Parâmetros genéticos de características de carcaça e de crescimento de bovinos da raça Nelore

Economic values of reproductive, growth, feed efficiency and carcass traits in Nellore cattle

A bioeconomic model was developed to calculate the economic value (ev) of reproductive and growth performance, feed efficiency and carcass traits of a seedstock Nellore herd. Data from a full-cycle cattle operation (1,436 dams) located in the Brazilian Cerrado were assessed. The ev was calculated by the difference in profit before and after one-unit improvement in the trait, with others remaining unchanged. The ev was standardized by the phenotypic standard deviation of each trait. Preweaning average daily gain (ADG) was the most economically important trait evaluated (R$ 58.04/animal/year), followed by age at first calving (R$ 44.35), postweaning ADG (R$ 31.43), weight at 450 days (R$ 25.36), accumulated productivity (R$ 21.43), ribeye area (R$ 21.35), calving interval (R$ 19.97), feed efficiency (R$ 15.24), carcass dressing per cent (R$ 8.27), weight at 120 days (R$ 6.22), weight at 365 days (R$ 6.06), weight at weaning (210 days, R$ 5.82), stayability (R$ 5.70) and the probability of early calving (R$ 0.32). The effects of all traits on profits are evidence that their selection may result in the economic and genetic progress of the herd if there is genetic variability.

Genetic analysis of carcass and meat quality traits in Nelore cattle1

The objective of this study was to estimate genetic parameters for carcass and meat quality traits, as well as their genetic correlations using pedigree and genomic information. A total of 3,716; 3,702; 3,439; 3,705; and 3,714 records of 12th-13th rib LM area (LMA), backfat thickness (BF), HCW, marbling score (MARB), and Warner-Bratzler peak shear force (WBSF), respectively, were used. Animals were genotyped with BovineHD BeadChip and GeneSeek Genomic Profiler Indicus HD - GGP75Ki panel. The (co)variance components were estimated by Bayesian inference using a multitrait ssGBLUP analysis. The animal model included fixed effects of contemporary group (defined by the combination of farm and year of birth, and management group at yearling) and age of animal at slaughtering as a covariate (linear). Direct additive genetic and residual effects were fitted as random. The posterior means and SD of heritabilities for LMA, BF, HCW, MARB, and WBSF were 0.28 (0.03), 0.21 (0.04), 0.21 (0.04), 0.12 (0.04), and 0.11 (0.03), respectively. The posterior means for genetic correlations between LMA and meat quality were positive and moderate with MARB (0.38 ± 0.12) and negative with WBSF (-0.47 ± 0.12). Low genetic correlations were estimated between BF and WBSF (-0.03 ± 0.16) and between HCW and MARB (-0.04 ± 0.14), indicating that these traits are not controlled by the same set or linked genes. Carcass traits (LMA, BF, and HCW) presented moderate heritability providing quick response to the selection purpose. The estimates of heritability for meat quality traits (MARB and WBSF) were low and indicate that the rate of genetic improvement for these traits would be slow. Genetic correlations indicated that selection for carcass traits would not be strongly antagonistic for improving meat quality.

Economic selection indexes for Hereford and Braford cattle raised in southern Brazil

Economic selection indexes (EI) are considered the best way to select the most profitable animals for specific production systems. Nevertheless, in Brazil, few genetic evaluation programs deliver such indexes to their breeders. The aims of this study were to determine the breeding goals (BG) and economic values (EV, in US$) for typical beef cattle production systems in southern Brazil, to propose EI aimed to maximize profitability, and to compare the proposed EI with the currently used empirical index. Bioeconomic models were developed to characterize 3 typical production systems, identifying traits of economic impact and their respective EV. The first was called the calf-crop system and included the birth rate (BR), direct weaning weight (WWd), and mature cow weight (MCW) as selection goals. The second system was called the full-cycle system, and its breeding goals were BR, WWd, MCW, and carcass weight (CW). Finally, the third was called the stocking and finishing system, which had WWd and CW as breeding goals. To generate the EI, we adopted the selection criteria currently measured and used in the empirical index of PampaPlus, which is the genetic evaluation program of the Brazilian Hereford and Braford Association. The comparison between the EI and the current PampaPlus index was made by the aggregated genetic-economic gain per generation (Δ). Therefore, for each production system an index was developed using the derived economic weights, and it was compared with the current empirical index. The relative importance (RI) for BR, WWd, and MCW for the calf-crop system was 68.03%, 19.35%, and 12.62%, respectively. For the full-cycle system, the RI for BR, WWd, MCW, and CW were 69.63%, 7.31%, 5.01%, and 18.06%, respectively. For the stocking and finishing production system, the RI for WWd and CW was 34.20% and 65.80%, respectively. The Δ for the calf-crop system were US$6.12 and US$4.36, using the proposed economic and empirical indexes, respectively. Respective values were US$19.87 and US$18.22 for the full-cycle system and US$20.52 and US$18.52 in the stocking and finishing system. The efficiency of the proposed EI had low sensitivity to changes in the values of the economic and genetic parameters. The 3 EI generated higher Δ when using the proposed economic weight compared to the Δ provided by a PampaPlus index, suggesting the use of proposed EI to obtain greater economic profitability in relation to the current empirical PampaPlus index.

Genotype × environment interaction for age at first calving, scrotal circumference, and yearling weight in Nellore cattle using reaction norms in multitrait random regression models

The aim of this study was to evaluate the effect of genotype × environment interaction (G×E) on age at first calving (AFC), scrotal circumference (SC), and yearling weight (YW) and to estimate genetic correlations between these traits in Nellore cattle using reaction norms in multitrait random regression models. In this study, 28,871, 41,386, and 89,152 records of Nellore cattle for AFC, SC, and YW, respectively, were used. The data were obtained from farms located in the north, northeast, midwest, and southeast regions of Brazil that participate in the DeltaGen Breeding Program. Environmental levels were defined as a function of contemporary groups, that is, animals born in the same herd and year, from the same management group (from birth to yearling), and of the same sex. Postweaning weight gain was used as a criterion to evaluate the environmental conditions for all traits. For reaction norm analyses, residual variances were modeled with homogeneous and heterogeneous classes. The model for SC and YW included the fixed effects of contemporary group and age of the animal as a covariate as well as random direct additive genetic and residual effects. The same model, excluding the covariate age of the animal, was used for AFC. The heritability estimates were low to high for AFC (0.09 to 0.50), high for SC (0.51 to 0.67), and moderate to high for YW (0.33 to 0.71). The genetic correlations (within each trait) along the environmental levels varied from -0.27 to 1.0 for AFC, from 0.73 to 1.0 for SC, and from 0.26 to 1.0 for YW. The genetic correlations between different traits in different environments varied from -0.14 to -0.60 between AFC and SC, from -0.05 to -0.32 between AFC and YW, and from -0.05 to 0.72 between YW and SC. The genetic correlations have had different magnitudes for AFC, SC, and YW, which could indicate the presence of G×E. The present results should support researchers and farmers in defining selection criteria to improve growth traits and sexual precocity. Our results suggest that animals for breeding have to be selected in the same environment and management conditions as their progeny will be reared.

Growth performance, and carcass and meat quality traits in progeny of Poll Nellore, Angus and Brahman sires under tropical conditions

This study aimed to characterise progeny of sires representing major families in the Poll Nellore breed. Fourteen Poll Nellore sires, two Angus sires and one Brahman sire were mated by AI to ~400 multiparous Poll Nellore dams. Calves were raised and stocked on pasture in central Brazil until reaching ~18 months of age, then fed a sugarcane bagasse-based diet on an ad libitum basis until reaching market weight and finish (average 23 months). There were 236 Poll Nellore (N), 38 Angus × Poll Nellore (AN) and 31 Brahman × Poll Nellore (BN) calves born in total. The weaning and 423-day weight weights, and growth rates and pre- and post-weaning were greater (P < 0.05) in males than in female calves, and were influenced by breed and by sire within the N animals. The weaning weights were higher (P < 0.05) in AN and BN than in N calves. The 423-day weight weights were greater (P < 0.05) in AN calves, followed by BN, with straightbred N being lightest. Feedlot average daily gain was unaffected (P > 0.05) by sex or by sire within N, but was lowest (P < 0.05) in N cattle, and highest in AN and BN animals, which did not differ (P > 0.05). Heifers reached the end of the study with lower bodyweight (BW) and dressing percentage than steers, resulting in lower carcass weights, smaller longissimus muscle areas (LMA), but greater 12th to 13th rib backfat (BF) and similar marbling score and mean shear force. However, the proportion of carcasses grading Choice or Prime was numerically greater in heifers than in steers (23.6% vs 9.8%). AN cattle reached greater harvest weights than BN, and those were heavier than N cattle (P < 0.001). However, dressing percentages were lowest in AN animals, so that there was no significant difference in carcass weight between AN and BN cattle. AN carcasses also had greater LMA, BF and marbling scores than the N carcasses. The proportion of carcasses grading Choice or Prime was numerically greater in AN cattle than in the BN and N groups (25.9%, 11.8% and 15.9%, respectively). Steaks from AN calves were more tender than N steaks, with the BN steaks being intermediate. There was significant variation among N sires for final BW, dressing percentage, carcass weight, LMA and marbling score, but not for BF or mean shear force. The percentages of carcasses of N cattle grading Choice or Prime ranged from 0% to 61.5%. Three N sires produced progeny with greater than 40% of carcasses grading Choice or above (Berílio OB, Furador OB, and Litoral OB). Likewise, three N sires (Blitz OB, Furador OB and Sossego OB) had progeny with 67%, 62% and 75%, respectively, of steaks classified as tender. This study confirmed that Zebu cattle have inferior carcass and meat quality relative to AN crossbreds under tropical conditions, however there is substantial variation within the N breed for these traits, and several sires have a proportion of their progeny comparable in terms of meat tenderness to those of Angus sires.