The new trend of pig breeding in the world
I. Determination of breeding objectives
In the past, the breeding goal of pigs was simple: reduce back fat and increase growth rate. Later, as the breeding work progressed, the breeding goals were also complicated, including:
1. Increase the growth rate and feed utilization rate of growing-finishing pigs (grain weight gain on main elections);
2. Raise lean body mass and muscle quality;
3. Raising the fertility and breeding rate of the sow (number of young pigs selected for the main sow year).
In addition, attention should also be paid to the number of nipples, the firmness and resistance (or health) of the legs. This breeding target is still used in many European and American countries, but some deficiencies have also been discovered.
Now, the breeding goal of pigs is defined in combination with biological and economic methods, that is, through systematic breeding measures, the cultivated pigs can obtain the highest possible economic benefits under the expected production conditions in the future. This breeding goal considers two issues:
1. Select the target trait;
2. Calculate the marginal benefit (or economic importance) of the target trait.
Second, the performance measurement
1. Determination of the performance of the measurement station and the farm
The national pig breeding program is often based on the determination of the performance of stations and pig farms. The stations are mainly targeted at excellent young boars, and the pig farms are mainly targeted at young sows and boars. The purpose of these two assays is to understand pig growth, carcass and meat quality. With the development of artificial insemination and computer technology, the BLUP animal model can compare breeding values ​​across fields.
2. Measurement method
(1) Measurement stations in Norway
The performances of Landrace, Great White, and Duroc were determined, including daily gains of 25-100 kg, backfat thickness, feed conversion, leg firmness and semen quality. The measuring station measures 2,300 boars each year, selects the best 50 boars every year, and carries out artificial insemination. These excellent boars are used in the core field in the first 5 months and used in commercial fields after 5 months.
(2) Livestock farms in Norway
In a well-prepared field, the litter size, number of litters per litter, day length and back fat thickness at 100 kg body weight were determined for three species (Landrace, Great White, Duroc). A total of 3,000 boars are measured annually and 23,500 sows are measured.
(3) Measurement stations in Denmark
Three boars per litter were measured, weighing 25 kg at the beginning, feeding in the same pen and 90 kg ending. The daily weight gain, back fat thickness, feed conversion rate, lean meat percentage, and meat quality were measured. The data were entered into a computer and processed by the Central Animal Husbandry Institute. The results were regularly announced. The first 5%-10% of the excellent boars are sent to the artificial insemination station for expansion and other excellent boars are sold to each pig farm or pig farmer. More than half of the pig farmers can operate artificial insemination. Artificial insemination was performed in two dilutions (one at the boar and one at the time of mating) and two insemination procedures. The semen was stored at room temperature (20°C). The average age of boars used in artificial insemination stations is 15 months.
(4) Measurement Methods in the United States
The station sent a notification to each pig farm. Three boars and one boar were selected for each boar. The best boar was selected and sent to the artificial insemination station at the end. 25% Excellent people return to each field for use.
Third, the selection method and effect
1. Growth and selection methods and effects of carcass traits
In the past 30 years, the selection mainly focused on the growth and carcass traits of moderate heritability. The application of BLUP breeding values ​​after the mid-1980s accelerated the genetic improvement of these traits. For example, in Canada from 1985, the BLUP animal model was used to estimate the breeding value of backfat thickness and up to 100 kg body weight. So far, the annual genetic progress of the two traits has been reduced by 0.35 mm/year and shortened by 1.5 days/year. Increasing the profit of each commodity pig by 1.30 Canadian dollars means that the Canadian pig industry will increase profits by 20 million US dollars year by year until the two traits reach their optimum value.
Decreased feed intake is now a major factor affecting the growth of lean tissue. It is important to find out how to eat more pigs that can convert feed into more lean rather than fat. The electronic feeding system can achieve the goal of improving the feed conversion rate by changing the feed intake curve. For example, increase the feed intake during the 20-40 kg weight period, because the pig's feed conversion rate is very high. At present, it is urgent to measure the feeding behavior of pigs, the growth curve of lean meat, and the changes in feed types.
Fluoroalkyls have a genetic advantage of increasing lean meat production but increase the sudden death rate of PSE meat and pigs. The ideal way is to eliminate all the fluoroalkyl groups in the parent and mother. Now the University of Toronto's testing method has achieved this goal. The Cotswold company has a very high lean meat line. It contains Pietrain's pedigree. After 10 years of breeding, the fluoroalkyl frequency in the strain is already 90% dropped to zero. The reduction in lean meat consumption due to the removal of fluoroalkyl has been restored through the selection of other genes that increase meat mass, while the color of the meat has improved by 40%.
In the parent group's core group, two-dimensional scanners have been routinely applied. Ultrasound images of the longissimus dorsi muscle cross section can be automatically analyzed by a computer after being processed by software. It is expected that in the next 2-3 years, the mesoscopic layer can be automatically analyzed. Fat lean ratio and fat content between muscles. More advanced instruments such as CT scans can determine the muscle properties in detail, such as hydrodynamics, but they are expensive and difficult to promote. Hampshire pigs contain the RN gene. This gene will reduce the production of muscle processing, but it can improve the taste; Duroc hybrid pigs can improve the muscle tenderness, the higher the intramuscular fat content, so that the tenderness is improved, but to what extent It is not clear. If you keep your backs, you may choose to increase the growth rate of lean meat and may improve the meat quality.
2. Selection methods and effects of reproductive traits
The French method of selection for the over production line is based on the farrowing records of the first four sows in the large group, selecting 2% of the superfamily sows to form a basic group, and then backcrossing with their son to polymerize the overproduction genes. This method increased the number of litter size in Large White pigs by 1.5, and was verified in many subsequent experiments. It is believed that this method can effectively improve pig reproductive performance. This method also has the disadvantage that these high-producing sows have lower lean growth power than the original nucleus population, and that the time required for the distribution of these high-yielding genes to the entire pig production (selection cycle) is 7 years.
Now, using artificial insemination technology, several groups were established genetic relationship, and then through the mixed model BLUP method, with the help of a computer to screen high-quality pigs of good genetic quality, and then artificial insemination, accelerated the proliferation of high-yield genes.
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