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Genetic Parameter Estimates of Yearling Live Animal
Ultrasonic Measurements in Brangus Cattle
A. M. Stelzleni, 1 T. L. Perkins, 2 A. H. Brown, Jr., 1 F. W. Pohlman, 1 Z. B. Johnson, 1 and B. A. Sandelin 1
Story in Brief
The objective of this study was to estimate genetic parameters for real-time ultrasound measurements of longissimus
muscle area (LMAU), 12th-rib back fat thickness (FTU), percent intra-muscular fat (PFAT), and yearling weight
(YW) for 1,299 yearling Brangus bulls and heifers. A single ultrasound technician took all measurements. Number of
observations was 1,298, 1,298, 1,215, and 1,170 for LMAU, FTU, PFAT, and YW, respectively. Genetic parameters
were estimated for each trait using single- and multiple-trait DFREML procedures (MTDFREML). Each trait was analyzed
as a single-trait, then in combination with each other trait in a series of two-trait models. Means for LMAU, FTU,
PFAT, and YW were 11.13 ± 2.25 in 2 , 0.22 ± 0.10 in, 3.27 ± 0.92 %, and 1030.51 ± 188.23 lb, respectively. Heritabilities
obtained from single-trait analysis of LMAU, FTU, PFAT and YW were 0.31, 0.26, 0.16, and 0.53, respectively. Average
heritabilities from the two-trait analyses for LMAU, FTU, PFAT, and YW were 0.31, 0.27, 0.15, and 0.53, respectively.
Genetic correlations for LMAU and FTU, LMAU and PFAT, LMAU and YW, FTU and PFAT, FTU and YW, and PFAT
and YW were -0.09, -0.25, 0.44, 0.36, 0.42, and 0.31, respectively. These data suggest a substantial additive genetic
effect for YW, FTU, and LMAU implying a strong relationship between phenotypic value and breeding value for these
traits.
Introduction
Collection of ultrasound measurements is faster, easier,
and more economical than traditional methods of collecting
carcass data that include harvesting of animals. Green (1996)
stated the amount of useful carcass data that can be easily and
economically collected is unlimited. Some beef cattle breed
associations collect yearling live-animal ultrasound measurements
of carcass traits for purebred bulls and heifers. These
measurements are to be used in collaboration with genetic
performance records already used by seedstock and commercial
cattle breeders. Research and literature reporting on
analysis of genetic parameters for carcass trait measurements
taken by live-animal ultrasound techniques is plentiful.
Before these data can be effectively utilized, each association
must state proven heritabilities and correlations for their
respective breeds for ultrasound measurements of these carcass
traits. The objective of this research was to obtain accurate
estimates of heritabilities and genetic correlations for
carcass traits of yearling bulls and heifers in the Brangus
breed.
Experimental Procedures
Animals and Data Collection. Purebred Brangus cattle
(n = 1,299) had real-time ultrasound (RTU) measurements
taken for inclusion in this study. Of these animals 226 were
heifers and 1,073 were yearling bulls. All animals were
scanned by a single ultrasound technician, and were taken in
accordance to the Beef Improvement Federation guidelines
(BIF, 1996). At the time of ultrasounding, measurements
were taken of the 12th-rib longissimus muscle area (LMAU),
12th-rib fat thickness (FTU), percent intra-muscular fat
(PFAT), and yearling weight (YW). Other data collected
included location of ranch, sex of animal, age of animal, and
animal registration number in accordance with the
International Brangus Breeders Association (IBBA; San
Antonio, TX). All animals included in the study had pedigrees
traced back to paternal and maternal grandparents.
The equipment used in the collection of data was the
Aloka 500V system (distributed by Aloka USA, Inc.,
Wallingford, CT) along with a superflab to ensure proper fit
of the transducer to the curvature of the animal's natural body
shape. The software used was the Critical Vision (CVIS) software
(Critical Vision, Inc., Atlanta, GA). Placement of the
transducer was determined by palpating the left side of the
animal between the 12th and 13th ribs. Once the scanning
area was determined, the location was oiled, curried free of
dirt and debris, and oiled again before transducer placement.
The transducer was placed toward the midline and parallel to
the 12th and 13th rib bones and moved laterally until the
longissimus muscle came into full view on the screen. Fat
thickness was estimated at the 3/4 position from the chine
bone end of the longissimus muscle (U.S.D.A. beef carcass
grade standards) using the cross sectional ribeye image. A
1 Department of Animal Science, Fayetteville
2 Southwest Missouri State University, Springfield
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