7).

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Additionally, the 4:1 treatment group had higher (P < 0.05) serum EPA concentrations

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than other groups (Table 6). The EPA concentrations in breast muscle were higher in the

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8:1 and 2:1 groups than in the 10:1 group (Table 8; P < 0.05). However, there were no

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significant differences in DHA concentrations among all groups (Tables 7 and 8; P >

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0.05). EPA and DHA were not detected in thigh muscle (Table 9). The proportions of

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C18:3n3 and n-3 PUFAs (C18:3n3, C20:5n3, and C22:6n3) in serum and tissues (liver,

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breast, and thigh muscle) increased linearly (P < 0.01) with decreasing dietary n-6:n-3

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PUFA ratios (Tables 6, 7, 8, and 9). In contrast, the proportions of n-6 PUFAs (C18:2,

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C20:3n6, and C20:4n6) and the n-6:n-3 PUFA ratios in serum and tissues decreased

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linearly (P < 0.01) with decreasing dietary n-6:n-3 PUFA ratios (Tables 6, 7, 8, and 9) .

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Hepatic gene expression

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Figure 1A–D shows the relative gene expression in the liver of ducks. Hepatic

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FADS2 mRNA expression was higher in the 8:1 group than in the 13:1 and 2:1 groups

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(Figure 1A; P < 0.05). ELOVL5 mRNA expression was higher in the 6:1 group than in

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the 13:1, 10:1, and 2:1 groups (Figure 1B; P < 0.05). FADS1 mRNA expression


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increased in the 8:1 and 4:1 groups (Figure 1C; P < 0.05), and ELOVL2 mRNA

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expression was the highest in the 4:1 group (Figure 1D). The hepatic expression of

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FADS2, ELOVL5, FADS1, and ELOVL2 increased on a quadratic function with

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decreasing dietary n-6:n-3 PUFA ratios; however, the 13:1 group had lower mRNA

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expression levels (P < 0.05) than the other groups.

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Discussion

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Previous studies have shown that n-6 and n-3 PUFA supplementation improves the

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serum lipid concentrations and muscle fatty acid composition of pigs and chickens7, 32.

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Our study investigated the effect of dietary n-6:n-3 PUFA ratios on growth performance,

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lipid levels, and fatty acid profile of ducks at 15–42 days of age.

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In this study, dietary n-6:n-3 PUFA ratios had no effects on growth performance of

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ducks. Dietary LA:ALA ratios of 17:1, 8:1, 4:1, and 2:1 have no effects on the growth

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performance of chicken over 16 weeks of age33. In poultry, linseed oil does not affect

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feed conversion rate34, and the effects of dietary oil supplements on the growth

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performance of broilers are inconclusive35-37. This result could be attributed to similar fat

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content in the experimental diets or similar feed intake during the trial.

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A recent study revealed that dietary ALA does not affect serum TG concentrations38.

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Some studies have reported that long chain n-3 PUFAs supplementation would reduce

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serum TG concentrations39 and ALA-rich vegetable oils lower serum TG levels in rats40.

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However, our findings showed that ducks fed the 2:1 treatment had higher serum TG

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concentrations than other groups. The results were not consistent with previous findings,

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which suggested that diets with high enough levels C18:3n-3 may contribute to glycerol

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esterification in the liver, thereby increasing serum TG levels. On the other hand, serum

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TC and HDL concentrations were higher in the 13:1 and 8:1 groups than those of 6:1 and

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2:1 groups, consistent with previous reports41, 42. Low n-6:n-3 PUFA ratios may reduce

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TC synthesis by inhibiting HMG-CoA reductase activity and changing the fatty acid


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composition of biofilms and lipoproteins to enhance the metabolic activity of lipoprotein,

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thereby promoting the breakdown of lipoproteins. A certain n-6:n-3 PUFA ratio may

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reduce blood lipids. The effect of n-6:n-3 PUFA ratios on animal lipid metabolism

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requires further studies.

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In our experiments, ducks fed the 6:1 treatment had lower hepatic fat content than

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those fed the 4:1 treatment. The lowest fat contents in breast muscle and thigh muscle

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were observed in the 4:1 and 6:1 groups, respectively. Studies have shown that low

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proportions of fatty acids (6:1 and 3:1) contribute to reduced fat deposition in geese6. In a

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recent study, dietary n-6:n-3 PUFA ratios of 5:1 facilitated the absorption and utilization

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of fatty acids in pigs32. This difference may be due to the species and fat sources used.

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Adipose fatty acid composition reflects the type of lipid and fatty acid fed to

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animals43. It should be noted that the conversion of ALA into long-chain PUFAs could be

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affected by the relative amounts of LA and ALA in diets44. Therefore, LA:ALA was

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important in the conversion of ALA into long-chain PUFAs45. The proportions of

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C18:3n3 significantly increased in the serum and muscle of ducks with decreasing dietary

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n-6:n-3 PUFA ratios, consistent with previous reports46, 47. In this study, n-6 PUFAs and

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n-6:n-3 PUFA ratios decreased and n-3 PUFA increased in duck serum and tissue with

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decreasing dietary n-6:n-3 PUFA ratios. Reducing dietary n-6 and increasing dietary n-3

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PUFA could increase C18:3n-3 and n-3 PUFA concentrations in livestock and poultry7, 48.

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Plant oils rich in ALA have been used to enhance the n-3 PUFA incorporation into duck

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meat. Therefore, dietary supplementation with different n-6:n-3 PUFA ratios may be an



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effective method of changing the fatty acid profile of meat ducks. The n-6 PUFA and n-3

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PUFA sources should be taken into account. Based on our findings, hepatic DHA was not

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significantly different among treatment groups; however, the 2:1 treatment group had the

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highest hepatic EPA levels. In Shaoxing ducks, sunflower oil-supplemented diets

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significantly increased leg muscle EPA contents, but had no significant effects on DHA43,

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consistent with our results. Linseed oil increased both EPA and docosapentaenoic acid in

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the breast muscle of chickens7 and n-3 PUFAs (especially EPA and DHA) in muscle of

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broilers49. The limited accumulation of EPA and DHA observed in ducks may be

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explained by some factors. EPA and DHA contents and poultry diets had the result of the

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relationship between the relevant content50. The longer-chain PUFAs could compete with,

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or be displaced by, increased ALA in the phospholipid fraction, which could prevent

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PUFAs from accumulating. There is little information available on the differences among

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meat-producing ducks in desaturase and elongase activities and in the expression of

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related genes responsible for desaturation and extension during the synthesis of PUFAs

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(C20-C24) from dietary ALA and LA.

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PUFAs represent the main dietary regulator of desaturase and elongase enzymes23, 51.

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The ∆-5 and ∆-6 desaturases are the rate-limiting enzymes in the synthesis of long-chain

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PUFAs52; Elongases enzymes are required for the synthesis of EPA and DHA from ALA.

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The FADS cluster and the ELOVL family may play an important role in the activities of

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desaturases and elongases53. FADS1 and FADS2 were strongly associated with LC-PUFAs

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and desaturase activity54. Our findings showed that the hepatic expression of FADS2,


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ELOVL5, FADS1, and ELOVL2 increased on a quadratic function with decreasing dietary

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n-6:n-3 PUFA ratios. However, there were no significant differences in hepatic n-3 long

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chain PUFAs (especially EPA and DHA) between the 8:1 and 6:1 treatment groups. In

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these groups, the genes were highly expressed but the enzymatic activities were not

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enhanced. Interestingly, the conversion of n-3 and n-6 fatty acids shared the same

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enzymes series (desaturase and elongase). There was competition between the n-3 and

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n-6 fatty acid families; an excess of one leads to a significant reduction in the conversion

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of the other55, 56. High FADS and ELOVL expression levels provide a target for breeding

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poultry that readily synthesizes EPA and DHA from ALA.

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In conclusion, dietary n-6:n-3 PUFA ratios affect serum lipid concentrations, tissue

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fat content, and fatty acid profile and regulate the expressions of FADS and ELOVL in

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ducks of 15–42 days of age. Additionally, decreasing dietary n-6:n-3 PUFA ratios resulted

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in a nutritionally-enriched meat with a higher content of beneficial n-3 PUFAs, especially

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C18:3n-3, and a lower n-6:n-3 PUFA ratio. Further studies should explore the effect of

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n-6:n-3 PUFA ratios on the relationship between the liver cells and lipid metabolism.

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Funding

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This work was supported by the Special Fund for Agro-scientific Research in the

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Public Interest, China (201303143-07), the China Agriculture Research System

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(CARS-43-14), the National Youth Fund Project of China (31501959), the National Key

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Research Program (2016YFD0500509-07).

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428

Figure caption

429

Figure 1. Relative hepatic mRNA expression levels of FADS2 (A), ELOVL5 (B), FADS1

430

(C), and ELOVL2 (D) in ducks fed different n-6:n-3 PUFA ratios. The equation represents

431

the quadratic regression curve, and R2 represents the correlation coefficient. Values are

432

presented as mean (n = 6) and standard errors (vertical bars).

433

represent significant differences (P < 0.05).

434


a,b,c

Different letters


435

Tables

436

Table 1. Composition and nutrient levels of experimental diets (air-dry basis, %) Dietary n-6 : n-3 PUFA ratio Item 13:1 10:1 8:1 6:1 4:1 Ingredient Corn 54.05 54.05 54.05 54.05 54.05 Flour 13.70 13.70 13.70 13.70 13.70 Soybean meal 23.65 23.65 23.65 23.65 23.65 Rice bran 2.70 2.70 2.70 2.70 2.70 Soybean oil 2.00 1.88 1.76 1.57 1.22 Linseed oil 0.00 0.12 0.24 0.43 0.78 Limestone 1.30 1.30 1.30 1.30 1.30 Dicalcium phosphate 1.20 1.20 1.20 1.20 1.20 Salt 0.40 0.40 0.40 0.40 0.40 1 Premix 1.00 1.00 1.00 1.00 1.00 Total 100 100 100 100 100 Nutrient level 12.51 12.51 12.51 12.51 12.50 ME (MJ/kg)2 3 CP 17.29 17.37 17.44 17.18 17.31 3 CF 4.23 4.52 4.25 3.75 4.13 3 0.87 0.91 0.89 0.90 0.85 Ca 2 Non phosphorous 0.41 0.41 0.41 0.41 0.41 2 0.91 0.91 0.91 0.91 0.91 Lysine 2 Methionine 0.41 0.41 0.41 0.41 0.41 2 Digestible threonine 0.63 0.63 0.63 0.63 0.63 C16:03 7.44 7.68 8.36 7.51 7.60 C18:03 1.02 0.95 0.59 1.15 0.86 3 C18:1 15.48 22.27 17.32 15.73 19.51 3 C18:2n-6 70.66 62.95 65.75 64.92 57.95 3 C18:3n-3 5.40 6.14 7.98 10.69 14.08 2 n-6:n-3 ratio 13.09 10.25 8.23 6.07 4.12

437 438 439 440 441 442

1

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2:1 54.05 13.70 23.65 2.70 0.40 1.60 1.30 1.20 0.40 1.00 100 12.49 17.58 3.82 0.93 0.41 0.91 0.41 0.63 8.15 0.82 18.52 48.85 23.59 2.07

Vitamin and mineral premixes supplied per kilogram diet: vitamin A, 9,000 IU; vitamin D3, 3,000 IU; vitamin E, 79 mg; vitamin B2, 8 mg; vitamin K3, 2 mg; pantothenic acid, 3.2 mg; niacin, 11 mg; folic acid, 1.5 mg; biotin, 1 mg; Co, 1 mg; Mn, 49 mg; Cu, 6 mg; Zn, 60 mg; I, 2 mg; Se, 0.18 mg. 2 Calculated values. 3 Analysed based on triplicate determinations.


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443


Table 2. Primer sequences for real-time PCR amplification of hepatic genes Target gene

Primer sequence (5′–3′)

Size/bp

F: CACAGCCTGTTGAGTATGGC FADS2

186 R: GGATCCCAGAACGCCATAGA F: TCCACAGTGCCTTTCCTCAT

FADS1

191 R: TGCTGGAAGTGGAGGTGATT F: AGGACCAAAGTACATGCGGA

ELOVL5

203 R: ACCACCAGAGGACACGTATG F: CTCAGGGCTCACCTCATTGT

ELOVL2

116 R: AGGTTCTGGCACTGCAAGTT F: ATGTTCGTGATGGGTGTGAA

GAPDH

176 R: CTGTCTTCGTGTGTGGCTGT F: TACGCCAACACGGTGCTG

β-actin

215 R: GATTCATCATACTCCTGCTTG

444

FADS2, fatty acid desaturase 2; FADS1, fatty acid desaturase 1; ELOVL5, elongation of very

445

long-chain fatty acids enzyme 5; ELOVL2, elongation of very long-chain fatty acids enzyme 2.

446



447

Page 24 of 32

Table 3. Effects of dietary n-6:n-3 PUFA ratios on growth performance of ducks at 15–42 d of age Dietary n-6:n-3 PUFA ratio Item

P value 13:1

10:1

8:1

6:1

4:1

2:1

BW (kg)

3.51 ± 0.04

3.42 ± 0.05 3.40 ± 0.04 3.43 ± 0.03 3.41 ± 0.06 3.43 ± 0.06

0.52

ADG (g/d)

252 ± 2.76

240 ± 3.26

239 ± 4.77 243 ± 4.48 243 ± 2.91 243 ± 3.92

0.52

ADFI (g/d)

98.3 ± 1.29

96.3 ± 1.92 95.2 ± 1.49 96.6 ± 1.22 95.8 ± 2.02 98.2 ± 1.77

0.53

F/G

2.52 ± 0.05

2.52 ± 0.04 2.58 ± 0.04 2.52 ± 0.08 2.49 ± 0.05 2.53 ± 0.06

0.99

448


Page 25 of 32

449


Table 4. Effects of dietary n-6:n-3 PUFA ratios on serum lipid levels of ducks at 42 d of age (µmol/mL) Dietary n-6:n-3 PUFA ratio Item

450

P value 13:1

10:1

TG

0.69 ± 0.05b

0.82 ± 0.04b

TC

4:1

2:1

0.85 ± 0.08b

1.51 ± 0.12a

Effects of Dietary n-6:n-3 PUFA Ratios on Lipid Levels and Fatty Acid

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