What are the easily overlooked problems in the process of selecting and retaining replacement gilts?

(1) The selection and retention procedure is unreasonable, and the selection process is simplified: In some pig farms, the selection and retention process for replacement gilts is very simple, with no fixed procedure. It is only after the breeding pigs finish testing that a simple evaluation is made and they are selected and retained. This can easily lead to an imbalance in the number of animals retained from each bloodline and a decline in the production performance of breeding pigs. Therefore, the selection and retention of replacement gilts must rely on a fixed procedure. Generally, the selection and retention of replacement gilts must go through three processes: primary selection, intermediate selection and final selection. Primary selection is when moving from the farrowing stage to the rearing stage, determining a candidate group 4 times the number to be retained for breeding; intermediate selection means that when moving from nursery to fattening, 50% of the individuals are selected from the candidate group and retained as the candidate replacement breeding group; final selection means that after the completion of testing, outstanding individuals are selected according to the test results to determine the replacement gilt group. Each stage has different selection criteria. Primary selection is mainly based on the test results of the ancestors and some traits that the individual itself can express, such as individual weight greater than 1.2 kg, teat number of more than 7 pairs and neatly arranged, no blind teats, inverted teats, etc., and no genetic disorders in full siblings; intermediate selection mainly looks at growth rate and body conformation traits; the final selection criterion is to combine the above test data with the final testing results, calculate a comprehensive index for the breeding pigs, with daily gain from 30-100 kg and backfat thickness at more than 120% of the average level, and paternal line index and maternal line index at more than 100%. Only by strictly following a certain selection and retention procedure for replacement gilt selection can blindness in selection and retention be avoided, thereby improving the production level of the entire population.

(2) Over-reliance on performance test results while neglecting the selection of body conformation. In the process of replacement gilt selection and retention, performance test results are certainly important, but the evaluation of body conformation cannot be ignored either. Only with a strong constitution and compact structure can normal reproductive function be maintained, and some conformation traits are also strongly correlated with production performance. For example, it has been reported that the correlation between the curvature of the forelimb pastern and growth rate is 0.44. If individuals with normally developed forelimb pasterns are selected, their growth rate will also increase rapidly. Individuals with a compact body structure and strong constitution also have a longer service life. Grindflok et al. observed that for sows with poor locomotion performance, the proportion still in the herd by the fourth parity was lower than 21%. Therefore, when selecting and retaining replacement individuals, attention must be paid to the development of the individual's limbs, observing the coordination of movement and evaluating the compactness of the body structure; in addition, teat number is also an important conformation trait. In the process of replacement gilt selection and retention, it is necessary to ensure that the number of functional teats in replacement gilts is more than 7 pairs, the spacing between teats is uniform, and there must be no blind teats, inverted teats, or volcanic teats.