BONE GROWTH AND DISTRIBUTION IN SWINE AS INFLUENCED BY LIVEWEIGHT, BREED, SEX, AND RATION

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Abstract
Individual bones of the skeleton, dissected from one-half of the carcass were weighed and expressed as a percentage of total bone for 23 Duroc × Yorkshire, 42 Hampshire × Yorkshire, and 27 Yorkshire × Yorkshire barrows and gilts fed either low energy (LE) (2757 kcal DE/kg and 15.3% protein) or high energy (HE) (3652 kcal DE/kg and 19.9% protein) rations and slaughtered at either 68, 91, or 114 kg liveweight. To determine bone measurements at the start of the experiment bone data were collected from seven barrows and seven gilts of the same breed groups slaughtered at 23 kg liveweight. The scapula, humerus, radius, and ulna, femur, and tibia bones, in addition to being weighed, were measured to determine length and circumference. Increases in bone length were proportionate to liveweight up to 91 kg, after which growth rate decreased for all measured bones except the humerus. Growth in circumference increased rapidly for all measured bones up to 68 kg liveweight, after which increases were of lesser magnitude. Between 23 and 68 kg liveweight, increases in bone circumference were slightly greater than those in length. Weight for each measured bone increased linearily relative to liveweight. Among breed groups Duroc × Yorkshire pigs had the greatest radius and ulna circumference and Hampshire × Yorkshire the smallest tibia weight (P < 0.05). Gilts had a greater scapula length and weight and a greater femur and tibia length than did barrows (P < 0.05). Pigs fed the low energy ration exceeded those fed the high energy ration in scapula length (19.67 vs. 19.08 cm) and weight (171.52 vs. 157.25 g). Sex-liveweight and sex-ration interactions occurred for femur weight and percent scapula, respectively. Percentage bone in the carcass decreased as liveweight increased but percent bone within the hind and front quarters remained relatively constant after 68 kg liveweight. The influence of breed, sex, and ration on percentages of individual bones were observed only for the scapula, radius, and ulna and sternum and rib cartilage. A decrease in percent thoracic vertebrae and increase in percent ribs and lumbar vertebrae indicated an anterior-posterior pattern of skeletal development. Differentiation in bone distribution appeared to be essentially complete at or before 23 kg liveweight.