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2010-Boligon_et_al_b - Estimation of genetic parameters for...

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Albuquerque A. A. Boligon, J. A. V. Silva, R. C. Sesana, J. C. Sesana, J. B. Junqueira and L. G. testicular volume measured at different ages in Nellore cattle Estimation of genetic parameters for body weights, scrotal circumference, and 2009-12-04T11:46:14-08:00; 2010, 88:1215-1219.doi: 10.2527/jas.2008-1719 originally published online J ANIM SCI http://jas.fass.org/content/88/4/1215 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by guest on May 22, 2011 jas.fass.org Downloaded from
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ABSTRACT: Data from 129,575 Nellore cattle born between 1993 and 2006, belonging to the Jacarezinho cattle-raising farm, were used to estimate genetic pa- rameters for scrotal circumference measured at 9 (SC9), 12 (SC12), and 18 (SC18) mo of age and testicular volume measured at the same ages (TV9, TV12, and TV18) and to determine their correlation with weaning weight (WW) and yearling weight (YW), to provide information for the definition of selection criteria in beef cattle. Estimates of (co)variance components were calculated by the REML method applying an animal model in single- and multiple-trait analysis. The follow- ing heritability estimates and their respective SE were obtained for WW, YW, SC9, SC12, SC18, TV9, TV12, and TV18: 0.33 ± 0.02, 0.37 ± 0.03, 0.29 ± 0.03, 0.39 ± 0.04, 0.42 ± 0.03, 0.19 ± 0.04, 0.26 ± 0.05, and 0.39 ± 0.04, respectively. The genetic correlation between WW and YW was positive and high (0.80 ± 0.04), in- dicating that these traits are mainly determined by the same genes. Genetic correlations between the growth traits and scrotal circumference measures were positive and of low to moderate magnitude, ranging from 0.23 ± 0.04 to 0.38 ± 0.04. On the other hand, increased genetic associations were estimated between scrotal cir- cumference and testicular volume at different ages (0.61 ± 0.04 to 0.86 ± 0.04). Selection for greater scrotal circumference in males should result in greater WW, YW, and testicular volume. In conclusion, in view of the difficulty in measuring testicular volume, there is no need to change the selection criterion from scrotal circumference to testicular volume in genetic breeding programs of Zebu breeds. Key words: beef cattle, genetic correlation, heritability ©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:1215–1219 doi:10.2527/jas.2008-1719 INTRODUCTION In Brazil, genetic breeding programs of beef cattle mainly use productive traits, such as BW at differ- ent ages, as selection criteria. These traits are easily measured, are positively correlated with other traits of economic interest, and respond to individual selection because they present heritability coefficients of medium magnitude. Scrotal circumference is a potentially useful indicator of reproductive traits and has been used to compose selection indices for Nellore cattle. This trait is easily measured, highly heritable, and correlated with sperm quality, BW, and reproductive performance (Bourdon and Brinks, 1986; Morris et al., 2000; Boli- gon et al., 2007; Yokoo et al., 2007; Dias et al., 2008).
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