ABSTRACT This study was conducted to evaluate the relationship among digestibility, residual feed intake (RFI), and enteric methane emission in growing Nellore cattle (Bos indicus) divergently classified based on RFI phenotype and breeding value (EBV-RFI). Animals (n = 122) subjected to performance testing (forage:concentrate ratio of 60:40) in two test groups were classified based on RFI. A sample of 80 animals classified as low (−0.748±0.076 kg DM/day) or high (0.775±0.075 kg DM/day) RFI was evaluated regarding feed compounds digestibility, fecal excretion, and methane emission (CH4, g/day). Statistical mixed models included fixed effects of RFI (or EBV-RFI), linear effect of initial age as covariate, and the random effects of the test group. There was no difference in the digestibility of feed compounds between the most and least efficient animals. However, dry matter intake (DMI; 6.92 vs. 8.66 kg DM/day) and feed conversion (7.93 vs. 9.42 kg/kg) were lesser in low RFI animals. On average, low RFI animals emitted 14.3 g less CH4 per day (174 vs. 188 g CH4/day); however, CH4 emission expressed as g/kg DMI (23.1 vs. 20.1) and the percentage of gross energy intake lost as CH4 (8.13 vs. 7.08%) were greater for these animals. These results showed the benefits of using more feed efficient animals in the beef production chain, i.e., animals that exhibit lower feed intake, lower fecal excretion, and lower enteric methane emission without differences in weight gain or body weight. However, the variations in feed efficiency among them cannot be explained by differences in dry matter or feed compounds digestibility. More efficient animals emit less enteric methane than less efficient animals, probably as a result of lower DMI. RFI, , (RFI) Bos indicus EBVRFI. EBVRFI EBV . (EBV-RFI) n 122 forageconcentrate forage concentrate 6040 60 40 60:40 8 −0.748±0.076 07480076 0 748 076 (−0.748±0.07 DM/day DMday DM 0.775±0.075 07750075 775 075 (0.775±0.07 excretion CH4, CH (CH4 g/day. gday g/day g/day) EBVRFI, EBV-RFI) covariate group However (DMI 692 6 92 6.9 vs 866 66 8.6 7.93 793 7 93 (7.9 942 9 42 9.4 kg/kg kgkg average 143 14 3 14. 174 (17 18 CH4/day CH4day CHday CH4/day) however gkg 23.1 231 23 1 (23. 20.1 201 20 8.13 813 13 (8.1 7.08% 708 08 chain ie i e i.e. (RFI (EBV-RFI 12 604 4 60:4 −0.748±0.07 0748007 74 07 (−0.748±0.0 0.775±0.07 0775007 77 (0.775±0.0 (CH EBV-RFI 69 6. 86 8. 7.9 79 (7. 94 9. 17 (1 23. 2 (23 20. 8.1 81 (8. 7.08 70 i.e 60: −0.748±0.0 074800 (−0.748±0. 0.775±0.0 077500 (0.775±0. 7. (7 ( (2 (8 7.0 −0.748±0. 07480 (−0.748±0 0.775±0. 07750 (0.775±0 −0.748±0 0748 (−0.748± 0.775±0 0775 (0.775± −0.748± 074 (−0.748 0.775± 077 (0.775 −0.748 (−0.74 0.775 (0.77 −0.74 (−0.7 0.77 (0.7 −0.7 (−0. 0.7 (0. −0. (−0 0. (0 −0 (− −

ABSTRACT The objective of this study was to evaluate characteristics of the testicular parenchyma and vascular parameters of the pampiniform plexus obtained by ultrasound, semen quality parameters, and sperm freezability in Nellore bulls classified based on residual feed intake (RFI). Twenty-seven bulls (21.82±0.88 months of age) evaluated for feed efficiency were sampled for the study, including 15 with low RFI (−0.592±0.09 kg dry matter/day) and 12 with high RFI (0.792±0.10 kg dry matter/day). In ultrasound and Doppler assessment, the most efficient animals (low RFI) showed higher pulsatility and resistive indexes, as well as a tendency towards greater heterogeneity of the testicular parenchyma (0.625±0.032 vs. 0.508±0.032, 1.012±0.072 vs. 0.802±0.072, and 12.9±0.96 vs. 10.2±0.96, respectively, for low vs. high RFI). However, these animals tended to have lower peak diastolic velocity (5.19±0.50 for low RFI vs. 6.54±0.50 for high RFI). Analysis of fresh semen showed a lower percentage of minor defects in low RFI animals (2.67±1.19%) compared with high RFI animals (8.10±1.19%), without differences in the other parameters in fresh or thawed semen and after thermoresistance testing. Evaluation of flow cytometry parameters showed a higher quality of mitochondrial respiration in semen samples of low RFI animals (22.04±2.50%) compared with high RFI animals (12.29±2.71%). Therefore, although RFI exerts an effect on the Doppler parameters of the pampiniform plexus, it is not sufficient to affect the quality of fresh or thawed semen. RFI. . (RFI) Twentyseven Twenty seven 21.82±0.88 2182088 21 82 0 88 (21.82±0.8 age 1 −0.592±0.09 0592009 592 09 (−0.592±0.0 matter/day matterday matter day 0.792±0.10 0792010 792 10 (0.792±0.1 matter/day. assessment indexes 0.625±0.032 06250032 625 032 (0.625±0.03 vs 05080032 508 0.508±0.032 10120072 012 072 1.012±0.07 08020072 802 0.802±0.072 129096 9 96 12.9±0.9 102096 2 10.2±0.96 respectively However 5.19±0.50 519050 5 19 50 (5.19±0.5 654050 6 54 6.54±0.5 2.67±1.19% 267119 67 (2.67±1.19% 8.10±1.19%, 810119 8.10±1.19% , 8 (8.10±1.19%) testing 22.04±2.50% 2204250 22 04 (22.04±2.50% 12.29±2.71%. 1229271 12.29±2.71% 29 71 (12.29±2.71%) Therefore (RFI 21.82±0.8 218208 (21.82±0. −0.592±0.0 059200 59 (−0.592±0. 0.792±0.1 079201 79 (0.792±0. 0.625±0.03 0625003 62 03 (0.625±0.0 0508003 0.508±0.03 1012007 01 07 1.012±0.0 0802007 80 0.802±0.07 12909 12.9±0. 10209 10.2±0.9 5.19±0.5 51905 (5.19±0. 65405 6.54±0. 2.67±1.19 26711 (2.67±1.19 81011 8.10±1.19 (8.10±1.19% 22.04±2.50 220425 (22.04±2.50 122927 12.29±2.71 7 (12.29±2.71% 21.82±0. 21820 (21.82±0 −0.592±0. 05920 (−0.592±0 0.792±0. 07920 (0.792±0 0.625±0.0 062500 (0.625±0. 050800 0.508±0.0 101200 1.012±0. 080200 0.802±0.0 1290 12.9±0 1020 10.2±0. 5.19±0. 5190 (5.19±0 6540 6.54±0 2.67±1.1 2671 (2.67±1.1 8101 8.10±1.1 (8.10±1.19 22.04±2.5 22042 (22.04±2.5 12292 12.29±2.7 (12.29±2.71 21.82±0 2182 (21.82± −0.592±0 0592 (−0.592± 0.792±0 0792 (0.792± 0.625±0. 06250 (0.625±0 05080 0.508±0. 10120 1.012±0 08020 0.802±0. 129 12.9± 102 10.2±0 5.19±0 519 (5.19± 654 6.54± 2.67±1. 267 (2.67±1. 810 8.10±1. (8.10±1.1 22.04±2. 2204 (22.04±2. 1229 12.29±2. (12.29±2.7 21.82± 218 (21.82 −0.592± 059 (−0.592 0.792± 079 (0.792 0.625±0 0625 (0.625± 0508 0.508±0 1012 1.012± 0802 0.802±0 12.9 10.2± 5.19± 51 (5.19 65 6.54 2.67±1 26 (2.67±1 81 8.10±1 (8.10±1. 22.04±2 220 (22.04±2 122 12.29±2 (12.29±2. 21.82 (21.8 −0.592 05 (−0.59 0.792 (0.79 0.625± 062 (0.625 050 0.508± 101 1.012 080 0.802± 12. 10.2 5.19 (5.1 6.5 2.67± (2.67± 8.10± (8.10±1 22.04± (22.04± 12.29± (12.29±2 21.8 (21. −0.59 (−0.5 0.79 (0.7 0.625 06 (0.62 0.508 1.01 08 0.802 10. 5.1 (5. 6. 2.67 (2.67 8.10 (8.10± 22.04 (22.04 12.29 (12.29± 21. (21 −0.5 (−0. 0.7 (0. 0.62 (0.6 0.50 1.0 0.80 5. (5 2.6 (2.6 8.1 (8.10 22.0 (22.0 12.2 (12.29 (2 −0. (−0 0. (0 0.6 0.5 1. 0.8 ( 2. (2. 8. (8.1 22. (22. (12.2 −0 (− (8. (22 (12. − (8 (12 (1

ABSTRACT The objective of this study was to develop accurate regression equations to predict body composition of Nellore cattle using chemical composition of the 9th, 10th, and 11th ribs and to evaluate the models proposed by analyzing mean and linear bias. Sixty-seven Nellore bulls were slaughtered and slaughter body weight (SBW), hot carcass weight (HCW), and 9th-, 10th-, and 11th-rib-cut weight (RCW) were measured. Empty body composition was obtained after grinding, homogenizing, sampling, chemical analysis, and pooling (blood, skin, head + feet, viscera, and carcass). Chemical components were determined in rib cut, carcass, and empty body: protein (RCP, HCP, and EBP), fat (RCF, HCF, and EBF), ash (RCA, HCA, and EBA), and water (RCWt, HCWt, and EBWt). Stepwise options were used to determine variables to be included and excluded from regressions. Predictive ability of equations was verified using standard error of prediction, coefficient of determination, and Cp statistic. Regression estimates were tested to evaluate the models in a database different from that used for equation development. The best equations found to predict carcass components, in kg, were: HCF = -0.994 + 0.123 × SBW - 9.201 × RCW + 34.249 × RCF (R² = 0.86) and HCWt = 2.733 - 0.172 × SBW + 0.821 × HCW - 23.939 × RCF + 12.186 × RCWt (R² = 0.96). For empty body, the best equations, in kg, were: EBF = -1.4 + 0.166 × SBW - 10.073 × RCW + 40.202 × RCF (R² = 0.90) and EBWt = 3.524 + 0.272 × SBW + 0.373 × HCW - 11.727 × RCW + 31.079 × RCWt (R² = 0.98). Body weight has a high predictive power and should be included in equations to estimate body composition of Nellore cattle. Unbiased models are valid as an indirect method for determining body composition in beef cattle.

Feed intake and average daily gain (ADG) in Nellore cattle were determined to calculate residual feed intake in two performance tests: first during the growth phase (RFIgrowth) and then during a measurement of the methane emission phase (RFImet). During the RFIgrowth test, 62 males and 56 females were classified as low-, medium-, and high-RFI. Enteric methane emission was measured in 46 animals; 23 males used for RFImet measurement plus 23 females (22 low-RFIgrowth and 24 high-RFIgrowth). Diet consisted of Brachiaria brizantha cv. Marandu hay (445 g/kg DM) and concentrate (555 g/kg DM). During the RFIgrowth and RFImet phases, DMI was lower in the animals with low RFI, with no difference in ADG. Residual feed intake was -0.359 and 0.367 kg DM/d for low- and high-RFI animals. Enteric methane emission (g/d, g/kg BW0.75 and g/kg ADG) did not differ between RFIgrowth classes. Enteric methane emission (g/d) was higher in high RFImet and lower in low RFImet males. Spearman correlations among traits obtained during both tests, which were high between metabolic BW (r = 0.959) and between DMI (r = 0.718), and zero between ADG (r = -0.062), resulted in moderate correlation between RFIgrowth and RFImet (r = 0.412). However, it is not possible to confirm that high-efficiency animals release less enteric methane, since different results were obtained when enteric methane was compared between the RFIgrowth and RFImet classes.

Empty body and carcass chemical composition were determined in 67 Nellore bulls from Selection Nellore (NeS) and Control Nellore (NeC) herds of an animal breeding program for growth, slaughtered at 570 days of average age, after 100 days of feedlot. Selection Nellore animals had, respectively, 360 and 430 kg of initial and slaughter body weight, and NeC animals had 318 and 373 kg for the same traits. Animals were slaughtered and empty body composition was determined by chemical analysis of the components blood, hide, head and feet, viscera and carcass. Tissue deposition rates and gain chemical composition were also determined based on gains estimated by comparative slaughter technique. Significant differences were detected between NeS and NeC animals for slaughter body weight, empty body weight, empty body gain rate, and contents of water, protein, ash and retained energy in empty body, showing that selected animals had greater body sizes and growth rates. There were no significant differences in fat contents in empty body and carcass, suggesting that selected animals had higher growth rates as compared with the control, and were slaughtered with good body and carcass fat contents in the same feedlot time. Control Nellore animals showed a 10% higher gain in fat percentage than NeS in the period. This shows that the growth of bone and muscle ceased earlier and NeC group accumulated more fat. Animals selected for growth have heavier carcasses and greater tissue deposition rates with proportional composition similar to unselected animals.

The objective of this study was to evaluate the correlated responses to selection for growth in feed efficiency and carcass traits of Nellore animals. A total of 121 animals of the Nellore control (NeC) and selection herds were subjected to performance testing and classified regarding residual feed intake (RFI). Sixty-seven of these animals were selected and finished until reaching 4 mm of subcutaneous fat thickness between the 12th and 13th ribs. The animals were slaughtered at a mean age of 541 days and mean live weight of 423 kg for NeS and of 363 kg for NeC, and carcass traits were measured. Animals in NeS presented higher initial and slaughter weights, dry matter intake, hot and cold carcass weight, weight of retail cuts, and carcass yield than NeC animals for the same slaughter age and feedlot time. No significant differences in RFI were observed between herds, showing that the weight gain from selection for growth did not cause changes in the energy efficiency of the animals.

The objectives of this study were to estimate heritabilities and genetic and phenotypic correlations between carcass traits measured by ultrasound and other economically important traits generally used as selection criteria in beef cattle and to estimate the genetic changes in the carcass traits as a result of selection for post-yearling weight. Carcass traits measured by ultrasound at two ages (12 and 18 months) and the correlation of these traits with weight, hip height and body condition score of males (yearling) and females (post-yearling) were analyzed. Multi-trait analysis was performed using the restricted maximum likelihood method under an animal model. To demonstrate the effect of selection for growth, phenotypic and expected breeding value means of the carcass traits and weights according to selection line (Nellore control line, selection line and traditional line) were estimated using records from animals born in the last 3 years (2006 to 2008). The heritability estimates were high for longissimus muscle area (LMA) at 12 and 18 months of age (0.47 and 0.40, respectively). For fat thickness measures, heritabilities ranged from 0.37 to 0.29. Genetic correlations of the same trait between the two ages were high for LMA (0.95). The Nellore breed shows medium to high genetic variability in carcass traits measured by ultrasound at 12 and 18 months of age, and a greater response is expected if selection for backfat thickness is performed at about 12 months of age. Selection for higher body weight will lead to an increase of LMA at the two ages without reducing subcutaneous fat thickness.

O objetivo neste estudo foi determinar o melhor período de avaliação para medidas de desempenho, consumo e eficiência alimentar. Durante 112 dias, 60 machos da raça Nelore, recém-desmamados, submetidos à prova de ganho de peso, foram alimentados em baias individuais para determinação do consumo alimentar e do desempenho. O peso corporal dos animais foi determinado a cada 28 dias, depois de jejum de 16 horas de líquidos e sólidos. As alterações na variância, variância relativa e correlações de Pearson e Spearman entre os dados dos períodos de avaliação reduzidos (28, 56 e 84 dias) e período total (112 dias) foram usados para determinar a melhor duração do período de avaliação. A duração do período de avaliação para ganho médio diário, consumo de matéria seca, conversão alimentar e consumo alimentar residual pode ser reduzida para 84, 28, 84 e 84 dias, respectivamente, pois tal redução não diminui significativamente a confiabilidade das avaliações em animais alimentados em baias individuais.

This study was conducted to determine optimum test duration for measuring performance, feed intake and feed efficiency. Sixty young Nellore bulls were submitted to feeding performance test and fed in individual pens to determine feed intake and performance over 112 days. Body weight was determined every 28 days, after fasting of water and feed for 16 hours. Changes in variance, relative variance and Pearson and Spearman correlations among data from shortened test periods (28, 56 and 84 days) and full test period (112 days) were used to determine optimum test duration. Test duration for average daily gain, dry matter intake, feed:gain ratio and residual feed intake could be shortened to 84, 28, 84 and 84 days, respectively, without reducing significantly the reliability of measurements for animals fed in individual pens.

Foram comparados dois rebanhos Nelore, um selecionado para maior peso pós-desmame e outro controle, selecionado para a média de peso pós-desmame, para avaliar os efeitos de 29 anos de seleção sobre a eficiência alimentar. Sessenta machos Nelore com 205 kg e 267 dias de idade (41 selecionados e 19 controle), foram avaliados em baias individuais durante a prova de ganho de peso. O desempenho e o consumo de matéria seca foram utilizados para determinar as seguintes medidas de eficiência: conversão alimentar; consumo alimentar residual; ganho residual; eficiência parcial de crescimento; taxa de crescimento relativo; e taxa de Kleiber. Após o período experimental de 112 dias, os animais controle apresentaram menor peso vivo final em comparação aos selecionados, contudo, não diferiram quanto ao consumo de matéria seca (% do peso vivo), à área de olho-de-lombo e às espessuras de gordura subcutânea na altura da 12ª costela e na região da picanha. O consumo de matéria seca (kg/dia) e o ganho médio diário dos animais selecionados foram, respectivamente, 19,4 e 26,4% superiores aos dos controle. O maior ganho médio diário dos animais selecionados promoveu melhora significativa, em torno de 6%, na conversão alimentar; 70 g/dia no ganho residual; e de 17% na taxa de Kleiber. As demais medidas de eficiência (consumo alimentar residual, eficiência parcial de crescimento e taxa de crescimento relativo) não diferiram entre os rebanhos. Os 29 anos de seleção para peso pós-desmame não afetaram a eficiência alimentar de bovinos Nelore.

Two Nellore herds were compared, one selected for greater postweaning weight and the other, control, selected for average postweaning weight, to evaluate the effects of 29 years of selection on feed efficiency. Sixty Nellore males (41 selected and 19 control) averaging 205 kg and 267 days of age were evaluated in individual pens during performance test. Performance and dry matter intake were used to determine the following feed efficiency traits: feed conversion; residual feed intake; residual gain; partial growth efficiency; relative growth rate and Kleiber ratio. After the 112-day experimental period, control animals showed lower body weight when compared to selected animals, however, they did not differ for dry matter intake (% of body weight), rib-eye area and fat thickness at the 12th rib subcutaneous region and on the rump region. Dry matter intake (kg/day) and average daily weight gain from selected animals were, respectively, 19.4% and 26.4% higher than the control ones. The highest average daily weight gain by selected animals promoted significant improvement, around 6%, on feed conversion; 70 g/day on residual gain; and 17% on Kleiber rate. The other feed efficiency traits (residual feed intake, partial growth efficiency and relative growth rate) did not differ between herds. The 29-year selection for post-weaning weight did not affect feed efficiency of Nellore cattle.

Foram desenvolvidas equações para estimar a composição química corporal de bovinos de três grupos genéticos (Caracu, CaS; Nelore seleção, NeS; e Nelore controle, NeC) a partir das composições química e física do corte da 9ª-10ª-11ª costelas. Utilizaram-se 56 machos não-castrados (20 CaS, 20 NeS e 16 NeC) abatidos aos 20-24 meses de idade. A composição química em água, proteína, extrato etéreo e minerais foi determinada no corte das costelas e em amostras obtidas após moagem completa e homogeneização de todos os tecidos corporais, separados em sangue, couro, cabeça + patas, vísceras e carcaça. Os componentes físicos músculo, gordura e ossos foram também separados no corte das costelas. As melhores estimativas dos componentes do corpo vazio foram obtidas utilizando-se como estimadores os mesmos componentes no corte das costelas. A utilização dos totais de água e extrato etéreo do corte das costelas permitiu estimar com precisão os totais de água, extrato etéreo e proteína no corpo vazio dos animais. O uso das quantidades de músculo e gordura no corte das costelas possibilitou estimar com eficiência os totais de água, extrato etéreo e proteína no corpo vazio. Para estimação do total de cinzas do corpo vazio, foram encontradas três equações múltiplas (uma para cada grupo genético) com coeficientes de determinação satisfatórios. Essas equações incluíram como estimadores as quantidades de músculo e gordura nas costelas. As composições química e física do corte das costelas possibilitam estimar satisfatoriamente os componentes químicos do corpo vazio dos animais. Equações descritas na literatura permitem estimar com precisão os teores de extrato etéreo e água no corpo vazio dos animais deste estudo.

Linear regressions were developed to estimate the chemical empty body composition of cattle from three genetic groups (Caracu, CaS; Selected Nellore, NeS; and Control Nellore, NeC) using the physical and chemical compositions of the 9th-10th-11th rib section. Fifty six intact males (20 CaS, 20 NeS and 16 NeC) were slaughtered at 20-24 months of age. The content of water, protein, ether extract and ashes were determined in rib section and on samples obtained after grinding and homogenization of all body tissues (blood, hide, head + feet, viscera and carcass). The physical components muscle, fat and bones were also determined in the rib section. The best estimates of empty body components were obtained using the same estimator components as in rib section. The amounts of water and ether extract of the rib section accurately allowed to estimate the total water, ether extract and protein in the empty body of animals. The amounts of muscle and fat in the rib section allowed estimating with efficiency the total of water, ether extract and protein in the empty body of animals. To estimate the empty body total ashes three multiple equations were developed (one for each genetic group) with satisfactory coefficients of determination. These equations included as estimators the amounts of muscle and fat in the rib section. The physical and chemical compositions of the rib section can satisfactorily estimate the chemical components of the empty body of animals. Equations described in the literature can estimate with precision the amounts of ether extract and water in the body empty of animals of this study.

Foram avaliados os efeitos da seleção para peso pós-desmame sobre características de carcaça e rendimento de cortes cárneos comerciais de 44 bovinos machos não-castrados selecionados ou não para peso aos 378 dias, nascidos em 1999, Foram utilizados animais dos grupos genéticos Nelore Seleção (NeS), Nelore Controle (NeC) e Caracu Seleção (Ca). Os animais foram distribuídos aleatoriamente em duas categorias experimentais: grupo de alimentação restrita (AR) e grupo de alimentação ad libitum (AL). Em ambas as categorias, foram alocados oito animais dos grupos genéticos NeS e Ca e seis animais do grupo NeC. O período experimental foi determinado pelo tempo de acabamento dos animais, ou seja, quando atingiram, no mínimo, 4 mm de espessura de gordura subcutânea, avaliada por ultra-som, sobre o músculo Longissimus dorsi, na posição entre a 12ª e 13ª costelas. Em cada grupo genético, à medida que o acabamento preconizado para cada animal da categoria AL foi atingido, o animal da categoria AR mais semelhante quanto ao peso e à condição corporal no início do experimento foi também abatido. O efeito do grupo genético foi significativo para a maioria das características estudadas, porém, não houve interação significativa entre grupos genéticos e regimes alimentares. Os animais Ca e NeS tiveram maiores pesos de abate, sendo que animais Ca necessitaram de mais tempo de confinamento para atingirem o ponto de acabamento preconizado. O maior peso de abate desses animais também influenciou outras características correlacionadas, como pesos de carcaça, traseiro, dianteiro e ponta-de-agulha. A seleção para peso aumentou os pesos de abate, de carcaça e dos cortes primários. Os animais NeS apresentaram carne menos macia, mas ainda dentro dos padrões de maciez considerados satisfatórios (força de cisalhamento abaixo de 5 kgf).

Data from 44 bulls of the genetic groups Selection Nellore (NeS), Control Nellore (NeC) and Caracu (Ca) herds born in 1999 were used to evaluate the effects of selection for post weaning weight on carcass traits and meat cuts yields at 378 days of age (P 378). The animals were randomly distributed into two experimental classes: restricted feeding (AR) and ad libitum feeding (AL) including 8 animals from the NeS and Ca groups and 6 animals from the NeC group. Animals of each class were slaughtered in pairs when the animals AL group reached 4 mm of ultrasonic fat thickness on Longissimus dorsi muscle, between the 12th and 13th ribs. The interaction between genetic group and feeding class was not significant for most of the traits evaluated. The genetic group effect was significant. Animals of the Ca and NeS groups were heavier at slaughter and Ca animals required longer feedlot period to reach the desired fat thickness. Higher slaughter weights of these animals changed their carcass, hindquarter, forequarter and spare ribs weights. The selection for P 378 in the Nellore group resulted in heavier weights at slaughter, heavier carcasses and primary cuts, but lower meat tenderness, although within reasonable values of shear force (below 5.0 kgf).

Foi determinada a composição química corporal no peso de corpo vazio de 56 bovinos machos não-castrados selecionados ou não para peso aos 378 dias (P378), nascidos em 1999. Utilizaram-se animais dos grupos genéticos Nelore Seleção (NeS), Nelore Controle (NeC) e Caracu Seleção (Ca), distribuídos aleatoriamente em três grupos experimentais: AI - grupo de abate inicial; AR - grupo de alimentação restrita; e AL - grupo de alimentação ad libitum. No grupo de abate inicial, foram utilizados quatro animais por grupo genético e, nas categorias AR e AL, havia oito animais NeS e Ca e seis NeC. Após o período de adaptação, os animais do grupo AI foram abatidos e os demais foram submetidos ao ensaio de alimentação. O período experimental foi determinado pelo tempo de acabamento dos animais do grupo AL, ou seja, quando atingiram 4 mm de espessura de gordura, avaliada por ultra-som. Em cada grupo genético, à medida que o acabamento preconizado para os animais AL foi atingido, o animal AR com peso e condição corporal mais semelhante a esse no início do experimento também foi abatido. O efeito do grupo genético foi significativo, porém, não houve efeito da interação grupos genéticos × regimes alimentares sobre a maior parte das características estudadas. A seleção para peso pós-desmame não promoveu alterações indiretas na composição corporal. Animais Ca apresentaram porcentagens menores de gordura e maiores de proteína no corpo vazio, provavelmente em virtude do maior tamanho corporal desses animais.

Data from 56 bulls of the genetic groups Selection Nellore (NeS), Control Nellore (NeC) and Caracu (Ca) herds born in 1999 were used to evaluate the effects of selection for weight at 378 days of age (P 378) on the chemical composition of empty body weight. The animals were randomly distributed to three experimental classes: initial slaughter (AI), restricted feeding (AR) and ad libitum feeding (AL). The AI class included 4 animals of each genetic group and the AR and AL classes included 8 animals from the NeS and Ca groups and 6 animals from the NeC group. After the adaptation period was finished, animals of the AI class were slaughtered and those from the other classes (AR and AL) started the feeding period which was defined by the time required by the animals of the AL class to reach 4 mm of fat thickness. Animals of the AR class of all genetic groups were also slaughtered. The selection for post-weaning weight did not promote any change on body composition of the animals. The interaction between genetic group and feeding class was not significant for most of the traits evaluated. The genetic group effect was significant. Lower fat and higher protein percentages of empty body were observed in animals of the genetic group Ca, probably due to their larger mature body size.