Characterization of objective feet and leg joint measurements between selection and second gestation and between separate gestation ages in swine

Abstract Text: The objective of this study was to evaluate feet and leg joint angle measurements between time of selection and after first parity. A secondary objective was to evaluate feet and leg joint angle measurements across gestation days. Gilts were selected from a single gilt population and then moved to three different farms. Digital images of profile and rear stance were obtained from maternal gilts at selection (n = 319 gilts; average age 21.6 ± 1.8 wks; range 19 to 25) and during second gestation (n = 277; average gestation 26.7 ± 17.2 days; range 0 to 87). Joint angles for knee, front and rear pastern, hock, and rear stance were measured using angle feature in image analysis software. To evaluate symmetry and joint angle differences due to age, only females with repeated measures at selection and 0 to 21 days of second gestation (126 females) were used. Mixed model equations were used including parity (zero or one) and side where images were taken (left or right) as fixed effects. Parity was included as repeated variable. Knee and rear pastern angles decreased (weakened) and hock angles increased (straightened) as age progressed (P < 0.05). All joint measurements were symmetric between left and right legs (P > 0.05) except for the hock where a difference (P < 0.05) was observed. To evaluate gestation age effects on joint angles, only the measurements taken during the second gestation were used. Data was analyzed using mixed model equations including farm and side as fixed effects and gestation age as continuous covariate. Animal was included as random variable. Farm was a significant source of variation for knee, front and rear pasterns, and rear stance angle measurements (P < 0.05). Additionally, asymmetry was detected in knee, and front and rear pasterns (P < 0.05). Front pastern and hock angles increased (straightened) as gestation age increased, while knee angle decreased (weakened) (P < 0.05). Results suggest that as age increases leg structure changes, with rear leg joints showing greater variation from selection to first parity than front leg. Front leg differences may be significantly different across ages however, angle differences are small. Results suggest environmental factors such as farm where animals are housed contribute to angle differences. Small angle changes in front leg could indicate structure that carries over the life of the animal, however, rear leg structure still requires further investigation for longevity implications.

Keywords: Digital imagery, feet and leg conformation, gilts