By Benny Mote Ph.D., Swine Extension Specialist, UNL Department of Animal Science
Replacement gilts are selected primarily on structure and conformation. These selection decisions, however, occur while gilts are still growing. Few studies have tracked sow conformational traits over time, and even fewer have done so by directly measuring the traits in an objective manner rather than by utilizing a subjective scoring system. Therefore, we measured conformational traits beginning at 112 days of age through parity 3 weaning. This is an ongoing project, and conformational traits will be tracked through parity 4 weaning upon completion.
In order to obtain conformational trait measurements, sows were filmed from five different directions: front, left side, rear, above the front and rear foot on the left side of the body, and in front of the left rear foot. Provided culling did not occur for reproductive failure, severe structural issues, or other welfare concerns, each sow was filmed a total of 12 times. More specifically, sows were filmed at 112 and 209 days of age; early, middle, and late gestation and at weaning in parity 1; and middle and late gestation and at weaning in parities 2 and 3. Still images were captured from the videos, and a total of 33 conformational traits were directly measured on the images. Results from 10 traits measured from the side view are presented here (figure 1): body length, body depth at the shoulder and flank, height at the shoulder and flank, knee angle, hock angle, front and rear pastern angles, and rump slope angle.
Body size increased rapidly from 112 to 209 days of age, then growth continued at a slower pace after the beginning of parity 1 (figure 2). A small decrease in body size occurred at weaning each parity due to weight loss during lactation, but growth resumed during the subsequent parity. Total growth from 112 days of age to parity 3 weaning was 17 inches (25.26-42.35 inches) in body length, 7 inches (10.48-17.38 inches) in body depth at the shoulder, 5 inches (9.18-14.54 inches) in body depth at the flank, 11 inches (18.14-28.96 inches) in height at the shoulder, and 11 inches (19.43-30.50 inches) in height at the flank.
Knee angle and front and rear pastern angles decreased over time, while hock angle and rump slope did not change by an appreciable amount (figure 3). Knee angle decreased by 8.5 degrees between 112 and 209 days of age (164.12-155.63 degrees) and by another 5 degrees between 209 days of age and parity 3 weaning (155.63-150.72 degrees). The knees got more flex during late gestation and lactation each parity as the litter grew and udders filled, but straightened back up by about a degree during the first half of gestation each parity. Front pastern angle decreased by 7 degrees (60.89-53.74 degrees) and rear pastern angle decreased by 9 degrees (64.64-55.50 degrees) between 112 days of age and parity 3 weaning. The difference between the time point with the smallest angle and the time point with the largest angle was 2 degrees (146.97 degrees at parity 3 mid gestation – 149.06 degrees at 209 days of age) for hock angle and 3 degrees (114.71 degrees at parity 3 mid gestation – 118.05 degrees at 209 days of age) for rump slope.
This study reveals that some conformational traits continually change over time. Sows continue to grow through parity 3 weaning. Knee angle and front and rear pastern angles decreased by 13, 7, and 9 degrees from 112 days of age to parity 3 weaning, respectively. Production stage influences conformational traits including body size and knee angle. Producers should take note of these conformational changes over time, particularly the decrease seen in knee angle and front and rear pastern angle, during selection of replacement females to bring into the sow herd.