The objectives of this study were to
study the relationship between in vivo ultrasound measurements
and cold carcass measurements at 4 anatomical
points of the backbone, and to establish regression
equations to estimate carcass composition within
the cold carcass weight range for Ternasco lambs (8
to 12.5 kg) by using ultrasonic measurements taken at
a single location. Measurements of subcutaneous fat
and skin thickness and of muscle depth and width were
taken over the 10th to 11th and 12th to 13th thoracic
vertebrae and the 1st to 2nd and 3rd to 4th lumbar
vertebrae. These measurements were taken at 2 and
4 cm from the nearest end of the LM to the backbone
and at 1/3 of the LM width with the probe perpendicular
to and parallel to the backbone. The left sides
of the carcasses were dissected into muscle, fat, and
bone. Body weight (22.6 kg) and cold carcass weight
(10.8 kg) were representative of Ternasco light lambs.
Muscle depth measured at 2 cm, 4 cm, and 1/3 of LM
width remained regular, with slight ups and downs
along the spine. All the pairs of in vivo ultrasound and
cold carcass measurements were significantly different
(P < 0.05) and had small correlations. All the ultrasound
measurements of muscle depth at any location
or at any distance to the backbone were less than their
equivalent cold carcass measurements, with differences
ranging from 0.8 to 5.9 mm. Differences between ultrasound
fat thickness + interface (US_FDGI) and cold
carcass fat thickness were less than differences between
ultrasound fat thickness and cold carcass fat thickness,
ranging from −0.9 to −1.0 mm for the former and from
−2.1 to −0.5 mm for the latter. The small differences in
absolute values between US_FDGI and cold carcass fat
thickness suggest that US_FDGI is the best measure
of the real fatness level of the lambs. The best prediction
equations for muscle, bone, and fat were developed
with in vivo ultrasound data measured at the 1st to
2nd lumbar vertebrae perpendicularly to the backbone,
but they had limited predictive value. To predict the
muscle content of carcass, BW and muscle depth were
included, and they explained 59% of variation. Fiftyone
percent of total fat was predicted by BW and fat
thickness, whereas only 17% of the variation in bone
was predicted by 2 fat-related variables. The BW of
lambs was an important predictor to improve regression
equations but ultrasound measurements were the
most important variables when a narrow range of BW
was used.
