Selection for resistance to swine mycoplasmal pneumonia over 5 generations in Landrace pigs

The objective of this experiment was to evaluate the selection of a pig line with improved resistance to swine mycoplasmal pneumonia and meat production in Landrace pigs. The selection was conducted over 5 generations using estimated breeding values of daily gain (DG), backfat thickness (BF), and mycoplasmal pneumonia scores (MPS). In order to evaluate various lung lesions, we established two different rearing environments (regularly cleaned vs. not cleaned) for the pigs. The heritability estimates for DG, BF, and MPS were found to be 0.65, 0.60, and 0.07, respectively. To compensate for the low heritability of MPS we examined the genetic correlation of immunity traits with MPS to determine their usefulness in a selection index. Cortisol (COR) plasma levels at 105 kg body weight had a high positive genetic correlation (0.65) with MPS, and therefore used as an immunity trait. The average breeding values in the fifth generation, as expressed in standard deviation units, were 1.32 for DG, −0.70 for MPS, and −0.04 for BF and COR. The selection traits showed good genetic progress in 5 generations demonstrating the possibility of selecting for both disease resistance and high meat production in animals.