| High sow removal rates pose a global problem and have a negative impact on herd productivity, producer profitability, and consumer acceptability. Worldwide, the main reasons for early culling are reproductive failure and leg/locomotion problems. Hence, this dissertation aimed to identify gilt composition and conformation traits associated with good sow lifetime performance. The specific objectives were: 1) to estimate genetic parameters for gilt growth, compositional, and structural soundness traits in commercial maternal lines, 2) to estimate genetic associations for growth, compositional, and structural soundness traits with sow longevity and lifetime reproduction, and 3) to investigate growth, compositional, and structural soundness trait effects on sow removal.;In order to address these issues, a large-scale sow longevity project was initiated at a typical U.S. commercial sow farm in October 2005. The data included 1,449 gilts; 462 females from a grandparent maternal line and 987 from a parent maternal line. Gilts were evaluated for compositional and structural soundness traits at an average body weight (BW) of 124 kg and age of 190 d. Growth was expressed as the number of days to 113.5 kg BW (DAYS) and compositional traits included loin muscle area (LMA), 10th rib backfat (BF10), and last rib backfat (LRF). Subjective structural soundness evaluation was completed using a nine-point scale and included body structure traits [length (BL), depth (BD), width (BWD), rib shape (BRS), top line (BTL), and hip structure (BHS)], leg structure traits [front legs: legs turned (FLT), buck knees (FBK), pastern posture (FPP), foot size (FFS), and uneven toes (FUT); rear legs: legs turned (RLT), leg posture (RLP), pastern posture (RPP), foot size (RFS), and uneven toes (RUT)], and overall leg action (OLA).;The first study revealed greater heritability estimates (possibilities for faster genetic change) for compositional and body structure traits compared to leg soundness traits. Genetic correlations indicated that upright FPP, severe FBK, and small FFS coincide with inferior OLA. Great BL and high BTL were identified as detrimental body structure types, because they were associated with deterioration of other structural soundness traits. An unfavorable trend was observed among the correlations between DAYS, BF10, and LRF with structural soundness traits, but the estimates were mainly low to moderate. It was concluded that using information across trait groups might enhance genetic progress in leg soundness traits.;According to the second study findings, selection for fewer DAYS has an adverse effect on sow longevity and lifetime reproduction, but LMA was genetically favorably correlated with longevity traits and lifetime total number of piglets born. Great BL, flat BRS, and narrow BWD seemed detrimental to sow longevity and lifetime reproduction, whereas, correlations of leg soundness traits with longevity and lifetime reproduction were mainly low and non-significant (P > 0.05). However, RLP was moderately correlated with traits describing lifetime reproductive efficiency; upright RLP coincided with poorer efficiency.;The third study concerned phenotypic overall risk and competing risk analyses. The results indicated that younger age at first farrowing and greater number of piglets born alive increased sow survivability. Regarding growth and compositional traits, replacement gilts should at minimum have DAYS value of 167 d, LMA of 43 cm2, and BF10 of 14 mm at 113.5 kg BW. The soundness traits associated with increased culling risk included greater than intermediate BL, shallow BD, suboptimal FBK, upright FPP, uneven FUT, and severely impaired OLA. Additionally, upright RLP and weak RPP tended to increase culling risk. It is recommended that commercial herds screen replacement gilts for the abovementioned traits. |
