Changes in Feet and Leg Joint Angles during First Gestation in Gilts Divergently Selected for Residual Feed Intake

Studies have suggested that feet and leg conformation can change as sows age. It has been visually observed that gilt feet and leg conformation deteriorates from the end of the finisher period to first parity. The objective of this study was to evaluate the feet and leg joint angle changes measured during gestation using objective evaluation methods from lines that were divergently selected for residual feed intake (RFI). Yorkshire gilts from the 10^th generation of Iowa State University’s RFI lines (low RFI n=23 and high RFI n=17) were evaluated. Prior to image capturing, gilts were subjectively classified as lame and non-lame. On days 30, 60 and 90 of gestation, gilts were moved to an individual stall where profile digital images were obtained. Joint angles for knee, front and rear pastern, and hock were measured using the angle feature in image analysis software. Data were analyzed using linear mixed models with gestation days, RFI line and lameness score included as fixed effects. Changes in joint angle across gestation days were observed for the knee and the front and rear pasterns (P < 0.05). Angles decreased 1.1 ± 0.5, 2.7 ± 0.9 and 3.1 ± 1.0 degrees in the knee and in the front and rear pastern, respectively from days 60 to 90 (P < 0.05). A similar tendency for these anatomical locations was observed between days 30 and 90 (P < 0.10). Low RFI gilts had straighter front pasterns (60.9 vs. 57.9 ± 0.85 degrees) and rear pasterns (66.1 vs. 58.7 ± 1.1 degrees) compared to High RFI gilts (P < 0.05). Lame gilts had greater knee joint angles (160.8 lame vs. 159.8 ± 0.43 degrees sound); front (60.1 lame vs. 58.6 ± 0.78 degrees sound) and rear pastern joint angles (63.7 lame vs. 61.1 ± 0.96 degrees sound; P < 0.05). Hock joint angle was not associated with any fixed effects in the model (P > 0.05). Under the conditions of this study, differences in joint angles were observed as gestation progressed in gilts; however, such differences were minimal and their biological relevance is unclear. Nonetheless, results suggest that life events such as gestation, lameness etiology, as well as genetic selection, play a role in gilt structural changes.