Vet Column 9-6-10 |

Vet Column 9-6-10

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

Ultrasound technology provides an alternative for predicting carcass characteristics associated with carcass composition not only for animals prior to processing, but also for breeding animals in an effort to improve composition. Whether the technology is used for beef cattle, swine, sheep, or goats, scientifically assessing the correlation between the ultrasound measurements and the actual carcass data is essential for applying the technology.

Although the use of ultrasound technology for predicting carcass composition appears rather straightforward, issues such as technician variation, machine differences, and image interpretation, among others, all come into play. Researchers from Virginia Polytechnic Institutes and State University recently published data regarding the accuracy of using ultrasound technology in predicting market lamb carcass composition with an eye toward developing certification standards for ultrasound technicians.

In October of 2007, four experienced ultrasound technicians were asked to ultrasonically scan 172 market lambs from the State Fair of Virginia. Images of the loin muscle and backfat were captured on the right sides of lambs between the 12th and 13th ribs. All lambs had been closely sheared and washed for show before scanning. When images for each lamb were deemed suitable by the technician, they were captured and recorded to a laptop computer. All lambs were scanned twice by the same technician.

Images were sent to a centralized ultrasound processing laboratory in Ames, Iowa for interpretation. Each image was interpreted independently by each of three professional interpreters to determine loin muscle area and backfat.

Actual carcass data were collected within three days of scanning. Carcasses were ribbed between the 12th and 13th ribs by plant personnel and measurements taken on chilled carcasses. Backfat measurements were taken at the midpoint of the loin muscle and the loin muscle area was measure using a dot grid.

In this study, the correlation for backfat measurements was 0.78 and for loin muscle area was 0.66. This compares to previous studies where the range of correlation coefficients between ultrasonic predictors and actual carcass measures for lamb backfat thickness was 0.72 to 0.81 and for loin muscle area was 0.75 to 0.88. Average differences between repeated measures were more variable among technicians and interpreters than the differences between ultrasound values and actual carcass measures.

Results from this study support the generally accepted idea that ultrasound technology can predict backfat and loin muscle area in lambs with acceptable accuracy when current protocols are used by trained technicians and images are traced by experienced interpreters. Ultrasound estimates of carcass traits, therefore, are useful as a selection tool to improve lamb carcass composition.

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