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Title: Modeling the relationship between scanned rump and 12th-rib fat in young temperate and tropical bovines: Model development and evaluation
Contributor(s): Walmsley, Bradley J (author); Wolcott, Matthew Lee  (author); McPhee, Malcolm John  (author)
Publication Date: 2010
DOI: 10.2527/jas.2009-2633
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Abstract: A decision support tool for predicting subcutaneous fat depths called BeefSpecs, based on the Davis growth model (DGM), has been developed by the Cooperative Research Centre for Beef Genetic Technologies. Currently, the DGM predicts 12th-rib fat thickness (RFT, mm). To allow predictions of fat thickness at the P8 rump (P8FT, mm) site, the standard carcass fat measurement in the Australian beef industry, a relationship was developed between ultrasound RFT and P8FT in steers and heifers from temperate (Angus, Hereford, Shorthorn, and Murray Grey) and tropical (Brahman, Belmont Red, and Santa Gertrudis) breed types. Model development involved fitting various combinations of sex, breed type (BrT), BW, age, and RFT to produce 6 models. The models were challenged with data from 3 independent data sets: 1) Angus steers from 2.4 generations of divergent selection for and against residual feed intake; 2) 2 tropically adapted genotypes [Brahman and tropically adapted composites (combinations of Belmont Red, Charbray, Santa Gertrudis, Senepol, and Brahman breeds)]; and 3) a study using sires from Charolais, Limousin, Belgian Blue, and Black and Red Wagyu breeds and 3 genetic lines of Angus to create divergence in progeny in terms of genetic potential for intramuscular fat percent and retail beef yield. When challenged with data from Angus cattle, the mean biases (MB, mm) for models A to F were –1.23, –0.56, –0.56, –0.02, 0.14, and 0.04, and the root mean square errors of predictions (mm) were 1.53, 0.97, 0.97, 0.92, 0.93, and 0.91, respectively. When challenged with data from Brahman cattle, MB were 0.04, –0.22, –0.14, 0.05, –0.11, and 0.02 and root mean square errors of predictions were 1.30, 1.29, 1.27, 1.23, 1.37, and 1.29, respectively. Generally, model accuracy indicated by MB tended to be less for model E, which contained age rather than BW as a covariate. Models B and C were generally robust when challenged with data from Angus, Brahman, and Tropical Composite cattle as well as crossbred cattle with temperate sires. Model D, which did not contain age, performed the most consistently and was selected for inclusion in the DGM: P8FT, mm = –3.6 (±0.14) + 1.3 (±0.13) x sex + 0.11 (±0.13) x BrT + 0.014 (±4.8E–⁴) x BW + 0.96 (±0.01) x RFT – 0.73 (±0.08) x sex x BrT – 3.8E–³ (±4.2E–⁴) x sex x BW – 0.09 (±0.01) x sex x RFT + 1.3E–³ (±3.7E–⁴) x BrT x BW + 0.24 (±0.01) x BrT x RFT (adjusted R² = 0.86; SE = 0.013). Model D has been implemented in BeefSpecs to predict P8FT.
Publication Type: Journal Article
Source of Publication: Journal of Animal Science, 88(5), p. 1848-1859
Publisher: American Society of Animal Science
Place of Publication: United States of America
ISSN: 1525-3163
Field of Research (FOR): 070201 Animal Breeding
Socio-Economic Objective (SEO): 830301 Beef Cattle
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
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Appears in Collections:Animal Genetics and Breeding Unit (AGBU)
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