Non-invasive methods for the determination of body and carcass composition in livestock: dual-energy X-ray absorptiometry, computed tomography, magnetic resonance imaging and ultrasound: invited review

Abstract

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.

Imaging technologies to study the composition of live pigs: A review

“…A common feature of most non-invasive techniques for body or carcass composition measurements is a reliance on electromagnetic or mechanical energy, which can pass completely or partially through body or carcass tissue, such as muscle, adipose tissue and bone (Scholz et al, 2015), with the exception of VIA, that provides images directly from one or several cameras.…”

“…Moreover, recent advances have markedly improved scan speeds (~3 min per scan) and measurement precision, increasing the attractiveness of DXA for body composition measurement of animals under both commercial and research conditions (Suster et al, 2003). However, regarding the time of image acquisition it is conditioned by the expense of accuracy, for instance, a whole body scan with a rather slow but very accurate pencil-beam scanner can take 35 min, whereas a whole body scan with a cone-beam scanner takes less than 3 min (Scholz et al, 2015). The expense to purchase a new unit averages $ 35,000 USD (Walpert, 2000).…”

“…The whole body composition estimation is available immediately after the scan is completed. A regional analysis to quantify the 2D tissue distribution requires manual manipulation time, depending on the number and anatomical characteristics of the regions of interest (Scholz et al, 2015).…”

“…However, segmentation demands special attention when using measurements obtained from pixels or voxels because there is not an agreed standard for segmentation based on HU values or signal intensity and segmentation depends on the specific equipment, its calibration and researcher preference. Differences in CT protocols may lead to variations of HU values of up to 20% (Scholz et al, 2015).…”

Prediction of carcass energy content of Pelibuey ewes by ultrasound measurements

“…Due to the high cost represented by dissection, grinding and chemical analysis, alternative methods for determining the composition of the carcass and body of farm animals have been studied (Silva et al 2015, Silva 2016 cause they are considered non-invasive (Scholz et al 2015), are easier and cheaper to implement and can be applied to live animals (Silva et al 2015, Silva 2016. Among current techniques, the most notable are ultrasound (Aguilar-Hernández et al 2016), biometric measures (Fonseca et al 2017, BautistaDiaz et al 2017) and digital image analysis .…”