Joslaine Noely dos Santos Gonçalves Cyrillo

Selection for feed efficiency traits and correlated genetic responses in feed intake and weight gain of Nellore cattle1

The objectives of this study were to estimate genetic parameters for indicator traits of feed efficiency and to recommend traits that would result in better responses to selection for increased weaning weight (weaning weight adjusted to 210 d of age [W210]), ADG, and metabolic BW (BW(0.75)) and lower DMI. Records of W210 from 8,004 Nellore animals born between 1978 and 2011 and postweaning performance test records from 678 males and females born between 2004 and 2011 were used. The following feed efficiency traits were evaluated: G:F, partial efficiency of growth (PEG), relative growth rate (RGR), Kleibers ratio (KR), residual feed intake (RFI), residual weight gain (RWG), and residual intake and gain (RIG). Covariance and variance components were estimated by the restricted maximum likelihood method using multitrait analysis under an animal model. Estimates of genetic gain and correlated responses were obtained considering single-stage and 2-stage selection. Heritability estimates were 0.22 ± 0.03 (W210), 0.60 ± 0.08 (DMI), 0.42 ± 0.08 (ADG), 0.56 ± 0.06 (BW(0.75)), 0.19 ± 0.07 (G:F), 0.25 ± 0.09 (PEG), 0.19 ± 0.07 (RGR), 0.22 ± 0.07 (KR), 0.33 ± 0.10 (RFI), 0.13 ± 0.07 (RWG), and 0.19 ± 0.08 (RIG). The genetic correlations of DMI with W210 (0.64 ± 0.10), ADG (0.87 ± 0.06), and BW(0.75) (0.84 ± 0.05) were high. The only efficiency traits showing favorable responses to selection for lower DMI were G:F, PEG, RFI, and RIG. However, the use of G:F, PEG, or RFI as a selection criterion results in unfavorable correlated responses in some growth traits. The linear combination of RFI and RWG through RIG is the best selection criterion to obtain favorable responses in postweaning growth and feed intake of Nellore cattle in single-stage selection. Genetic gains in feed efficiency are expected even after preselection for W210 and subsequent feed efficiency testing of the preselected animals.

Estimativas de tendências e parâmetros genéticos do peso padronizado aos 378 dias de idade, medidas corporais e perímetro escrotal de machos Nelore de Sertãozinho, SP

The objectives of this study were to estimate the genetic trends and also the genetic and phenotypic parameters for body weight at 378 days (W378), body measurements and scrotal circumferences of Nellore males from selected and control populations of the Estacao Experimental de Zootecnia de Sertaozinho (SP), Brazil. The heritability estimates, considering sire and animal model were, respectively, 0.53± 0.12 and 0.36 for W378 days; 0.38±0.11 and 0.58 for hip height; 0.31±0.10 and 0.10 for chest girth; 0.40± 0.11 and 0.13 for body length; 0.39± 0.11 and 0.30 for dorsal line length; 0.33± 0.10 and 0.12 for rump length; 0.08 ± 0.07 and 0.14 for distance between pin bones; 0.23± 0.09 and 0.08 for distance between hip bones and 0.57± 0.13 and 0.44 for scrotal circumference. The highest genetic correlation between W378 and body measurements was found for chest girth (0.86 ± 0.08), and the others ranged from 0.46 to 0.72. Based on the median to high heritability values found for the majority of traits, it is expected to exist a good amount of additive genetic variability controlling their variation. In addition, due to the highest correlation between W378 and most of the traits, it is probable that most part of the genes that control post-weaning weight might control the growth of different regions of animal body. The good values for the genetic correlation and heritability explain the positive genetic trends for direct and secondary traits in the selection for W378.

Efeitos da seleção para peso pós-desmame sobre medidas corporais e perímetro escrotal de machos Nelore de Sertãozinho (SP)

The objective of this study was to evaluate the indirect effects of selection for post-weaning weight on body measures and scrotal perimeter of 809 Nellore males from selected herds (NeS and NeT) and control herd (NeC), of the Estacao Experimental de Zootecnia de Sertaozinho. The statistical analyses were performed by using a sire mixed model where the random source of variation, sires, was nested within herds. The fixed effects were herds, year of performance test (PGP), age of cow and age of the animal as a covariate. The average genetic change for final weight, corrected for 378 days of age (W378), calculated as a deviation from the NeC herd, were 40.2 and 44.3 kg for the NeS and NeT herds, respectively. The correlated changes, for the other traits were, in the same order, 4.5 and 4.5 cm for hip height (HH); 6.2 and 7.0 cm for chest girth (CG); 5.8 and 6.3 cm for body length (BL); 2.9 and 2.0 cm for dorsal line length (DL); 1.7 and 2.4 cm for rump length (RL); 1.0 and 1.3 cm for distance between pin bones (DPB); 1.8 and 2.6 cm for distance between hip bones (DHP); and 1.3 and 2.2 cm for scrotal perimeter (SP). The results of this study showed that the direct selection for postweaning weight promoted correlated positive responses in the body dimensions and also in the scrotal perimeter of Nellore males.

Dias ao Parto de Fêmeas Nelore de um Experimento de Seleção para Crescimento: I - Modelo de Repetibilidade

Registros de datas de entrada na monta e respectiva data do parto, referentes a 1.247 femeas Nelore dos rebanhos experimentais da Estacao Experimental de Zootecnia de Sertaozinho (IZ - SP), selecionadas para altos (selecao e tradicional) e para medios (controle) pesos ao sobreano foram usados para obter a variavel dias ao parto, a fim de estudar o efeito da selecao para crescimento sobre o desempenho reprodutivo. Arquivos de novilhas e de vacas e novilhas foram analisados incluindo e nao incluindo as nao paridas. Nenhuma diferenca significativa foi detectada entre os registros provenientes das vacas dos rebanhos selecionados e do controle, apesar das vacas do rebanho selecao apresentarem as maiores medias de dias ao parto na maioria dos arquivos estudados. Concordando com os resultados obtidos para o efeito de rebanho, o peso a selecao foi significativo somente para as vacas e novilhas, considerando as nao paridas, com tendencia das mais pesadas a selecao apresentarem menores valores para dias ao parto. Modelos nos quais nao foi considerado o peso a selecao forneceram os mesmos resultados para o efeito de rebanho. As herdabilidades variaram de 0,02 a 0,16, sendo as mais altas obtidas em arquivos nos quais foram incluidos os registros das nao paridas, indicando que a observacao de caracteres de reproducao somente das femeas ferteis contribui para mascarar as diferencas geneticas entre os animais, e quando esta variabilidade e re-introduzida, designando-se penalidades as femeas que nao pariram, as diferencas geneticas entre os animais aparecem. Existem evidencias que a selecao para peso nao comprometeu o desempenho reprodutivo das femeas, mesmo sendo criadas em condicoes ambientais similares.

Efeitos de raça e da seleção para peso pós-desmame sobre características de confinamento e de carcaça da 15ª progênie dos rebanhos Zebu e Caracu de Sertãozinho (SP)

Quarenta e quatro machos inteiros provenientes de rebanhos selecionados para peso aos 378 dias (P378), nascidos em 1995, foram confinados na Estacao Experimental de Zootecnia de Sertaozinho, Estado de Sao Paulo. As amostras, representando a media geral de P378 em cada rebanho, foram formadas por oito animais Guzera (GuS) e nove para cada um dos grupos Gir (Gi), Nelore (NeS), Nelore Controle (NeC) e Caracu (Ca). O abate ocorreu aos 580 dias de idade e condicao corporal 8, em uma escala de 1 a 9. As medias minimas e maximas ajustadas, para as principais caracteristicas, envolvendo todos os grupos, foram: ganho medio diario de peso, 817 (NeC) e 1061 g (Ca); peso de abate (PAB), 408,3 (Gi) e 513,6 kg (Ca); peso de carcaca (PCAR), 230,2 (Gi) e 285,0 kg (Ca); rendimento de carcaca, 55,6 (GuS) e 58,1% (NeC). No corte entre a 9a-11a costelas, foram: musculo: 55,7 (NeC) e 64,7% (Ca); gordura: 18,6 (Ca) e 26,9% (NeC); osso: 16,7 (Ca) e 19,2% (Gi); espessura de gordura (ESPGOR): 6,4 (Ca) e 7,5 mm (GuS); area de olho de lombo: 62,8 (Gi) e 76,6 cm2 (Ca); forca de cizalhamento: 4,4 (Ca) e 5,4 kg (Gi) e perdas totais no cozimento: 23,4 (NeC) e 26,1% (Ca). Considerando o grupo Nelore, a selecao para peso provocou maiores PAB e PCAR, sem alterar o rendimento, a composicao fisica da costela ou a qualidade da carcaca e da carne. Animais Ca tiveram maior PAB, porem menor rendimento, maior musculosidade e menores niveis de gordura e espessura de gordura. Ja GuS, com rendimento semelhante ao Ca, apresentou maior ESPGOR. Nao se observaram diferencas entre os grupos geneticos quanto aos indices de maciez e perdas no cozimento da carne.

Parâmetros genéticos do peso no início da estação de monta, considerado indicativo do peso adulto de matrizes Nelore

Genetic parameters were estimated for weight at the beginning of breeding season (PEM), considered as an indicative of mature weight of Nelore cows. Data file comprised 7,902 records from 1,556 cows from to a selection experiment conducted at the Estacao Experimental de Zootecnia de Sertaozinho, SP, Brazil. PEM were analyzed either as the last weight available for each cow in the data file (PEM_U) or as repeated records, including all weights (PEM_R). The analyses were also performed excluding the records of cows culled before reaching 4 years of age, and for both the last (PEM_U2) and the repeated (PEM_R2) records. Variance components were estimated by restricted maximum likelihood, fitting single and multiple trait animal models. The multiple trait models included the selection weights adjusted for 378 (males only) and 550 (females only) days of age. Heritability estimates obtained from the single trait analyses were 0.30±0.05, 0.37±0.06, 0.35±0.04 and 0.42±0.05, for PEM_U, PEM_U2, PEM_R and PEM_R2, respectively. Corresponding values for the multiple trait analyses were 0.34, 0.42, 0.56, and 0.57. Repeatability estimates for PEM_R and PEM_R2 were 0.58±0.01 and 0.69±0.01 for the single, and 0.61 and 0.72 for the multiple trait analyses, respectively. Estimates of genetic changes were significantly positive and equal to 0.40±0.08 and 0.35±0.07 percent of the mean per year, for the two selected lines in the experiment. The results obtained in the present study indicated the multiple trait repeated records models as the most appropriate for analyzing the PEM as an indicative of mature weight. The PEM could be included in a selection program aiming at monitoring a desirable mature weight.

Dias ao Parto de Fêmeas Nelore de um Experimento de Seleção para Crescimento: II - Modelo de Regressão Aleatória

Os parâmetros geneticos para dias ao parto foram estimados usando um modelo de regressao aleatoria, com polinomios ortogonais da idade na monta (em anos) como covariavel. Os registros de dias ao parto (4.118) foram provenientes de 926 vacas de tres rebanhos Nelore experimentais, sendo os rebanhos selecao e tradicional selecionados para maior peso ao sobreano, e o rebanho controle selecionado para a media do peso ao sobreano. As variâncias genetica aditiva e permanente de ambiente foram descritas por uma funcao polinomial de ordem 4, com nove medidas de erro, resultando em variâncias fenotipica e genetica aditiva altas nas idades mais avancadas, principalmente apos a 6a monta. As herdabilidades estimadas aumentaram de 0,08 a 0,28 da 1a a 6a monta. As correlacoes geneticas foram medias entre o primeiro desempenho e os demais (0,32 a 0,66), altas entre os desempenhos adjacentes (0,98 a 0,99), e um pouco menores entre os nao adjacentes (0,63 a 0,98). A selecao para peso nao alterou o valor genetico medio das vacas dos rebanhos selecionados, entretanto, os valores geneticos medios das vacas do rebanho controle mostraram tendencia de queda no decorrer dos anos.

Phenotypic and Genetic Correlations of Feed Efficiency Traits with Growth and Carcass Traits in Nellore Cattle Selected for Postweaning Weight.

This study evaluated phenotypic (rph) and genetic correlations (rg) between 8 feed efficiency traits and other traits of economic interest including weight at selection (WS), loin-eye area (LEA), backfat thickness (BF), and rump fat thickness (RF) in Nellore cattle. Feed efficiency traits were gain:feed, residual feed intake (RFI), residual feed intake adjusted for backfat thickness (RFIb) and for backfat and rump fat thickness (RFIsf), residual body weight gain (RG), residual intake and body weight gain (RIG), and residual intake and body weight gain using RFIb (RIGb) and RFIsf (RIGsf). The variance components were estimated by the restricted maximum likelihood method using a two-trait animal model. The heritability estimates (h2) were 0.14, 0.24, 0.20, 0.22, 0.19, 0.15, 0.11 and 0.11 for gain:feed, RFI, RFIb, RFIsf, RG, RIG, RIGb and RIGsf, respectively. All rph values between traits were close to zero, except for the correlation of feed efficiency traits with dry matter intake and average daily gain. High rg values were observed for the correlation of dry matter intake, average daily gain and metabolic weight with WS and hip height (>0.61) and low to medium values (0.15 to 0.48) with the carcass traits (LEA, BF, RF). Among the feed efficiency traits, RG showed the highest rg with WS and hip height (0.34 and 0.25) and the lowest rg with subcutaneous fat thickness (-0.17 to 0.18). The rg values of RFI, RFIb and RFIsf with WS (0.17, 0.23 and 0.22), BF (0.37, 0.33 and 0.33) and RF (0.30, 0.31 and 0.32) were unfavorable. The rg values of gain:feed, RIG, RIGb and RIGsf with WS were low and favorable (0.07 to 0.22), while medium and unfavorable (-0.22 to -0.45) correlations were observed with fat thickness. The inclusion of subcutaneous fat thickness in the models used to calculate RFI did not reduce the rg between these traits. Selecting animals for higher feed efficiency will result in little or no genetic change in growth and will decrease subcutaneous fat thickness in the carcass.

Genome-Wide Association Study for Carcass Traits in an Experimental Nelore Cattle Population

The purpose of this study was to identify genomic regions associated with carcass traits in an experimental Nelore cattle population. The studied data set contained 2,306 ultrasound records for longissimus muscle area (LMA), 1,832 for backfat thickness (BF), and 1,830 for rump fat thickness (RF). A high-density SNP panel (BovineHD BeadChip assay 700k, Illumina Inc., San Diego, CA) was used for genotyping. After genomic data quality control, 437,197 SNPs from 761 animals were available, of which 721 had phenotypes for LMA, 669 for BF, and 718 for RF. The SNP solutions were estimated using a single-step genomic BLUP approach (ssGWAS), which calculated the variance for windows of 50 consecutive SNPs and the regions that accounted for more than 0.5% of the additive genetic variance were used to search for candidate genes. The results indicated that 12, 18, and 15 different windows were associated to LMA, BF, and RF, respectively. Confirming the polygenic nature of the studied traits, 43, 65, and 53 genes were found in those associated windows, respectively for LMA, BF, and RF. Among the candidate genes, some of them, which already had their functions associated with the expression of energy metabolism, were found associated with fat deposition in this study. In addition, ALKBH3 and HSD17B12 genes, which are related in fibroblast death and metabolism of steroids, were found associated with LMA. The results presented here should help to better understand the genetic and physiologic mechanism regulating the muscle tissue deposition and subcutaneous fat cover expression of Zebu animals. The identification of candidate genes should contribute for Zebu breeding programs in order to consider carcass traits as selection criteria in their genetic evaluation.

Genomic Regions Associated with Feed Efficiency Indicator Traits in an Experimental Nellore Cattle Population

The objective of this study was to identify genomic regions and metabolic pathways associated with dry matter intake, average daily gain, feed efficiency and residual feed intake in an experimental Nellore cattle population. The high-density SNP chip (Illumina High-Density Bovine BeadChip, 777k) was used to genotype the animals. The SNP markers effects and their variances were estimated using the single-step genome wide association method. The (co)variance components were estimated by Bayesian inference. The chromosome segments that are responsible for more than 1.0% of additive genetic variance were selected to explore and determine possible quantitative trait loci. The bovine genome Map Viewer was used to identify genes. In total, 51 genomic regions were identified for all analyzed traits. The heritability estimated for feed efficiency was low magnitude (0.13±0.06). For average daily gain, dry matter intake and residual feed intake, heritability was moderate to high (0.43±0.05; 0.47±0.05, 0.18±0.05, respectively). A total of 8, 17, 14 and 12 windows that are responsible for more than 1% of the additive genetic variance for dry matter intake, average daily gain, feed efficiency and residual feed intake, respectively, were identified. Candidate genes GOLIM4, RFX6, CACNG7, CACNG6, CAPN8, CAPN2, AKT2, GPRC6A, and GPR45 were associated with feed efficiency traits. It was expected that the response to selection would be higher for residual feed intake than for feed efficiency. Genomic regions harboring possible QTL for feed efficiency indicator traits were identified. Candidate genes identified are involved in energy use, metabolism protein, ion transport, transmembrane transport, the olfactory system, the immune system, secretion and cellular activity. The identification of these regions and their respective candidate genes should contribute to the formation of a genetic basis in Nellore cattle for feed efficiency indicator traits, and these results would support the selection for these traits.