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1.
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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奶牛育种改良中,累代集中优秀公牛和尖子母牛交配,容易造成近亲交配。现代各国的种子公牛部是从世界范围选择来的,几乎无一例外。有显赫父牛和外祖父的公牛,对奶牛群也确实可获得显著的改良效果。据对美国东北部最近的调查,20万头奶牛中,近交系数 F<5％的近交率占牧场牛群的 相似文献
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《中国畜牧兽医文摘》2015,(1)
<正>随着现代化养殖技术的发展,人工授精技术在牛群养殖中得到了广泛的应用,牛群养殖规模正在逐渐增大,牛难产发病率增加。母牛出现难产如果处理不及时,母牛和犊牛均可能死亡。即使科学处理,也会留下后遗症,影响养殖户的经济利益。准确分析难产病因,采取有效的措施,做好难产预防,是保证奶牛经济效益的基础。1病因1.1初配年龄掌握不当在牛群养殖中,有一些养殖户对牛群繁殖较为急切,在母牛没有达到成熟的交配条件时就让其配种,结果胎儿过大导致牛难 相似文献
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为了获得遗传进展,即在遗传素质下一代必须优于上一代。要培育出产量高,使用年限长的牛群,生产牧场首先必须根据牧场自身的生产水平,确立本场育种目标。然后在牧场牛群中挑选超过育种目标的奶牛和能改良下一代生产性能,使牛群和生产水平更接近育种目标的种公牛相交配,逐渐达到牧场的育种目标。在实现这一目标的过程中,必须做好以下几个环节。1.建立生产性能记录体系 牧场必须有自己牛只的生产性能记录。精确的 相似文献
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于芳 《畜牧兽医科技信息》2010,(5):58-59
人工授精是用器械采取公畜的精液,再用器械把精液输入到发情母畜生殖道内,以代替公母畜自然交配的一种配种方法.采用人工授精技术,可以使优秀种公牛冷冻精液大面积推广,迅速提高后代的生产水平,避免牛群繁殖疾病的交叉传染,可防止各种疾病,提高供配种效率,降低牛群管理成本. 相似文献
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1选配
肉牛的选配是指在牛群内,根据牛场育种目标有计划地为母牛选择最适合的公牛,或为公牛选择最适合的母牛进行交配,使其产生基因型优良的后代,不同的选配,有不同的效果。 相似文献
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近亲交配是全球荷斯坦牛群普遍面临的问题，2004年5月美国农业部动物遗传改良计划实验室（AIPL）公布了美国荷斯坦牛近交情况。1960年为0，1970年为0．4％，1980年为0．8％，1990年为2．5％，2000年为4．5％，2004年增长到4．9％，并有进一步增长趋势。 相似文献
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Inbreeding depression estimates obtained by regression of the individual performance on the inbreeding were studied by stochastic simulation under various genetic models (solely additive, partial dominance, overdominance and epistasis), and mating strategies (random mating versus selection). In all models, inbreeding depression estimates based on the individual pedigree inbreeding coefficients were compared with estimates based on the true level of autozygosity. For the model with partial dominance and selection, the estimates of inbreeding depression from pedigree information were more negative (lower) than those based on true inbreeding coefficients whereas, in contrast, they were less negative (higher) for the models with overdominance and selection. The difference in the variation of true and pedigree individual inbreeding coefficient indicated that biased estimates might occur even in random mating populations. The estimation of inbreeding depression was further complicated when epistatic effects were present. The sign and the magnitude of the inbreeding effect (depression) estimates might be rather heterogeneous if additive by dominance effects are present because they are strongly dependent on the gene frequency. It was also shown that inbreeding depression is possible in models with negative additive by dominance effects. In models with dominance by dominance inheritance it was difficult to assess the non-linear relationship between performance and inbreeding, while at the same time, non-linear estimates based on pedigree information were extremely biased. The results obtained indicate that new or additional methodologies are required if reliable conclusions about consequences of inbreeding depression are needed. 相似文献
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A D Narayan 《British poultry science》1976,17(3):303-311
1. The effect of regular full-sib and double first cousin mating on body weight and rate of gain over six generations of Japanese quail was determined. 2. The depression of characters was more pronounced in the full-sib than in the double first cousin mating system, the relative depression due to parental inbreeding and offspring inbreeding depending on the magnitude of parental effect and individual's own genotypic effect on the character. 3. The body weight and rate of gain taken at an early age showed greater depression due to parental inbreeding whereas that taken near sexual maturity was depressed mainly due to individual's own inbreeding. 相似文献
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不同来源大白猪总产仔数近交衰退评估 总被引：2，自引：2，他引：0
旨在评估两个不同来源大白猪群体经过近8个世代的选育后总产仔数（total number of piglets born，TNB）近交衰退的程度。本研究对1 937头大白猪使用GeneSeek GGP Porcine HD芯片进行分型，其中1 039头来自加系大白猪和898头来自法系大白猪，且两品系均有表型记录和系谱记录，系谱共由3 086头大白猪组成。分别使用系谱、SNP和ROH进行个体近交系数估计，并将近交系数作为协变量利用动物模型对总产仔数进行近交衰退评估。为了精准定位导致总产仔数衰退的基因组片段，又进一步对每条染色体以及显著染色体分段计算近交系数并估计其效应，检测是否能引起总产仔数发生近交衰退现象。对于加系群体，FROH、FGRM和FPED估计的近交系数均值分别为0.124、0.042和0.013，其中FROH和FPED相关最高，相关系数为0.358；对于法系群体，FROH、FGRM和FPED均值分别为0.123、0.052和0.007，其中FROH和FGRM相关最高，相关系数为0.371。利用3种不同计算方法所得近交系数用于估计近交衰退时，加系群体的总产仔数均检测到显著的近交衰退，而且当FROH、FGRM和FPED每增加10%时，总产仔数分别减少0.571、0.341和0.823头；但法系群体仅有FROH估计的总产仔数检测到显著近交衰退，FROH每增加10%时，总产仔数减少0.690头。为了锁定相关的染色体和基因组区段，首先利用ROH估计每条染色体近交系数并进行近交衰退分析发现，加系群体中检测到第6、7、8和13号染色体产生了显著近的总产仔数交衰退，而法系群体未检测到与近交衰退相关的染色体。然后，又将与加系总产仔数近交衰退显著相关的4条染色体平均分为2、4、6、8个片段进行近交衰退检测，其中平均分成8段后的染色片段的长度范围为15.1~25.8 Mb。在第6、7和8号染色体分别检测到1、2和3个与总产仔数相关的近交衰退染色体片段。这些区域注释到了CUL7、MAPK14和PPARD基因与胎盘发育相关，AREG和EREG基因与卵母细胞成熟有关。本研究利用3种近交系数计算方法对两个不同来源的大白猪总产仔数进行近交衰退评估，在加系大白猪中3种估计方法都能检测到近交衰退的现象，而法系群体中只有FROH才能检测到。而且通过ROH方法进一步确定了能引起加系大白猪总产仔数衰退的4条染色体和6个特定的染色体区段，还注释到了与繁殖相关的候选基因。这为揭示近交衰退的遗传机制提供了新的研究手段，也为基因组选种选配提供了参考依据。 相似文献
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The objective of this study was to analyze the development of inbreeding and estimate inbreeding depression in the Danish populations of 3 major meat type sheep breeds. The pedigrees contained 29,336 Texel, 22,838 Shropshire, and 11,487 Oxford Down. The rate of inbreeding was approximately 1% per generation for all breeds, but the rate of increase in co-ancestry was somewhat lower (0.45 to 0.71), indicating that more inbreeding has been accumulating than would be expected if mating was at random. Inbreeding depression for birth weight, ADG from birth until 2 mo, and litter size was estimated for all 3 breeds using a minimum of 15,000 records per trait and breed. All traits showed depression due to inbreeding of the animal itself. For most combinations of trait and breed, there was also a significant reduction of the phenotype due to inbreeding in the dam. The size of inbreeding depression was 1.2 to 2.6% of the mean, resulting in an increase in the inbreeding coefficient of the individual of 0.10, and estimates were similar for similar increases in maternal inbreeding. The rate of inbreeding in these breeds needs to be reduced in the future to avoid a further decline in birth weight, ADG, and litter size. 相似文献
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T. Honda T. Nomura & F. Mukai 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2005,122(5):340-348
The solution to the inbreeding problem for livestock breeds in commercial use is often complicated by hierarchical population structure, in which favourable genes are accumulated in the upper level of the hierarchy (breeding population) by artificial selection and the genetic progress achieved is transferred to the lower level through migration of males. When the breeding population is subdivided into several isolated lines, rotational mating with the lines has been shown to be quite an effective system to reduce the short‐ and long‐term inbreeding of commercial females in the lower level. In practice, however, some amount of migration should be allowed among the lines to reduce the rate of inbreeding in each line. In this study, we developed the recurrence equation for the inbreeding coefficient of the commercial females maintained by the rotational mating with partially isolated lines. Numerical computations were carried out to evaluate the effect of the migration on the efficiency of the rotational mating. It was shown that even with a small amount of migration among the lines, the inbreeding of commercial females is substantially inflated. However, when four or five lines are available, the inbreeding coefficient of commercial females can be suppressed to an acceptable level, irrespective of the effective size of line and the migration rate. Application of the mating system to the population of Japanese Black cattle was also examined. 相似文献
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The objective of this research was to estimate the amount of inbreeding and effective population size of the Japanese Black breed using pedigree records from bulls and heifers registered between 1985 and 1997. Inbreeding was quantified by three F-statistics: actual inbreeding, inbreeding expected under random mating, and inbreeding due to population subdivision. During the period of 1985 to 1997, the inbreeding expected under random mating increased from 2.3% to 5.0%, whereas the increase of actual inbreeding was more gradual (from 4.7% to 5.4%). The inbreeding due to population subdivision decreased almost linearly and reached 0.5% in 1997, indicating that genetic subdivision of the Japanese Black cattle population has essentially disappeared. The effective size of the breed was estimated from the increasing rate of inbreeding expected under random mating. In the earlier half of this period (1986 to 1990), the breed maintained an effective size of approximately 30. However, after 1991 the effective size sharply decreased and the harmonic mean between 1993 and 1997 was only 17.2. The main cause of this reduction of the effective size was considered to be the intensive use of a few prominent sires. To increase the effective size, an upper limit in the use of AI semen per sire should be imposed. 相似文献
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L. Silió M.C. Rodríguez A. Fernández C. Barragán R. Benítez C. Óvilo A.I. Fernández 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2013,130(5):349-360
Multilocus homozygosity, measured as the proportion of the autosomal genome in homozygous genotypes or in runs of homozygosity, was compared with the respective pedigree inbreeding coefficients in 64 Iberian pigs genotyped using the Porcine SNP60 Beadchip. Pigs were sampled from a set of experimental animals with a large inbreeding variation born in a closed strain with a completely recorded multi‐generation genealogy. Individual inbreeding coefficients calculated from pedigree were strongly correlated with the different SNP‐derived metrics of homozygosity (r = 0.814–0.919). However, unequal correlations between molecular and pedigree inbreeding were observed at chromosomal level being mainly dependent on the number of SNPs and on the correlation between heterozygosities measured across different loci. A panel of 192 SNPs of intermediate frequencies was selected for genotyping 322 piglets to test inbreeding depression on postweaning growth performance (daily gain and weight at 90 days). The negative effects on these traits of homozygosities calculated from the genotypes of 168 quality‐checked SNPs were similar to those of inbreeding coefficients. The results support that few hundreds of SNPs may be useful for measuring inbreeding and inbreeding depression, when the population structure or the mating system causes a large variance of inbreeding. 相似文献
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Selection on the best estimate of the breeding value of individuals should, in large populations, provide the maximal response in breeding value. However, many breeders deal with the selection of small numbers of animals from relatively small populations and therefore there is a trend for inbreeding to rise because of genetic drift. Moreover, as the evaluation of candidates is traditionally based on methodologies including information from relatives [selection indices, best linear unbiased predictor (BLUP)] more individuals are selected from the best families and so closely related individuals will generate most of the offspring. This effect is more important for traits with low heritability as phenotype gives little information on the breeding value of the individuals and more weight is given to relatives’ data. The need for controlling inbreeding refers not only to a better use of the genetic variability available and to a reduced inbreeding depression in the selected trait, but also to a reduced depression of fitness-related traits, which may be the most serious drawback at present due to the increase in inbreeding in domestic populations (M euwissen and W oolliams 1994). In recent years considerable work has been carried out on the design of strategies to maintain genetic diversity in selection programmes. These strategies are aimed at simultaneously optimizing genetic gain and inbreeding, either by reducing the rate of inbreeding (or variance of response) while keeping genetic gains at a predetermined level, or by increasing selection response under a restriction on inbreeding (or on variance of response). Following T oro and P& eacute ; rez -E nciso (1990) the different strategies can be classified according to the factor on which they act: (i) the selection criterion used; (ii) the mating system imposed; (iii) the number of selected individuals and their contribution to the next generation. The first group of strategies proposes the use of a suboptimal selection criterion that reduces the weight given to family information or the use of an upward-biased heritability in BLUP evaluation (T oro and P& eacute ; rez -E nciso 1990; see G rundy et al. 1998a for the latest development of this idea). The second group of strategies proposes action on the mating system including factorial mating designs, minimum co-ancestry mating (using linear programming) or compensatory mating (see review by C aballero et al. 1996). The third group of strategies includes the ones considered in the present work. The first possibility is to modify the contribution of the selected individuals of generation t to the selected individuals of generation t + 1, by practising some form of within-family selection with respect to BLUP values. Two strategies of this type were considered: modified within-family selection (MWFS) and restricted co-ancestry selection (RCS). The second possibility is to modify the contribution of the selected individuals of generation t to the evaluated individuals of generation t + 1 (instead of to the selected individuals) by a strategy called weighted selection (T oro and N ieto 1984). Three strategies were considered in this case: weighted selection (WS), restricted co-ancestry weighted selection (RCWS) and pair weighted selection (PWS). More specifically, the aim of the present paper is to show how these five strategies can be implemented using mathematical programming techniques. A small example comparing all of these strategies with standard truncation selection (TS) is also given for illustration. 相似文献
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By M. Analla J. M. Montilla J. M. Serradilla 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》1999,116(6):481-488
Inbreeding is known to affect metric traits. Reduction of additive genetic variance, as well as phenotypic values are its most significant deleterious effects. Yet the emergence of disorders due to recessive gene action constitutes another important aspect. Despite the fact that some effect of inbreeding can be positively used in selection schemes (T oro 1993), breeders are aware of the deleterious effects and try to avoid them. This is particularly true when the selection nucleus and the related population are of small size. Several authors (H agger 1991; V errier et al. 1993; W ray and G oddard 1994) have stressed that the application of sophisticated methods of selection, particularly BLUP-based techniques (H enderson 1973) is to be reconsidered in the light of inbreeding effects. Comparisons of selection methods should therefore account for inbreeding depression (T oro and P jrez -E nciso 1990; Q uinton et al. 1992). Other authors believe that inbreeding depression is not so important, at least in the meat production industry (G ama and S mith 1993) for traits with high heritabilities. Nevertheless, the net effect of inbreeding in a selection programme will depend on the magnitude of the selection response relative to the depression due to the accumulated inbreeding. Depending on whether genetic gain and inbreeding depression compensate for each other, the level of inbreeding of the animals may need to be accounted for in the selection process (K eller et al. 1989; R oehe et al. 1993; K lieve et al. 1994; B risbane and G ibson 1995). On the other hand, the response to inbreeding is not the same for all animals. There is an important range of variation for the estimates of inbreeding depression reported in the literature (e.g. L amberson and T homas 1984). Differences in such a response with respect to identifiable sources of variation should be examined. The objective of this work was to study the relationship between the depression due to inbreeding and litter size of ewes and weights of lambs; and to identify sources of a possible differential response to inbreeding between animals coming from different genetic line, sex, or type of birth. 相似文献
20.
J.P. Gutiérrez I. Cervantes & F. Goyache 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2009,126(4):327-332
Computation of inbreeding rate (Δ F ) must consider that inbreeding is delayed with one generation with respect to the idealized population when addressed using individual inbreeding coefficients. The expression relating inbreeding in generation t with inbreeding rate F t = 1 – (1– ΔF ) t should be more correctly written in real animal populations as F t = 1 – (1– ΔF ) t −1 , as changes in allele frequencies occur in the equivalent co-ancestries in the previous generation. This simple approach is tested on simulated and real pedigrees thus demonstrating that: (i) the adjusted individual increase in inbreeding becomes stable in populations under random mating while the unadjusted parameter does not; (ii) regression of the unadjusted parameter over generations in pedigrees under random mating is highly significant while after correction it is not significant; and (iii) the variance of the adjusted parameter is reduced with the generations. 相似文献