New Genetic Improvement Breeding Techniques for Main Economic Traits of Livestock and Poultry (Meat, Egg, Milk)

Raising the economical traits of livestock and poultry such as meat, eggs, and milk can be considered in several aspects such as genetic breeding, nutrient feed, disease control, barn environment and management. Genetic breeding is the genetic improvement of livestock; disease has both genetic factors (such as susceptibility) and environmental factors (such as pathogens); nutritious feed and barn, equipment, etc. are environmental factors, but there are also genetic and environmental factors. Interactions. Therefore, it is a systematic project for the operators to improve the production level and economic efficiency of livestock and poultry through management, not only to enable all links to operate effectively, but also to achieve optimal coordination and cooperation. I. Genetic Basis for Improvement of Economic Traits 1. Quantitative Basis of Genetics Genetics is a branch of genetics that combines the principles of genetics and statistical methods to study the genetic regularity of population quantitative traits. For half a century, quantitative genetics has played an extremely important role in improving measurable economic traits, such as quantitative traits, such as meat, eggs and milk. Compared with the original group or the unmodified local breeds, the lean meat of the pigs increased by 20-25%; the market age of the broilers reaching 2kg was 40-50 days earlier; the number of eggs laid by the chickens increased. 100-120; Dairy cows produce 3000-4000 kg of milk during lactation. In the past 50 years, the genetic improvement of major economic traits such as meat, eggs, and milk has been shown in Table 1. The genetic basis of economic traits, such as meat, egg, and milk, is multi-gene, which is characterized by continuous variation. Its improvement requires the recording of production performance and genetic parameters, and conversion of phenotypic values ​​into breeding values, thereby improving the accuracy of selection. 2. The basis of cytogenetics Livestock and poultry are highly advanced animals of both sexes. The inheritance of traits is achieved through germ cells, ie sperm and eggs. Artificial insemination and semen freezing technology have expanded the genetic effects of excellent comrades; superovulation and oocyte in vitro maturation have expanded the heritability of excellent female animals; embryo transfer or nuclear transfer technology has also expanded the role of outstanding sire and dams, providing a large number of Genetically superior offspring; embryo cutting is the genetically superior individuals through the "asexual reproduction" for replication or "clone." Chromosome aberrations and chromosome ploidy in cytogenetics are rare in livestock and poultry breeding. The Robertsonian translocation has been reported in both cattle and pigs, but they have not yet reached the level of application. There are few reports of mammal polyploidy and parthenogenetic reproduction of birds. However, there are occasional reports. Few people conduct in-depth studies. Double diploidization of horses and donkeys may produce fertile double diploid lice, but this concept in the 1950s has not yet become a reality. 3. The molecular genetic basis The current understanding of genetic material has entered the molecular level, namely, DNA and ribonucleic acid (RNA). Since the Swedish multi-genome hypothesis (Polygene hypothesis) was proposed by the Swedish biologist Nilsson-Ehle in 1909, the multiple genes of quantitative traits have been studied and analyzed statistically as a genetic entity. Although the number of multiple genes that determine quantitative traits can be estimated using statistical methods, it is not possible to determine the location of a single gene and the chromosome on which it is located. The development of modern molecular biology technology makes it possible to study Quantitative Trait Locus (QTL) at the molecular level. This requires the isolation and cloning of genes that determine quantitative traits, the study of their structure and function, and eventually the molecular level. The purpose of improving quantitative traits. Second, the breeding of new technologies The new technologies discussed here have three implications: First, the technology developed in recent years to genetically improve livestock species has a significant effect (such as the use of DNA polymorphism detection of pig stress syndrome); Second, research Although the methods and technologies are not up-to-date, they have only been popularized and applied in recent years (such as BLUP breeding value). Third, they are not new technologies from a single point of view, but they have played an unprecedented role after reassembly (such as "Super Pig" and "Eat-saving Small Layer Chicken"). This article is only illustrated by some examples and does not include all new breeding technologies. 1. Biotechnology (1) Detection and utilization of major genes for quantitative traits Over the past 20 years, it has been discovered that some quantitative traits are not only controlled by micro-effect polygenes, but also by one or a few major genes (Major gene )Impact. For example, the booroola gene in sheep, the ewes homozygous for this locus, have an average of 1.1-1.7 lambs per litter than the ewes without the gene; heterozygous ewes also need to produce 0.9- 1.2 head. This gene has now been mapped to the sixth chromosome of a sheep. Another example is swine halothane-susceptible genes. The recessive homozygous individuals of the gene are prone to stress syndrome. They are prone to sudden death in the case of hunger, biting, transportation, and driving, and the meat is of poor quality. However, pigs with this gene have a clear advantage over pigs without the gene in terms of growth rate and lean meat percentage. The penetrance of the recessive homozygote due to halothane determination method is not complete, its range is from 50% to 100%, and the penetrance rate is influenced by the pig's month age and sex. This means that the halothane assay not only fails to discriminate individuals with the genotypes NN and Nn, because their performance is halothane-insensitive, and a significant proportion of individuals with the genotype nn do not appear to be sensitive. The PCR-RFLP method can be used to clearly obtain DNA maps of three different genotypes, which brings great convenience to detection of halothane-susceptible gene individuals (Nn, nn) ​​in pig breeding. This gene has now been mapped to a linkage group on the sixth chromosome of pigs (Vogeli, 1994). (2) Marker-assisted selection of quantitative traits In quantitative genetics studies, a quantitative trait to be improved is referred to as a target trait, and thus a gene or a genome that determines this trait is referred to as a target gene. At present, polygenes that determine quantitative traits cannot be located accurately. However, if a polymorphism of a recognizable gene or genome can be found or a chromosome fragment is closely related to the target trait, it can be used as a target trait. The genetic marker of choice. Genetic markers can also be applied to gene transfer, gene mapping, and gene mapping studies. In addition to the above-mentioned genetic markers at the molecular and cellular levels, markers can be selected at the population level using known major genes or single genes, such as the double muscle genes of beef cattle, the multiple lamb genes of sheep, and stress sensitivity of pigs. Genes, chicken miniaturization genes, fast and slow feather genes, etc. (3) Prediction of heterosis The heterosis of livestock and poultry can be predicted by blood type factors, plasma protein polymorphisms, DNA polymorphisms, and experimental animal experiments. For example, DNA polymorphisms can identify genetic differences among individuals within a family, family, and family. Using Hinf I/ 3'-HVR-alpha globin probes, DNA fingerprint bands with very high polymorphism in pigs, chickens, and ducks can be obtained. These polymorphisms provide a good reference for analyzing the distances between relatives of the lines. Using DNA polymorphisms to determine varietal or inter-line differences, and based on this, the genetic distance is more stable than other indicators, so it is also more accurate to predict heterosis. 2. Computer Technology (1) BLUP Calculation Method of Breeding Values ​​BLUP (Best Linear Unbiased Prediction) method was first used by CR Henrichson in 1973 to commemorate academics in Lush. The system was introduced at the seminar, although his research on the linear model was completed as early as the early 1950s. The application of this method to breeding was postponed for 20 years due to the limitations of computational tools at the time. The BLUP breeding value estimation method can improve the accuracy of seed selection due to: (1) making full use of all the relatives' information; (2) eliminating the bias caused by the environment; (3) correcting the results of matching Deviations; (4) can consider the genetic differences between different generations of different generations; (5) when using multiple individual records, can be minimized due to the bias caused by elimination. In recent years, due to the popularization of computers and the application of biotechnology in animal breeding, the estimation methods of BLUP breeding values ​​have been developed, such as the development from communal animal models to animal models; the estimation of single trait breeding values ​​has been developed as a multi-trait breeding value estimate; Breeding value of the breeding system is estimated to develop breeding value estimation for non-regular breeding systems such as embryo transfer and embryo cutting. (2) Computer image analysis is applied to the establishment of computer image analysis systems and graphic databases for livestock breeding, linking breeding data, germplasm resources, morphological characteristics, ecological environment, etc. with “numbers” and “shapes” related to livestock breeding. , Large to the behavior of the group, small to the karyotype characteristics can be fully observed and measured through the image, so that the effect of breeding can be improved from both macroscopic and microscopic aspects. For example, in the linear assessment of cow shape, 14 of the 15 body traits can be identified by the computer through the image, and only 1 (the characteristics of milk) needs to be judged by human-machine combination. The use of computer programs written in C language, from video recording, digitization, correction, recognition, scoring, and synthesis are all controlled by the program, which basically achieves the automation of linear assessment of dairy cows' body shape and is conducive to the selection and improvement of milk production traits. Another example is the use of computer images to analyze the thickness of living fat layers and muscle layers and eye muscle area of ​​meat livestock (cattle and pig) through ultrasonic analysis, which improves the accuracy of selection of meat animals. (3) Application of Geographic Information System (GIS) to conservation and utilization of livestock and poultry genetic resources Preserving the genetic diversity of livestock and poultry breeds is of great significance for increasing the yield of meat, eggs, and other quantitative traits. The protection of livestock and poultry genetic resources is also a systematic project. It is a combination of "protective biology" in life sciences and "geographical information systems" in earth sciences. The establishment of a geographical information system for livestock and poultry breeder resources can provide an overall and dynamic understanding of the existing genetic resources. The system can monitor changes in the quantity and distribution of geographical characteristics and characteristics of various livestock and poultry breeds over a long period of time. , as well as the establishment of an alarm system for the number of endangered livestock and poultry. Recently, China Agricultural University has completed computer software systems such as the appearance (photos), quantity, distribution, and production performance of domestic major breeds such as cattle, sheep, pigs, and poultry according to livestock and poultry species names or by province, city, and autonomous region. 3. System engineering technology System engineering mainly studies "systems". The system is an organized or organized overall and consists of the organic links between the various parts (elements) and the parts that make up the whole. Although the following describes some of the re-assembly of mature technology, but from the perspective of system theory, the organic links between various types of mature technologies have brought unprecedented new benefits. (1) Optimizing the breeding program The formulation of an optimized breeding program with the goal of maximum economic efficiency is an important part of modern livestock and poultry breeding. For example, in the optimization breeding program of pigs, considering the biological and economic objectives, growth, carcass quality, fecundity, and feed conversion efficiency should be taken as the main traits to improve. By calculating the marginal benefit of the trait and analyzing the economic importance of each target trait, an optimized breeding scheme with rapid genetic improvement and high economic benefit can be developed. The size of the breeding core group, population structure, breeding life, selection methods, feeding techniques, input-output analysis, etc. should also be considered in an optimization breeding program. In the study of broiler optimization breeding programs, the author of this paper proposed the method of shortening the generation gap, and the parent and female strains have reached 13 generations per year. The breeding program has the following advantages compared with the current domestic and foreign programs: 1. There are upper and lower limits on the choice of maternal body weight. This measure directly selects the uniformity of weight gain and indirectly selects the egg production performance; 2. The choice of maternal egg production. Abolishing the current system of recordings of self-occluded egg-laying boxes. Instead, record the performance of laying eggs according to the cock family, and then determine whether or not to eliminate the entire family based on breeding objectives. 3. Replace the current “remaining after-selection” method with respect to egg production performance. After the first election, the "stay method" improved the accuracy of selection. 4. Primary time. The 6-week-old seed selection was selected as a 5-week old seedling, which reduced the stress caused by limiting feeding after selection. 5. Choosing paternity with the hatching rate of hatching eggs improves the fertilization rate, the hatching rate and the viability of the chicks. (2) The MOET (Multiple Ovulation and Embryo Transfer) breeding program is a systematic project that combines superovulation and embryo transfer techniques with core group breeding techniques. It is mainly used in dairy cattle, beef cattle and other singleton animals. The implementation of this breeding program can not only increase the fecundity of the cows and increase the number of excellent individuals, but also can shorten the generational interval through sibling assays. The success of the MOET breeding program is largely determined by the availability of a core population of high-producing cows as a donor for embryo transfer, allowing the rapid expansion of good genetic resources. China has initiated research on the breeding of dairy cows MOET in the “Eighth Five-Year Plan” national science and technology research project. (3) The “Ideal Pig” and “Super Pig” plans In terms of the requirements for the production of commercial pigs, the parents and maternity of the cross-breeding parents should have different characteristics. The requirements for ideal paternal pigs are: strong breeding ability, strong limbs, good semen quality; high growth rate and lean meat percentage; large lean meats distributed at high economic value; dominant white homozygote; permissible for halothane sensitivity The heterozygote of the gene (Nn). The requirements for an ideal maternal pig are: high fecundity, strong maternality; good appetite, moderate growth rate and lean meat percentage; no halothane-susceptible gene requires a genotype of NN. The British Webb proposed a plan to use embryonic engineering to produce "super rice." The goals of this plan are: 1. To provide 32 pigs for each sow per year; to reach 100 kg live weight in 2.100 days; 3. to achieve a carcass lean rate of 65%. After completing the above three indicators, each sow has an annual output of 1400 kg of lean meat. His specific approach is shown in Figure 1. (4) Selection and breeding of grain-saving small layer chickens The selection and breeding of small layer chickens is a systematic project of reformation and matching such as breeding, nutrition, cages, environment of chicken houses and breeding techniques. It was bred using a dwarfing gene (dw) on the sex chromosomes of chickens. This is a defect of the growth hormone receptor gene, resulting in shortened long bones and impeded growth, but reproductive traits such as egg production are almost normal. At present, more widely used for this gene is that in broilers, the parental parent is a dwarf animal, which can save feed and increase the stocking density. The descendants of dwarf hens and normal hybrids are both male and female and can be used for the production of normal commercial broilers. The "star chicken" of France's Issa is produced using this seed production method. The College of Animal Science and Technology, China Agricultural University, has been introducing the dw gene in "star chicken" into the medium-sized brown shell layer chicken since 1990, and has selected small-sized layer chickens with more than 90% of layer-descent. This small chicken is used as a parent to crossbred with common brown shell chickens, and the descendants of commercial chickens are dwarf brown-shelled chickens. If they are crossed with common white-shell chickens, the descendant commercial chickens are dwarf and light brown-shelled laying chickens. These two types of commercial chickens are 20-25% smaller than normal type, and can increase the breeding density by 25-30%. Although total eggs are less 1.0-1.2 kg, they can save 8-10 kg of feed. So the total economic benefit is much higher than that of an ordinary laying hen. Especially the grain-saving (up to 2.0-2.2:1 ratio of raw material to egg) is more suitable for the Chinese market. If one-third of the 1.5 billion laying hens in China are raised to small layer hens, they can save 4 to 5 billion kg of feed. Wu Changxin: Animal Geneticist and Breeder. Born on November 15, 1935, was born in Jing County, Zhejiang. Graduated from Beijing Agricultural University in 1957. From 1979 to 1981, she studied animal genetics and breeding in the Department of Genetics at the University of Edinburgh, England. He has served as Professor of Beijing Agricultural University, Director of Animal Husbandry and Dean of the College of Animal Science and Technology. Deputy Editor-in-Chief of the Journal of Genetics. In 1995 he was elected a member of the Chinese Academy of Sciences. Has long been engaged in animal genetics and livestock breeding research and teaching.

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