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O objetivo deste trabalho foi estimar os coeficientes de herdabilidade da idade ao primeiro parto, dias para o parto (DPP), duração da gestação (DG) e perímetro escrotal (PE) bem como a correlação genética entre perímetro escrotal e estas características reprodutivas medidas nas fêmeas, na raça Nelore. A idade ao primeiro parto foi avaliada em fêmeas expostas pela primeira vez ao touro em torno de 14 meses de idade (IPP14), e em fêmeas expostas ao touro em torno de 26 meses (IPP26). Foram analisados conjuntos de dados que variaram de 6.030 a 94.637 observações. As análises foram processadas utilizandose modelos animais bi-característica. Os coeficientes de herdabilidade obtidos em relação às características reprodutivas foram: 0,19 (IPP14), 0,02 (IPP26), 0,07 (DPP), 0,26 (DG), e 0,47 (PE). As correlações genéticas obtidas foram: -0,39 (PE e IPP14), -0,19 (PE e IPP26), 0,02 (PE e DPP) e 0,02 (PE e DG). Concluiu-se que a idade ao primeiro parto pode ser utilizada como critério de seleção para precocidade sexual, e que a seleção de touros com base no mérito genético para PE pode resultar na diminuição da idade ao primeiro parto de suas filhas. A baixa herdabilidade obtida quanto aos DPP, associada com a sua baixa correlação com PE, sugerem a necessidade do estudo de outras características que possam avaliar diretamente a fertilidade da fêmea.

Estimating genetic parameters of male and female fertility and reproduction traits is essential for optimizing beef cattle breeding programs. In general, only markers located on autosomal chromosomes are used for genetic evaluations. Sex chromosomes tend to be excluded due to the compensation mechanism of dosage of genes linked to the X chromosome, which is the second largest chromosome in the cattle genome and harbors many genes potentially influencing these traits. Therefore, we estimated genomic-based variance components, including the X chromosome in the variance components analysis for female precocity, fertility, and andrological traits based on the single-step GBLUP procedure and Bayesian inference. The dataset consisted of ~120,000 records for the probability of pregnancy at 14 months (PP14), early rebreeding (REBA), and stability (STAY). From the breeding soundness exam (BSE) of bulls, 20,000 records were obtained for semen quality, andrological biometry, semen defects, and bull fitness (BULL_FIT). The pedigree contained 660,608 animals, where 11,012 animals were genotyped for 770,111 SNPs. All traits have reasonable additive genetic variation and are heritable, with a substantial contribution from the X chromosome, indicating that genetic progress for these traits is feasible. The heritability estimates (h2) explained by autosomal and X chromosome SNPs was low and low-to-moderate, respectively, for female reproductive performance traits, such as REBA [0.17 (auto); 0.07 (sex chr)], PP14 (0.42;0.05), and STAY (0.32;0.01). For male traits, the heritability estimates based on the autosomes and X chromosome, respectively, ranged from 0.02 to 0.04 and from 0.01 to 0.03 for semen quality traits; from 0.10 to 0.68 and from 0.02 to 0.07 for morphological traits; from 0.10 to 0.12 and from 0.01 to 0.02 for semen defects traits; for bull evaluation (BULL_FIT) were observed h2 for autosomes 0.18 and 0.10 for sexual chromosome X. The results observed in this study indicate a substantial contribution of the X chromosome on fertility and reproductive performance traits. These findings will serve as background information for designing breeding programs for genetically improving semen production and quality and reproductive performance in Nellore cattle. [ABSTRACT FROM AUTHOR]

The Montana Tropical® Composite is a recently developed beef cattle population that is rapidly expanding in Brazil and other tropical countries. This is mainly due to its improved meat quality and adaptation to tropical climate conditions compared to Zebu and Taurine cattle breeds, respectively. This study aimed to investigate the genetic architecture of ultrasound-based carcass and meat quality traits in Montana Tropical® Composite beef cattle. Therefore, we estimated variance components and genetic parameters and performed genome-wide association studies using the weighted single-step Genomic Best Linear Unbiased Prediction (GBLUP) approach. A pedigree dataset containing 28,480 animals was used, in which 1,436 were genotyped using a moderate-density Single Nucleotide Polymorphism panel (30K; 30,105 SNPs). A total of 9,358, 5,768, 7,996, and 1,972 phenotypic records for the traits Longissimus muscle area (LMA), backfat thickness (BFT), rump fat thickness (RFT), and for marbling score (MARB), respectively, were used for the analyses. Moderate to high heritability estimates were obtained and ranged from 0.16 ± 0.03 (RFT) to 0.33 ± 0.05 (MARB). A high genetic correlation was observed between BFT and RFT (0.97 ± 0.02), suggesting that a similar set of genes affects both traits. The most relevant genomic regions associated with LMA, BFT, RFT, and MARB were found on BTA10 (5.4–5.8 Mb), BTA27 (25.2–25.5 Mb), BTA18 (60.6–61.0 Mb), and BTA21 (14.8–15.4 Mb). Two overlapping genomic regions were identified for RFT and MARB (BTA13:47.9–48.1 Mb) and for BFT and RFT (BTA13:61.5–62.3 Mb). Candidate genes identified in this study, including PLAG1 , LYN, WWOX , and PLAGL2 , were previously reported to be associated with growth, stature, skeletal muscle growth, fat thickness, and fatty acid composition. Our results indicate that ultrasound-based carcass and meat quality traits in the Montana Tropical® Composite beef cattle are heritable, and therefore, can be improved through selective breeding. In addition, various novel and already known genomic regions related to these traits were identified, which contribute to a better understanding of the underlying genetic background of LMA, BFT, RFT, and MARB in the Montana Tropical Composite population. [ABSTRACT FROM AUTHOR]

The aim of this study was to estimate genetic parameters and identify genomic regions associated with carcass traits obtained by ultrasound and visual scores in Nellore cattle. Data from ~66,000 animals from the National Association of Breeders and Researchers (ANCP) were used. The variance components for backfat thickness, rump fat thickness and Longissimus muscle area (LMA) were estimated considering a linear model whereas a threshold model for body structure (BS), finishing precocity (FP) and musculature (MS) traits. The SNP solutions were estimated using the ssGBLUP approach by considering windows of 10 consecutive SNPs. Regions that accounted for more than 1.0% of the additive genetic variance were used. Genes identified within the significant windows, such as FOXA3, AP2S1, FKRP, NPASI and ATP6V1G1, were found to be related with MS, while OMA1 and FFGY with BS and FP traits. The PLTP, TNNC2 and GPAT2 genes were found in the regions associated with LMA, as well as TKT, FNDC5 and CHRND can strongly be related with fat deposition. Gene enrichment analysis revealed processes that might be directly influenced the organism growth and development. These results should help to better understand the genetic and physiological mechanisms regulating growth and body composition, muscle tissue development and subcutaneous fat expression, and this information might be useful for future genomic studies in Nellore cattle. [ABSTRACT FROM AUTHOR]

The objective of the present study was to investigate the impact of considering population structure in cow genotyping strategies over the accuracy and bias of genomic predictions. A small dairy cattle population was simulated to address these objectives. Based on four main traditional designs (random, top‐yield, extreme‐yield and top‐accuracy cows), different numbers (1,000; 2,000 and 5,000) of cows were sampled and included in the reference population. Traditional designs were replicated considering or not population structure and compared among and with a reference population containing only bulls. The inclusion of cows increased accuracy in all scenarios compared with using only bulls. Scenarios accounting for population structure when choosing cows to the reference population slightly outperformed their traditional versions by yielding higher accuracy and lower bias in genomic predictions. Building a cow‐based reference population from groups of related individuals considering the frequency of individuals from those same groups in the validation population yielded promising results with applications on selection for expensive‐ or difficult‐to‐measure traits. Methods here presented may be easily implemented in both new or already established breeding programs, as they improved prediction and reduced bias in genomic evaluations while demanding no additional costs. [ABSTRACT FROM AUTHOR]

The Montana Tropical ® Composite is a recently developed beef cattle population that is rapidly expanding in Brazil and other tropical countries. This is mainly due to its improved meat quality and adaptation to tropical climate conditions compared to Zebu and Taurine cattle breeds, respectively. This study aimed to investigate the genetic architecture of ultrasound-based carcass and meat quality traits in Montana Tropical ® Composite beef cattle. Therefore, we estimated variance components and genetic parameters and performed genome-wide association studies using the weighted single-step Genomic Best Linear Unbiased Prediction (GBLUP) approach. A pedigree dataset containing 28,480 animals was used, in which 1,436 were genotyped using a moderate-density Single Nucleotide Polymorphism panel (30K; 30,105 SNPs). A total of 9,358, 5,768, 7,996, and 1,972 phenotypic records for the traits Longissimus muscle area (LMA), backfat thickness (BFT), rump fat thickness (RFT), and for marbling score (MARB), respectively, were used for the analyses. Moderate to high heritability estimates were obtained and ranged from 0.16 ± 0.03 (RFT) to 0.33 ± 0.05 (MARB). A high genetic correlation was observed between BFT and RFT (0.97 ± 0.02), suggesting that a similar set of genes affects both traits. The most relevant genomic regions associated with LMA, BFT, RFT, and MARB were found on BTA10 (5.4-5.8 Mb), BTA27 (25.2-25.5 Mb), BTA18 (60.6-61.0 Mb), and BTA21 (14.8-15.4 Mb). Two overlapping genomic regions were identified for RFT and MARB (BTA13:47.9-48.1 Mb) and for BFT and RFT (BTA13:61.5-62.3 Mb). Candidate genes identified in this study, including PLAG1 , LYN, WWOX , and PLAGL2 , were previously reported to be associated with growth, stature, skeletal muscle growth, fat thickness, and fatty acid composition. Our results indicate that ultrasound-based carcass and meat quality traits in the Montana Tropical ® Composite beef cattle are heritable, and therefore, can be improved through selective breeding. In addition, various novel and already known genomic regions related to these traits were identified, which contribute to a better understanding of the underlying genetic background of LMA, BFT, RFT, and MARB in the Montana Tropical Composite population., (Copyright © 2020 Grigoletto, Ferraz, Oliveira, Eler, Bussiman, Abreu Silva, Baldi and Brito.)