title: Phenotypic and genetic  parameters compared during repeated measures of longissimus muscle area and  subcutaneous fat thickness in Nelore cattle.
abstract: Real-time  ultrasound is currently used for in vivo carcass evaluation of beef  cattle. We estimated heritability and repeatability coefficients for  ultrasound-measured carcass traits in Nelore cattle. We measured longissimus  muscle area, backfat thickness, and rump fat thickness in male and female  animals ranging in age from 10 to 26 months. The variance components were estimated  by single-trait analysis using the derivative-free restricted maximum  likelihood method, under an animal model. The complete data file included 3077  records of 1172 animals born between 2003 and 2008. Two analyses were performed  using a repeatability model: a) all records of longissimus muscle area, backfat  thickness, and rump fat thickness of animals aged 10 to 26 months, and b)  considering two age periods (11 to 17 and 18 to 24 months). The heritability  estimates ranged from 0.33 to 0.46 for longissimus muscle area, from 0.20 to  0.26 for backfat, and from 0.26 to 0.29 for rump fat, demonstrating that direct  selection for these traits can provide genetic gain. The repeatability  estimates were moderate, ranging from 0.42 to 0.73. The highest repeatability  estimates were obtained for longissimus muscle area in both the first (0.70)  and second (0.73) analyses. The repeatability estimates suggest that ultrasound  measures are precise; higher precision was obtained for longissimus muscle area  than for subcutaneous fat thickness. The latter could be obtained during  periods of greater feed availability to increase precision.
authors.affiliation: Instituto de Zootecnia, Centro APTA de Bovinos de Corte, Sertãozinho, SP, Brasil.
authors.forename: T R
authors.initials: TR
authors.lastname: Pinheiro
authors.forename: M E Z
authors.initials: ME
authors.lastname: Mercadante
authors.forename: L G
authors.initials: LG
authors.lastname: Albuquerque
authors.forename: J N S G
authors.initials: JN
authors.lastname: Cyrillo
authors.forename: R H
authors.initials: RH
authors.lastname: Branco
mesh_terms: D000367:Age Factors; D000818:Animals; D001823:Body Composition / Q000235:genetics*; D001835:Body Weight; D001938:Brazil; D001947:Breeding; D002417:Cattle / Q000033:anatomy & histology* / Q000235:genetics; D005260:Female; D056726:Genetic Association Studies; D005838:Genotype; D008297:Male; D008957:Models, Genetic; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D010641:Phenotype; D019655:Quantitative Trait, Heritable; D015203:Reproducibility of Results; D050151:Subcutaneous Fat / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D014463:Ultrasonography