Conditions and Implementation Methods for Purebred Selection and Breeding of Beef Cattle
Beef cattle, that is, cattle raised for meat, are a type of cattle mainly raised for beef production. The characteristics of beef cattle are: a full body build, fast weight gain, high feed conversion efficiency, good meat production performance, and good meat quality and taste. Beef cattle not only provide people with meat products but also provide other subsidiary food products. The prospects for beef cattle farming are broad. In particular, on November 30, 2011, the Ministry of Agriculture issued the National Beef Cattle Genetic Improvement Plan (2011-2025), which provided broader space for advancing the genetic improvement process of cattle herds and improving beef cattle production levels and economic benefits. Purebred selection and breeding of beef cattle greatly increases the production efficiency of beef cattle, so what conditions are needed for purebred selection and breeding of beef cattle and how is it implemented?
Purebred selection and breeding is also called selection and breeding within the breed. It refers to the method of continuously improving cattle herd quality and production performance within a cattle breed through selection, mating selection, and cultivation. Many foreign beef cattle breeds and numerous local yellow cattle strains in China were all developed through this method; existing beef cattle breeds still need to continue implementing the purebred selection and breeding system to increase beef cattle production efficiency. In the beef cattle industry, it is still necessary to rely on purebred breeding to provide breeding bulls, as well as to provide large numbers of feeder cattle for fattening.
(1) Conditions for purebred selection and breeding. Generally, purebred selection and breeding is carried out under the following circumstances.
1. Local beef-type breeds. These breeds have relatively consistent body conformation and appearance and relatively high production performance, and possess stable heredity. In order to further improve their production performance and promote greater consistency in their body conformation and appearance, the method of purebred selection and breeding is needed to consolidate and enhance certain excellent traits and characteristics. This method is also called improved breed selection and breeding. Examples include China's excellent local breeds such as Qinchuan cattle, Nanyang cattle, Jinnan cattle, Luxi cattle, Yanbian cattle, Fuzhou cattle, Jiaxian Red cattle, and Bohai Black cattle. Through purebred selection and breeding, some shortcomings in appearance and structure are gradually corrected, and their production performance is improved.
2. Excellent beef cattle breeds. These breeds have been cultivated by people to become specialized beef cattle breeds, have very high meat production performance, and possess stable heredity. In order to increase population numbers, maintain breed characteristics, and continuously improve quality, planned purebred selection and breeding is needed. Examples include foreign beef cattle breeds such as Charolais cattle, Limousin cattle, Angus cattle, Piedmontese cattle, Simmental cattle, Hereford cattle, and Shorthorn cattle. All require the method of purebred selection and breeding to maintain purebred status, expand populations, and meet the needs of promotion and crossbreeding.
3. Local beef-type breeds. Although these breeds are not high in economic value and cannot fully meet people's needs, certain traits and characteristics, such as environmental adaptability, disease resistance, tolerance of coarse feed, and certain or relatively prominent advantages in some aspects of production performance, require that necessary numbers be retained within a certain region as a gene pool for crossbreeding. This method is also called conservation selection and breeding.
4. Beef-type crossbreds. After these crossbreds enter the stage of intercross fixation, purposeful selection and mating selection are needed to fix their excellent traits, so that the quality of the whole herd is further improved and tends toward uniformity. The breeding work at this stage, although not carried out within a single breed, is similar to the method of selection and breeding within a breed; this selection and breeding method is also called self-population breeding.
(2) Mating methods for purebred selection and breeding populations. It mainly includes two aspects: consanguineous breeding (inbreeding) and strain breeding.
Consanguineous breeding: Consanguineous breeding refers to mating combinations between bulls and cows that have blood relationships. Inbreeding is also called close breeding. The parameters reflecting the degree of close relationship are the inbreeding coefficient and the relationship coefficient. The inbreeding coefficient is a measure indicating the reduction in the proportion of heterozygous genes. Consanguineous breeding can both purify certain excellent genes and also make certain recessive unfavorable genes homozygous and exposed, manifesting as undesirable traits and becoming undesirable individuals, such as reduced body size, weakened constitution, reduced production performance, and abnormal development. Methods to prevent inbreeding depression are: first, use close mating only once or twice, then use moderate or distant mating to maintain excellent traits; second, strictly select and prevent mating between bulls and cows that share common defects; third, strictly eliminate undesirable individuals with mutant types and recombined homozygous inferior genotypes.
(3) Strain breeding. Strain breeding is an advanced stage of breeding work and is a commonly used breeding method in purebred selection and breeding. Its characteristic is to purposefully cultivate differences in type within the cattle herd, so that the beneficial traits of the herd continue to be maintained and expanded into the offspring. For individuals or groups that perform outstandingly in a certain aspect, using homogeneous mating selection can continue to maintain the excellent traits of the breed in this aspect. Using this method, several strains are established within a breed, each strain having its own characteristics, and later through combination (crossing) between strains, the entire cattle herd can be improved in many aspects. Therefore, strain breeding can both achieve the goal of maintaining and consolidating the excellent characteristics and traits of the breed, and at the same time allow these excellent characteristics and traits to be combined in individuals.
1. Methods and steps for establishing a strain
(1) Creating and selecting the strain ancestor. The primary issue in establishing a strain is cultivating the strain ancestor; only with a strain ancestor can a strain be established. The strain ancestor must be an outstanding excellent breeding bull; it must not only perform well itself but also be able to pass its own excellent characteristics and traits on to its offspring. If the strain ancestor's characteristics and traits are not prominent, especially if its heredity is unstable, then when mated with homogeneous cows, the resulting offspring will not necessarily all possess the strain's characteristics and traits. Therefore, when an ideal strain ancestor has not yet been found in the cattle herd, one should not rush to establish a strain, but should start by actively creating and cultivating a strain ancestor. When cultivating a strain ancestor, one can select several cows meeting the strain requirements from the breeding cow herd or nucleus herd, mate them with a relatively ideal breeding bull, and through cultivation and progeny testing of the resulting male calves, select five and retain one to establish a strain. In order to avoid possible unstable heredity in the offspring of the strain ancestor, during the process of creating and cultivating the strain ancestor, inbreeding mating may be appropriately adopted to consolidate heredity. However, in order to prevent reduced viability of offspring due to inbreeding and genetic defects caused by the combination of certain unfavorable genes, father-daughter or mother-son mating should be avoided, and the inbreeding coefficient should generally not exceed 12.5%.
(2) Carefully selecting the foundation cows of the strain. Once an excellent strain ancestor bull is available, individual mating can be carried out with homogeneous cows. The homogeneous cows to be mated must be carefully selected; only cows meeting the strain requirements can be mated with the strain ancestor bull. The foundation cows of this strain must also have a considerable number. Generally, when establishing each strain, there must be at least 100-150 adult cows available for strain establishment, because the more foundation cows available for strain establishment, the more the role of the breeding bull can be brought into play, especially in the case of breeding with frozen semen, where the number of foundation cows for a strain should be greatly increased.
(3) Selecting and breeding successors to the strain ancestor. In order to maintain an established strain, successors to the strain ancestor must be cultivated. Generally speaking, the sons of the strain ancestor bull can serve as successors of the strain. Cultivating successors to the strain ancestor must also follow the requirements for cultivating the strain ancestor bull, selecting outstanding breeding bulls through progeny testing. Because the generation interval of cattle is relatively long, after establishing the strain it is necessary to pay early attention to cultivating and selecting successors to the strain bull. Generally, a strain gradually disappears after continuing for three generations. If there is no need for this strain to exist, there is no need to consider the issue of strain continuation. If a particularly valuable strain needs to be retained, the following methods should be adopted: 1. Continue the established strain by selecting descendant bulls with more blood relationship to the original strain ancestor as successors of the strain. 2. Re-establish a corresponding new strain, that is, cultivate a new strain ancestor.
2. Combination of strains. The establishment of strains is to increase differences within the strain and maintain the breed's rich heredity. The combination of strains (that is, crossing between strains) is to increase the uniformity of the breed. Through the combination of strains, the excellent characteristics and traits between strains are mutually supplemented, thereby improving cattle herd quality.
3. Adopting topcrossing to prevent inbreeding degeneration. Strain breeding is an important means of selection work. However, inbreeding often produces offspring degeneration. To solve this problem, the methods that can be adopted are: first, control the degree of inbreeding reproduction, and the inbreeding coefficient should not be too high; in addition, when inbreeding degeneration occurs, allow inbred bulls to mate with unrelated cows to obtain heterosis within the same breed, so as to achieve the purpose of strengthening the cattle herd constitution and improving production performance. This is called "topcrossing."
4. Several common strain categories. A strain developed from one breeding bull with outstanding performance is also called a single strain. In addition, because the methods and focus of strain establishment differ, there are also the following strain categories.
(1) Inbred line. An inbred line is a group of cattle developed through continuous mating between siblings; its inbreeding coefficient often exceeds the average inbreeding coefficient of the large herd by dozens of times, for example reaching as high as 20% or more.
(2) Group strain. Cattle with similar excellent traits are first formed into a foundation group, without considering whether they are siblings or close relatives. Then closed breeding within the group is carried out to consolidate and expand the group with these excellent characteristics and traits. This method of strain establishment is also called the population succession method, and the developed strain cattle group is called a group strain.
(3) Specialized strain. A strain that has special performance in a certain aspect and is specially used for crossing with another certain strain is called a specialized strain.
(4) Local strain. In breeds with a relatively wide distribution and a relatively large number of breed members, differences in local groups within the breed often form due to differences in natural geographical conditions, feed types, and management methods in various places, as well as differences in regional selection standards; these are called local strains. For example, among China's yellow cattle breeds, Bashan cattle include local strains such as Xuanhan cattle, Xizhen cattle, Pingli cattle, and Miaoya cattle.