Abstract
The aim of the present study was to evaluate the genetic and environmental factors affecting records of longissimus muscle area (LMA) and backfat thickness (BF) obtained between the 12th and 13th ribs, and rump fat thickness (RF) between the hook and pin bones, measured by real-time ultrasound in Nelore cattle. Also, weight records of 22,778 animals born from 1998 to 2003, in ten farms across six Brazilian states were used. Carcass traits as measured by ultrasound of the live animal were recorded from 2002 to 2004 in 2590 males and females with ages varying from 450 to 599 days. Fixed models including farm, year and season of birth, sex and type of feed effects, and the covariates age of dam (AOD) and age of animal at measurement were used to study the effect of environmental factors on these traits. The genetic parameters for LMA, BF and RF were estimated with two and three-trait animal models with 120-day weights using a restricted maximum likelihood method. All environmental effects significantly affected carcass traits, with the exception of year of birth for BF and RF and AOD for LMA. The heritability estimates for LMA, BF and RF were 0.35, 0.51 and 0.39, respectively. Standard errors obtained in one-trait analyses were from 0.07 to 0.09. Genetic correlation estimates between LMA and the two traits of subcutaneous fat were low (close to zero) and 0.74 between BF and RF, indicating that the selection for LMA should not cause antagonism in the genetic improvement of subcutaneous fat measured by real-time ultrasound.
Highlights
Meat production in tropical areas is dependent, mainly, on Bos indicus (Zebu) breeds
The objective of the present study was to investigate the main environmental factors that affect carcass traits measured by real-time ultrasound, as well as their heritability and genetic correlations estimates, which are of fundamental importance for the development and implantation of genetic breeding programs for these traits
All effects included in the model significantly affected the ultrasound measurements (P b 0.05), except year of birth which had no significant effect on backfat thickness (BF) or rump fat thickness (RF)
Summary
Meat production in tropical areas is dependent, mainly, on Bos indicus (Zebu) breeds. Brazil has the greatest commercial cattle herd in the world and the majority, about 80%, is comprised of Zebu and their. M.J. Yokoo et al / Livestock Science 117 (2008) 147–154 crossbreds. Since 1995, the Brazilian Association of Zebu Breeders (ABCZ) has registered about three million animals and more than 75% of them are Nelore Over the last 15 years the interest in using genetically evaluated animals has been increasing. Most breeding evaluation programs in tropical countries have generally been focused on weight and scrotal circumference measures at different ages, whereas carcass traits have been neglected
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