【作者】 赵景鹏；

【导师】 文杰；

【作者基本信息】 中国农业科学院 ， 动物营养与饲料科学， 2010， 博士

【摘要】 肌纤维及其类型是评价肉品质的重要指标,为了揭示肉鸡肌纤维特性和肉质性状形成的组织学基础以及日粮营养浓度对其调控机制,本研究共设计了4个试验。试验一以两个品种的肉鸡(爱拔益加-AA,商用鸡种;北京油鸡-BJY,中国地方鸡种)为试验材料,探讨了肌纤维特性在肉质性状形成过程中的变化规律。两个品种雄性雏鸡共240只(每个品种120只),分别被随机分为6个重复,每个重复20只鸡。在0、7、21、35、42、63和91日龄,每个品种每个重复随机选取2只鸡屠宰取样。结果表明,两个品种机体发育模式存在较大差异,AA鸡比BJY鸡具有更好的蛋白质和脂肪沉积能力。肌肉核酸浓度变化影响肉鸡的蛋白质代谢过程,可被用来预测肌肉发育潜力,但其实用价值和准确度需要进一步验证。肌纤维特性(肥大和类型转化)的变化因日龄而异,其对肉质性状的影响具有品种特异性。试验二探讨了能蛋比相同的不同日粮营养浓度对AA鸡和BJY鸡生长性能、胴体特征和血液反应的影响。试验日粮含高、中、低3种养分浓度,分期配制。前期料(1-21天)分别含有23%、21%和19%的粗蛋白和3059、2793和2527 kcal/kg的代谢能,中期料(22-35天)分别含有21%、19%和17%的粗蛋白和3150、2850和2550 kcal/kg的代谢能,后期料(AA,36-42天;BJY,36-91天)分别含有19%、17%和15%的粗蛋白和3230、2890和2550 kcal/kg的代谢能。432只雄性雏鸡(每个品种216只)随机分为6个处理,每个处理6个重复,每个重复12只鸡。AA鸡具有较好的体增重(P < 0.001)、饲料转化率和胴体产出,但腹脂和胴体脂肪沉积较多(P < 0.001)。在两个品种中,高日粮营养浓度提高了日增重、蛋白和能量利用效率,降低了采食量和饲料转化率(P < 0.05)。此外,高营养浓度日粮分别增大了品种之间的前期采食量、蛋白和能量利用效率差异,缩小了胴体化学组成差异。这些结果表明:(1)遗传选择显著影响肉鸡对于日粮养分浓度的反应;(2)在饲喂低营养浓度日粮时,两个鸡种之间的生产性能差异最小;(3)在饲喂高营养浓度日粮时,两个鸡种之间的胴体品质差异最小;(4)胴体组成几乎不受日粮营养水平影响,两个鸡种对于日粮养分浓度的血浆代谢物反应类似;(5)两个鸡种在三个饲养阶段内的适宜日粮可以根据以上结果判断。试验三通过对AA鸡和BJY鸡饲喂具有恒定能蛋比的不同营养浓度的日粮,研究了营养诱导的生长速度差异对于它们的肌肉特性和品质的影响。试验日粮与试验二相同,根据3个饲养阶段分别配制,两两之间相差2%的粗蛋白。试验测定了胸大肌(PM)和股二头肌(BF)中的肌纤维组织特性变化、早期肌肉代谢和肌肉品质。结果表明,在各自的上市日龄,与BJY鸡相比,AA鸡具有显著较高的血浆蛋白质和脂类代谢物浓度、白肌与红肌和中间型纤维比率、pH值、L*和b*值,较低的血浆葡萄糖代谢物浓度、肌纤维直径、肌肉能量储备、a*值、滴水损失(DL)和剪切力(SF)(P < 0.01)。高营养浓度日粮提高了AA鸡的肌纤维大小,降低了糖原含量,减小了肌肉酸化的速率和幅度;同时,促进了BJY鸡红肌和中间型纤维向白肌纤维的转化,增加了能源储备,加快了宰后肌肉pH值的下降(P < 0.05)。在每一品种内,大多数肌肉品质指标(如剪切力、滴水损失和肉色)的变化与日粮处理引起的组织学和生物化学变化一致。总之,日粮营养浓度能够通过改变肌肉组织结构和最初代谢变化影响肌肉品质,其中,许多反应具有品种和组织特异性。试验四以试验一、二和三为基础,采用实时荧光定量方法,研究了不同品种肉鸡不同类型肌球蛋白重链基因mRNA相对表达丰度的变化,探讨了日粮营养浓度对肌肉发育影响的作用途径。结果表明,肉鸡反映肌纤维类型组成的MyHC基因表达具有明显的发育性变化规律,不同品种之间差异巨大,尤其是在生长的拐点期。AA鸡快白肌纤维含量的增加和快红肌纤维比例的下降与其快速生长(肌肉快速发育)有关,BJY鸡肌肉中较高的慢红肌纤维含量是其优良的肉质性状形成的基础。日粮营养浓度通过改变生长轴基因表达,能够影响不同品种肉鸡的不同纤维特性,具体机理尚需深入研究。更多还原

【Abstract】 The hypertrophy and type conversion of muscle fibers is an important physiological process, being a link among all meat quality traits. With an aim to expose the formation mechanism of muscle fiber characteristics and meat quality traits and their nutritional modulation by dietary nutrient density in different broiler breeds, this comprehensive study includes 4 expeiments.Trial 1 investigated the developmental chages of muscle fiber characteristics underlying the formation of meat quality traits in 2 distinct broiler breeds of male chickens (Arbor Acres, AA, a commercial line, and Beijing-You, BJY, a Chinese nonimproved line). Male hatchlings (120 of each breed) were randomly assigned to 6 pens of 20 birds in each breed. The zootechnical parameters were recorded at 0, 7, 21, 35, 42, 63 and 91 d of age, and a muscle sample was obtained from 12 birds of each group, respectively, in the pectoralis major (PM) and biceps femoris (BF). Results showed that genetic improvement resulted in large differences of developmental pattern between breeds. AA broilers had better deposit capacity of protein and fat than did BJY chickens, leading to the allometric growth (overgrowth) of muscular mass and abdominal fat at the cost of internal organs. Altered nucleic acid concentrations of skeletal muscles were involved in the protein metabolism from different genotype challenges, although their value and accuracy in prediction of muscle development needed to be validated further. Muscle fiber properties were changed with age, whose impact on meat quality traits was breeds dependent.Trial 2 was conducted to evaluate the effects of varying nutrient density with constant ME:CP ratio on growing performance, carcass characteristics and blood responses in AA broilers and BJY chickens. Experimental diets were formulated with high, medium or low nutrient densities for 3 growing phases. Starter diets (1 to 21 d) contained 23, 21 and 19% CP with 3,059, 2,793 and 2,527 kcal/kg of ME; grower diets (22 to 35 d) were 21, 19 and 17% CP with 3,150, 2,850 and 2,550 kcal/kg of ME; and finisher diets (36 to 42 d for AA and 36 to 91 d for BJY) diets had 19, 17 and 15% CP with 3,230, 2,890 and 2,550 kcal/kg of ME. Male hatchlings (216 of each breed) were randomly assigned to 6 replicates of 12 birds in each treatment. Arbor Acres broilers had better (P < 0.001) body weight gain (BWG), feed conversion ratio (FCR) and carcass yield, but had greater (P < 0.001) abdominal and carcass fat deposition. In both breeds, the higher nutrient density increased (P < 0.05) BWG, protein efficiency ratio (PER) and energy efficiency ratio (EER), while decreasing (P < 0.05) feed intake and FCR. The breed differences were increased for FCR, PER and EER in the starter period and decreased for carcass chemical composition respectively by higher nutrient density. These findings indicate that: 1. genetic improvement has a significant effect on broiler responses to dietary nutrient density; 2. performance differences between breeds are lessened with diets of low nutrient density; 3. carcass quality differences are less when birds were fed diets of high nutrient density; 4. carcass composition are hardly modified by nutrient density and both breeds exhibit similar metabolite responses to dietary concentrations; 5. optimal diets are deduced for these breeds for the 3 growing phases.Trail 3 has evaluated the effects of varying growth rate, by feeding at different planes of nutrition with constant ME:CP ratio, on muscle characteristics and meat quality in AA broilers and BJY chickens. Experimental diets, differing on average by 2% CP, were formulated as trial 2 with high, medium, or low nutrient densities for 3 growing phases. Male hatchlings (216 of each breed) were randomly assigned to 6 pens of 12 birds in each treatment. Altered histological characteristics of muscle fibers, early postmortem muscle metabolism and meat quality were investigated in the PM and BF muscles. At their market age, AA broilers had significantly higher concentrations of plasma protein and lipid metabolites, ratios of white to red and intermediate fibers, pH, L* and b* values, and lower concentrations of plasma glucose metabolites, muscle fiber diameter, muscle contents of energy stores, a* value, drip loss (DL) and shear force (SF) than did the BJY (P < 0.01). Higher nutrient density increased size of the muscle fibers, decreased glycogen reserve and reduced the rate and extent of acidification in the AA, while accelerating transformation of red and intermediate to white fibers, enhancing energy stores and hastening the decrease in pH in the BJY (P < 0.05). In each breed, most meat quality variables (e.g. SF, DL and color) were consistent with the histological and biochemical changes caused by the feeding strategy. Together, dietary nutrient density can influence meat quality as a result of altered histological and initial energy/metabolic characteristics of the muscle. Many of the responses to diet differed between AA and BJY and between the 2 muscles studied.Based on previous experiments, trail 4 describes the long-term changes of mRNA expression levels for different myosin heavy chain (MyHC) genes using real-time quantitative PCR in AA broilers and BJY chickens, and explores the possible mechanism underlying the effect of dietary nutrient density on muscle development. Results suggested that the relative expressions of MyHC genes, reflecting the type composition of muscle fibers, exhibited a clear temporal-spatial dynamics. Significant differences were observed between breeds, especially at the inflection stages in growth curve. The remarkably decreased MyHC I fibers and inereased MyHC IIB fibers contributed to the fast muscle deposition as well as the accelerated body growth in AA broilers, while the higher proprtion of MyHC I and IIA fibers corresponded to better meat quality in BJY chickens. Dietary nutritional levels could affect muscle fiber characteristics of different broiler breeds as a result of altered expressions of growth axis genes, yet the causal mechanism needed to be investigated further.更多还原