Genome-enabled prediction of reproductive traits in Nellore cattle using parametric models and machine learning methods.

This study aimed to assess the predictive ability of different machine learning (ML) methods for genomic prediction of reproductive traits in Nellore cattle. The studied traits were age at first calving (AFC), scrotal circumference (SC), early pregnancy (EP) and stayability (STAY). The numbers of genotyped animals and SNP markers available were 2342 and 321 419 (AFC), 4671 and 309 486 (SC), 2681 and 319 619 (STAY) and 3356 and 319 108 (EP). Predictive ability of support vector regression (SVR), Bayesian regularized artificial neural network (BRANN) and random forest (RF) were compared with results obtained using parametric models (genomic best linear unbiased predictor, GBLUP, and Bayesian least absolute shrinkage and selection operator, BLASSO). A 5-fold cross-validation strategy was performed and the average prediction accuracy (ACC) and mean squared errors (MSE) were computed. The ACC was defined as the linear correlation between predicted and observed breeding values for categorical traits (EP and STAY) and as the correlation between predicted and observed adjusted phenotypes divided by the square root of the estimated heritability for continuous traits (AFC and SC). The average ACC varied from low to moderate depending on the trait and model under consideration, ranging between 0.56 and 0.63 (AFC), 0.27 and 0.36 (SC), 0.57 and 0.67 (EP), and 0.52 and 0.62 (STAY). SVR provided slightly better accuracies than the parametric models for all traits, increasing the prediction accuracy for AFC to around 6.3 and 4.8% compared with GBLUP and BLASSO respectively. Likewise, there was an increase of 8.3% for SC, 4.5% for EP and 4.8% for STAY, comparing SVR with both GBLUP and BLASSO. In contrast, the RF and BRANN did not present competitive predictive ability compared with the parametric models. The results indicate that SVR is a suitable method for genome-enabled prediction of reproductive traits in Nellore cattle. Further, the optimal kernel bandwidth parameter in the SVR model was trait-dependent, thus, a fine-tuning for this hyper-parameter in the training phase is crucial.

State of inbreeding and genetic trends for estimated breeding values in IVF embryos and oocyte donors in the Brazilian Guzerá cattle.

The main objective of this study was to verify genetic trends for milk production (MY305) and age at first calving (AFC). Were also considered levels of inbreeding practiced in the Brazilian dual-purpose Guzerá population (TPOP) comparing it with the same parameters estimated for two sub-populations derived from the reference (TPOP): female donors submitted to ovum-pick up (DPOP) and in vitro embryos produced (EPOP) between 2003 and 2013. Estimated breeding values (EBV) and inbreeding coefficients (F) were regressed by the year of birth (or year of in vitro fertilization) of each animal or embryo in order to obtain annual trends for these parameters separately for each of the three populations studied. A positive quadratic (ß2 = +0.000075) effect was detected for the F values in TPOP. Both DPOP and EPOP showed positive linear coefficients (ß1), respectively, +0.00084 (P < 0.001) and +0.00024 (P > 0.05). Annual mean F for EPOP was higher than TPOP and DPOP through the time series studied. The frequency of individuals with more than 7% F was higher in DPOP. Genetic trends for AFC were -0.187 days/year (P > 0.05); -0.557 days/year (P < 0.05) and -1.48 days/year (P < 0.05), respectively for TPOP; DPOP and EPOP. Genetic trends for MY305 were +6.75 kg/year (P < 0.001); +8.2 kg/year (P < 0.001) and +10.5 kg/year (P < 0.05), respectively for TPOP; DPOP and EPOP. For both traits analyzed, EPOP showed the highest regression coefficients, which confirms a higher selection pressure and lower generation intervals previously expected from this sub-population. Results reported in the present study suggest that mean F is increasing in the Guzerá population. Efforts for controlling inbred mating on in vitro fertilization should be considered, as the presence of a bottleneck effect seems to be getting shape on DPOP and EPOP.

Pedigree analysis and inbreeding effects over morphological traits in Campolina horse population.

Genetic improvement, without control of inbreeding, can go to loss of genetic variability, reducing the potential for genetic gains in the domestic populations. The aim of this study was to analyze the population structure and the inbreeding depression in Campolina horses. Phenotype information from 43 465 individuals was analyzed, data provided by the Campolina Breeders Association. A pedigree file containing 107 951 horses was used to connected the phenotyped individuals. The inbreeding coefficient was performed by use of the diagonal of the relationship matrix and the genealogical parameters were computed using proper softwares. The effective population size was estimated based on the rate of inbreeding and census information, and the stratification of the population was verified by the average relationship coefficient between animals born in different regions of Brazil. The effects of inbreeding on morphological traits were made by the use of inbreeding coefficient as a covariate in the model of random regression. The inbreeding coefficient increased from 1990 on, impacting effective population size and, consequently, shrinking genetic variability. The paternal inbreeding was greater than maternal, which may be attributed to the preference for inbred animals in reproduction. The average genetic relationship coefficient of animals born in different states was lower than individuals born within the same state. The increase in the inbreeding coefficient was negatively associated with all studied traits, showing the importance to avoid genetic losses in the long term. Although results do not indicate a severe narrowing of the population until the present date, the average relationship coefficient shows signs of increase, which could cause a drastic reduction in genetic variability if inbred mating is not successfully controlled in the Campolina horse population.

Inbreeding effects on in vitro embryo production traits in Guzerá cattle.

Inbreeding has been associated with the impairment of reproductive performance in many cattle breeds. Although the usage of reproductive biotechnologies has been increasing in bovine populations, not much attention has been given to the impact of inbreeding over cow's performance on artificial reproduction. The objective of this study was to estimate the impact of inbreeding on in vitro embryo production in a Guzerá breed population. The inbreeding coefficient (F), calculated as half of the co-ancestry of the individual's parents, was used as an estimate of inbreeding. The inbreeding coefficients of the donor, sire (used on in vitro fertilization) and of the embryos were included, separately, in the proposed models either as classificatory or continuous variables (linear and quadratic effects). The percentage of non-inbred individuals (or embryos) and mean F of donors, embryos and sires were 29.38%; 35.76%; 42.86% and 1.98±2.68; 1.32±3.13; 2.08±2.79, respectively. Two different models were considered, one for oocyte production traits and other for embryo production traits. The increase of F of the donor significantly (P<0.05) impaired the number of viable oocytes (N OV), number of grade I oocytes (N GI) and number of cleaved embryos (N CLV). Moreover, the donor's F influenced the percentage of grade I oocytes (P GI), percentage of viable embryos (P EMB) and percentage of cleaved embryos that turned into embryos (P CXE). No significant (P>0.05) effects were observed for the sire (father of the embryos) inbreeding coefficient over the traits analysed. Embryo's F influenced (P<0.05) the number of viable embryos (N EMB), percentage of viable embryos (P EMB) and percentage of cleaved embryos that turn into embryos (P CXE). Results suggested that an increase in the inbreeding coefficient might impair the embryos ability to survive through challenges imposed by the in vitro environment. Submitting highly inbred Guzerá female donors to in vitro embryo production may, in the long-term, have negative implications on the number of embryos obtained per cow and increase the relative costs of the improvement programmes based on this technology. High levels of inbreeding should be avoided when selecting Guzerá female donors and planning in vitro fertilization mating.

Count Bayesian models for genetic analysis of in vitro embryo production traits in Guzerá cattle.

Four models for in vitro embryo production traits in Guzerá cattle were compared: Gaussian (untransformed variable - LIN and transformed in logarithmic scale - LOG), Poisson (POI) and zero-inflated Poisson (ZIP). Data consisted of 5716 ovum pick-up and in vitro fertilization records performed in 1205 cows from distinct regions of Brazil. Analyzed count traits were the number of viable oocytes (NOV), number of grade I oocytes (NGI), number of degenerated oocytes (NDG), number of cleaved embryos (NCLV) and number of viable produced embryos (NEMB). Heritability varied from 0.17 (LIN) to 0.25 (POI) for NOV; 0.08 (LOG) to 0.18 (ZIP) for NGI; 0.12 (LIN) to 0.20 (POI) for NDG; 0.13 (LIN) to 0.19 (POI) for NCLV; 0.10 (LIN) to 0.20 (POI) for NEMB depending on the considered model. The estimated repeatability varied from 0.53 (LOG) to 0.63 (POI) for NOV; 0.22 (LOG) to 0.39 (ZIP) for NGI; 0.29 (LIN) to 0.42 (ZIP) for NDG; 0.42 (LIN) to 0.59 (POI) for NCLV; 0.36 (LIN) to 0.51 (POI) for NEMB. The goodness of fit, measured by deviance information criterion and mean squared residuals, suggested superiority of POI and ZIP over Gaussian models. Estimated breeding values (EBV) obtained by different models were highly correlated, varying from 0.92 for NOV (between LIN-POI) and 0.99 for NGI (between POI-ZIP). The number of coincident animals on the 10% top EBV showed lower similarities. We recommend POI and ZIP models as the most adequate for genetic analysis of in vitro embryo production traits in Guzerá cattle.

Genomic study and Medical Subject Headings enrichment analysis of early pregnancy rate and antral follicle numbers in Nelore heifers.

Zebu animals () are known to take longer to reach puberty compared with taurine animals (), limiting the supply of animals for harvest or breeding and impacting profitability. Genomic information can be a helpful tool to better understand complex traits and improve genetic gains. In this study, we performed a genomewide association study (GWAS) to identify genetic variants associated with reproductive traits in Nelore beef cattle. Heifer pregnancy (HP) was recorded for 1,267 genotyped animals distributed in 12 contemporary groups (CG) with an average pregnancy rate of 0.35 (±0.01). Disregarding one of these CG, the number of antral follicles (NF) was also collected for 937 of these animals, with an average of 11.53 (±4.43). The animals were organized in CG: 12 and 11 for HP and NF, respectively. Genes in linkage disequilibrium (LD) with the associated variants can be considered in a functional enrichment analysis to identify biological mechanisms involved in fertility. Medical Subject Headings (MeSH) were detected using the MESHR package, allowing the extraction of broad meanings from the gene lists provided by the GWAS. The estimated heritability for HP was 0.28 ± 0.07 and for NF was 0.49 ± 0.09, with the genomic correlation being -0.21 ± 0.29. The average LD between adjacent markers was 0.23 ± 0.01, and GWAS identified genomic windows that accounted for >1% of total genetic variance on chromosomes 5, 14, and 18 for HP and on chromosomes 2, 8, 11, 14, 15, 16, and 22 for NF. The MeSH enrichment analyses revealed significant ( < 0.05) terms associated with HP-"Munc18 Proteins," "Fucose," and "Hemoglobins"-and with NF-"Cathepsin B," "Receptors, Neuropeptide," and "Palmitic Acid." This is the first study in Nelore cattle introducing the concept of MeSH analysis. The genomic analyses contributed to a better understanding of the genetic control of the reproductive traits HP and NF and provide new selection strategies to improve beef production.

Parameters of a dynamic mechanistic model of cattle growth retain enough biological interpretation for genotype-to-phenotype mapping.

This study aimed to investigate the predictability of a phenotype when using a dynamic model of cattle growth. Genotypic and phenotypic information on Nellore (Bos indicus) cattle were used in a genome-wide association analysis designed to contrast the biological interpretation of core parameters [conversion efficiency of metabolizable energy to net energy for gain (kg) and adjusted final shrunk body weight (AFSBW)] to their associated genomic regions and nearby quantitative trait loci (QTLs). Single nucleotide polymorphisms (SNPs) were used to develop prediction equations for kg and AFSBW, which enter the model for simulative prediction purposes. QTLs and genes, one related to mature body weight and another to growth efficiency, are consistent with the model equations. Significantly associated SNPs were used to compute parameters, which yielded reasonable model outcomes when compared with regular parameter computations. Our results provide evidence of the biological validity of using such parameters as component traits of higher phenotypes and the possibility of using genomic data for genotype-to-parameter mapping.

Systems genetics and genome-wide association approaches for analysis of feed intake, feed efficiency, and performance in beef cattle.

Feed intake, feed efficiency, and weight gain are important economic traits of beef cattle in feedlots. In the present study, we investigated the physiological processes underlying such traits from the point of view of systems genetics. Firstly, using data from 1334 Nellore (Bos indicus) cattle and 943,577 single nucleotide polymorphisms (SNPs), a genome-wide association analysis was performed for dry matter intake, average daily weight gain, feed conversion ratio, and residual feed intake with a Bayesian Lasso procedure. Genes within 50-kb SNPs, most relevant for explaining the genomic variance, were annotated and the biological processes underlying the traits were inferred from Database for Annotation, Visualization and Integrated Discovery (DAVID) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Our results indicated several putative genomic regions associated with the target phenotypes and showed that almost all genomic variances were in the SNPs located in the intergenic and intronic regions. We further identified five main metabolic pathways related to ion transport, body composition, and feed intake control, which influenced the four phenotypes simultaneously. The systems genetics approach used in this study revealed novel pathways related to feed efficiency traits in beef cattle.

A genomewide association mapping study using ultrasound-scanned information identifies potential genomic regions and candidate genes affecting carcass traits in Nellore cattle.

The aim of this study was to identify candidate genes and genomic regions associated with ultrasound-derived measurements of the rib-eye area (REA), backfat thickness (BFT) and rumpfat thickness (RFT) in Nellore cattle. Data from 640 Nellore steers and young bulls with genotypes for 290 863 single nucleotide polymorphisms (SNPs) were used for genomewide association mapping. Significant SNP associations were explored to find possible candidate genes related to physiological processes. Several of the significant markers detected were mapped onto functional candidate genes including ARFGAP3, CLSTN2 and DPYD for REA; OSBPL3 and SUDS3 for BFT; and RARRES1 and VEPH1 for RFT. The physiological pathway related to lipid metabolism (CLSTN2, OSBPL3, RARRES1 and VEPH1) was identified. The significant markers within previously reported QTLs reinforce the importance of the genomic regions, and the other loci offer candidate genes that have not been related to carcass traits in previous investigations.

Impact of reference population on accuracy of imputation from 6K to 50K single nucleotide polymorphism chips in purebred and crossbreed beef cattle.

Genotyping with lower density but lower cost panels enables more animals to be genotyped for genomic selection. Imputation enables the determination of missing SNP genotypes in animals genotyped with a low-density panel by using information from a reference population genotyped with a higher density panel, which should increase accuracy of genomic EBV. In this study, population imputation, using linkage disequilibrium among markers, was implemented using the software BEAGLE, FIMPUTE 2.2, and IMPUTE2 in a multibreed, crossbred taurine beef cattle population genotyped with the Illumina SNP50. Different combinations of reference populations and imputed animals were defined based on breed composition. Number of animals (n = 250 to 4,932) and the presence of closer relatives in the reference population (only for Angus animals) were investigated. The overall average imputation accuracy for purebred animals ranged from 94.20 to 97.93% using FIMPUTE, from 95.35 to 98.31% using IMPUTE2, and from 90.02 to 96.38% when BEAGLE software was used. Imputation accuracy of crossbred animals ranged from 54.15 to 97.53% (FIMPUTE), from 57.04 to 97.46% (IMPUTE2), and from 54.35 to 95.64% (BEAGLE). Higher imputation accuracies were obtained when closer relatives along with the breed composition of imputed animals was well represented in the reference population. Within breed imputation from 6K to 50K did not improve when an additional purebred population was added to the reference population. FIMPUTE reduced the run time by 13 to 52 times compared to BEAGLE and 51 to 108 times compared to IMPUTE2.

Uso de redes neurais artificais na predição de valores genéticos para peso aos 205 dias em bovinos da raça Tabapuã / Use of artificial neural networks in breeding values prediction for weight at 205 days in Tabapuã beef cattle

Dados de 19240 animais Tabapuã, provenientes de 152 fazendas localizadas em diversos estados brasileiros, nascidos entre 1976 e 1995, foram utilizados para predição do valor genético do peso aos 205 dias de idade (VG_P205) por meio de redes neurais artificiais (RNAs) e usando o algoritmo LM - Levenberg Marquardt - para treinamento dos dados de entrada. Por se tratar de rede com aprendizado supervisionado, foram utilizados, como saída desejada, os valores genéticos preditos pelo BLUP para a característica P205. Os valores genéticos do P205 obtidos pela RNA e os preditos pelo BLUP foram altamente correlacionados. A ordenação dos valores genéticos do P205 oriundos das RNAs e os valores preditos pelo BLUP (VG_P205_RNA) sugeriram que houve variação na classificação dos animais, indicando riscos no uso de RNAs para avaliação genética dessa característica. Inserções de novos animais necessitam de novo treinamento dos dados, sempre dependentes do BLUP.

Data from 19,240 Tabapuã animals from 152 farms located in different states of Brazil, born from 1976 to 1995, were used to predict the genetic value of body weight at 205 days of age (BV_P205) of Tabapuã beef cattle using Artificial Neural Networks (ANN) and LM algorithm - Levenberg Marquardt training for data entry. Due to the use of networks with supervised learning, the predicted breeding values for P205 from BLUP were used as desired output. The breeding values for P205 obtained from RNA and those predicted by BLUP were highly correlated. The ranked breeding values for body weight at 205 days through RNA and those predicted by BLUP (VG_P205_RNA) showed a variation in the classification of animals indicating risks in the use of ANNs procedure for genetic evaluation of this trait. Insertions of new animals require new training data always dependent on BLUP.

Interação genótipo x ambiente e estimativas de parâmetros genéticos dos pesos aos 205 e 365 dias de idade de bovinos Nelore / Genotype by environment interaction and genetic parameter estimates for 205 and 365 body weight of Nelore cattle

Dados de pesos aos 205 (P205) e 365 (P365) dias de idade, de 46.408 animais Nelore, nascidos entre 1976 e 2000, provenientes de 530 rebanhos dos diversos estados brasileiros, foram utilizados para avaliar as interações genótipo x ambiente (IGA) e estimar herdabilidades direta e materna dos pesos pelo método da máxima verossimilhança restrita. O modelo estatístico utilizado incluiu efeitos fixos de grupo contemporâneo, idade da vaca ao parto (covariável) e efeitos aleatórios genéticos aditivo direto e materno. As correlações genéticas, estimadas para as características P205 e P365, cada uma considerada como característica distinta em cada uma das regiões Sul (S), Sudeste (SE), Centro-Oeste (CO), Norte (N) e Nordeste (NE), foram, respectivamente, 0,86 e 0,84, 0,64 e 0,35, 0,75 e 0,42, 0,79 e 0,86, 0,92 e 0,81, 0,95 e 0,83, 0,83 e 1,00, 0,88 e 0,81, 0,33 e 0,85, 0,63 e 0,99 para S e SE, S e CO, S e N, S e NE, SE e CO, SE e N, SE e NE, CO e N, CO e NE e N e NE. As baixas correlações genéticas indicaram que há efeito da interação genótipo x ambiente nas combinações que envolvem as regiões S/CO, S/N, S/NE, CO/NE e N/NE para P205 dias de idade e S/CO e S/N para P365 dias de idade, havendo, portanto, necessidade de avaliação genética regional quando se consideram regiões bastante distintas.

Body weight records at 205 (205BW) and 365 (365BW) days of age of 46,408 Nelore animals, born from 1976 to 2000 period in 530 Nelore herds of several states of Brazil, were used to evaluate genotype by environment interactions and to estimate genetic and maternal heritability by restricted maximum likelihood methodology. The statistical model included the fixed effects of contemporary group and age of cow (covariate), and the random direct and maternal additive genetic effects. The genetic correlation for 205BW and 365BW, each one considered as different traits in each of the South (S), Southeast (SE), Central west (CO), North (N) and Northeast (NE) regions were 0.86 and 0.84, 0.64 and 0.35, 0.75 and 0.42, 0.79 and 0.86, 0.92 and 0.81, 0.95 and 0.83, 0.83 and 1.00, 0.88 and 0.81, 0.33 and 0.85, 0.63 and 0.99 for S/SE, S/CO, S/N, S/NE, SE/CO, SE/N, SE/NE, CO/N, CO/NE and N/NE, respectively. There is a significant genotype by environment interaction for 205BW in the combination involving the S/CO, S/N, S/NE, CO/NE, and N/NE regions. There are significant genotype by environment interaction effects in the combination involving the S/CO and S/N regions for 365BW. Based on genetic x environment interaction results, regional genetic evaluation is recommend for the very distinct regions.

Desenvolvimento do software DRLinhagem para detecção de linhagens citoplasmáticas e avaliação de seu efeito sobre os pesos à desmama e ao ano de idade de animais Nelore no Centro-Oeste brasileiro / Development of a DRLinhagem software to detect citoplasmatic lines and their effects on weaning and yearling weights of Nelore animals from the center west part of Brazil

Dados de 769.925 animais da raça Nelore, nascidos de 1965 a 2000, em 30 regiões distintas do Brasil, foram utilizados como base de dados para desenvolvimento de um programa computacional flexível, de fácil uso, que permitisse a identificação de linhagens fundadoras de rebanhos, com filtro por país, estado, região ou rebanho. Foi escolhida a região Centro-Oeste, representativa do Brasil, para o estudo pormenorizado do efeito citoplasmático sobre característica de peso aos 205 e 365 dias de idade de animais Nelore. Os componentes de variância de linhagem citoplasmática foram iguais a 0,58x10-3 para peso aos 205 dias e 0,80x10-3 para o peso aos 365 dias e contribuíram com 1,00x10-5 por cento e 9,90x10-6 por cento da variância fenotípica total. Os componentes de variância aditivo direto foram responsáveis por 11 e 21 por cento da variação fenotípica total dos pesos aos 205 e 365 dias de idade

Records on 769,925 Nelore animals born from 1965 to 2000, in 30 regions of Brazil were used as base data to develop a flexible a ease use computational program for identifying maternal base lines in herds, allowing filter by country, state, region and herd. The Center-West region was selected for a detailed study of cytoplasmatic lines on weaning and yearling weights of Nelore animals. The estimated variance components for citoplasmatic lines were .58 x 10-3 and .80 x 10-.8 for weaning and yearling weights, respectively, and accounted for 1.00x10-5 and 9.90x10-6 of total weights variance, respectively. The direct additive component accounts for 11 and 12 percent of the total phenotypic variance of weaning and yearling weights

Exigência de metionina + cistina total para codornas de corte em crescimento / Total methyonine + cystine requirement for meat type quails during the growing phase

Estudou-se a exigência de metionina + cistina total para codornas de corte em crescimento durante os períodos inicial (sete a 21 dias) e final (22 a 42 dias de idade). O delineamento experimental foi inteiramente casualizado, com cinco repetições de 13 codornas por unidade experimental. Os tratamentos consistiram de seis níveis de metionina + cistina total (0,73; 0,79; 0,85; 0,91; 0,97 e 1,03 por cento). Foram estudadas as variáveis: ganho de peso (g), peso final no período (g), consumo de dieta (g) e conversão alimentar (g de dieta/g de peso). As respostas de desempenho foram obtidas por meio de modelos de regressão linear e quadrática. Codornas de corte alimentadas com dietas contendo 0,95 por cento de metionina + cistina total no período inicial (sete a 21 dias) e 0,73 por cento de metionina + cistina total no período final (22 a 42 dias) de criação obtêm máximo ganho de peso.

Total methyonine + cystine requirements during the initial (7-21 days of age) and final period ( 22-42 days of age) of the growing phase were estimated for meat type quails in a completely randomized experimental design with six treatments, five replicates and 13 quails per experimental unit. Weight gain (g), body weight (g), feed consumption (g) and feed : weight gain ratio (g/g) were evaluated for quails fed on .73, .79, .85, .91, .97 and 1.03 percent methyonine + cystine diets. Meat type quails fed .95 percent and .73 percent methyonine + cystine diets during the initial (7-21days of age) and final period (22-42 days of age) of the growing phase show maximum weight gain.

Efeito de diferentes níveis de proteína e energia sobre o rendimento de carcaça de codornas européias / Effect of protein and energy levels on carcass yield of European quails

Avaliou-se o rendimento de carcaça de codornas européias de corte (Coturnix coturnix coturnix) no 42º dia de idade, alimentadas com dietas contendo quatro níveis de proteína e dois níveis de energia. O delineamento experimental foi inteiramente ao acaso, com seis repetições e oito codornas por unidade experimental. Os tratamentos constituíram de um fatorial 2I4, ou seja, dois níveis de energia (2900 e 3100kcal EM/kg) e quatro níveis de proteína (22, 24, 26 e 28 por cento proteína bruta na dieta). As variáveis estudadas foram: peso vivo, peso de carcaça, rendimento de carcaça, peso de coxa, rendimento de coxa, peso de peito, rendimento de peito, peso de gordura abdominal, rendimento de gordura abdominal, peso de vísceras comestíveis e rendimento de vísceras comestíveis. Não houve efeito significativo dos níveis de energia e nem dos níveis de proteína sobre nenhuma das características de carcaça analisada.

Critérios de seleção para características de crescimento em bovinos da raça Nelore / Selection criteria for growth traits in Nellore cattle

Foram utilizados 28.050 registros de bovinos Nelore para estabelecer critérios de seleção para bovinos de corte, considerando as características ganho médio diário do nascimento à desmama (GND), dias para o animal ganhar 160kg do nascimento à desmama (D160), ganho médio diário da desmama ao sobreano (D240) e dias para o animal ganhar 240kg da desmama ao sobreano (D240). As estimativas de herdabilidade foram: GND, 0,20; D160, 0,19; GDS, 0,07; e D240, 0,03. Considerando os efeitos maternos, a herdabilidade da característica D160 foi 0,16 e a da GND, 0,06. Verificou-se correlação genética alta e negativa entre GND e D160 (-0,95) e negativas entre efeito genético direto do GND e efeito genético materno da mesma característica (-0,24) e entre efeitos genéticos diretos do GND e do D160 (-0,15). Houve associação positiva entre o efeito genético materno de GND e direto de GDS (0,33), e correlação nula entre o efeito genético direto das características D160 e D240. Conclui-se que a velocidade de crescimento pode ser modificada adotando-se como critério de seleção qualquer uma das duas características do período pré-desmama, apesar deles não selecionarem os mesmos animais, principalmente se na adoção do critério forem considerados os efeitos maternos no período pré-desmama e os efeitos genéticos diretos no período pós-desmama. As magnitudes das correlações estimadas entre as características nos períodos pré e pós-desmama foram baixas, indicando que os animais poderiam ser selecionados no período pré-desmama, independente do critério de seleção adotado na pós-desmama.