Growth, carcass and tenderness data from 415 Polled Nellore animals were analyzed in order to estimate the genetic correlations between tenderness (WBSF) and growth (ILW, FLW and ADG) and carcass (BF, RF and LMA) traits. The covariance components and genetic parameters were estimated using the Gibbs Sampling method. The heritability estimated for WBSF was of low magnitude (0.11 ± 0.022). The genetic correlations between WBSF and the other traits were of low magnitude, with values of - 0.15; -0.18; -0.13; 0.10; -0.12 and 0.18, between WBSF and ILW, FLW, ADG, BF, RF and LMA, respectively. The results support the conclusion that selection for improved tenderness will not affect genetic progress in other economic traits and vice-versa, but more studies are required for a better knowledge of the genetic relationships between meat tenderness and other traits for Polled Nellore cattle

CASTRO, L.

FARIA, C.

GONZALEZ, R. D. S.

LOPES, F.

LÔBO, R.

MAGNABOSCO, C. de U.

NAKAGAWA, A.

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Proceedings, 10th World Congress of Genetics Applied to Livestock Production  Genetic Correlations Estimate between Meat Tenderness, Growth and Carcass Traits in  a Population of Polled Nellore Cattle in Brazil   L. Castro1,4, C. Magnabosco2,3, R. Sainz2,8, C. Faria5, R. Lôbo6, A. Nakagawa7 and F. Lopes2,4 1Federal University of Goias, Goânia-GO, Brazil, 2Embrapa-Brazilian Agricultural Research Corporation,  3CNPq-National Council for Scientific and Technological Development, 4Capes-Coordination for the  Improvement of Higher Education Personnel, Brasilia-DF, Brazil, 5Federal University of Uberlandia,  Uberlândia-MG, Brazil,  6ANCP-Brazilian Society of Breeders and Researchers, Ribeirão Preto-SP,  Brazil, 7OB Brand, Pontes de Lacerda-MT, Brazil, 8University of California, Davis-CA, EUA   ABSTRACT: Growth, carcass and tenderness data from 415 Polled Nellore animals were analyzed in order to esti-mate the genetic correlations between tenderness (WBSF) and growth (ILW, FLW and ADG) and carcass (BF, RF and LMA) traits. The covariance components and genetic pa-rameters were estimated using the Gibbs Sampling method. The heritability estimated for WBSF was of low magnitude (0.11 ± 0.022). The genetic correlations between WBSF and the other traits were of low magnitude, with values of -0.15; -0.18; -0.13; 0.10; -0.12 and 0.18, between WBSF and ILW, FLW, ADG, BF, RF and LMA, respectively. The results support the conclusion that selection for improved tenderness will not affect genetic progress in other econom-ic traits and vice-versa, but more studies are required for a better knowledge of the genetic relationships between meat tenderness and other traits for Polled Nellore cattle. Keywords: beef cattle; carcass; shear force    Introduction  Brazil was the largest beef exporter in the world by volume in 2012, producing about 9.6 million tons of beef and, of these, approximately 1.8 million tons were destined for export (USDA (2013)). However, most of the beef exported by Brazil is considered of medium and low quality by international buyers, mainly due to low tender-ness. Therefore Brazil lags behind other global beef export-ers in export value, losing to countries such as the U.S. and Australia (IBGE (2011)). Most Brazilian beef comes from Bos indicus animals, known to be less tender than beef from Bos taurus beef breeds. However, research developed with Nellore cattle (Sainz et al. (2005)) has demonstrated the existence of genetic variability for beef tenderness, indicat-ing that this trait can be improved through genetic selection.  Very few Brazilian structured Zebu herds include beef tenderness in their breeding programs, even though genetic improvement of beef tenderness in Zebu popula-tions is of major importance. That is because Brazilian packers do not pay for meat quality as in other countries, rather they pay only for quantity. However, there are stud-ies showing that consumers would be willing to pay more for meat quality, especially regarding meat tenderness (Boleman et al. (1997)). Several researchers have studied carcass, food in-take and growth traits, such as weight at different ages, growth curves and features related to growth rate of Nellore cattle (Hoque et al., (2009), Bouquet et al., (2010), Lopes et al., (2012)). However, research to evaluate meat quality, especially tenderness and its relationships with growth and carcass quality traits of Zebu cattle in Brazil, are limited. In this context, we aimed to estimate the (co)variance compo-nents and genetic parameters for meat tenderness, growth and carcass traits, so we can have a better knowledge of the genetic relationships between those traits in the Polled Nellore cattle breed.  Materials and Methods  Data were obtained from two slaughters conducted in 2004 and 2008 that were part of a study by Marca OB Ranch, the Brazilian Agricultural Research Corporation – Embrapa, and the University of California - Davis for char-acterization and genetic selection for meat tenderness in Polled Nellore. Twenty two sires representing the main Nellore bloodlines were mated with 552 Polled Nellore cows. The progenies of these matings were raised on pas-ture, finished in feedlot for three months and slaughtered with ages ranging from 24 to 26 months old. Complete pedigree and phenotypic evaluations for carcass and meat tenderness data of 415 progeny of purebred Polled Nellore sires and dams were produced, forming a relationship ma-trix containing 956 animals.  The analyzed traits were: initial live weight (ILW); final live weight (FLW); average daily gain (ADG); longis-simus muscle area (LMA); rump fat thickness (RF); backfat thickness at the 12th-13th rib (BF); and Warner-Bratzler shear force (WBSF), determined using the Longissimus dorsi muscle after ageing for seven days at 4ºC (Wheeler et al. (2005)).  The variance components needed to obtain the ge-netic parameters were estimated by the Gibbs Sampling method (Van Tassel and Van Vleck (1996)), using the MTGSAM program. The basic linear model for single trait and bivariate analyses was: 𝑦 = 𝑋𝛽 + 𝑍𝑢 + 𝑒, where  𝑦 = vector of the dependent variable, 𝛽 = vector of fixed ef-fects, 𝑋 = incidence matrix that associates 𝛽  with 𝑦, 𝑍 = incidence matrix that associates the vector 𝑢  to 𝑦 , 𝑢 = vector of additive genetic effects, and e = vector of residual effects. The linear model included  additive genetic and residual random effects,  fixed effects of sex and contempo-rary group (formed by year of slaughter and slaughter date) and the systematic effect of age as covariate. For the prior values of additive and residual (co)variances the uninforma-tive or "flat" distribution was used. In the implementation of  Gibbs Sampling a chain of 1,500,000 cycles was used, the first 500,000 cycles were discarded and the samples taken every 1,000 cycles, totaling 1,000 Gibbs samples. For convergence evaluation, the GIBANAL software (Van Kaam (1997)) was used.  Results and Discussion  The variance components estimation for WBSF showed that this trait does not have significant values of additive genetic variance. This can be observed by the low additive genetic variance estimate (0.148) and the high residual (1.222) and phenotypic (1.370) variances present-ed. These values of direct additive genetic and phenotypic variances generated a heritability estimate of 0.11 ± 0.022, suggesting that only 11% of the WBSF genes have direct additive genetic effects, while 89% of the effects that con-trol this feature are present in the residual, this being com-posed of epistatic, dominance, genotype-environment inter-actions and environmental effects.  The heritability estimate found in this study is sim-ilar to the value of 0.17 for Brahman animals and their crossbreds reported by Elzo et al. (1998). By contrast, pre-vious studies with Brahman cattle have reported heritability values for WBSF as high as 0.29 (Smith et al. (2007)) and as low as 0.02 (Crews and Franke (1998)). Clearly, the heritability of meat tenderness varies widely. Various re-ports in the literature demonstrate heritabilities ranging from low to high magnitude, whether within or between breeds (Johnston et al. (2003), Minick et al. (2004), Boukha et al. (2011)). However, there are few studies that are di-rectly comparable with the results found in this study, be-cause most of the research with gene prospection of meat quality features refers to Bos taurus breeds and their cross-breds with Zebu cattle (Elzo et al., (1998), Johnston et al. (2003)). That happens because taurine breeds have been selected, for some time now, in breeding programs that include carcass and meat quality as selection criteria, as opposed to zebu breeds, especially Nellore cattle.  The genetic correlations (Table 1) between the growth traits (ILW, FLW and ADG) and WBSF were nega-tive and of low magnitude (-0.15, -0.18 and -0.13, respec-tively), indicating that selection for WBSF will not influ-ence directly the selection for weight and vice versa. A negative and low magnitude (-0.12) correlation also oc-curred between WBSF and fat thickness measured on the rump (RF), indicating that the joint selection for these traits will not influence their phenotypic expression. For other carcass traits, BF and LMA, despite also being of low mag-nitude, the genetic correlations with WBSF were positive (0.10 and 0.18, respectively). Although the positive genetic correlation estimate between WBSF and LMA can be ex-plained by the increase in muscle size with age and conse-quently decreased meat tenderness, these results must be interpreted with caution due to the very large 95% confi-dence regions. Genetic correlations between WBSF and carcass traits (BF and LMA) were also observed by Koch et al. (1982) who obtained a value of -0.01 for genetic correla-tion between WBSF and BF, and a value of -0.02 between WBSF and LMA. Although these genetic correlations were negative, opposite to those obtained in this study, they were also of very low magnitude, indicating that the selection for WBSF should not influence the selection for the mentioned carcass traits.  Table 1. Descriptive statistics of the (co) variance com-ponents and heritability estimates and genetic correla-tions between WBSF and ILW, FLW, ADG, BF, RF and LMA traits, in Polled Nelore cattle, obtained from biva-riate analyses in animal model. Traits (Co)variance components Genetic parameters 21aσ 22aσ 21aσ 21eσ 22eσ 21h  22h  12gr WBSF1  x ILW2  Mean 0.13 639.99 -1.32 1.24 83.97 0.09 0.88 -0.15 SD 0.12 138.38 4.40 0.14 100.80 0.09 0.15 0.55 CR 95% 0.007 to 0.434 289.090 to 845.975 -10.31 to 6.920 0.931 to 1.493 0.01        to        0.90 0.01 to 0.32 0.44 to 1.00 -0.98 to 0.99 WBSF1  x FLW2  Mean 0.16 1430.17 -2.61 1.22 363.55 0.11 0.79 -0.18 SD 0.18 420.64 8.21 0.16 317.91 0.11 0.19 0.56 CR 95% 0.009 to 0.681 544.525 to 2065.225 -21.11 to 12.330 0.823 to 1.476 0.730  to 1047.675 0.01 to 0.45 0.34 to 1.00 -0.99 to 0.88 WBSF1  x AG2  Mean 0.19 0.03 -0.01 1.20 0.02 0.13 0.61 -0.13 SD 0.18 0.02 8.21 0.17 0.01 0.12 0.30 0.62 CR 95% 0.010 to 0.640 0.000    to 0.050 -0.110  to 0.09 0.830 to 1.480 0.000        to    0.040 0.01 to 0.42 0.06 to 1.00 -0.99 to 0.97 WBSF x BF2 Mean 0.19 2.49 0.07 1.21 3.90 0.12 0.37 0.10 SD 0.18 1.91 0.05 0.17 1.52 0.12 0.26 0.60 CR 95% 0.009 to 0.621 0.240    to 7.240 -0.794 to 0.974 0.843 to 1.499 0.235        to    6.115 0.01 to 0.43 0.04 to 0.97 -0.96 to 0.99 WBSF1  x RF2 Mean 0.15 4.54 -0.11 1.23 1.48 0.11 0.74 -0.12 SD 0.14 1.57 0.47 0.15 1.18 0.10 0.21 0.60 CR 95% 0.004 to 0.531 1.425    to 7.105 -1.079 to 0.807 0.894 to 1.482 0.030        to     4.040 0.01 to 0.37 0.26 to 1.00 -0.99 to 0.97 WBSF1  x LMA2  Mean 0.20 17.23 0.29 1.18 38.81 0.14 0.29 0.18 SD 0.22 16.23 1.35 0.19 13.17 0.14 0.25 0.63 CR 95% 0.008 to 0.895 0.525  to 59.345 -3.055 to 3.327 0.637 to 1.479 6.12        to      56.43 0.01 to 0.54 0.01 to 0.90 -0.97 to 0.99 1: Warner-Bratzler shear force of the Longissimus dorsi (WBSF); 2: initial live weight (ILW) , final live weight (FLW), average daily gain (ADG), longissimus muscle area (LMA), backfat thickness at the 12th-13th rib (BF), rump fat thickness (RF); 21aσ : additive genetic variance of 1; 22aσ : additive genetic variance of 2; 21aσ: additive genetic covariance between 1 and 2; 21eσ : residual variance of 1; 22eσ : residual variance of 2; 21h : heritability of 1; 22h : heritability of 2; 12gr : genetic correlation between 1 and 2; SD: standard deviation; CR: credibility region at 95%.   The heritability estimates obtained for the traits re-lated to carcass quality by bivariate Bayesian analysis, measured in vivo by ultrasound, were 0.29, 0.37 and 0.74 for LMA, BF and RF, respectively. These values range from moderate (LMA and BF) to high (RF) magnitude, but the heritability estimates obtained in this study for the growth traits as ILW, FLW and ADG were of high magni-tude, with values of 0.88, 0.79 and 0.61, respectively. Liter-ature values of heritabilities for weight, especially for year-ling weight and weight gain, vary widely. Bergmann (2003) reported variation from 0.08 to 0.83 for direct heritability for yearling weight in studies with various breeds of beef cattle, and the author further stated that due to the great use of the trait as a selection criterion, several authors have been concerned with obtaining more accurate estimates of the genetic parameters.   The heritabilities obtained in the present study in-dicate that these traits can be passed from one generation to the next, in other words, there may be genetic progress in applying the selection for the same. Thus, in a breeding program it will be possible to select and improve both car-cass and / or growth traits as well as the tenderness trait, not through a correlated response, but rather due to the high heritabilities of the individual traits.  There was also a wide amplitude of values of the credibility region at 95% (CR 95%) in the bivariate anal-yses presented here, such as the correlation between WBSF and the initial live weight (ILW). This credibility region at 95% (95% CR) ranged from -0.98 to 0.99, indicating that the analyzed parameter can assume any value within that range. This high amplitude of the credibility region at 95% occurred with all analyzed parameters and may indicate that the collected data was insufficient to generate more con-sistent analyses and further studies should be conducted to obtain a greater volume of information on the meat tender-ness trait. In general, when considering only the Zebu breeds, especially Nellore, studies addressing tenderness as an object of selection are rather scarce. However, experi-ments to evaluate this trait are of high cost and long dura-tion, which further complicates large scale collection of tenderness data.  Conclusion  The estimates of (co)variance components and ge-netic parameters for meat tenderness indicated that most of genes responsible for meat tenderness trait (WBSF) have no direct additive genetic effect. The selection for meat ten-derness in Polled Nellore will not affect deposition of sub-cutaneous fat in carcass nor the animals’ muscularity and vice versa.   Furthermore, results of this study also demonstrat-ed no correlated response between tenderness and growth traits, such as weight and weight gain, indicating that joint selection for those traits will not influence phenotypic ex-pression of tenderness.  These results indicate that meat tenderness can be used as selection criteria in breeding programs independently of other selected traits.  Acknowledgements  The firs author thanks Capes (Coordination for the Improvement of Higher Education Personnel) and CNPq (National Council for Scientific and Technological Devel-opment) for the scholarship and funding and also the OB Brand for providing the data.  Literature Cited  Bergmann, J. A. G. (2003). Proc 4th Workshop Seleção Em Bovi-nos De Corte, volume 4:1-8. Boleman, S. J., Boleman, S. L., Miller, R. K. et al. (1997). J. Anim. Sci. 75:1521-1524. Bouquet, A., Fouilloux, M.-N., Renand, G. et al. (2010). Livest. Sci. 129:38-48. Boukha, A., Bonfatti, V., Cecchinato, A. et al. (2011). 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Genetic correlations estimate between meat tenderness, growth and carcass traits in a population of polled nellore cattle in Brazil.

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