Purebred breeding is also called breeding of this species. It refers to the method of continuously improving the herd quality and its production performance through selection, selection and breeding within the breed of cattle. Many beef breeds in foreign countries and many local yellow cattle seeds are cultivated through this method; existing breeds of beef cattle still need to continue to implement the system of pure breeding to increase the efficiency of beef production. In the beef cattle industry, it is still necessary to rely on purebred breeding to provide breeding cattle and a large number of shelf cattle for fattening. (1) The breeding conditions for purebred breeding are generally selected for purebred breeding. 1. Local varieties of meat The variety has a relatively uniform body appearance and high production performance, and has a stable heredity. In order to further improve its production performance and promote its uniform appearance, it is necessary to use pure breeding methods to consolidate and improve the characteristics of certain good traits. This method is also known as seed breeding. Such as China's excellent local breeds Qinchuan cattle, Nanyang cattle, Jinnan cattle, Luxi cattle, Yanbian cattle, Fuzhou cattle, Pixian Red Bull and Bohai Black cattle. Through thoroughbred breeding, we will gradually correct some shortcomings in the appearance structure and improve its production performance. 2. Beef breeder breeds This breed has been cultivated by people to make it a specialized beef breed with high meat production and stable heredity. In order to increase the number of groups, maintain the characteristics of varieties, and constantly improve the quality, it is necessary to plan a thoroughbred breeding. Such as foreign beef breeds such as Charolais, Limousin, Angus, Piedmont, Simmental, Hereford, and Shorthorn. All need to adopt pure breeding methods, maintain pure breeding, expand the population for the promotion and cross breeding needs. 3. Local breeds of meat have low economic value and cannot fully meet people's needs, but certain traits and characteristics, such as adaptability to the environment, disease resistance, resistance to roughage, and certain aspects of production performance, are certain or prominent. Advantages, which need to retain the necessary amount in a certain area, as a gene bank for cross breeding. This method is also called preservation seed breeding. 4. After the crossbred hybrid has entered the cross-fixation stage, it needs a purposeful selection and selection of the seed, and the good quality of the cross-breeding is fixed so that the quality of the whole group is further improved and tends to be neat. Although the breeding work at this stage is not conducted within one breed, it is similar to the method of breeding within a variety. This breeding method is also called self-breeding. (2) Breeding of Pure Breeding Breeding Rhymes It mainly includes two aspects of kin-breeding (inbreeding) and crystallization breeding. Affinity breeding: Affinity breeding refers to mating groups of related male cows. Inbreeding is also called inbreeding. The parameters reflecting the degree of close relatives are the inbreeding coefficient and the kinship coefficient. The inbreeding coefficient is a measure of the decrease in the proportion of heterozygous genes. Affinity breeding can not only refine some of the good genes, but also expose some recessive genes that are homozygous and reveal themselves as bad traits and become unhealthy individuals, such as smaller body size, weaker constitution, lower production performance, and malformed development. Wait. The method of preventing inbreeding recession is as follows: First, inbreeding is performed only once or twice, then mating with a relative or relative in order to maintain its good traits; Second, strict selection is made to prevent mating of males with common defects; It is the poor individual who strictly eliminated those mutants and recombined homozygous inferior genotypes. (3) The breeding of grain-based breeding lines is an advanced stage of breeding work. It is a breeding method commonly used in pure breeding. It is characterized by the purpose of cultivating differences in the type of cattle, so that the beneficial traits of the herd continue to be maintained and extended to future generations. Individuals or groups that have outstanding performance in one aspect can continue to maintain the good traits in this area by using homogenous matching methods. Using this method, a number of crystal systems are established within a variety, each strain has its own characteristics, and later through the combination of crystal systems (hybridization), the entire herd can be improved in many ways. Therefore, the crystal breeding can not only achieve the purpose of maintaining and consolidating the superior characteristics and characteristics of the varieties, but at the same time can make these excellent characteristics be combined in the individual. 1. Methods and Steps for Establishing a Line (1) Creating and Choosing a Lineage The first issue in establishing lineages is to nurture a family ancestor and establish a line with a family ancestor. The ancestral family must be a superior excellent breed of bull. It not only performs well in itself, but also inherits its own excellent characteristics to future generations. If the characteristics of ancestors are not significant, especially if they are genetically unstable, the resulting offspring may not always have the characteristic characteristics of the line when they are selected with a homogenous cow. Therefore, when no ideal ancestor has been found in the herd, it will not respond to the construction of the system and should start from actively creating and nurturing ancestors. When nurturing ancestors, it is possible to select a number of heads of cows that meet the requirements of the breed from the herds or nucleus populations, and match them with the more ideal breed bulls. First, establish a strain. In order to avoid possible hereditary instability in the progeny of the ancestors, inbreeding can be appropriately adopted in the process of creating and nurturing ancestors to consolidate heredity. However, in order to prevent the emergence of inherited defects due to the decrease of offspring viability and the combination of some unfavorable genes due to inbreeding, it is advisable to avoid the mating of the father and daughter or mother and son, and the inbreeding coefficient is generally not more than 12.5%. (2) Carefully selecting the base of the strain The cows have excellent ancestral bulls and can be individually matched with the homogenous cows. The homologous cows to be carefully selected must be carefully selected and must be cows that meet the requirements of the strains. To mate with the ancestral bull. There must be a considerable number of basic cows in this crystal system. Generally, when each crystal system is built, there must be at least 100-150 adult cows that can be built, because the number of foundation cows that can be built The more they are, the more they can play the role of breeding bulls, especially in the case of application of frozen semen breeding, the number of base cows in a crystal system should be greatly increased. (3) In order to maintain the established crystal system, the successor of the breeding system ancestor must cultivate the successor of the ancestor. In general, the son of the ancestral bull can be the successor of the line. In order to nurture a successor to a family, it is also necessary to select outstanding bulls through the identification of descendants according to the requirements of nurturing ancestors. Because of the long interval of cattle generation, it is necessary to pay attention to the inheritance of the breeding and selection bulls as soon as possible after establishing the LK strain. A crystal system generally disappears after three generations. If this crystal system is not necessary, there is no need to consider the continuation of the line. If there are special valuable strains that need to be retained, the following methods should be adopted: 1 Continue the continuation of the established strains by selecting and retaining the descendant bulls, who are closely related to the original lineage, as successors to the crystal system. 2 Re-establish the corresponding new line, that is, to re-train the lineage. 2. The establishment of the combined crystal system of the strain is to increase the internal differences of the strain and maintain the hereditary nature of the variety. The combination of regent lines (ie, cross-breeding) is to increase the identity of the varieties. Through the combination of crystal systems, the excellent characteristics of the lines are complemented with each other to improve the herd quality. 3. The use of top-crossing to prevent inbreeding degenerated crystalline breeding is an important means of seed selection. However, the descendants of the offspring often appear in inbreeding. In order to solve this problem, the method that can be used is: First control the degree of inbreeding, the inbreeding coefficient should not be too high; In addition, when inbreeding degradation occurs, inbreeding bulls can be mated with unrelated cows. In order to achieve the purpose of enhancing the mass of the cattle and improving the production performance, the hybrid superiority effect is obtained within the same species, which is called â€œtop crossâ€. 4. A common line of several lineages developed by a prominent breed of bull is also called monophyletic. In addition, due to the different emphasis on the method and purpose of establishing the system, there are several types of strains. (1) Inbreeding Inbred is a group of herds developed by continuous sibling mating, and its inbreeding coefficient is often more than tens of times larger than the coefficient of inbreeding of large herds of cattle, for example, up to 20%. (2) The group is composed of basic groups that have similarly good traits, but not whether they are siblings or close relatives. Then the method of breeding within the group is implemented to consolidate and expand the group with the excellent characteristics. There is also the establishment of this method of establishment as a group substituting method, and the developed cattle strain group is called a group system. (3) Specialized strains have special properties in one aspect, and are strains that are specifically crossed with other specific strains, and are referred to as specialized strains. (4) Among the varieties of local strains that are widely distributed and have a large number of varieties, they often form different local taxa within the species due to differences in natural geographical conditions, feed types and management methods, and regional selection criteria. For local strains. Such as China's yellow cattle breeds Bashan beef, there Xuanhan cattle, Xizhen cattle, Pingli cattle, temple yak and other local strains.
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