Genomic analysis of mobility measures on 5-month-old gilts associated with structural soundness

Sow lameness results in premature culling, causing economic loss and well-being issues. A study, utilizing a pressure-sensing mat (GAIT4) and video monitoring system (NUtrack), was conducted to identify objective measurements on gilts that are predictive of future lameness. Gilts (N = 3656) were categorized to describe their lifetime soundness: SOUND, retained for breeding with no detected mobility issues; LAME_SOW, retained for breeding and detected lame as a sow; CULL_STR, not retained due to poor leg structure; LAME_GILT, not retained due to visible signs of lameness; and CULL, not retained due to reasons other than leg structure. The GAIT4 system creates a series of measurements for each hoof and a lameness score (GLS) while NUtrack records animal movement and posture durations each day. To determine if measurements from the GAIT4 and NUtrack systems were associated with lifetime soundness, mixed model analyses were conducted in R including fixed effects of breed of sire, contemporary group and lifetime soundness score and random effect of animal. A second mixed model was run without lifetime soundness score and estimates of animal effects were then used to conduct ssGBLUP analyses using 3 generations of pedigree and genotypes from ~50k SNP on > 60% of phenotyped animals. Genomic heritabilities were estimated, SNP effects were back-solved and significance based on Bonferroni corrected permutation tests. GAIT4 traits indicative of lameness (LAME_GILT and CULL_STR vs SOUND; P < 0.05) were the standard deviation of GLS, average stride length, and average stance time, while significant NUtrack measurements were eating, standing, lateral lying, total lying, speed, distance, and rotations. In addition, rotations differed (P < 0.05) between SOUND vs LAME_SOW and distance tended to be different (P < 0.10). Estimates of heritability for predictive NUtrack traits were ~0.3 and GAIT4 traits were ~0.2. There were 382 significant SNP effects in 47 genomic regions, four regions on chromosomes 1, 4, 11 and 14 accounted for over 60% of the associations. Genome-level imputed genotypes linked several regions with possible causative genes. Objective measurements from the GAIT4 and NUtrack systems at 5 months of age were heritable, able to detect unsound animals, and were associated with lifetime soundness.