Factors affecting repeatability of tissue depth determination by
real-time ultrasound in sheep
M.J. Young, J.M. Deaker, C.M. Logan
Animal and Veterinary Science Group, Lincoln University,
Canterbury, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1992, 52: 37-40
Measurement accuracy for ultrasonic tissue depths was examined
in order to determine the relative importance of factors affecting it.
Repeatabilities for ultrasonic fat depth (UFD) and ultrasonic muscle
depth (UMD) were assessed from repeated runs (2) in three groups of
animals; Dorset Down ewes (LW=45.4kg, 7.5mo, n=50), Coopworth rams
(LW=51.5kg, 11mo, n-50) and Dorset Down rams (LW=38kg, 4.5mo, n=50).
Repeatability values were higher for UMD (0.77, 0.95 & 0.87 for the 3
groups, respectively) than for UFD (0.63, 0.84 & 0.82, respectively).
Lower repeatabilities were due to high within-animal variance rather
than low between-animal variance. Measurements made on videotaped
images demonstrated that image registration had a great effect on
repeatability, with image interpretation having a negligible effect. A
comparison of two operators differing in experience showed that fat
depth was measured equally accurately by both operators but that the
experienced operator measured muscle depth more accurately. It was
concluded that tissue depths can be accurately assessed from one
measurement.
Keywords: NZSAPAB;
Repeatability; backfat; fat depth; muscle depth; ultrasound
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Last Updated 25-01-1997
