Objetivou-se com este trabalho avaliar desempenho, parâmetros de eficiência e correlações fenotípicas entre medidas de eficiência energética de animais Nelore selecionados para peso pós-desmame e classificados quanto ao consumo alimentar residual, calculado pela diferença entre o consumo observado e o predito, com base no peso vivo médio metabólico e no ganho médio diário. Assim, os animais foram classificados em três grupos: alto (> média + 0,5 desvio-padrão; menos eficientes); médio (± 0,5 desvio-padrão da média); e baixo (< média - 0,5 desvio padrão; mais eficientes) consumo alimentar residual. Não foram observadas diferenças nos pesos vivos inicial e final, no ganho médio diário e no consumo de matéria seca entre os grupos. Animais com baixo consumo alimentar residual mostraram-se também com melhor eficiência alimentar, conversão alimentar e eficiência parcial de crescimento e não apresentaram diferenças em relação aos outros grupos quanto à taxa de crescimento relativo e taxa Kleiber. O consumo alimentar residual apresentou correlação significativa com eficiência alimentar (_0,25), conversão alimentar (0,25), eficiência parcial de crescimento (_0,37) e consumo de MS (0,16) e não apresentou correlação significativa com peso vivo (0,04), ganho médio diário (_0,02), taxa de crescimento relativo (_0,03) e taxa de Kleiber (_0,05). Foram encontradas correlações significativas entre conversão alimentar e peso vivo inicial (0,34) e ganho médio diário (_0,46). Eficiência parcial de crescimento apresentou correlação significativa comtodos os outros parâmetros de eficiência analisados. O consumo alimentar residual, em comparação às demais medidas de eficiência energética, apresenta grande potencial na eficiência produtiva, sendo independente de crescimento e tamanho dos animais.

The objective of this work was to evaluate performance, efficiency parameters and phenotypic correlations among measurements of energy efficiency of Nellore cattle selected for post weaning weight and classified according to residual feed intake, calculated by the difference between observed and predicted intake, based on average metabolic body weight and average daily gain. Thus, animals were classified within three groups: high (> mean + 0.5 standard deviation, less efficient); medium (±0.5 standard deviation of the mean); and low (< mean - 0.5 standard deviation, more efficient) residual feed intake. No differences were observed at initial and final body weights, average daily gain and dry matter intake among groups. Animals with low residual feed intake also had greater feed efficiency, feed conversion and partial efficiency of growth and did not differ from the other animals regarding to relative growth rate and Kleiber ratio. Residual feed intake was significantly correlated to feed efficiency (-0.25), feed conversion (0.25), partial efficiency of growth (-0.37) and dry matter intake (0.16) but it did not present significant correlation with body weight (0.04), average daily gain (-0.02), relative growth rate (-0.03) and Kleiber ratio (-0.05). Significant correlations were found between feed conversion and initial body weight (0.34) and average daily gain (-0.46). Partial efficiency of growth presented significant correlation with all other efficiency parameters analyzed. Residual feed intake has high potential in productive efficiency, when compared to the other energy efficiency measurements, being independent of growth and size of the animals.

Data from 1 698 animals belonging to an experimental Caracu herd were analysed with the objective of calculating the population selection differentials, generation intervals, effective size and inbreeding coefficients, and to estimate the direct and correlated responses for growth traits after 23 years of selection for post-weaning weight. The following traits were analysed: birth weight (BW), weaning weight corrected to 210 days of age (W210), weight corrected to 378 days for the males (W378), weight corrected to 550 days for the females (W550) and hip height for the males (HGTm) at the end of a feedlot test, and for the females (HGTf) at 550 days of age. The sire (W378) and dam (W550) weighted selection differentials for post-weaning weight were 1.10 and 0.28 standard deviation units and generation intervals 5.2 and 6.2 years, respectively. Mean inbreeding coefficient increased in the last five years, from 0.49 to 1.95%. The heritability estimates were 0.38, 0.27, 0.36, 0.37, 0.35 and 0.41 for BW, W210, W378, W550, HGTm and HGTf, respectively. The annual genetic trend estimates were 0.98 ± 0.17 kg/year for W378 and 0.27 ± 0.15 kg/year for W550. The estimates for the correlated responses to selection were 0.08 ± 0.02 kg/year for BW, 0.48 ± 0.11 kg/year for W210, 0.06 ± 0.02 cm/year for HGTm and 0.02 ± 0.02 cm/year for HGTf. These results confirmed that direct selection for post-weaning weight based on individual performance was relatively effective in achieving progress in all the growth traits.

Utilizaram-se 86 bovinos, castrados e não-castrados, com peso médio de 329kg e 20 meses de idade, sendo 12 Gir, 20 Guzerá, 20 Nelore e 20 Caracu - todos selecionados para peso aos 378 dias de idade (P378) - e 14 Nelore controle-selecionados com base no diferencial de seleção nulo para P378. A dieta, usada na relação volumoso:concentrado de 60:40 na matéria seca (MS), continha 14,8% de proteína bruta na MS e silagem de milho. O delineamento experimental utilizado foi o inteiramente ao acaso, em esquema fatorial 5 x 2 (grupos genético e classe sexual). Os ganhos médios diários de 1,51kg para Nelore seleção e 1,53kg para Guzerá foram semelhantes e maiores que os dos demais grupos genéticos, os quais não diferiram entre si. Não houve diferenças de ganho entre animais castrados e não-castrados. O consumo de MS em kg/dia foi maior para Nelore, Guzerá e Caracu selecionados (10,30; 10,04 e 10,71kg/dia, respectivamente), e os valores para os demais foram semelhantes entre si. A eficiência bionutricional foi pior para a raça Caracu (2,13) e melhor para Nelore controle (1,58). Os animais Caracu precisaram de maior tempo em confinamento (133 dias) para atingir 4mm de espessura de gordura subcutânea, sendo os valores para as demais raças próximos entre si.

Eighty-six castrated and non-castrated, approximately 20-month-old bovines averaging 329kg were used. They were 12 Gyr, 20 Nellore, 20 Guzerá and 20 Caracu, which were submitted to selection to weight at 378 day-old (W378) and 14 control Nellore - chosen based on nule selection differential to W378. The diet contained 14.8% of crude protein in dry matter (DM) and corn silage was used in the ratio of 60:40% forage: concentrate in DM basis. A completely randomized design in a 5 x 2 factorial arrangement (breed and sexual condition) was used. The average daily gain of 1.51kg and 1.53kg for selected Nellore and Guzerá did not differ, however surpassed those from the other breeds, which did not differ from each other. There was no difference between castrated and non-castrated animals. The dry matter intake in kg/day were higher for selected Nellore, Guzerá and Caracu (10.30; 10.04 and 10.71kg/day, respectively) and the values observed for the two other groups did not differ from each other. The bionutritional efficiency was worse for Caracu (2.13) and better for control Nellore (1.58). Caracu needed to remain in feeding 133 days longer to reach 4mm of subcutaneous fat thickness. The time in feeding for the others groups were similar.

Foram avaliados cinco grupos genéticos quanto à eficiência bionutricional (índice resultante da primeira função canônica de uma análise bivariada que envolveu ganho de peso e consumo de matéria seca) sendo seis animais da raça Nelore (N), cinco 1/2Romosinuano-1/2Caracu (RSC), quatro 1/2Senepol-1/2Caracu (SEC), quatro 1/2Belmont Red-1/2Caracu (BRC) e sete 1/2Valdostana-1/2Nelore (VAN). Não foi observada diferença significativa no desempenho dos animais mestiços Caracu, cuja média de eficiência bionutricional foi 519,8. O Nelore apresentou a menor eficiência bionutricional, 425,07, e os animais F1 Valdostana-Nelore, 499,30. Tendência semelhante foi observada para o ganho de peso. Os mestiços que envolveram raças européias adaptadas (RSC, SEC, BRC) apresentaram média de ganho de peso de 1,69kg/dia, enquanto os F1s Valdostana-Nelore alcançaram 1,57kg/dia e os da raça Nelore 1,29kg/dia. Não houve diferença no consumo diário de matéria seca entre os grupos genéticos, média de 7,76kg de MS ingerida/dia. Os grupos genéticos apresentaram conversão alimentar semelhante, com média de 4,87kg de MS ingerida/kg de ganho de peso.

Five genetic groups were evaluated by bio-nutritional efficiency (index obtained from the first canonical function in a bivariate analysis encompassing weight gain and dry matter intake): six Nellore (N), five 1/2Romosinuano-1/2Caracu (RSC), four 1/2Senepol-1/2Caracu (SEC), four 1/2Belmont Red-1/2 Caracu (BRC) and seven 1/2Valdostana-1/2Nellore (VAN). No differences were observed among the Caracu crosses for bio-nutritional efficiency, which averaged 519.8. Nellore showed the smallest performance (425.07), while the Vasdostana-Nellore F1's averaged 499.30. Similar trend was observed for daily weight gain. The crossbred animals involving European adapted breeds (RSC, SEC, BRC) showed an average gain of 1.69kg/day, while the F1's Valdostana-Nelore and the Nellore gains were, respectively, 1.57kg/day and 1.29kg/day. No difference for dry matter (DM) intake among genetic groups which averaged 7.76kg DM intake/day was observed. As far as feed conversion is concerned, no difference among genetic groups, which averaged 4.87kg of DM intake/kg of weight gain, was observed.