BREEDING & GENETICS
PIH-101
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Selection for Feet and Leg Soundness
Authors:
Howard Miller, Mississippi State University
Gene Isler, Ohio State University
Lewis Runnels, Purdue University
Ralph Wilson, Colorado State University
Reviewers:
Joe Behrens, Windthorst, Texas
Ben Bereskin, USDA, Beltsville, Maryland
Robert Fritschen, University of Nebraska
The swine industry needs more sound, durable breeding animals capable of a high level of productivity in present day housing and facilities. Seedstock producers commonly consider unsoundness to be caused by some modern housing systems. However, in most cases modern housing rearing merely expresses those defects already present. A pig, sound on feet and legs and reared on pasture or dirt lot, may be a structurally unsound pig in some modern systems. Other factors that may affect structural soundness include genetics, level of production, sex, nutrition, disease, floor surface, equipment location, and space available for exercise. Boar test stations and on-farm testing facilities provide an excellent opportunity to visually detect sound and unsound pigs that are fed and managed similarly.
Selection for feet and leg soundness is a subjective, visual process that is a necessary part of a progressive pork production scheme. Improvement through selection is possible, since recent studies report soundness to be medium in heritability. Several factors affecting feet and leg soundness are discussed here.

Skeletal Structure
Feet and leg soundness problems may occur in front and rear legs in all ages and sex classes of pigs. Boars are generally evaluated to be the poorest in leg structure. Poor rear leg structure may prevent a boar from successfully staying mounted on a female during mating. Unsound front legs may limit a boar's desire to mount a female. Affected pigs assume a posture of flexion of the front legs at the knee (buck knees) and elbow. The rear legs may be partially flexed and carried under the body to maintain stability. Affected pigs are straight-legged on rear legs and gait is peggy, short-strided, and painful.
These signs are common with young boars aged 5-8 months when moved to new premises.

Skeletal structures in Figures 1 and 2 were drawn, in part, as the result of radiologic examination of live pigs. Emphasis was placed on angles formed at (M) front legs and (N) rear legs.

Undesirable front and rear leg structure is indicated in Figure 1; whereas "desirable" bone conformation is illustrated in Figure 2. The rear leg structure in Figure 1 has a rump that is too steep and the tail setting is too low. The angle (N) is larger in Figure 1 than in Figure 2. The hip, stifle, and hock joints (E, F, and G, respectively) lock in a straightline position with each step or in the breeding-mounted (boar) position. Boars that are too straight in the rear legs will occasionally fall backwards (sit down on the ground) during breeding. The rear feet may exhibit excessive sole wear with subsequent swelling of the pads and lameness. UNDESIRABLE.

The spine (Figure 1) is arched very high; the angle (M) is greater than 90 degrees, which positions the shoulder blade bone more directly over the front leg bones. Additional pressure may be applied at the elbow joint (B) and at the knee joint (C). The front leg knee joints often buckle. The abnormally straight front leg posture in Figure 1 results in abrasive wear of the pads and toes as shown in Figure 3. UNDESIRABLE.

In Figure 2 skeletal side view, note the flatter top, more level rump, and higher tail setting. The front legs slope from the shoulder, as you view them from the side (resembling a curved sickle blade). The angle (M) allows the normal shock-absorbing effect at the elbow joint (B). The angle (N) in Figure 2 is smaller than in Figure 1; the rear leg joints are properly angled to allow the hip, stifle, and hock joints to absorb pressure equally. The pasterns (D) are sloping and long to provide a cushioning effect,
Cooperative Extension Work in Agriculture and Home Economics. State of Indiana. Purdue University and U. S. Department of Agriculture cooperating. H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have egual opportunity and access to its programs and facilities without regard to race, color, sex. religion, national origin, age or handicap.