硒代蛋氨酸的生物学功能及其在猪生产中的应用

硒（Se）是机体必需的微量元素，其生理作用主要表现在抗氧化、免疫和抗肿瘤等方面。机体缺硒会引发骨骼肌变性或坏死、肝坏死和心肌纤维变性等疾病，因此，硒在人和动物营养方面越来越被人们重视。硒代蛋氨酸（Se-Met）作为有机硒的一种，比亚硒酸钠等无机硒具有更高的生物利用率和更低的毒性，是替代无机硒的有效有机硒源。应现阶段动物生产中对硒的需要，作者以Se-Met为研究对象，介绍了Se-Met在动物机体中的吸收代谢机制，并在此基础上与无机硒进行了比较分析，突出了Se-Met作为有机补硒剂的优越性；简述了Se-Met在机体抗氧化、免疫和抗肿瘤方面的功能、作用机制以及在猪生产中的应用效果；并进一步阐释了Se-Met在猪生产中的应用现状，通过对日增重、日采食量和料重比等生长指标，以及猪肉的pH、滴水损失、硒沉积量和肉色等肉品质指标的分析，进一步确定了Se-Met在猪生产中广泛应用的可能性，为今后猪营养中Se-Met等有机硒广泛替代无机硒提供了参考依据和理论基础，并期望为后续研究提供参考。     

The Biological Function of Selenomethionine and Its Application in Pigs Production

As an essential nutrient,selenium plays important role in antioxidation,immunity and antitumor.Selenium deficiency in the body can cause diseases such as skeletal muscle degeneration or necrosis,liver necrosis and myocardial fibrosis.Therefore,it has been paid more and more attention in human and animal nutrition.As a kind of organic selenium,selenomethionine (Se-Met) has higher bioavailability and lower toxicity than sodium selenite,and it is an effective organic selenium source to replace inorganic selenium.In response to the current demand for selenium sources in animal production,this article takes Se-Met as the research object,introduces the absorption and metabolism mechanism of Se-Met in the body,and on this basis,makes a comparative analysis with inorganic selenium,highlighting the advantages of Se-Met as an organic selenium supplement.The function and mechanism of Se-Met in the body's antioxidation,immunity and antitumor,and the effect of its application in animal production are briefly described.The application status of Se-Met in pig production is explained,and through the analysis of growth indicators such as daily weight gain,daily feed intake,and feed-to-weight ratio,as well as meat quality indicators such as pH,drip loss,selenium deposition,and meat color of pork,the possibility of Se-Met being widely used in animal production is further determined.This article aims to provide practical reference and theoretical basis for the widespread replacement of inorganic selenium by organic selenium such as Se-Met in animal nutrition in the future,and provide references for subsequent scientific research.     

Organic selenium supplementation increased selenium concentrations in ewe and newborn lamb blood and in slaughter lamb meat compared to inorganic selenium supplementation

Background

Selenium is part of the antioxidant defence system in animals and humans. The available selenium concentration in soil is low in many regions of the world. The purpose of this study was to evaluate the effect of organic versus inorganic selenium supplementation on selenium status of ewes, their lambs, and slaughter lambs.

Methods

Ewes on four organic farms were allocated five or six to 18 pens. The ewes were given either 20 mg/kg inorganic selenium as sodium selenite or organic selenium as selenized nonviable yeast supplementation for the two last months of pregnancy. Stipulated selenium concentrations in the rations were below 0.40 mg/kg dry matter. In addition 20 male lambs were given supplements from November until they were slaughtered in March. Silage, hay, concentrates, and individual ewe blood samples were taken before and after the mineral supplementation period, and blood samples were taken from the newborn lambs. Blood samples from ewes and lambs in the same pens were pooled. Muscle samples were taken from slaughter lambs in March. Selenium concentrations were determined by atomic absorption spectrometry with a hydride generator system. In the ANOVA model, selenium concentration was the continuous response variable, and selenium source and farm were the nominal effect variables. Two-sample t-test was used to compare selenium concentrations in muscle samples from the slaughtered lambs that received either organic or inorganic selenium supplements.

Results

In all ewe pens the whole blood selenium concentrations increased during the experimental period. In addition, ewe pens that received organic selenium had significantly higher whole blood selenium concentrations (mean 0.28 μg/g) than ewe pens that received inorganic selenium (mean 0.24 μg/g). Most prominent, however, was the difference in their lambs; whole blood mean selenium concentration in lambs from mothers that received organic selenium (mean 0.27 μg/g) was 30% higher than in lambs from mothers that received inorganic selenium (mean 0.21 μg/g). Slaughter lambs that received organic selenium had 50% higher meat selenium concentrations (mean 0.12 mg/kg wet weight) than lambs that received inorganic selenium (mean 0.08 mg/kg wet weight).

Conclusion

Organic selenium supplementation gave higher selenium concentration in ewe and newborn lamb blood and slaughter lamb meat than inorganic selenium supplementation.     

Influence of Graded Levels of Organic Zinc on Growth Performance and Carcass Traits of Broilers

This study investigated the effect of graded levels of organic Zn (Bioplex Zn) on growth performance and carcass traits of broilers fed diets containing organic Se (Sel-Plex). Dietary treatments consisted of adding 0, 15, 30, 45, or 60 ppm organic Zn to a basal diet containing 60 ppm Zn from an inorganic source. Feed and water were provided ad libitum. Body weight, feed intake, feed conversion, and carcass traits were evaluated. Carcass evaluation was also performed on the last day of the experimental period. Body weight, feed intake, feed conversion, and weights of individual meat cuts were not statistically influenced by increasing organic Zn levels in the diet. However, a significant increase in skin tearing strength was observed in response to increasing levels of dietary organic Zn. Zinc plays a role in epithelial cell layers and collagen synthesis, thus affecting susceptibility of skin to tearing. These data indicated that organic Zn does not affect growth performance of broilers but increases resistance of skin to tearing, therefore improving carcass quality.     

Modification of the effects of aflatoxin B1 and warfarin in young pigs given selenium

Selenium may be related to the hepatic metabolism of the coumarin compounds aflatoxin B1 and warfarin. Selenium evidently increased the pharmacologic activity of warfarin, probably due to a displacement of warfarin from albumin by selenium, the close relationship among selenium, vitamin E, and sulphur-containing groups (eg, glutathione), or the antioxidant effect of selenium. A diet containing selenium in a concentration of 2.5 mg/kg of feed was protective against the toxic effects of both coumarins in pigs given 4 daily oral doses of 0.2 mg/kg of body weight. Selenium, as glutathione peroxidase, at least in part, protects the hepatic cells against the toxic effects of aflatoxin B1 and warfarin. The protection was demonstrated by alteration of clinical responses and hematologic (prothrombin times), electrophoretic, and clinical chemistry values. It also was demonstrated that selenium at 2.5 mg/kg of feed does not produce toxic effects; however, dietary selenium at a concentration of 5 mg/kg (and in the presence of both toxic agents) was toxic for young pigs within the 3-week experimental period. Warfarin was more active as an anticoagulant than aflatoxin B1.     

硒多糖的来源、提取及其生物学功能研究进展

硒多糖是硒与多糖结合在一起的有机硒化合物，是一种新型的硒源，具有清除自由基、保护神经活性、增强免疫力、抗肿瘤、抗炎等多种功能。硒多糖具有特殊的化学结构——硒氧键（O=Se=O），有别于普通多糖，其能够发挥硒和多糖的双重功效，活性远高于硒或多糖。本文就硒多糖的来源、提取、分离纯化及生物学功能等方面的研究进展进行综述，以期为未来畜牧业新型饲料添加剂的开发、应用和推广提供理论依据。 [关键词] 硒多糖|来源|提取|生物学功能     

Effect of different dietary concentrations of inorganic and organic copper on growth performance and lipid metabolism of White Pekin male ducks

1. The effect of different dietary concentrations of inorganic and organic copper on performance and lipid metabolism of White Pekin ducks (WPD) was investigated from 1-49 d of age. A common basal diet was supplemented with 4, 8, 12 and 150?mg/kg of copper (Cu) from inorganic and organic sources to obtain 9 treatments, including 4 concentrations of Cu x two sources, and the unsupplemented control group. Each treatment contained 5 replicates of 9 male ducks each.

2. Supplementation of Cu at 8?mg/kg in inorganic form was adequate for growth of male WPD from 1-56 d of age. Inorganic Cu significantly decreased feed intake and improved feed conversion ratio, compared with the organic form.

3. Plasma Cu significantly increased, while plasma Zn significantly decreased, due to Cu supplementation. Organic Cu showed better efficacy than inorganic for improving liver Cu concentration, Cu excretion and apparent Cu retention.

4. Dietary Cu concentration significantly affected percentage blood and Hgb and abdominal fat deposition. In addition, inorganic Cu increased percentage blood and abdominal fat deposition compared with the organic source.

5. Supplementation of 150?mg/kg of Cu significantly decreased liver and meat lipids, cholesterol, and colour and tenderness of meat; while liver protein and moisture was increased. In addition, dietary 150?mg/kg of Cu supplementation significantly decreased plasma lipids, triglycerides and cholesterol, while increasing plasma AST and ALT.

6. Organic Cu was more potent for decreasing plasma triglycerides than the inorganic source. However, plasma cholesterol was only significantly decreased with the inorganic source of Cu, compared with the unsupplemented control.

7. The organic Cu was safer as a feed additive for WPD, especially at the lower concentrations up to 12?mg; while some mild to moderate changes may be developed at the higher doses, when fed at pharmacological concentrations as a growth promoter.     

产蛋种鸡日粮中不同水平维生素E与有机和无机硒的效果研究

在３×５的两因子试验中,研究了不同添加水平维生素Ｅ（４、１４和２４ｍｇ／ｋｇ）与有机和无机硒（亚硒酸钠０．２０、０．３５和０．５０ｍｇ／ｋｇ,酵母硒０．３５和０．５０ｍｇ／ｋｇ）对褐壳蛋种母鸡在２０～４０周龄阶段生产繁殖性能和有关血液指标的影响。结果表明,产蛋母鸡的采食量、产蛋率、蛋重、产蛋量、饲料转化率和死淘率在３个维生素Ｅ添加水平间无差异;除了添加酵母硒０．５０ｍｇ／ｋｇ组蛋鸡的蛋重和产蛋量显著低于酵母硒０．３５ｍｇ／ｋｇ组以外,其它各项生产性能指标在各硒处理组间差异不明显。维生素Ｅ和硒可增加彼此在血液中的存留;当日粮中只补加维生素Ｅ４ｍｇ／ｋｇ时,将日粮亚硒酸钠硒添加水平由０．２０ｍｇ／ｋｇ提高到０．３５～０．５０ｍｇ／ｋｇ可使血浆α－生育酚含量由０．５０μｇ／ｍｌ上升到接近１．０μｇ／ｍｌ左右。     

Dietary selenium increases vitamin E contents of egg yolk and chicken meat

1. The influence of different forms of dietary selenium (Se) on vitamin E (alpha-tocopherol) and Se contents of egg yolk and chicken meat was investigated. 2. Eggs were collected from laying hens subjected to 4 different dietary treatments after 24 weeks of age. Treatments compared the effects of inorganic Se supplementation (selenite) to those of organic (Se-enriched yeast, Se-enriched alga Chlorella) supplements. In a second experiment the effect of the above organic dietary Se supplementation on the alpha-tocopherol contents of meat from broiler chickens was evaluated. 3. Dietary Se supplementation increased the alpha-tocopherol content of egg yolks from 297 mg/kg dry matter in treatment without supplementation to 311 mg/kg when selenium was supplemented as selenite, and to 370-375 mg/kg when organic supplements were used. The Se and alpha-tocopherol contents of breast and thigh meat in broilers were significantly increased by organic dietary Se supplementation. 4. The inclusion of organic dietary Se sources in the diets of laying hens and broilers would enhance the nutritional value (vitamin E and Se contents) of products (eggs and meat) for human consumption.     

Effect of different sources and levels of selenium on performance,meat quality,and tissue characteristics of broilers

The objective of this study was to evaluate the effects of dietary levels of inorganic and organic selenium (Se) on performance, meat physicochemical characteristics, and Se deposition in the tissues of broilers chickens. A total of 2,880 one-day-old broilers (Cobb 500 strain) were divided into 96 experimental pens of 30 birds each. The 12 experimental treatments were arranged in a factorial design of 4 × 3 [selenium levels of 0.15, 0.30, 0.45, and 0.60 ppm, and organic (selenium yeast, SY) or inorganic (sodium selenite, SS) sources of selenium and their association (SY + SS)], with 8 replicates in a completely randomized design. No differences (P > 0.05) among Se levels or sources were detected with regard to any performance parameters. The average values of ADFI, ADG, and FCR were 106 g/bird per day, 63 g/bird per day, and 1.684 kg/kg, respectively. No differences (P > 0.05) were found between treatments regarding pH (5.79) and shear force (30.08 kgf). Those birds receiving 0.15 ppm of Se showed a significantly higher (21.92%) cooking loss of breast meat (P < 0.05). The organic form of Se decreased cooking loss, and the smallest loss was found when the diet was supplemented with 0.60 ppm of Se (15.87%). Deposition of Se in the liver increased from 0.97 (0.15 ppm of Se) to 2.43 mg/kg (0.60 ppm of Se) when using SY. The concentration of Se in the breast meat increased linearly from 0.23 to 1.42 mg/kg with increasing dietary levels of SY. Therefore, dietary supplementation with 0.15 ppm of Se, independent of source, can maintain normal bird performance. The SY was more efficient in depositing Se to the liver and breast muscle than the SS.     

Effects of dietary substitution of zinc‐methionine for inorganic zinc sources on growth performance,tissue zinc accumulation and some blood parameters in broiler chicks

This study was designed to evaluate the effects of dietary inclusion of zinc‐methionine (ZnMet) as a replacement for conventional inorganic zinc sources on performance, tissue zinc accumulation and some plasma indices in broiler chicks. A total of 450‐day‐old Ross male broiler chicks were randomly assigned to five pen replicates of nine experimental diets. Dietary treatments consisted of two basal diets supplemented with 40 mg/kg added Zn as feed‐grade Zn sulphate or Zn oxide in which, Zn was replaced with that supplied from ZnMet complex by 25, 50, 75 or 100%. At 42 days of age, three randomly selected birds from each pen were bled to measure plasma metabolites; then, the chicks were slaughtered to evaluate carcass characteristics. Results showed that dietary treatments affected (p < 0.05) feed intake during the starter period, and chicks on Zn oxide diets consumed more feed than sulphate counterparts. Furthermore, dietary substitution of inorganic Zn sources by ZnMet caused improvements (p < 0.01) in body weight gain during all experimental periods. Dietary supplementation of ZnMet improved feed conversion efficiency during 1–21 and 1–42, but not in 21–42 days of age. Complete replacement of inorganic Zn by that supplied from ZnMet caused an increase (p < 0.05) in relative liver weight. Similarly, dietary inclusion of ZnMet increased breast meat and carcass yields and reduced abdominal fat percentage (p < 0.05). Incremental levels of ZnMet increased (p < 0.05) zinc concentrations in liver and thymus, and the highest zinc accumulations were seen in 100% ZnMet‐supplemented birds. Interestingly, introduction of ZnMet into the diets partially in place of inorganic sources resulted in decreases (p < 0.01) in plasma uric acid and triglycerides concentrations. The present findings indicated that dietary ZnMet inclusion in replacement of inorganic sources in addition to improving growth performance, reduced plasma uric acid and triglycerides concentrations, consequently decreased abdominal fat pad and increased carcass meat yield.     

纳米硒在动物营养中的研究进展

硒(Se)是动物机体必需的微量元素,在机体抗氧化体系、免疫细胞功能、促生长及精子的形成和游动、前列腺素的功能等方面起着重要作用。动物体内已知存在35种以上的含硒蛋白质,其中谷胱甘肽过氧化物酶(GPx1-GPx6)和硫氧还蛋白还原酶(TrxR1-TrxR3)在机体抗氧化体系中发挥着重要的作用。国内生产中通常应用亚硒酸钠作为补硒制剂,但亚硒酸钠在使用中存在吸收率低、过氧化作用及潜在的污染等问题。有机硒和纳米硒具有吸收率高、生物活性强、环境污染小等优点。与有机硒相比,纳米硒有更显著的低毒高效性,是已发现的毒性最低的补硒制剂。近年来,纳米硒替代有机硒、无机硒源的研究已成为热点。     

Dietary vitamin E (alpha-tocopherol acetate) and selenium supplementation from different sources: performance, ascites-related variables and antioxidant status in broilers reared at low and optimum temperatures

1. This study compared the effect of dietary supplementation with organic or inorganic selenium (Se) sources plus control amounts or large amounts of vitamin E (alpha-tocopherol acetate) in broilers raised at control (20 to 24 degrees C) or low (14.5 to 16.8 degrees C) temperatures after 2 weeks of age. 2. The following dietary treatments were used from one day old. Diet 1, the control diet, comprised a commercial diet containing 0.15 mg/kg inorganic Se and 50 mg vitamin E/kg feed. Diet 2 was the same as diet 1, supplemented with 0.15 mg/kg inorganic Se. Diet 3 was the same as diet 2 but was supplemented with 200 mg/kg vitamin E. Diet 4 was the same as diet 1, but inorganic Se was replaced with 0.30 mg/kg organic Se. Diet 5 was the same as diet 4, supplemented with 200 mg/kg vitamin E. 3. Low temperature reduced the growth rate of broilers; however, at 6 weeks, there were no differences in the body weights of birds fed on organic Se supplemented diets housed at low or control temperature. The feed conversion ratio was significantly affected by low temperature but not by diet. The heterophil/lymphocyte ratio was higher in chicks after one week in the cold, indicating mild stress. Blood triiodothyronine levels were significantly higher in birds after 1 and 4 weeks in the cold but thyroxin was not affected. 4. Organic Se supplementation increased relative lung weight at the control temperature, which might lead to greater respiratory capacity. Relative spleen weight significantly decreased in broilers fed diets supplemented with inorganic Se under cold conditions, a possible indication of chronic oxidative stress. 5. At the low temperature, supplementation with organic Se alone, or with inorganic Se and vitamin E increased glutathione peroxidase (GSHPx) activity and glutathione (GSH) concentration in the liver of broilers, which may indicate increased activity of birds' antioxidant defence against suboptimal environments.     

Application Progress of Selenium and Selenoprotein in Aquaculture北大核心CSCD

随着水产养殖产业的高速发展,水产养殖集约化规模扩大,养殖动物密度增大,容易造成氧化应激反应,这迫使水产养殖从业者亟需寻找无毒无害且高效的饲料添加剂以提高水产动物的抗应激能力。硒(Se)是一种人体和动物生长繁育必需的微量元素,其生物学功能主要通过硒蛋白表达,饲料中添加适量的硒能够增强水产动物的抵抗力。本文综述了硒和硒蛋白的种类以及硒对水产动物的生理机制,同时对硒在水产养殖中的应用进行综述,旨在总结不同硒源作为水产饲料添加剂在改善水产动物生长、免疫与肉质等方面的作用,为其在水产养殖中的高效应用提供科学参考。     

Seasonal variation in selenium status of different classes of grazing goats in a semi-arid region of Pakistan

The selenium status of three different classes of goats ((i) female lactating, (ii) female non-lactating, and (iii) male goats) grazing semi-arid pasture in the southern part of the Punjab province, Pakistan and that of selenium concentration of soil and dietary sources, ingested by those animals were investigated during two different seasons of the year (winter and summer). Soil, forage, feed, water from the pasture and blood plasma, urine, faeces, and (if applicable) milk from these goats were collected fortnightly. The samples were analyzed for selenium concentrations. Soil selenium showed both seasonal and sampling periods effect on its concentration while forage selenium was affected only by the seasonal changes. No significant effect of seasons or fortnights on feed selenium level was observed. In fecal samples selenium concentration in lactating and non-lactating and plasma of male goats were affected by sampling periods. While fecal selenium in male goats showed significant effect on its concentration both seasonal and within fortnights. Severe deficient level of soil selenium during both seasons and marginal deficient level of forage selenium during summer were observed. Selenium concentrations in feed slightly exceeded the requirements of ruminants in feed during both seasons of the year. Plasma selenium concentrations in all goat classes were higher in winter than that in summer showing no seasonal or fortnight variation and its concentration was slightly lower in lactating goats as compared to other classes. On the bases of these results, it is concluded that overall selenium status of the goats based on plasma selenium concentration may be considered adequate mainly due to the mineral supplement provided all over the year, since soil and forage selenium concentrations were low to deficient.     

家禽有机硒营养研究进展

硒是动物所必需的微量元素之一,为谷胱甘肽过氧化物酶的重要成分,能消除体内有害自由基。有机硒相对于无机硒毒性小,生物利用率高,生物活性强。本文就目前国内外对有机硒在家禽营养中的研究进展及应用现状进行综述。     

酵母硒在动物生产中的研究与应用

硒(selenium)是人和动物必需的微量元素,它与调节生长、提高机体免疫力、抗癌、抗氧化、抗应激、延缓衰老及防治地方病等有着密切的关系。国内的补硒方法是添加亚硒酸钠,但亚硒酸钠毒性大,吸收转化率低及造成环境污染。近年来,人们逐渐把目光转向毒性小且生物利用率高的有机硒上,其中酵母硒成为研究与应用的热点。     

有机硒对猪生长性能影响的荟萃分析

本文旨在研究补充有机硒及无机硒对猪生长性能的影响。检索１９８０年１月至２０１０年１２月期间发表的有机硒或无机硒对猪生长性能影响的随机对照研究,用荟萃分析（Ｍｅｔａ分析）方法计算合并标准均数差（ＳＭＤ）及 ９５％可信区间（９５％ＣＩ）。共有 １５篇研究纳入 Ｍｅｔａ分析,包括 ３６２个研究对象。Ｍｅｔａ分析结果显示：料重比 ＳＭＤ为 －０．９６,９５％ＣＩ为（－１．６９,－０．２３）（Ｐ＜０．０５）;平均日采食量 ＳＭＤ为 ０．５５,９５％ＣＩ为（０．１６,０．９３）（Ｐ＜０．０５）;平均日增重 ＳＭＤ为 ０．３９,９５％ＣＩ为（０．０９,０．７０）（Ｐ＜０．０５）。由此可见,补充有机硒比补充同等剂量的无机硒更能降低养殖猪的料重比,增大平均日采食量及平均日增重,从而提高养殖猪的生长性能。     

The effects of dietary oxidized fat and selenium source on performance,glutathione peroxidase,and glutathione reductase activity in broiler chickens

Normal or elevated selenium status of broilers, which is influenced by dietary selenium sources, improves the bird’s ability to overcome the adverse effects of reactive oxygen metabolites. The objective of this study was to evaluate the effects of feeding graded levels of peroxidized poultry fat on blood and hepatic glutathione peroxidase (GSH-Px), and hepatic glutathione reductase activity in broiler chickens fed either inorganic sodium selenite (SEL) or organic selenium enriched in the organic selenium yeast product Sel-Plex (SP). Nine starter diets, varying in levels of oxidized fat (0, 3, and 6 mEq/kg) and dietary selenium sources, were fed to 360 male chicks from hatch to 21 d of age. Sel-Plex or SEL was added to the basal diet to provide either 0 or 0.2 ppm of supplemental selenium in the diets. Blood and hepatic samples were obtained for each treatment group at 21 d of age. Neither peroxidized fat nor selenium source significantly altered the activity of hepatic glutathione reductase (P ≤ 0.05). Blood GSH-Px was influenced significantly by both fat and selenium source (P ≤ 0.05), but the fat × selenium source interaction was not significant (P ≥ 0.3). A selenium source effect on the hepatic GSH-Px activity (P ≤ 0.05) was evidenced by higher GSH-Px activity, even in the basal diet with no added peroxidized fat. An increase in GSH-Px activity was seen in the erythrocyte and hepatic samples in both the SEL and SP treatments when peroxidized fat was given at 3 mEq/kg, but in the erythrocytes and in the hepatic tissues from SEL-supplemented birds, there was an apparent inhibition of GSH-Px activity. This inhibition was not seen in the hepatic tissue samples from SP-fed birds. Because elevated GSH-Px activity is indicative of oxidative stress, it was concluded that dietary SP supplementation resulted in better selenium and redox status in broilers than did SEL. These results indicate that the dietary selenium supplied in an organic form (selenium yeast as SP) improved the selenium and redox status in broilers, leading to greater resistance to oxidative stress than when the inorganic form of selenium (SEL) was fed.     

The feeding of ad libitum dietary protein to organic growing-finishing pigs

The effects of three dietary protein levels on growth, meat, and carcass traits were studied in organic pigs fed a three-phase diet. Assuming lysine was the first limiting amino acid, feeds were formulated to ileal digestible (ID) lysine content, with the ID lysine:crude protein ratio set at a constant of 4%. Feeds were also formulated to an isocaloric rate (net energy: 9.4 MJ/kg during the first feeding phase, 9.25 MJ/kg during the second feeding phase and 9.1 MJ/kg during the finisher phase), with a high (HP), a medium (MP) or a low (LP) protein content ranging from 20% to 14% crude protein (CP). ID lysine content of the LP and MP feed was, respectively, 80% and 90% of the ID lysine content of the HP feed. The nutrient formulation of the HP feed was similar to nutrient levels commonly used in conventional Belgian pig farming. From 20 to 40 kg liveweight, the pigs showed better feed conversion ratios, with an increasing dietary protein concentration (r(2)=0.84). This effect was not observed in the second and third phases, although a significant effect of protein concentration on voluntary feed intake in the second phase did occur (P=0.018), probably as a compensation for the lower protein concentration in the LP diet. Analysis of the carcasses showed a lower meat percentage with lower protein concentration (P<0.05), whereas influences on meat quality were limited. It was concluded that whereas during the first phase of growth, higher protein concentration leads to better performance, from the second phase onwards (45 kg), at least with isocaloric diets, a decrease in protein content (corresponding to a 10% reduction in dietary ID lysine levels compared to conventional pig fattening) may be used in organic growing-finishing pig nutrition.