Currently, U.S. swine producers are investigating ways to improve sow longevity. As feet and leg unsoundness and locomotor issues represent one of the major reasons behind sows leaving the breeding herd, particularly younger sows, a potential solution may be tied back to increased scrutiny of feet and leg structure during replacement gilt selection. However, this solution is further complicated by the training and accuracy of the individuals responsible for selecting replacement gilts.
During the Summer of 2019, 4,494 replacement gilts were evaluated for feet and leg conformation by four evaluators of varying experience at three replacement gilt grower farms within a commercial production system in Iowa and in conjunction with PIC. In addition to the structural evaluation, each gilt was weighed, fitted with two identification tags and had a DNA sample extracted from the ear with the Allflex Tissue Sampling Unit (Allflex USA, Irving, Texas).
Evaluator 1 was considered the "Gold Standard" and had prior experience utilizing the scoring system. Evaluator 2 had experience working with and handling multiple species of livestock, including swine and dairy cattle. Evaluator 3 had extensive experience working with swine and was trained in gilt selection. Evaluator 4 had extensive livestock evaluation experience.
Evaluators 1-3 were responsible for assessing eight structural and locomotive traits, including locomotion score, front leg conformation, rear leg conformation, front pastern, rear pastern, front foot position, rear foot position and rib shape. Evaluator 4 was responsible for assessing toe size differences and overall foot size while the animals were in the scale. Pictorial descriptions of the subjectively evaluated conformational traits can be found in Figure 1.
The total population of replacement gilts (n= 4,494) was used to assess interpersonal reproducibility, which is a statistic that evaluates the relationship between measurements on an animal by two separate evaluators. A group of 1,500 replacement gilts at Farm 2 were scored at two separate timepoints, 17 and 22 weeks of age, in an attempt to see changes in structure over time. Additionally, a subset of 600 animals were scored from that group at both ages to evaluate intrapersonal repeatability for Evaluators 1-3.
All animals and subsets at Farm 2 were used to evaluate intrapersonal repeatability, which is a statistic that evaluates the relationship between two measurements by the same evaluator. Thus, the goal of this study was to estimate the repeatability and reproducibility of the subjectively evaluated structural traits assessed.
Averaged across all evaluators, the averages (± SD) for each trait were as follows: LS 0.06 (± 0.24), FLC 6.07 (± 0.82), RLC 5.44 (± 0.70), FP 3.63 (± 0.85), RP 3.98 (± 0.91), FFP 4.29 (± 0.56), RFP 4.06 (± 0.52), RS 4.33 (± 0.94), TS 4.81 (± 0.61) and FS 1.99 (± 0.35). When compared to the Gold Standard, Evaluators 2 and 3 displayed bias in their evaluation of the animals, resulting in over- and under-estimation of the phenotypic presentation of a given trait. For Evaluator 2, bias values ranged from -0.69 (RS) to 0.58 (RLC). For Evaluator 3, bias values ranged from -0.68 (RS) to 1.20 (RLC).
When evaluating interpersonal reproducibility, Evaluator 2 and the Gold Standard had exact agreement ranging from 31% (RP) to 91% (LS), and agreement within 1 score ranging from 82% (RS) to 100% (LS). Evaluator 3 and the Gold Standard had EXACT ranging from 32% (RLC) to 93% (LS), and WITHIN1 ranging from 82% (RLC) to 100% (LS). When evaluating intrapersonal repeatability, the Gold Standard had EXACT ranging from 36% (RP) to 99% (LS) and WITHIN1 ranging from 84% (RP) to 100% (LS). Evaluator 2 had EXACT ranging from 40% (RP) to 87% (LS) and WITHIN1 ranging from 88% (RS) to 100% (LS). Evaluator 3 had EXACT ranging from 40% (RLC) to 99% (FFP) and WITHIN1 ranging from 89% (RP) to 100% (LS, FFP and RFP). Evaluator 4 had EXACT ranging from 58% (TS) to 89% (FS) and WITHIN1 ranging from 99% (TS) to 100% (FS).
For producers, assessing interpersonal reproducibility and intrapersonal repeatability is critical to ensure that proper training is occurring for the individuals responsible for gilt selection. If an individual is reproducible, they are able to visually assess an animal and make the same judgements about that animal as the trainer would. If the individual is repeatable within themselves when they reevaluate an animal, it indicates that the individual is consistent and accurate in their use of the scoring system to evaluate the animals. It is imperative for producers to have individuals selecting replacement gilts who are accurate and consistent when making selection decisions so the animals that have the greatest chance for improved longevity make it into the breeding herd.
Presently, all of the replacement gilts have been placed into the sow farms. They were distributed to four different sow farms within the commercial system, two group-housed gestation and two stalled gestation facilities. We will continue to track these females through three parities in an attempt to discern which scores within the traits are risk factors for early removal from the breeding herd. Additionally, we intend to determine which traits and scores within those traits are more ideal for sows that are housed in open-pen gestation. The DNA samples that were collected will also be analyzed and associated with the observed phenotypic presentation of the traits evaluated.
This project is part of the Improving Pig Survivability project and is funded by National Pork Board, the Foundation for Food and Agriculture Research and Pig Improvement Company.