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Characterization and symmetry study of objective feet and leg joint measurements in five separate lines of maternal gilts
The objectives of this study were to characterize the feet and leg joint angle measures from five replacement gilt lines and to evaluate the symmetry between same angles from each leg pairs. In total 319 maternal gilts at 21.6 ± 1.8 average weeks of age (range 19-25 weeks) were video recorded in a three day time span. In total, 1767 profile digital images (857 left and 910 right), and 671 rear stance digital images were extracted from the video recordings using computer software based on gilt body position and image quality, resulting in an average of 2.7 left, 2.8 right and 2.1 rear stance images per gilt. Joint angles for the knee, front and rear pastern, hock, and rear stance were measured using the angle feature in image analysis software. Mixed model equations were used to evaluate the effect of gilt line and age at measurement (included as a continuous linear covariate) as well as the symmetry of joint angle between the pairs of legs evaluated. The average measurements for each joint angle are as follows: knee 159.9° ± 3.2°, front pastern 56.5° ± 7.0°, hock 140.1° ± 7.4°, rear pastern 58.3° ± 7.8° and rear stance 92.3° ± 6.3°. Significant differences (P < 0.05) between gilt genetic lines were observed in the front and rear pastern angle measurements. Knee and hock angles increased as age at measurement progressed (P < 0.05). Joint measurements were symmetric between the gilts left and right legs (P > 0.05) except for the knee where a difference of 0.69° ± 0.26° (P < 0.05) was observed with the right being a higher degree angle. Results suggest that genetic line may play a role in pastern angle differences, and most of the difference was observed in the rear legs. Results appear to suggest that the knee should be measured separately on each gilts leg, or could warrant further examination of the technique in which the knee is measured. Further investigation is required about the biological implications of the angle changes on the knee and hock as age progress as well as knee asymmetry on replacement gilts as they enter the breeding herd. The individual importance of the range of these measurements will be evaluated using production records upon completion of the gilts’ first parity.
Keywords: Digital Imagery, Feet and Leg Conformation, Swine