畜禽良种繁育技术及其应用的经济学思考

畜禽良种在畜牧产业发展中发挥核心作用,是区域畜牧业发展的物质基础,也是各国畜牧业科技竞争的焦点。现代畜禽良种繁育技术是由一系列技术组成的技术群,在畜牧业生产中的应用有助于提升优质种畜禽使用效率,加快区域畜禽养殖的良种化进程,提高畜禽生产性能。介绍了主要畜禽良种繁育技术及在我国的应用现状,分析了现代畜禽良种繁育技术对畜禽群体饲草料转化效率及良种选育效率的影响,从经济学视角探讨了现代畜禽良种繁育技术与养殖场投入及产出的关系,以期为我国建立现代畜禽良种繁育体系提供参考。     

The role of reproductive technologies in breeding schemes for livestock populations in developing countries

The world is faced with the challenge to meet the increasing demand for livestock products while conserving animal genetic resource diversity and maintaining environmental integrity. Genetic improvement of local breeds can help to improve the livelihood of the livestock keepers, to increase the production of animal products and to conserve genetic diversity. Implementing breeding schemes in developing countries has proven to be very difficult. The objective of this paper is to discuss the role of reproductive technologies for the creation and dissemination of genetic improvement in livestock populations in developing countries. In the paper opportunities are discussed for implementing breeding schemes which minimize the need for extensive pedigree and performance recording. It is shown that genetic progress can be generated in a small population. Community-based breeding schemes offer a good starting point for involving farmers in improving local breeds. Artificial insemination to exchange genetic material between communities offers an opportunity to increase the rate of genetic improvement while restricting the rate of inbreeding. Furthermore, artificial insemination is a promising technique for dissemination of genetic gain to producers at a relatively low cost. Opportunities to use semen sexing in a crossbreeding scheme are presented. It is concluded that tailor-made solutions and long-term commitment are needed in order to meet the needs of farmers to increase their livelihoods and to meet the needs of the growing population of consumers.     

基于高通量测序技术的山羊遗传多样性及其生产性状研究进展

近年来,高通量测序技术的规模化应用及生物信息技术的普及,极大地推动了家畜基因组学的发展,实现了分子育种标记全基因组水平的快速、精准定位,为全基因组选择育种奠定了重要基础。数千年来的驯化和选择,形成了用途多样的山羊品种,如乳用、皮用、绒用及肉用等,为人类提供了丰富的生产和生活资料。国内外学者采用高通量测序技术对山羊的遗传多样性及生产性能的遗传机制进行了研究,以期找到与山羊种质特性相关的基因,从而为山羊的遗传改良提供新的标记。作者对近五年来基于高通量测序技术研究山羊的遗传多样性和产绒、产奶、繁殖等生产性状的研究进展进行了综述,以期为评估山羊优良种质特性和与生产性状相关的优异基因定位的工作提供参考。     

Research Progress on Goat Genetic Diversity and Production Traits Based on High-throughput Sequencing Technology

Recently, the widespread use of high-throughput sequencing technology and the development of bioinformatics have been greatly contributed to the development of farm animal genomics. Whole genome-wide analysis can facilitate the fine mapping of the molecular markers related to the production traits quickly and accurately, thus providing an important theoretical basis for genome selection breeding. Several thousand years of domestication and artificial selection produce many modern goat breeds with high production of milk, fiber, and meat, which become abundant production and living materials for human populations. Researchers have studied the genetic diversity and molecular mechanisms of production traits in goats using high-throughput sequencing technology, in order to identify candidate genes related to the excellent germplasm reliable markers for genetic improvement. In this review, we summarized the five-year research progress on the genetic diversity and production traits of goats including fiber, milk production and reproduction traits, mainly based on high-throughput sequencing technology. This paper provides a reference for the evaluation of the excellent goat genetic resources and the investigation of production trait related genes.     

How developments in cryobiology, reproductive technologies and conservation genomics could shape gene banking strategies for (farm) animals

Many local breeds are currently at risk because of replacement by a limited number of specialized commercial breeds. Concurrently, for many breeds, allelic diversity within breeds declines because of inbreeding. Gene banking of germplasm may serve to secure the breeds and the alleles for any future use, for instance to recover a lost breed, to address new breeding goals, to support breeding schemes in small populations to minimize inbreeding, and for conservation genetics and genomics research. Developments in cryobiology and reproductive technology have generated several possibilities for preserving germplasm in farm animals. Furthermore, in some mammalian and bird species, gene banking of material is difficult or impossible, requiring development of new alternative methods or improvement of existing methods. Depending on the species, there are interesting possibilities or research developments in the use of epididymal spermatozoa, oocytes and embryos, ovarian and testicular tissue, primordial germ cells, and somatic cells for the conservation of genetic diversity in farm- and other animal species. Rapid developments in genomics research also provide new opportunities to optimize conservation and sampling strategies and to characterize genome-wide genetic variation. With regard to gene banks for farm animals, collaboration between European countries is being developed through a number of organizations, aimed at sharing knowledge and expertise between national programmes. It would be useful to explore further collaboration between countries, within the framework of a European gene banking strategy that should minimize costs of conservation and maximize opportunities for exploitation and sustainable use of genetic diversity.     

Assessment of genetic diversity and conservation priority of Omani local chickens using microsatellite markers

Designing strategies for conservation and improvement livestock should be based on assessment of genetic characteristics of populations under consideration. In Oman, conservation programs for local livestock breeds have been started. The current study assessed the genetic diversity and conservation potential of local chickens from Oman. Twenty-nine microsatellite markers were analyzed in 158 birds from six agroecological zones: Batinah, Dhofar, North Hajar, East Hajar, Musandam, and East Coast. Overall, a total of 217 alleles were observed. Across populations, the average number of alleles per locus was 7.48 and ranged from 2 (MCW98 and MCW103) to 20 (LEI094). The mean expected heterozygosity (H _E) was 0.62. Average fixation index among populations (F _ST) was 0.034, indicating low population differentiation, while the mean global deficit of heterozygotes across populations (F _IT) was 0.159. Based on Nei’s genetic distance, a neighbor-joining tree was constructed for the populations, which clearly identified the Dhofar population as the most distant one of the Omani chicken populations. The analysis of conservation priorities identified Dhofar and Musandam populations as the ones that largely contribute to the maximal genetic diversity of the Omani chicken gene pool.     

Genetic Diversity and Population Structure of Arabian Horse Populations Using Microsatellite Markers

Understanding the genetic diversity and the relationships among the show Arabian horse populations is a current issue for breeders and professionals. This study aimed to define the relationship among the Desert breed, the Straight Egyptian, and the Polish Arabian populations by considering the historical background of their origin and to verify their genetic diversity. All selected samples were related to Arabian show activities. One hundred forty four hair samples were collected from horses at stud farms having notoriety in the breeding of Arabians from different geographic regions. A set of 17 microsatellites markers for parentage control were used for genotyping. Genetic diversity among and between these populations were evaluated using several statistical methods. All the microsatellites were informative and the marker set analyzed provided 145 alleles. The average number of alleles per locus was 6.52, 6.35, and 7 for the Desert breed, Straight Egyptian, and Polish Arabian, respectively. The high genetic diversity observed within the three populations (0.63-0.71) was associated with a high number of effective alleles. Desert breed and Polish Arabian populations appeared the closest, whereas the Egyptian population was more distant. The significant positive inbreeding coefficient F_IS found in Desert breed, Straight Egyptian, and Polish Arabian horses (0.09, 0.14, and 0.11, respectively) confirmed the deficit of heterozygosity observed in these populations. These results suggested that the three populations have high levels of gene flow or share the same origin and have a recent divergence. This study may highlight the risk of the loss of gene diversity in these populations and help to implement appropriate breeding programs to preserve genetic diversity.     

Marker-based estimates of between and within population kinships for the conservation of genetic diversity

In this article coefficients of kinship between and within populations are proposed as a tool to assess genetic diversity for conservation of genetic variation. However, pedigree-based kinships are often not available, especially between populations. A method of estimation of kinship from genetic marker data was applied to simulated data from random breeding populations in order to study the suitability of this method for livestock conservation plans. Average coefficients of kinship between populations can be estimated with low Mean Square Error of Prediction, although a bias will occur from alleles that are alike in state in the founder population. The bias is similar for all populations, so the ranking of populations will not be affected. Possible ways of diminishing this bias are discussed. The estimation of kinships between individuals is imprecise unless the number of marker loci is large (> 200). However, it allows distinction between highly related animals (full sibs, half sibs and equivalent relations) and animals that are not directly related if about 30–50 polymorphic marker genes are used. The marker-based estimates of kinship coefficients yielded higher correlations than genetic distance measures with pedigree-based kinships and thus to this measure of genetic diversity, although correlations were high overall. The relation between coefficients of kinship and genetic distances are discussed. Kinship-based diversity measures conserve the founder population allele frequencies, whereas genetic distances will conserve populations in which allele frequencies are the most different. Marker-based kinship estimates can be used for the selection of breeds and individuals as contributors to a genetic conservation programme.     

Genetic selection in farmed deer

Selection is the major tool used by breeders to improve the genetic quality of their livestock. Traditional methods of selection are well proven and useful in improving the economic merit of livestock. The performance of an animal is affected by its genetic quality and by the environment in which it is reared. While environmental improvement is expensive and requires continuous inputs, genetic improvement is cumulative and permanent, provided that selection is maintained. To select an animal on its genetic merit account must be taken of the environmental effects on its performance. Comparisons between the performance of animals on different farms or in different years are not valid unless they have genetic material in common. The speed at which genetic improvement is passed on to the rest of a population is affected by the variation and heritability of the traits being selected, the selection intensity and the generation interval. The deer population in the United Kingdom has a high degree of variation for important traits but the selection intensity is low and the generation intervals are larger than in other farmed species. Central performance testing, group breeding schemes and the use of artificial insemination are tools which will be important in the genetic improvement of farmed deer.     

Molecular characterization of breeds and its use in conservation

The conservation of farm animal resources is important for coping with future breeding needs and for facilitating the sustainable use of marginal areas. The increasing availability of molecular markers for most farm animal species and the development of techniques to analyse molecular variation is widening our capacity to characterise the genetic variation of breeds. In this paper we review the most popular molecular markers used in conservation and animal breeding studies, the different measures of genetic diversity that they provide, and their application for managing within-breed genetic diversity and for setting between-breed conservation priorities. We also address the relationship between genomic and marker heterozygosity, the relationship between molecular and quantitative measures of genetic diversity, and the characterization of breeds based on non-neutral markers.     

胡枝子属植物野生居群遗传多样性RAPD分析

利用RAPD标记分析胡枝子属14个野生居群遗传多样性,对其60个10碱基随机引物进行筛选,选择能产生多态性谱带的20个引物,共获得209个RAPD标记,182个显多态性,占总谱带数的87.08%。居群间观测等位基因数Aa和有效等位基因数Ae分别为1.8708和1.5868,Nei's基因多样性指数H和Shannon's信息指数I分别为0.3344和0.4921,揭示了居群间存在较高的遗传多样性。遗传距离介于0.1006-0.651之间,14个材料的聚类结果与形态学分类结果有相同的趋势。本研究对胡枝子属植物种质资源的保存和育种利用有一定参考价值。     

Genetic diversity of Swiss sheep breeds in the focus of conservation research

There is constant pressure to improve evaluation of animal genetic resources in order to prevent their erosion. Maintaining the integrity of livestock species as well as their genetic diversity is of paramount interest for long-term agricultural policies. One major use of DNA techniques in conservation is to reveal genetic diversity within and between populations. Forty-one microsatellites were analysed to assess genetic diversity in nine Swiss sheep breeds and to measure the loss of the overall diversity when one breed would become extinct. The expected heterozygosities varied from 0.65 to 0.74 and 10.8% of the total genetic diversity can be explained by the variation among breeds. Based on the proportion of shared alleles, each of the nine breeds were clearly defined in their own cluster in the neighbour-joining tree describing the relationships among the breeds. Bayesian clustering methods assign individuals to groups based on their genetic similarity and infer the number of populations. In STRUCTURE, this approach pooled the Valais Blacknose and the Valais Red. With BAPS method the two Valais sheep breeds could be separated. Caballero & Toro approach (2002) was used to calculate the loss or gain of genetic diversity when each of the breeds would be removed from the set. The changes in diversity based on between-breed variation ranged from −12.2% (Valais Blacknose) to 0% (Swiss Black Brown Mountain and Mirror Sheep); based on within-breed diversity the removal of a breed could also produce an increase in diversity (−0.6% to + 0.6%). Allelic richness ranged from 4.9 (Valais Red) to 6.7 (Brown Headed Meat sheep and Red Engadine Sheep). Breed conservation decisions cannot be limited to genetic diversity alone. In Switzerland, conservation goals are embedded in the desire to carry the cultural legacy over to future generations.     

A global strategy of using molecular genetic information to improve genetics in livestock

Traditional breeding programmes have largely contributed to disseminate the benefits of several quantitative traits in livestock. In developing countries such as Indonesia where animal population scattered throughout the country, it is difficult to invest for molecular research. On the other side, yet, it is worthy asset for breeding purposes. Based on theory and evidence, it has been proved that those scattered population evolved different genetic adaptations in response to a given natural pressure selection. A global strategy can be applied to the use of molecular genetic information for identification of economically important value. The use of genetic markers or more effective of marker-assisted selection (MAS) for desired important traits would be more valuable and useful and even more efficient in important trait selection of superior livestock. DNA marker technology would be very useful when applied for quantitative trait identification. Marker-assisted selection can be used for enhancing conventional breeding and works best for the traits with low heritability such as in reproductive traits and disease resistance. Application of conventional breeding for lower heredity traits would not be efficient because of waiting longer for generation interval, expensive in measurements, more population and more employees needed. Study of quantitative trait loci mapping is early investment to improve genetic merit. It can be performed once but can be used for exploring many genetic traits with economically important values. An effective option is biotechnology application in livestock for the development of genetic varieties such as stress tolerance, growth and carcass traits. Application of biotechnology approaches will enable improvement in productivity, reduction in costs, enrichment of milk compositions and extension of shelf life products.     

Research opportunities in the field of animal genetic resources

Animal genetic resources are those animal species that are used, or may be used, for the production of food and agriculture, and the populations within each of them. The working unit of a database for farm animal genetic resources is the breed, a term taken in its widest possible sense to mean a population within the species, possessing a number of particular traits that permit the grouping of these animals under a common label and are associated to geographical areas and human groups. Research opportunities cover a wide range of thematic areas. The biggest gap in knowledge is animal breeding for local populations in harsh environments. There is also a lack of research in functional genetics and genomics of adaptation and disease resistance traits. By comparison, breed characterization, in particular molecular characterization, has been a more popular research subject. The same can be said for conservation, although some fundamental questions on genetic diversity and risk of its loss are still unanswered. Research is required to understand the socio-economic, infrastructural, technical and formal constraints that limit the operation of sustainable conservation programs in less developed countries. Information systems on animal genetic resources need input from research and data capture networks, in order to achieve a reasonable degree of completeness. Economic analysis and issues related to gene flow and access and benefit sharing should also profit from more research.     

Assessing the diversity of preferences of suburban smallholder sheep keepers for breeding rams in Ouagadougou,Burkina Faso

Urbanisation in developing countries entails deep changes in the livestock sector and the management of animal genetic resources (AnGR). Sheep breeding around Ouagadougou (Burkina Faso) illustrates these changes and the need to coordinate genetic improvement in general and the use of crossbreeding in particular. For this, it is important to understand breeders’ choices and improvement strategy, to accompany them within a national plan for AnGR management. In a context of missing market for breeding rams, a stated choice experiment was conducted with 137 farmers, together with a characterisation of herd management practices. This survey analyses farmers’ preferences for breeding rams, estimating their willingness to pay (WTP) for different traits (attributes). Their practices were characterised by a high reliance on natural pastures (82% of farmers) and a minority of crossbreeding (23%). The highest WTP was observed for disease resistance. However, the subgroup of farmers practicing crossbreeding showed a tolerance to high susceptibility. A strong preference for the white colour was revealed. Although significant, the influence of sheep body size on decision-making showed a lesser importance, again with a distinct behaviour in the subgroup practicing crossbreeding. These results illustrate the need to take account of the diversity of goals and preferences among smallholder sheep keepers to gain their adhesion to a coordinated genetic improvement framework.     

Genetic Engineering Approaches to Pig Production*

Modern biotechnology promises a number of new applications in animal breeding and production. Although conventional pig breeding has achieved a high level of efficiency and productivity numerous problems have been encountered with animal health and the loss of meat quality. Selection based on phenotypic performance data of individual animals does not take into account the importance of specific genes and their relevance within a complex regulatory system. In most cases it is therefore difficult to trace back the genetic origins of clinically important disorders. The application of genetic engineering techniques in pig production will facilitate diagnosis, improvement of productivity, and animal health by allowing direct genetic manipulation. Attention must be focussed on the physical and genetic analysis of the procine genome. The isolation and characterisation of genes, DNA-markers, polymorphic DNA-fragments, and their chromosomal assignment will be important prerequisites and tools for the elucidation of genetic disorders. Especially the detection of heterozygous carriers of recessive disorders and their elimination from the breeding stock will increase selection accuracy and decrease the generation intervals. But also the rapid and simple detection of infectious diseases, which is sometimes difficult if not impossible at present, will improve animal health and welfare. Although the production of transgenic animals either by DNA-microinjection into zygotes or the use of embryonal stem cells manipulated in vitro is less straightforward than DNA-based diagnosis it will play an important role in the direct manipulation of the porcine genome and genes. Breeding programmes including the use of transgenic livestock have already been developed. There is no doubt that genetic engineering has reached a degree of practical feasibility, allowing it to play an important role in pig breeding in particular and animal production in general.     

Optimal village breeding schemes under smallholder sheep farming systems

Despite challenges in the implementation of livestock genetic improvement programs in developing regions, including centralized nucleus breeding schemes, these programs can contribute to the improvement of the livelihood of smallholder farmers. In this paper, we present a community- or village-based breeding scheme in which breeding activities are carried out by communities of smallholder farmers. We evaluated genetic responses and the rate of inbreeding from alternative village sheep breeding schemes that were based on a survey of existing flock structure and breeding management in a sheep-barley system in Ethiopia. This survey showed that individual flock sizes were small, and that the majority of farmers practiced mixed grazing and uncontrolled mating of their flocks in communal grazing lands within villages. Here we evaluated within-village schemes (selection across flocks within a village) and across-village schemes (selection across villages) at different intensities of ram selection (i.e. proportions of rams selected, P). Our results showed that under within-village schemes, intensity of selection could not be increased (i.e. P could not be decreased below 0.149) when the rate of inbreeding was constrained to an acceptable level of 0.01, resulting in low genetic gain. The most optimal scheme was found to be across-village selection with at least three villages cooperating and P = 0.05. Our results also indicated that genetic gain from village breeding schemes with mass selection and BLUP selection is comparable. Village breeding schemes can make a significant contribution to the genetic improvement of livestock in Ethiopia and other developing countries.     

Genetic diversity, inbreeding and breeding practices in dogs: results from pedigree analyses

Pedigree analysis constitutes a classical approach for the study of the evolution of genetic diversity, genetic structure, history and breeding practices within a given breed. As a consequence of selection pressure, management in closed populations and historical bottlenecks, many dog breeds have experienced considerable inbreeding and show (on the basis of a pedigree approach) comparable diversity loss compared to other domestic species. This evolution is linked to breeding practices such as the overuse of popular sires or mating between related animals. The popular sire phenomenon is the most problematic breeding practice, since it has also led to the dissemination of a large number of inherited defects. The practice should be limited by taking measures such as restricting the number of litters (or offspring) per breeding animal.     

Genetic selection and conservation of genetic diversity*

For 100s of years, livestock producers have employed various types of selection to alter livestock populations. Current selection strategies are little different, except our technologies for selection have become more powerful. Genetic resources at the breed level have been in and out of favour over time. These resources are the raw materials used to manipulate populations, and therefore, they are critical to the past and future success of the livestock sector. With increasing ability to rapidly change genetic composition of livestock populations, the conservation of these genetic resources becomes more critical. Globally, awareness of the need to steward genetic resources has increased. A growing number of countries have embarked on large scale conservation efforts by using in situ, ex situ (gene banking), or both approaches. Gene banking efforts have substantially increased and data suggest that gene banks are successfully capturing genetic diversity for research or industry use. It is also noteworthy that both industry and the research community are utilizing gene bank holdings. As pressures grow to meet consumer demands and potential changes in production systems, the linkage between selection goals and genetic conservation will increase as a mechanism to facilitate continued livestock sector development.     

Perspectives for feed-efficient animal production

Modern animal breeding programs are largely based on biotechnological procedures, including AI and embryo transfer technology. Recent breakthroughs in reproductive technologies, such as somatic cell nuclear transfer and in vitro embryo production, and their combination with the emerging molecular genetic tools, will further advance progress and provide new opportunities for livestock breeding. This is urgently needed in light of the global challenges such as the ever-increasing human population, the limited resources of arable land, and the urgent environmental problems associated with farm animal production. Here, we focus on genomic breeding strategies and transgenic approaches for making farm animals more feed efficient. Based on studies in the mouse and rat model, we have identified a panel of genes that are critically involved in the regulation of feed uptake and that could contribute toward future breeding of farm animals with reduced environmental impact. We anticipate that genetically modified animals will play a significant role in shaping the future of feed-efficient and thus sustainable animal production, but will develop more slowly than the biomedical applications because of the complexity of the regulation of feed intake and metabolism.