The general principle of beef cattle selection is: "choose good and bad, excellent and excellent". The choice of bulls and seed cows is to select the best individual from the best individuals, that is, "the best of the best." The census identification and assessment of large areas of cows and the timely elimination of inferiority are also the process of “selecting and eliminating inferiorâ€. In the selection of beef cattle cows, the choice of breeding bulls plays a key role in the improvement of the herd. The choice of a bull is firstly a review of the pedigree, followed by a review of the appearance and development of the bull, and finally the determination of the performance of the bull's descendants to determine whether its heritability is stable. The choice of breeding cow is based on its own production performance or on some traits related to production performance, in addition to reference to its pedigree, offspring, and side performance. Therefore, the choice of beef cattle mainly includes the genealogy, itself, descendants, and sideline selection. (A) Pedigree selection The use of pedigree records is an important way to compare the merits of cattle. In the beef cattle industry, the choice of the Mavericks and the performance performance of their parents, grandparents and grandparents are important for improving the accuracy of selection. According to the data, the correlation coefficient between the measured results of the descendants of bulls and the measured scores of the descendants of the father is o. 43, The correlation coefficient with his grandfather descendants measured results is o. 24, but the correlation coefficient between its mother's 1-5 milk yield during lactation is only 0.21, 0.16, 0.16, O. 28, 0.08. Therefore, when estimating the breeding value of a bull, the genetic information from the father and the genetic information from the mother cannot be equal. (B) the performance of its own choice (individual performance choices) When the calf grows to 1 year or older, you can directly measure some of its economic traits, such as 1 year old live weight, finishing weight gain efficiency. For carcass traits, auxiliary measurements can only be performed with devices such as ultrasonic analyzers and then compared with different individuals. For genetically high traits, this alternative approach is appropriate. The self-selection is based on the phenotypic value of the individual species and one or more traits of the breeding cattle to determine their species value, so as to determine whether the individual chooses to stay. This method is also called performance measurement and performance test. The specific approach is to compare it with other individuals in all herds, or to compare with the average level of the herd, in a condition where the environment is consistent and with accurate records. It can also be compared with the identification criteria. The body appearance of beef cattle mainly depends on the size of the body, whether the body structure is uniform, whether the appearance and coat color meet the requirements of the varieties, whether the male characteristics are dished, and whether there are obvious appearance defects. Such as the bull mother phase, the limbs do not start strong and strong, limbs are not correct, the back line is not flat, neckline thin, narrow chest and abdomen, sharp taper and so on. Reproductive esculent officials develop well, and testicles are normal in size and elastic. Anybody with obvious defects in body appearance or genital malformation, different sizes of pills are not suitable for species use. The appearance score of meat-breeding bulls must not be less than one grade, and they are required for special grades of bulls. In addition to the appearance, the body scale and body weight of the breeding bull were also measured, and grades were graded according to the breed criteria. In addition, you need to check the quality of semen. (3) Descendants test (performance or performance test) Descendants test is a kind of identification method for assessing the quality of bulls based on the performance of descendants in various aspects. This is the most reliable way to choose from. The specific method is to match the selected bull with a certain number of cows and determine the yak performance so as to evaluate the procedure for making the quality of the breeding cattle. The disadvantage is that it takes a long time, often waiting for the results of the descendants, the type of cattle being tested has grown old, losing a lot of available time and opportunities. In order to improve this defect, people have proposed some technical methods to shorten the measurement time. If the test bull is tested before the descendant's score, it can be used to store liquid nitrogen. After the result is determined and then determined by bQ, LX decides whether to use or disuse the original frozen semen. When the heritability is low, it is suitable for adopting this method. . The method used can be used to evaluate the value of a bull's seed, as well as the value of a cow's seed; it can be selected for both quantitative and qualitative traits. In production, it is mostly used to select breeding bulls. (4) Side-by-side selection (siblings or semi-brothers) Choosing side-by-side refers to selecting the individual's brothers, sisters, cousins, cousins ​​and so on. The closer their relationship with the individual, the greater the value of their choice of materials. The main purpose of the use of collateral materials is to demonstrate from the side some properties that cannot be ascertained by the individual (such as the bull's lactation force, breeding ability, etc.). This method saves time compared to the results of descendants. Heritability, breeding values ​​and other genetic parameters can be calculated by sideline materials. Meat traits for meat use species are mainly assessed based on semi-sibling material. The advantage of using semi-siberia material to estimate the breeding value of reserve bulls is that early identification of reserve bulls can be achieved, which can be at least four years shorter than the determination of offspring.
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