The effects of dietary fiber level on nutrient digestibility in growing pigs

The objective of this study was to investigate the effects of total dietary fiber level on nutrient digestibility and the relationship between apparent total tract digestibility of total dietary fiber, and soluble dietary fiber, insoluble dietary fiber and available energy. Sugar beet pulp was as the only fiber source. The experiment was designed as a 6 × 6 Latin square with an adaptation period of 7 d followed by a 5-d total collection of feces and urine. Feed intake tended to decrease (P =0.10) as total dietary fiber level increased. The apparent total tract digestibility of dry matter, crude protein and gross energy decreased (P <0.01) when total dietary fiber increased but the digestibility of soluble dietary fiber and insoluble dietary fiber increased (P <0.01). The digestible energy and metabolizable energy content of diets decreased (P <0.01) as the total dietary fiber increased.     

日粮纤维对不同妊娠阶段松辽母猪养分消化率影响研究

本试验以松辽黑猪为研究对象,以妊娠前中后三个时期为研究重点,以苜蓿草粉为纤维来源,通过饲喂高纤维含量的日粮,研究日粮纤维对母猪繁殖性能的影响。通过测定采食高纤维日粮母猪的常规繁殖生产成绩、血液生化指标、血清抗氧化酶活性、养分消化率以及血清繁殖激素分泌水平,为日粮纤维在松辽母猪生产上的合理利用提供参考。试验基础日粮以玉米和豆粕为主要原料,采用单因子试验设计,将胎次、配种时间、体重、背膘厚度基本一致的松辽母猪10头,随机分为两个处理组,每个处理组5个重复,每个重复1头猪。试验组日粮纤维水平7.2%,对照组日粮纤维水平3.8%,其他成分试验组和对照组基本一致。试验期为150 d。试验结果表明:妊娠前期采食日粮纤维的母猪,粗蛋白质、粗脂肪、干物质以及粗纤维的消化率均降低,而对照组母猪与试验组母猪在各个指标存在显著性差异(P﹤0.05),对照组较试验组分别高3.12%、2.36%、4.90%、1.36%。妊娠中期母猪在采食大量日粮纤维后,对照组的消化率与试验组消化率存在显著性差异(P﹤0.05),对照组粗蛋白质、粗脂肪、干物质较试验组相比,分别高5.29%、2.49%、5.35%。妊娠后期采食高纤维日粮后,其粗蛋白质、粗脂肪、干物质、粗纤维的消化率明显低于妊娠前期和中期,对照组与试验组在各个指标上存在显著差异(P﹤0.05),分别高出5.81%、1.91%、1.32%、3.18%。     

牛至油对生长猪生产性能和养分表观消化率的影响

选用健康、体重25kg左右的荣×大×杜杂交猪60头,随机分到2个组,每组6个重复,每个重复5头猪,每圈为1个重复,研究添加牛至油对生长猪生产性能和养分消化率的影响。试验组在对照组的基础上添加100g/t的牛至油,测定猪的生产性能和养分表观消化率。试验结果表明,在生长猪日粮中添加100g/t的牛至油具有改善猪只生产性能、提高养分表观消化率的趋势,可降低单位增重饲料成本。     

浅谈日粮纤维在猪的生产中的应用

概括了粮纤维在猪生产中的重要实践意义,以及积极的和消极的影响,并提出了实际生产中应注意的问题。     

不同能量水平日粮对深县猪生长性能、养分消化率和血液生化指标的影响

为了研究不同消化能水平日粮对深县猪生长性能、养分消化率和血液生化指标的影响,选用体重(15. 54±2. 25) kg的健康深县猪48头,随机分成3组,每组4个重复,每个重复4头猪,试验Ⅰ、Ⅱ、Ⅲ组饲粮消化能水平分别为11. 20、11. 70、12. 20 MJ/kg,预试期7 d,正式期28 d。结果显示:试验Ⅲ组的平均日增重显著高于试验Ⅰ组15. 56%(P<0. 05),试验Ⅲ组的料重比(F/G)显著低于试验Ⅰ组(P<0. 05);试验Ⅲ组粗蛋白、总能与粗脂肪表观消化率均显著高于试验Ⅰ组9. 89%、7. 29%、7. 21%(P<0. 05)。综合各项指标,在本试验条件下,生长期深县猪适宜的消化能水平为12. 20 MJ/kg。     

不同膳食纤维来源对断奶仔猪生长性能和养分消化率的影响

文章旨在评价饲粮中不同纤维来源对断奶仔猪生长性能和养分消化率的影响。试验选择84头体重接近的28日龄断奶仔猪,随机分为4组,分别饲喂对照组饲粮以及添加5%玉米纤维(CB)、小麦纤维(WB)、大豆纤维(SB)的饲粮,处理28d。试验结果:相比于对照组,CB、WB组料肉比(FCR)分别下降8.5%、7.9%(P<0.05);CB组仔猪总能量(GE)、有机物(OM)、干物质(DM)消化率分别降低2.1%、2.1%、2.9%(P<0.05),粗纤维(CF)、磷(P)消化率分别增加7.8%、29.3%(P<0.05);WB组仔猪GE、OM、DM消化率较对照组分别降低1.8%、3.9%、3.4%(P<0.05),CF、P消化率分别增加8.8%、19.3%(P<0.05);此外,SB组CF、OM、P消化率分别增加9.9%、5.1%、4.5%(P<0.05)。表明,饲粮中纤维显著影响仔猪生长,不同纤维源对仔猪生长性能及养分消化率的影响不同。     

日粮纤维对烟台黑猪及其杂交配套系养分消化率和氮平衡的影响

为研究日粮纤维对不同品种猪养分消化率和氮平衡的影响,试验选取体重相近、健康去势的烟台黑猪、鲁农2号猪各6头,采用有重复的3×3拉丁方设计,分别为基础日粮组,10%大豆皮替代基础日粮组,10%地瓜蔓替代基础日粮组。结果表明,添加10%地瓜蔓组显著降低两个品种猪养分消化率和氮平衡(P<0.05或P<0.01),而10%大豆皮组则影响不显著(P>0.05);纤维性饲料对鲁农2号猪养分消化率和氮平衡的影响幅度大于烟台黑猪。     

Effects of different ratios of soluble to insoluble dietary fiber on growth performance and intestinal health of piglets

This study investigated the impact of different ratios of soluble to insoluble dietary fiber(SDF:IDF)for-mulations by sugar beet pulp(SBP)supplementation on piglet growth performance,nutrient di-gestibility,immune function,intestinal morphology,intestinal microbiota and intestinal health.A total of 60 crossbred piglets(Duroc ×[Landrace × Yorkshire])at 40 d old with body weight of 10.0±0.3 kg were randomly assigned to 5 treatments with 6 replicates per treatment and 2 piglets per replicate in a 21-d trial.The dietary treatments included a corn-soybean meal diet(0％SBP supplementation;CON),and diets supplemented with 2％,4％,6％,and 8％SBP,representing different SDF:IDF ratios at 10.16％,13.53％,16.79％,19.86％,and 24.81％,respectively.The results indicated that the 8％SBP treatment had a negative effect on feed-to-gain ratio(linear,P=0.009)compared with the CON treatment(P=0.021).The apparent total tract digestibility(ATTD)of crude protein was lower in treatments supplemented with SBP(P=0.002)and showed a linear decrease(P=0.001),while the ATTD of IDF showed a linear increase(P=0.037)in four SBP treatments compared to the CON treatment.The 4％SBP treatment increased serum concentrations of triglyceride(quadratic,P=0.019)and K(linear,P=0.037),and decreased alanine transaminase concentration(quadratic,P=0.015)compared with the CON treatment.The concentrations of Cit,Cys,Ile,Leu,Orn,Arg,taurine,urea,1-methylhistidine,α-aminoadipic acid,α-aminobutyric acid and cystathionine in the 4％SBP treatment were highest among all treatments(P＜0.05).The serum concentrations of interleukin-6,interleukin-8,interleukin-10,transforming growth factor-β,and tumor necrosis factor-α in the 6％SBP treatment were higher than those in the CON treatment(P＜0.05),which also increased mucin-2 and G protein-coupled receptor 41 mRNA expression(P＜0.05)in colonic mucosa compared with the CON treatment and improved the intestinal barrier function.Diets containing more than 19.86％SDF:IDF could impair the intestinal health in piglets when SBP was used as the SDF source.Supplementing nursery piglet diets with 16.79％to 19.86％SDF:IDF is recommended for improving intestinal barrier function,increasing short-chain fatty acids concentra-tions,and improving intestinal microbiota composition.     

Chemical composition,energy and amino acid digestibility in double-low rapeseed meal fed to growing pigs

Background

The nutritional value of rapeseed meal may be variable due to the variation of its chemical composition. And a precise understanding of the nutritional value of an ingredient is beneficial for the accurate diet formulation and reduction of feed costs. This study was conducted to determine the chemical composition, digestible energy (DE) and metabolizable energy (ME) content, and apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of amino acids (AA) for growing pigs. Thirteen solvent-extracted double-low rapeseed meal (DLRSM) samples were obtained from the main double-low rapeseed producing areas in China.

Methods

The DE and ME contents of the 13 DLRSM samples were measured in growing pigs (six pigs per DLRSM sample, average initial body weight (BW) = 48.3 kg). The AID and SID of AA of 10 DLRSM samples were determined in 12 crossbred barrows (average initial BW = 35.3 kg) by using two 6 × 6 Latin square designs. Each Latin square comprised one N-free diet and 5 DLRSM test diets.

Results

The chemical composition of DLRSM varied among samples, and the coefficient of variation was greater than 10 % for ether extract (EE), neutral detergent fiber (NDF), acid detergent fiber (ADF), calcium (Ca), and total glucosinolates. The AA content of DLRSM varied among samples especially for lysine (Lys) and methionine (Met). On a dry matter (DM) basis, the apparent total tract digestibility (ATTD) of gross energy (GE), the DE and ME and the ME:DE ratio of DLRSM averaged 62.39 %, 2862 kcal/kg and 2723 kcal/kg, and 94.95 %, respectively. The mean value of SID of Lys was 70.52 % which varied from 66.54–76.54 %. The SID of crude protein (CP), Met, and threonine (Thr) averaged 72.81 %, 82.41 %, and 69.76 %, respectively.

Conclusions

There was great variability in chemical composition especially in the concentration of EE, NDF and ADF, but no significant differences in energy content of the DLRSM samples were observed. In addition, the AID and SID of all AA were relatively similar among DLRSM samples except for that of Lys.     

Comparison of the regression analysis technique and the substitution method for the determination of true phosphorus digestibility and faecal endogenous phosphorus losses associated with feed ingredients for growing pigs

Two digestibility experiments were carried out to comparatively measure true phosphorus (P) digestibility and the faecal endogenous P loss associated with soybean meal (SBM) and wheat middling meal (WM) for growing pigs by the simple linear regression analysis technique and the substitution method. Eight barrows, with an average initial body weight 21 kg, were randomly divided into two groups of four pigs with each group being fed four test diets according to a 4 × 4 Latin square design. Eight maize starch-based diets containing four levels (on dry matter basis) of P (0.20, 0.24, 0.36 and 0.42%) and P (0.181, 0.26, 0.36, and 0.43%) were formulated from SBM and WM as a sole source of P, respectively. Chromic oxide (0.30%) was used as a digestibility marker. Each experimental period comprised 8 d with a 4-d adaptation and a 4-d collection of faecal samples. Levels of the assay ingredient substitutions had no effects (P > 0.05) on true P digestibility and the endogenous P loss associated with SBM and WM measured by the substitution method. There were no differences (P > 0.05) between the regression technique and the substitution method in measuring the true P digestibility (SBM: 49.4 ± 3.51 vs. 50.6 ± 2.4; WM: 63.7 ± 5.0 vs. 63.2 ± 5.4%) as well as the faecal endogenous P loss (SBM: 0.62 ± 0.10 vs. 0.71 ± 0.11; WM: 0.65 ± 0.16 vs. 0.70 ± 0.17 g/kg dry matter intake) for the growing pig. Thus, true P digestibility and the faecal endogenous P loss in feed ingredients for pigs may be measured by using the regression analysis technique and the substitution method.     

Nutrient digestibility, blood profiles and fecal microbiota are influenced by chitooligosaccharide supplementation of growing pigs

This study was conducted to evaluate the effects of dietary chitooligosaccharide (COS) supplementation on growth performance, nutrient digestibility, blood profiles and fecal microbiota in growing pigs. A total of 144 [(Landrace × Yorkshire) × Duroc] pigs with an initial body weight of 23.6 ± 1.1 kg were allotted to one of the following dietary treatments: 1) basal diet; 2) basal diet with 44 mg/kg of tylosin (100 mg/kg tylosin); 3) basal diet with 5 g/kg of COS and 4) basal diet with 5 g/kg COS and 44 mg/kg tylosin. There were nine replications per treatment with four pigs per pen. Throughout the experiment, pigs that were treated with a combination of COS and tylosin had a lower ADFI (P = 0.02) and higher gain/feed ratio (P < 0.05) than the other treatments. In addition, administration of either COS or tylosin alone significantly increased the digestibility of dry matter, nitrogen and gross energy (P < 0.05). The red blood cell (RBC) and white blood cell (WBC) counts, as well as the serum albumin concentrations were not affected by COS or tylosin supplementation. However, the lymphocyte proportion and serum total protein concentration were increased in pigs fed tylosin supplemented diets compared with those pigs fed diets not supplemented with tylosin (P < 0.05). Administration of tylosin significantly increased serum IgG concentration (P = 0.02); however, treatment with COS or tylosin supplementation had no effect on the total cholesterol or triglyceride concentrations. The serum HDL cholesterol concentration was significantly increased in pigs treated with COS (P = 0.02) compared to the pigs fed diets without COS. The COS administration also decreased the number of fecal Escherichia coli (P < 0.01), whereas the number of fecal Lactobacilli was not influenced by either COS or tylosin administration. Results of the current study indicate that dietary supplementation of COS can improve nutrient digestibility and haematological profiles, as well as decrease of fecal E. coli populations in growing pigs.     

精油对生长猪蛋白质和氨基酸等回肠末端表观消化率的影响

试验旨在通过采用T型瘘管法,研究精油对生长猪蛋白质和氨基酸等回肠末端表观消化率的影响。试验选用6头(杜×长×大)去势公猪([28.6±1.3)kg],采用3×3双拉丁方试验设计,分别饲喂正对照日粮:玉米-豆粕型基础日粮+抗生素;负对照日粮:无抗基础日粮;精油组日粮:负对照+0.01%精油。每个试验期为7 d,前5 d为适应期,后2 d为食糜收集期。结果表明,在日粮中添加精油可提高(P<0.05)蛋白质、能量、精氨酸、赖氨酸、亮氨酸、色氨酸、蛋氨酸、丙氨酸、总必需氨基酸、总氨基酸的回肠末端表观消化率,并有提高干物质、苏氨酸、天冬氨酸、丝氨酸和酪氨酸表观消化率的趋势(P<0.10)。在日粮中添加0.01%的精油可提高生长猪蛋白质、能量、总必需氨基酸和总氨基酸的回肠末端表观消化率,并有提高干物质表观消化率的趋势。     

加工工艺和酶技术对猪和家禽高纤维日粮消化率的影响

在常用的重量法、纤维分析法的纤维馏分中,多糖的潜在转移阻碍了对非淀粉多糖消化效果的评价,在实际应用过程中应谨慎解释加工技术或酶处理对粗纤维、中性洗涤剂纤维或酸性洗涤剂纤维消化率的影响,而不是非淀粉多糖消化率的体内研究结果。非淀粉多糖组分组成及其组分消化率的详细信息有助于识别和理解加工过程中发生的变化。因此,本文综述了加工工艺对猪、禽非淀粉多糖理化性质的影响及其对非淀粉多糖降解的影响。     

Growth performance and puberty attainment in growing pigs fed dietary fumonisin B1

Twenty‐four male weaned piglets assigned to four diets containing 5.0, 10.0, 15.0 and 0.2 mg fumonisin B₁ (FB₁) /kg as diets 1, 2, 3 and control diet, respectively, were used to study the effect of dietary FB₁ on growth and puberty attainment in pigs in a 6‐month feeding trial. Lower feed intake during 0–4 months and a non‐significant (p > 0.05) but FB₁ concentration‐dependent decrease in live and DWGs in animals fed FB₁‐contaminated diets was observed at the end of the pubertal phase. The daily and the final live weight gains of animals fed diet 3 were 75.8% and 90.6%, respectively, of the control values. The mean ages at puberty by boars on diets 2 and 3 were significantly (p < 0.05) higher than those for animals on the control and diet 1. The animals on diet 3 attained puberty when mean live weight was 60.1 kg, some 30.3 days after the controls attained puberty, at 156.3 days, when the mean live weight was 46.9 kg. This study revealed that dietary FB₁ delays sexual maturity in growing pigs. Male weanling pigs for breeding should not be exposed to dietary FB₁ higher than 5 mg/kg for optimum growth and reproductive performance.     

Optimum tryptophan: Lysine ratio in diets for growing pigs: Analysis of literature data

Optimum tryptophan supply in diets for growing pigs shows considerable variation between studies; therefore, an attempt was made to analyse all available data reported in the literature. Due to the fact that, in most studies, lysine was the second-limiting amino acid, which means that lysine limits growth at a certain level of tryptophan intake, optimum supply has to be expressed as a ratio to lysine. The database was too small to give optimum supply as a concentration in the diet or as a daily amount. In total, 33 experiments were found, where tryptophan intake was offered in graded levels resulting in a tryptophan-dependent and -independent response phase. An additional 13 experiments showed either no dependent or no independent phase, which did not allow an optimum determination. The optimum tryptophan : lysine ratio (T : L_opt) was defined as the beginning of the plateau response-phase in feed intake or body weight gain. Mean T : L_opt was 0.174 (SD = 0.023; n = 33) and seemed to be unaffected by body weight, growth rate, lysine and protein concentration in the diet, or genetic improvement of the animals. However, precise detection of the optimum ratio is generally restricted due to the relatively large intervals between the ratios tested in the respective studies. Mean difference between T : L_opt and the nearest T : L ratio tested below (T : L_opt − 1) was 0.028 (SD = 0.011; n = 32). Therefore, it is likely that the true optimum ratio is below 0.174, and that the mean of both ratios ((T : L_opt + T : L_opt − 1) / 2) can be taken as a good estimation (mean = 0.160; SD = 0.024; n = 33). With respect to feed formulation for growing pigs, it was concluded that a figure of 0.17 for the optimum T : L ratio includes a safety margin large enough to cover most of the biological variations.     

The influence of lupin seed germination on the chemical composition and standardized ileal digestibility of protein and amino acids in pigs

The germination process can modify the chemical composition of nutrients in seeds, which can influence the digestibility and utilization of sprouts in animal diets compared to raw seeds. The aims of research were to provide controlled germination process of lupin seeds, monitor the changes in seed composition and determine the influence of the germination on the coefficients of standardized ileal digestibility (SID) of crude protein and amino acids in growing pigs, compared to raw lupin seeds. The seeds of two lupin species were used: yellow (RYL) (Lupinus luteus, cv. Lord) and blue (RBL) (Lupinus angustifolius, cv. Graf). Germination was provided in the dark at 24 °C for 4 days. Nutritional and antinutritional compositions of raw and germinated seeds (GYL and GBL, respectively) were analysed. Digestibility study was performed on pigs with an average body weight of 25 kg, and the pigs were surgically fitted with a T‐cannula in the distal ileum, with chromic oxide as an indicator. Seed germination increased the crude protein and fibre concentrations, but reduced the levels of the ether extract, nitrogen‐free extracts and all amino acids in protein. The content of alkaloids and raffinose family oligosaccharides decreased in both lupin species. Germination had no positive impact (p > 0.05) on the SID of crude protein and amino acids. Germination of lupin seeds negatively influenced the SID of lysine and methionine (p < 0.05). The results of the research revealed a decrease in the concentrations of antinutritional factors in the sprouts of yellow and blue lupins compared to raw seeds; however, no positive effect was observed on the coefficients of the standardized ileal apparent digestibility of protein and amino acids.     

Effects of corn gluten feed inclusion at graded levels in a corn-soybean diet on the ileal and fecal digestibility of growing pigs

Background

This study aimed to determine the effect of the inclusion of corn gluten feed (CGF) on the apparent and standardized ileal digestibility of protein and amino acids and the apparent ileal and total tract digestibility of energy in growing pigs. The study was performed using 16 barrows (weight, 45.3 ± 4.5 kg) that were fitted with a T cannula at the terminal ileum. There were four treatments: a corn-soybean diet without CGF and three corn-soybean diets containing increasing levels of CGF (65, 130, and 195 g/kg). Data were analyzed according to a randomized complete block design, four blocks with four pigs each (one pig per treatment). The trend of the response (linear or quadratic) was determined using orthogonal contrasts, and when a linear effect was determined, a linear equation was obtained.

Results

The results showed that the inclusion up to 195 g/kg of CGF in the corn-soybean diet did not diminish the ileal digestibility (apparent and standardized) of protein and amino acids (P > 0.05), except that of phenylalanine, cystine, and proline. A linear decrease (P < 0.05) per gram of CGF added to the diet in the apparent and standardized ileal digestibility of phenylalanine (0.011 and 0.015 percentage units, respectively), cystine (0.048 and 0.043 percentage units, respectively), and proline (0.045 and 0.047 percentage units, respectively) was noted. Similarly, ileal digestibility of dry matter and energy were adversely affected (reduced by 0.028 and 0.025 percentage units, respectively, per gram of CGF increment in the diet). A significant (P < 0.05) linear reduction in total tract digestibility with increase in CGF amount in the diet was observed for energy (0.027 percentage units), dry matter (0.027 percentage units), crude protein (0.020 percentage units), and neutral detergent fiber (0.041 percentage units) per gram of CGF added to the diet.

Conclusion

CGF did not affect the ileal digestibility of protein and most amino acids but reduced the ileal and total tract digestibility of energy.     

在玉米─大麦─豆粕型饲粮中添加β-葡聚糖酶对生长猪生产性能及营养物质表观消化率的影响

共采用３０ 头２０ 公斤重的杜×长×大生长猪,均分入３ 个处理组,分别饲以玉米－ 豆粕（ＣＳ） 、玉米－ 大麦－ 豆粕（ＣＢＳ） 和玉米－ 大麦－ 豆粕＋ ０－１ ％ β－ 葡聚糖酶（ 酶活性为２－８ 万Ｕ／ 克）（ＣＢＳＥ） 饲粮,饲喂至５０ 公斤,分别测定了猪的生产性能及总能（ＧＥ） 粗蛋白（ＣＰ） 、粗纤维（ＣＦ） 的表观消化率。结果表明：在生长猪的ＣＢＳ饲粮中添加β－ 葡聚糖酶后,对猪的日增重、料重比有改善的趋,从而接近ＣＳ 饲粮的效果,但差异不显著（Ｐ＞ ０－０５） ;但可显著提高猪对饲粮ＧＥ、ＣＦ 的表观消化率（Ｐ≤０－０５） ,对ＣＰ 的表观消化率没有显著的改善作用（Ｐ＞ ０－０５） 。     

Effects of different types of dietary non-digestible carbohydrates on the physico-chemical properties and microbiota of proximal colon digesta of growing pigs

The effect of different types of fibre on the intestinal digesta and microbial diversity was evaluated in growing pigs. The animals were fed during forty-two days with one of four experimental diets including a control group, a diet enriched with resistant starch type I, by coarse ground corn, and other two diets containing sugar beet pulp (8%) and wheat bran (10%) (as sources of soluble and insoluble non-starch polysaccharides respectively). Body weight (BW) and average daily feed intake (ADFI) were assessed at day 7, 21 and 42. Luminal samples of digesta from proximal colon were collected to analyse water retention capacity (WRC), concentration of short-chain fatty acids (SCFA) and the microbial diversity. Overall, animals fed with higher amounts of non-digestible carbohydrates had lower ADFI and BW. Sugar beet pulp provoked an increase of WRC, a higher concentration of SCFA, and a more stable microbial diversity throughout the experimental period. On the other hand, animals fed with wheat bran presented a lower bacterial diversity.     

裙带菜膳食纤维对高脂血症大鼠体内内皮素-1水平的影响

目的：研究裙带菜可溶性膳食纤维对体内内皮素－1水平的影响。方法：40只大鼠分为4组（n=10）：正常对照组、高脂模型组、膳食纤维低剂量组（5％）、膳食纤维高剂量组（10％）;经裙带菜可溶性膳食纤维处理8W后,检测血浆内皮素－l（ET－1）水平,并用RT－PCR检测内皮素－1（ET－1）mRNA表达水平。结果：裙带菜可溶性膳食纤维显著降低ET－1水平并伴随着（ET－1）mRNA表达下调。结论：裙带菜可溶性膳食纤维能降低高脂血症大鼠血浆ET－l的水平,这可能与ET－1mRNA表达水平的下调有关。