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Description:
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Purebred Beefmaster steers (n = 160 ) from five owners were fed at a commercial
feedlot in South Texas beginning in November of 2004 ; 68 steers possessed pedigree
information . Beginning in mid -November , steers were individually weighed and
evaluated for ultrasound body composition at 56 -d intervals by a certified technician .
Feeder calf frame (FRM ) and muscle (MUS ) scores were assigned at initial ultrasound
evaluation . Steers were fed and marketed through a lean -based , branded beef program
and were harvested in two groups in May and June of 2005 at a commercial beef plant .
Analyses were conducted to investigate the ability to predict carcass traits from the
different sources of information available on these cattle . Evaluation of carcass traits
were investigated using four sets of independent variables referred to as sources A , B , C ,
or D and ultrasound scan session (1 Â 4 ) . An analysis included initial weight at first scan
session (IWT ) , FRM and MUS as independent variables through GLM procedures . B
analyses utilized ultrasound measures of the longissimus area , intramuscular fat , fat
thickness , rump fat , and gluteus medius depth along with IWT as independent variables .
Multiple regression was performed on each carcass trait using IWT and ultrasound traits
at each scan session . Mallow s CP was used to select a model that best described each carcass trait . C analyses (GLM ) utilized variables from A and B analyses combined plus
ranch . D analyses (GLM ) included variables from C analyses plus sire nested within
ranch . Respective R -square values (scan 1 Â 4 ) for marbling score were .02 , .04 , .05 , and
.10 using A information , .14 , .17 , .42 , and .54 , using B information , .35 , .35 , .47 , and .55
using C information , and .56 , .59 , .65 , and .76 using D information . R -square values
ranged from .34 to .86 for carcass weight , .11 to .77 for fat thickness , .06 to .82 for ribeye
area , and .10 to .81 for yield grade . Ultrasound data obtained closer to harvest and
increasing amount of data related to genetic and management background showed
increased R -square values , but may be best utilized in conjunction with one another to
predict carcass traits and final carcass value . |