Influence of Age, Sex and Calcium and Phosphorus Levels on the Mechanical Properties of Various Bones in Swine

Seventy-two 4-week-old pigs were randomly assigned by sex (gilts, barrows, boars) to two dietary treatments and four age periods for determinations of the effects of age, sex and Ca and P levels on the mechanical properties of various bones in swine. Pigs were individually fed diets containing either .4, .4% Ca,P (Tl) or .8, .8% Ca,P (T2). Slaughter times (age period) were approximately 1 (Al), 3 (A3), 5 (A5) and 7 (A7) months after the initiation of the trial. The femur (Fern), humerus (Hum), third and fourth metacarpal (3MC, 4MC), third and fourth metatarsal (3MT, 4MT), third rib (Rib) and thoracic vertibrae were collected at each age period for mechanical tests and determination of percentage of ash. Bending moment, ultimate stress, yield stress and modulus of elasticity were determined by a flexure test in which the bone was treated as a simply supported, centrally-loaded beam (three-point loading). Bending moment of bones from boars was similar to that of bones from gilts or barrows. When expressed as force per unit area, the ultimate stress of bones from boars was less than that of bones from gilts or barrows. Percentage of ash did not differ significantly between sexes, but tended to be lower in bones from boars than in bones from gilts or barrows. Bones from pigs fed T2 had a higher bending moment than bones from pigs fed Tl, regardless of age. At Al, the Fern, Hum and Rib of pigs fed T2 were able to withstand a greater stress than the same bones of pigs fed Tl. At A3 and A5, the ultimate stress of all bones increased with increasing levels of dietary Ca,P. At A7, the Fem, 4MT and Rib failed to show a response to increased levels of Ca,P.