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所谓近交是指亲缘交配,它是指五代以内双方具有共同祖先的公母畜交配。在家畜中近交程度最大的是父女、母子和全同胞交配。其次是半同胞、祖孙、叔侄、姑侄、堂兄妹、表兄妹间的交配。近交是育种工作的重要工具,在培养或改良新品种中发挥着重要作用。但对于个体养殖户和... 相似文献
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孙乃峰 《北方牧业(奶牛)》2007,(12):45-46
相互有亲缘关系的个体间交配繁殖称为近亲繁育。相互有亲缘关系的个体,查其系谱必定有共同的祖先。离共同祖先越近的个体间其亲缘关系也越近。从畜牧学的观点来看,交配双方到共同祖先的世代数在六代以内的交配繁殖称为近亲繁殖,简称近交。近交有利也有害,只要控制得当,就可以兴利除弊.扬长避短,在培育新品种和改良牛群品质方面发挥重要作用。 相似文献
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<正> 皖南山区的地方品种——皖南花猪,在历史上由于山区交通的闭塞和山岭的阻隔,形成了若干个自然团锁群体。这些群体由于长期地实行着不同程度的亲缘交配和人工选择,淘汰了大量的不良性状,逐渐形成具有一定程度的近交不衰的猪群,而成为当今比较优良的地方品种。为了研究皖南花猪的近交不衰的特性,以及为今后的保种、育种工作提供依据,对我场的皖南花猪生产群进行不同程度近交结果的观察和分析。 相似文献
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遗传学上将有亲缘关系的个体间的交配称为近交,但在育种学上认为,如果双方间存在亲缘关系就叫近亲交配,简称近交。本文使用stata软件通过单因素方差分析研究了不同近交程度对大白猪背膘厚的表型值、EBV值和大白猪达100 kg体重的日龄的表型值、EBV值的影响。试验结果表明:近交系数低于12.5%时对背膘厚度和达100 kg日龄的表型值、EBV值的影响均不显著(P》0.05);近交系数高于1 2.5鬈时仅对达100 kg日龄EBV值的影响有极显著差异(P≤0.01),对其他三个性状影响均不显著(P>0.05)。可见,温和近交(近交系数<12.5%)对大白品种的猪背膘厚和达100 kg体重日龄的影响不显著。 相似文献
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人们在长期的农业生产实践中认识到近交衰退和杂交优势的事实,而且育种科学家巧妙地利用近交和杂交作为育种工作的技术和手段,使品种不断得到改良,但是为什么近交衰退和杂交都有优势呢?这是遗传学所要研究的问题,并且还要进一步研究又如何来应用理论改良现有家畜,产生社会上的经济效益。本文将作一概要性探讨,主要目的是为了帮助学好数量遗传理论,进一步来改良品种,提高商品率。什么叫近交呢?一般我们将有亲缘关系的公母畜进行交配繁殖,称为近交,而在群体上来看,那么近交指某一性状上是具有一定概率的同型交配。杂交是近交的相对反义术语,它指非亲缘个体间的交配,在群体上看,在某性状上是具有一定概率的异型交配。 相似文献
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近交(亲交)的遗传效果是使基因纯合。亲缘关系越近的个体间交配,基因纯合的概率越大。通过近交、可使优良基因集中于某些个体,从而获得优良的理想型种牛。从这一点看,近交是当前品系育种的有利手段。但是,近交又可使一些有害隐性基因纯合而暴露出来,以致产生近交退化现象,严重的影响奶牛的生产。我们知道,泌乳量的遗传力约为0.3,这样,它对遗传影响较敏感,近交对产奶量会产 相似文献
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魏静 《四川畜牧兽医学院学报》2009,(4):28-32
在现代法律秩序中,商会自治规范是制定法的基础和必要的补充,甚至在某些方面替代了制定法;商会自治规范主要包括商会组织规范、行为规范、惩罚规范以及争端解决规范等;其效力仅及于其内部成员;商会自治规范和制定法之间存在冲突,但也存在整合的基础。 相似文献
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本文概述了猪的毛色类型、猪的毛色遗传模式,着重综述了猪毛色基因分子基础的研究进展,指出存在问题并就未来发展方向做了思考。 相似文献
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REASONS FOR PERFORMING STUDY: Centesis of the bicipital bursa using an 8.9 cm long spinal needle has been reported but the alternative of employing a 3.8 cm long hypodermic needle requires validation. OBJECTIVE: To compare the efficacy of 2 different methods of centesis of the bicipital bursa and to evaluate the usefulness of ultrasonographic imaging to determine the location of solution administered when centesis of the bursa is attempted. METHODS: For Trial 1, 6 clinicians, who had no previous experience of centesis of the bicipital bursa, attempted to inject a solution composed of an aqueous radiopaque contrast medium and physiological saline solution (PSS) into the bicipital bursae of 2/12 horses using the previously described distal approach to inject one bursa and a proximal approach to inject the contralateral bursa. The bicipital tendon and bursa were examined ultrasonographically before and after injection; and both shoulders were examined radiographically to identify the location of the medium. In Trial 2, another 6 clinicians, also with no previous experience of centesis, repeated Trial 1, using 6 horses, but the radiopaque contrast medium was mixed with air instead of PSS. RESULTS: Accuracy of centesis using the proximal approach was 39% and that of the distal approach 28%. Ultrasonographic examination of the shoulder allowed the location of solution and air to be accurately predicted in all 12 shoulders examined. CONCLUSIONS: Clinicians who have had no previous experience performing centesis of the bicipital bursa are unlikely to be successful in centesis using either approach. Radiographic examination after injecting a radiopaque contrast medium may be necessary to assess the success of centesis especially if bursal fluid is not obtained during centesis. Injecting air along with the radiopaque contrast medium provides more accurate ultrasonographic confirmation of centesis and better radiographic definition than does injection without air. 相似文献
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Effects of size of ingestively masticated fragments of plant tissues on kinetics of digestion of NDF
Ingestively masticated fragments were collected and sized via sieving. Different sizes of esophageal masticate and ruminal digesta fragments, and ground fragments of larger masticated pieces were incubated in vitro, and undigested NDF remaining at intervals of up to 168 h of incubation was determined. The ruminal age-dependent time delay (tau) for onset of digestion of NDF was positively correlated (P < 0.004) with the mean sieve aperture estimated to retain 50% of the fragments between successive sieve apertures (MRA). Degradation rate of potentially degradable NDF (PDF) and level of indigestible NDF were not related (P > 0.10) to MRA of masticated and ground fragments. Estimates of tau were positively related to MRA, with slopes of bermudagrass < corn silage < ruminal fragments of corn silage. It was concluded that fragment size-, and consequently, ruminal age-dependent onset of PDF degradation of a mixture of different fragment sizes results in an age-dependent rate of degradation of the more rapidly degrading of two subentities of PDF. Models are proposed that assume a tau before onset of simultaneous degradation of PDF from two pools characterized as having gamma-modeled age-dependency and age-constant rates. The ruminal age-dependent pool seems to be associated with the faster-degrading pool, and its rate parameter increases with range in MRA in the population of fragments. Conceptually, the ruminal age-dependent rate parameter for PDF degradation seems to represent a composite of several effects: 1) effects of the size-dependent tau; 2) range in MRA of the population of ingestively masticated fragments; and 3) subentities of PDF that degrade via more rapid age-dependent rates compared with subentities of PDF that degrade via age-constant rates. The estimated fractional rates of ruminative comminution of ingestively masticated fragments (0.060 to 0.075/h) were of a magnitude similar to the mean fractional rates of PDF digestion (0.030 to 0.085/h), which implies that ruminative comminution may be first-limiting to fractional rate of PDF digestion. The in vivo roles of ingestive and ruminative mastication of fragments on PDF degradation must be considered in any kinetic system for estimating PDF digestion in the rumen. These results and others in the literature suggest that the rate of surface area exposure rather than intrinsic chemical attributes of PDF may be first-limiting to degradation rate of PDF in vivo. 相似文献
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乳酸杆菌作为益生菌广泛用于人和动物.本文综述了乳酸杆菌改善宿主健康的机制.乳酸杆菌可通过产生抗菌物质如乳酸、过氧化氢、细菌素,或者通过竞争营养或肠道黏附位点来抑制致病菌;通过诱导黏附素的分泌或阻止细胞凋亡而增强肠道的屏障功能,从而保护肠道.文章重点讨论了乳酸杆菌表面成分(表面蛋白、脂磷壁酸和肽聚糖)与肠道受体(C型凝集素受体、Toll样受体和Nod样受体),阐述了他们结合后启动免疫调节信号,调控肠道免疫功能以发挥改善健康作用的机制. 相似文献