There are studies indicating that Backfat thickness has a certain impact on reproductive performance, but the results vary. Research has found that the genetic correlation between backfat thickness and total litter size is between 0.18 and 0.25; Within the range of 11.1-14.0 mm, the reproductive performance of large white sows significantly improves with the increase of backfat thickness on the backfat meter; A relatively thin backfat thickness (9-13 mm) in the backfat analyzer will significantly reduce the total litter size, newborn litter weight, and number of weaned piglets. Gaughan et al. [1] found that the correlation between backfat thickness and reproductive performance in the backfat meter of large white pigs is low. The physical condition of sows varies with different stages of reproduction throughout the entire reproductive cycle. Previous studies have mainly focused on the impact of backfat thickness on the reproductive performance of sows during a certain stage of pregnancy, with strong specificity but not comprehensive. So it is necessary to study the effect of backfat thickness on the reproductive performance of sows throughout the entire breeding cycle, provide more comprehensive and detailed theoretical basis, and ensure the full utilization of sow reproductive performance.

In order to provide theoretical and practical guidance for the feeding management, nutritional regulation, and improvement of reproductive performance of sows during pregnancy, this study investigates the correlation between backfat thickness and partial reproductive performance of backfat meters during different stages of a breeding cycle for Large White and Changbai pigs, including mating, pregnancy at 30 days, pregnancy at 60 days, pregnancy at 90 days, and bed laying. The study analyzes the impact of backfat thickness on reproductive performance during different stages of pregnancy for Large White and Changbai pigs. The results showed that during the early stages of pregnancy, a higher backfat thickness value (>18.41 mm) on the backfat meter had a positive effect on improving the reproductive performance of large white pigs. Therefore, it is important to ensure adequate nutrition for sows during this stage; In the middle and late stages of pregnancy, the effect of higher backfat thickness obtained by the backfat meter is actually poor. When the backfat thickness of the backfat meter is in the moderate range (13.26 mm<x x x 17.13 mm), the reproductive performance of sows is the best. This further explains that the optimal backfat thickness required for different reproductive stages varies. Throughout the entire pregnancy process, the reproductive performance of Changbai pigs is better with moderate backfat thickness (13.82 mm<x x x 18.18 mm). Zhang Tao et al. [12] studied the relationship between backfat levels and changes throughout the entire reproductive cycle and the reproductive performance of large white reserve sows. The results showed that controlling backfat increase within 3.5 mm during pregnancy, backfat around 18.40 mm before delivery, and backfat loss within 3.0 mm during lactation is beneficial for improving the reproductive performance of both the mother and her offspring. Liu Bin et al. conducted a study on French white pigs and found that maintaining a moderate (15.5-20 mm) backfat thickness on the backfat meter during mating, 60 days of pregnancy, and bed laying can help increase sow litter size and litter weight at birth. High backfat thickness on the backfat meter at 30 days of pregnancy can enhance litter size and reduce the number of stillbirths and mummified fetuses. Therefore, it is important to maintain a moderate backfat thickness on the backfat meter during mating and 60 days of pregnancy. Houde et al. [14] found that in practical production, attention should be paid to the backfat thickness of the entire breeding cycle, and a more stable backfat thickness has a promoting effect on the improvement of reproductive performance.

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