The ability to accurately measure body or carcass composition is important for performance testing, grading and finally selection or payment of meat-producing animals. Advances especially in non-invasive techniques are mainly based on the development of electronic and computer-driven methods in order to provide objective phenotypic data. The preference for a specific technique depends on the target animal species or carcass, combined with technical and practical aspects such as accuracy, reliability, cost, portability, speed, ease of use, safety and for in vivo measurements the need for fixation or sedation. The techniques rely on specific device-driven signals, which interact with tissues in the body or carcass at the atomic or molecular level, resulting in secondary or attenuated signals detected by the instruments and analyzed quantitatively. The electromagnetic signal produced by the instrument may originate from mechanical energy such as sound waves (ultrasound – US), ‘photon’ radiation (X-ray-computed tomography – CT, dual-energy X-ray absorptiometry – DXA) or radio frequency waves (magnetic resonance imaging – MRI). The signals detected by the corresponding instruments are processed to measure, for example, tissue depths, areas, volumes or distributions of fat, muscle (water, protein) and partly bone or bone mineral. Among the above techniques, CT is the most accurate one followed by MRI and DXA, whereas US can be used for all sizes of farm animal species even under field conditions. CT, MRI and US can provide volume data, whereas only DXA delivers immediate whole-body composition results without (2D) image manipulation. A combination of simple US and more expensive CT, MRI or DXA might be applied for farm animal selection programs in a stepwise approach.

ABSTRACT:The purpose of the current study was to validate the use of CT for selection against osteochondrosis in pigs by calculating positive predictive value and comparing it to the positive predictive value of macroscopic evaluation, using histological examination as the reference standard. Eighteen male, hereditarily osteochondrosis-predisposed piglets underwent terminal examination at biweekly intervals from the ages of 82-180 days old, including CT scanning, macroscopic, and histological evaluation of the left distal femur. Areas of ischemic chondronecrosis (osteochondrosis) were confirmed in histological sections from 44/56 macroscopically suspected lesions, resulting in a positive predictive value of 79% (95% CI: 67-84%). Suspected lesions, that is; focal, radiolucent defects in the ossification front in CT scans corresponded to areas of ischemic chondronecrosis in 36/36 histologically examined lesions, resulting in a positive predictive value of 100% (95% CI: 90-100%). CT was superior to macroscopic evaluation for diagnosis of early stages of osteochondrosis in the distal femur of piglets. The current histologically validated observations can potentially be extrapolated to diagnostic monitoring of juvenile osteochondritis dissecans in children, or to animal models of human juvenile articular cartilage injury and repair. ß

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BackgroundA significant heritability has been documented for articular osteochondrosis. Selection against osteochondrosis has historically been based on macroscopic evaluation, but as computed tomography (CT) now is used to select boars with optimal body composition it can potentially also be used to screen for osteochondrosis. False negative diagnosis will occur if defects have not developed or have resolved prior to screening at a single time point.The aim of the current study was to assess the suitability of the use of CT at a single point in time as a screening tool in piglets for articular osteochondrosis, which is known to be a highly dynamic condition in which lesions develop and resolve over time.MethodsMale Landrace piglets (n = 18) were serial CT scanned from 2–8 times at biweekly intervals from 70–180 days of age. At each interval, 1–2 piglets were euthanased and the left distal femur processed for histological validation.ResultsA total of 795 defects were identified in the 112 available CT scans. Within the hind and fore limbs, the incidence of defects was highest in the stifle (n = 321) and elbow joints (n = 110), respectively. Ninety-eight per cent of the defects in the stifle and elbow joints had developed by the 7th examination interval when the piglets were a mean age of 159 days old. The proportion of defects that resolved was lowest in the stifle joint at 51% and highest in the elbow joint at 69%.ConclusionsScanning of the current piglets at an age of 159 days resulted in detection of 98% of the total number of defects that developed up to the maximum age of 180 days. The proportion of defects that resolved ranged from 51–69% for different joints, but may not adversely affect prevalence as this category of false negative diagnosis will result in selection of pigs that are disposed for healing. Optimally timed CT is a powerful screening tool for osteochondrosis.