Abstract Effects of protein supplementation, with and without starch supplementation, on nutritional performance and metabolic characteristics of cattle fed low- and medium-quality tropical forages were evaluated using 4 cannulated steers distributed according to a 4 × 4 Latin square. Experimental periods were divided into two subperiods. In the first subperiod, two animals received low-quality hay and two animals received medium-quality. Supplementation schemes were evaluated in the second subperiod: low-quality hay with protein (300 g of crude protein – CP/d); low-quality hay with protein (300 g CP/d) and starch (225 g/d); medium-quality hay with protein (300 g CP/d); and medium-quality hay with protein (300 g CP/d) and starch (225 g/d) supplementation. Without supplementation, medium-quality forage provided higher intake, digestibility, nitrogen balance (NB) and efficiency of nitrogen utilization (EFNU). Comparing subperiods, supply of supplements depressed medium-quality forage intake, but did not affect low-quality forage intake. Supplementation increased NB, EFNU and serum concentration of IGF1 in animals fed low-quality forage. Protein supplementation increases nitrogen retention in animals, an effect attributed mainly to anabolic stimuli. However, this effect is more prominent when animals are fed low-quality forages. No positive impact on animal metabolism was obtained with combination of supplemental protein and starch.

ABSTRACT The objective of this study was to compare the estimates of ether extract (EE) contents obtained by the Randall method and by the high-temperature method of the American Oil Chemist's Society (AOCS; Am 5-04) in forages (n = 20) and cattle feces (n = 15). The EE contents were quantified by using the Randall extraction or AOCS method and XT4 filter bags or cartridges made of qualitative filter paper (80 g/m²) as containers for the samples. It was also evaluated the loss of particles, and concentration of residual chlorophyll after extraction and the recovery of protein and minerals in the material subjected to extraction. Significant interaction was observed between extraction method and material for EE contents. The EE estimates using the AOCS method were higher, mainly in forages. No loss of particles was observed with different containers. The chlorophyll contents in the residues of cattle feces were not affected by the extraction method; however, residual chlorophyll was lower using the AOCS method in forages. There was complete recovery of the protein and ash after extraction. The results suggest that AOCS method produces higher estimates of EE contents in forages and cattle feces, possibly by providing greater extraction of non-fatty EE.

ABSTRACT. This study was realized to evaluate prediction models for body weight (BW) using body measurements as heart girth (HG), wither height (WH), hip width (HW), body length (BL) and hip height (HH), and develop new Equations to predict the BW of Holstein and crossbred heifers. Prediction Equations (1, 2, 3, 4, 5 and 6) proposed in previous studies were tested, while body measurements, which were more significant in terms of predicting BW, were used to obtain new Equations. Heart girth was the body measurement with the greater correlation with BW. Equation 4 presented the best prediction results, showing a low average deviation, high accuracy and precision. Equations 1 and 2 predicted with a high presence of bias, while 2 had the lowest value of the concordance correlation coefficient and a great contribution made by systematic error. The 3 model presented a high variability in predicting BW. For both Holstein and crossbred heifers, the Equations evaluated are inadequate for predicting BW. Among the Equations evaluated, the model using HG presented the best adjustment and the greater adjusted coefficient of determination. Body measurements relating to HG and BL were the most significant variables in predicting the BW, resulting in the following Equation: BW = - 372.89 + 2.8072 × HG + 1.6087 × BL.

RESUMO. Este estudo foi realizado para avaliar modelos de predição de peso corporal (PC), utilizando-se medidas corporais como perímetro torácico (PT), altura de cernelha (AC), largura de garupa (LG), comprimento corporal (CC) e altura de garupa (AG), e desenvolver novas Equações de estimação de PC para novilhas Holandesas e mestiças. Foram testadas Equações de predição (1, 2, 3, 4, 5 e 6) propostas em estudos anteriores e as medidas corporais mais relacionadas com PC foram utilizadas para gerar novas Equações. O perímetro torácico é a medida corporal mais correlacionada com PC. A Equação 4 apresentou os melhores resultados de predição com baixo desvio médio e alta precisão e exatidão. As Equações 1 e 2 apresentaram alto viés de estimação, enquanto 2 teve o menor valor de coeficiente de correlação e concordância, e grande contribuição de erro sistemático. O modelo 3 apresentou alta variabilidade na predição de PC. Tanto para novilhas Holandesas quanto mestiças, as Equações avaliadas não são eficientes em predizer PC. Entre as Equações avaliadas, o modelo usando PT apresentou o melhor ajuste e maior coeficiente de determinação ajustado. As medidas corporais de PT e CC foram as variáveis mais significativas na predição do PC, sendo utilizadas na obtenção da Equação: PC = - 372.89 + 2.8072 × PT + 1.6087 × CC.

SUMMARY The objective was to conduct a collaborative study to evaluate the mineral matter contents in feeds in seven feed analysis laboratories from institutions linked to the National Institute of Science and Technology in Animal Science (INCT-CA). Six feeds were evaluated: signal grass hey, sugarcane, corn silage, soybean meal, corn grain and citrus pulp. It was asked to each laboratory that the samples were analyzed for six days, consecutive or not, with three replicates per sample per day of evaluation. Variations were observed among laboratories, days of analysis and interaction effect of material and laboratory. The variation of results among laboratories accounted from 33.5 to 78.2% of the total random variation. It was verified that the repeatability represented 8.5 to 51.6% of reproducibility. It was noticed Horwitz ratios greater than 2 for three materials tested. It was found that 42.9% of the assessments show variations of the estimates as a function of days in which analysis was performed. Differences were also observed between procedures to assess mineral matter according to the different laboratories. The mineral matter contents estimate by each laboratory in this study have low reproducibility, which is aggravated by the interaction effect of material and laboratory.

RESUMO Objetivou-se conduzir estudo colaborativo para avaliação do teor de matéria mineral em alimentos em sete laboratórios de análise de alimentos de instituições integrantes do Instituto Nacional de Ciência e Tecnologia de Ciência Animal (INCT-CA). Avaliaram-se seis alimentos: feno de capim-braquiária, cana-deaçúcar, silagem de milho grão, farelo de soja, milho e polpa cítrica. Solicitou-se a cada laboratório que as amostras fossem analisadas por seis dias, consecutivos ou não, sendo realizadas três repetições por amostra por dia de avaliação. Foi observado variação entre laboratórios, dias de análise e efeito de interação de material e laboratório. A variação dos resultados entre laboratórios correspondeu de 33,5 a 78,2% da variação aleatória total. Verificou-se que a repetibilidade representou de 8,5 a 51,6% da reprodutibilidade. Observou-se razões de Horwitz superiores a dois para três dos materiais avaliados. Foi constatado que 42,9% das avaliações apresentaram variações das estimativas em função do dia no qual a análise foi realizada. Também foram verificadas diferenças entre procedimentos de avaliação de matéria mineral em função dos diferentes laboratórios. Os teores de matéria mineral estimados pelos laboratórios participantes deste estudo apresentam baixa reprodutibilidade, o que é agravado pela presença de efeito de interação do material avaliado e do laboratório.

SUMMARY A collaborative study was conducted to evaluate the crude protein (CP) content in feeds in seven feed analysis laboratories from institutions linked to the National Institute of Science and Technology in Animal Science (INCT-CA). Were evaluated four samples of different feeds (sugarcane, corn silage, soybean meal and corn grain) and four nitrogen compounds assumed as standards (urea, monobasic ammonium phosphate, ethylene diamine tetraacetic acid and ammonium sulfate) to measure the accuracy of the estimates. Each laboratory analyzed the samples for six days, consecutive or not, with three replicates per sample per day of evaluation. The variances among laboratories and within of laboratories (repeatability) represented 34.5 and 10.3% of the total variation, respectively. The evaluation of nitrogen recovered from the standards showed that 25% of observations presented a significant bias (P<0.001). The overall assessment of the samples demonstrated significant variations (P<0.001) in function of the day of analysis, interaction of material with laboratory, and among laboratories. Additionally, it was found that the variation among laboratories corresponded of 43.6 to 68.2% of the total of random variation, while the repeatability (intra-laboratory variation) represented of 11.9 to 42.8% of reproducibility. The CP contents estimated are dependent of the interaction effect of the evaluated material and laboratory, which reflect the differences between the procedures utilized by each laboratory.

RESUMO Estudo colaborativo foi conduzido para avaliação do teor de proteína bruta (PB) em diferentes amostras de alimentos em sete diferentes laboratórios de análise de alimentos de instituições integrantes do Instituto Nacional de Ciência e Tecnologia de Ciência Animal (INCTCA). Foram utilizadas amostras de quatro alimentos (cana-de-açúcar, silagem de milho, farelo de soja e milho grão) e quatro compostos que foram assumidos como padrões para aferição da exatidão das estimativas (ureia, fosfato de amônia monobásico, ácido etileno diamínico tetra-acético e sulfato de amônio). Cada laboratório analisou as amostras durante seis dias, consecutivos ou não, sendo realizadas três repetições por amostra em cada dia de avaliação. As variâncias entre laboratórios e dentro de laboratórios (repetibilidade) representaram 34,5 e 10,3 % da variação total. A avaliação das recuperações de nitrogênio a partir dos padrões permitiu evidenciar que 25% das observações apresentaram vícios significativos de recuperação (P<0,001). A avaliação global das amostras propiciou variações significativas (P<0,001) em função: do dia de análise, interação do material com o laboratório e entre laboratórios. Adicionalmente, verificou-se que a variação dos resultados entre laboratórios correspondeu de 43,6 a 68,2% da variação aleatória total, ao passo que a repetibilidade (variação intra-laboratorial) representou de 11,9 a 42,8% da reprodutibilidade. Os teores de PB estimados pelos laboratórios participantes são dependentes do efeito de interação do material avaliado e do laboratório, possível reflexo das várias diferenças entre os procedimentos utilizados por cada laboratório.

ABSTRACT This study was performed in order to evaluate the effect of dried yeast from sugar cane when replacing soybean meal in dairy heifers' diets. Twenty-four heifers, with an initial body weight (BW) of 178 kg, were distributed in a completely randomized design. The treatments were four levels of inclusion of dried yeast from sugar cane replacing to soybean meal (0, 33, 67 and 100% on a dry matter (DM) basis). While there was no difference in DM, neutral detergent fiber (NDF), metabolizable energy or roughage intakes, the intakes of non-fiber carbohydrates and concentrate were increased. The crude protein intake decreased according to the dried yeast from sugar cane when replacing soybean meal. The digestibility coefficients of DM and NDF showed no difference. Replacement of soybean meal with dried yeast from sugar cane had no effect on performance, because average daily gain and body measurements studied were similar for all animals and inclusion levels. Soybean meal can be completely replaced with dried yeast from sugar cane in diets for growing dairy heifers without restrictions; this will not affect the intake, digestibility, physical development of animals or metabolization of protein compounds.

RESUMO Objetivou-se avaliar o efeito da levedura seca de cana-de-açúcar em substituição ao farelo de soja em dietas de novilhas leiteiras. Vinte e quatro novilhas leiteiras com peso médio inicial (BW) de 178 kg foram distribuídas em delineamento inteiramente casualizado. Os tratamentos foram níveis de inclusão de levedura seca de cana-de-açúcar em substituição ao farelo de soja (0, 33, 67 e 100% com base na matéria seca (MS)). Não houve diferença para a ingestão de MS, fibra em detergente neutro (FDN), energia metabolizável e volumoso; entretanto, houve aumento na ingestão de carboidratos não fibrosos e concentrados. A ingestão de proteína bruta diminuiu de acordo com o aumento do nível de levedura em substituição ao farelo de soja. Os coeficientes de digestibilidade da MS e FDN não foram alterados. A substituição do farelo de soja pela levedura não promoveu efeito sobre o desempenho, pois o ganho médio diário e as medidas corporais estudados foram os mesmos para todos os animais, em todos os níveis de inclusão. O farelo de soja pode ser completamente substituído por levedura seca de cana-de-açúcar em dietas para novilhas leiteiras em crescimento, pois não afeta consumo, digestibilidade, desenvolvimento físico dos animais e metabolismo de compostos proteicos.

ABSTRACT The effect of replacing wheat bran with spineless cactus (0, 25, 50, 75, and 100%) in sugar cane-based diets on the intake of nutrients, feeding behavior, and rumen digestibility of steers was assessed using digested samples collected from the omasum. Five crossbred steers (1/2 Holstein-Zebu) were fitted with cannulas in the rumen and then assigned to a 5 × 5 Latin square design. Samples of omasal digesta were collected for three days. Rumen was evacuated via the rumen cannula to determine the rumen pool of dry matter (DM), neutral detergent fiber (NDF), indigestible NDF (iNDF), intake (ki), passage (kp) and degradation (NDF) rates, and the passage of iNDF (kpi). Nutrient intake displayed a quadratic effect, with maximum intakes of DM (5.73 kg d−1), non-fiber carbohydrates (NFC, 4.63 kg d−1), and digestible organic matter (DOM, 3.45 kg d−1) estimated at the replacement levels of 54.63, 60.00, and 43.17%, respectively. The replacement levels showed no effect on feeding, rumination, or idle times. There was a linear increase in the total apparent and ruminal digestibility of CP as the spineless cactus content in the diet was increased. There was no effect on total and partial digestibilities of OM and NDF or on intestinal digestibility of CP. No effect was observed on the rumen pool of DM, NDF, or iNDF. Furthermore, ki, kp, NDF degradation, and iNDF passage rates displayed a quadratic effect, with higher concentrations estimated for replacement levels of 56.07, 56.12, 59.00, and 55.20%, respectively. Replacing 55% wheat bran with spineless cactus in sugar cane-based diets is recommended.

ABSTRACT. The effects of the salt-to-metal catalyst ratio and amount of digestion mixture on total nitrogen content in different materials using the Kjeldahl method were evaluated. Four samples with low nitrogen contents and four samples with high nitrogen contents were analyzed. The study evaluated two ratios of salt (sodium sulfate) to metal catalyst (copper sulfate) in the digestion mixture (10:1 and 20:1) and three amounts of digestion mixture per sample (1.0, 1.5, and 2.0 g 200 mg-1). There was an interaction between low-nitrogen material and amount of digestion mixture on nitrogen contents. Samples of cattle feces and corn presented higher nitrogen content when 1.5 and 2.0 g of digestion mixture were used. The high-nitrogen materials presented higher nitrogen contents when 2.0 g of the digestion mixture was used. However, there was an interaction between high-nitrogen material and the ratio of the digestion mixture components. The cattle carcass sample showed higher nitrogen content when the 20:1 ratio was used. The digestion mixture amount in the Kjeldahl method must be 2.0 g with a salt-to-metal catalyst ratio of 20:1 when samples of approximately 200 mg are analyzed.

RESUMO. Avaliaram-se os efeitos da quantidade de mistura digestora e da razão dos componentes da mistura digestora utilizada no método de Kjeldahl para quantificação do nitrogênio total em diferentes materiais. Foram utilizadas quatro amostras com baixo teor de nitrogênio e quatro amostras com alto teor de nitrogênio. Avaliou-se a comninação de duas razões entre sal (sulfato de sódio) e catalisador metálico (sulfato de cobre) na mistura digestora (10:1 e 20:1) e três quantidades de mistura digestora por amostra (1,0; 1,5 e 2,0 g 200 mg-1). Para os materiais de baixo nitrogênio houve interação entre o material analisado e a quantidade de mistura digestora. Amostras de fezes bovinas e milho apresentaram maiores teores de nitrogênio com o uso de 1,5 e 2,0 g de mistura digestora. Para os materiais de alto nitrogênio verificou-se maior teor de nitrogênio com o uso de 2,0 g de mistura digestora. No entanto, houve interação entre material avaliado e razão na mistura digestora para amostras de alto nitrogênio. Amostra de carcaça bovina apresentou maior teor de nitrogênio utilizando-se a razão 20:1. A quantidade de mistura digestora para o método de Kjeldahl deve ser de 2,0 g com razão entre sal e catalisador metálico de 20:1 para amostras de aproximadamente 200 mg.

ABSTRACT. Several tannins at different inclusion levels of protein-rich food and water addition on the amount of rumen undegradable protein (RUP) and digestible RUP (RUPd) in the rumen were evaluated. Sixty treatments were analyzed, namely: three mixtures of tannin (with different concentrations of hydrolysable and condensed tannins) were added at four different amounts (0, 1, 2.5 and 5%) in three protein foods (soybean meal, whole soybean meal and peanut meal) with and without moisture. Samples were incubated in cattle, via rumen cannula, in triplicate, to quantify rumen degraded protein (RDP), rumen undegradable protein (RUP) and digestible RUP (RUPd). Divergence in protein nutritional rate, based on discriminating variables among the groups, was estimated by cluster analysis. Increase in RUPd of treatments required soybean meal with 2.5% tannin, with 85% of condensed tannins and 15% hydrolysable tannins, in an aqueous medium. The inclusion of tannin is recommended to test in in vivo evaluations for productivity increase and inclusion level used.

RESUMO. Este trabalho foi realizado para avaliar os tipos de taninos sob diferentes níveis de inclusão em alimentos protéicos com adição de água, sobre a quantidade de proteína não degradável no rúmen (PNDR) e PNDR digestível (PNDRd). Foram analisados 60 tratamentos, arranjados da seguinte forma: adição de três misturas de tanino (com diferentes concentrações de taninos hidrolisáveis e condensados) que foram adicionados em quatro diferentes quantidades (0; 1; 2,5 e 5%) sob três alimentos protéicos (farelo de soja, farelo de soja integral e farelo de amendoim) que passaram ou não por processo de umedecimento. As amostras foram incubadas em bovinos, via cânula ruminal, em triplicata, para a quantificação da proteína degradada no rúmen, PNDR e PNDRd. A divergência do valor nutricional proteico, baseada em variáveis discriminatórias entre os grupos, foi estimada por meio de análise de agrupamento. Para aumentar o teor de PNDR digestível da dieta recomenda-se a utilização de farelo de soja tratado, em meio aquoso, com 2,5% de tanino com 85% de tanino condensado e 15% de tanino hidrolisável. Recomenda-se testar a inclusão desse ingrediente em avaliações in vivo para determinar o aumento de produtividade e o nível de inclusão a ser adotado.

AbstractThe objective was to conduct a collaborative study to evaluate the dry matter contents in feeds in six feed analysis laboratories from institutions linked to the National Institute of Science and Technology in Animal Science (INCT-CA). Six feeds were evaluated: sugarcane, corn silage, elephant grass, soybean meal, citrus pulp, and corn mixed with urea (9:1). It was asked to each laboratory that the samples were analyzed for eleven days, consecutive or not, with three replicates per sample per day of evaluation. There were variations among laboratories, days of analysis and interaction effect of material and laboratory. Comparative evaluation between the average contents produced by the laboratories and the Karl Fischer method indicated that 11.1% of the assessments were found accurate. The variation of results among laboratories accounted from 54.1 to 79.2% of the total random variation. It was found that the repeatability represented 6.24 to 26.45% of reproducibility. There are Horwitz ratios less than 2 for all materials tested. It was noticed that 52.8% of the assessments show variations of the estimates as a function of days in which analysis was performed. High inter-laboratory variability was checked through the evaluation of questionnaires sent to laboratories to elucidate the main procedures used in each laboratory, which can possible explain the great variation of the estimates obtained here.

ResumoObjetivou-se conduzir estudo colaborativo para avaliação do teor de matéria seca em alimentos em seis laboratórios de análise de alimentos de instituições integrantes do Instituto Nacional de Ciência e Tecnologia de Ciência Animal (INCT-CA). Avaliaram-se seis alimentos: cana-de-açúcar, silagem de milho, capim-elefante, farelo de soja, polpa cítrica e mistura de milho grão com ureia (9:1). Solicitou-se a cada laboratório análises das amostras por onze dias, consecutivos ou não, sendo realizadas três repetições por amostra por dia de avaliação. Observou-se variação entre laboratórios, dias de análise e efeito de interação de material e laboratório. Avaliação comparativa das médias produzidas pelos laboratórios e pelo método de Karl Fischer indicou que 11,1% das avaliações foram exatas. A variação dos resultados entre laboratórios correspondeu de 54,1 a 79,2% da variação aleatória total. Verificou-se que a repetibilidade representou de 6,24 a 26,45% da reprodutibilidade. Observou-se razões de Horwitz inferiores a 2 para os materiais avaliados. Percebeu-se que 52,8% das avaliações apresentaram variações das estimativas em função do dia no qual a análise foi realizada. Elevada variabilidade inter-laboratorial foi verificada por intermédio da avaliação dos questionários enviados aos laboratórios para elucidação dos principais procedimentos adotados, evidenciando possíveis causas da alta variação dos resultados.

The objective of this work was to evaluate the accuracy of digestion techniques using nitric and perchloric acid at the ratios of 2:1, 3:1, and 4:1 v v-1, in one- or two-step digestion, to estimate chromium contents in cattle feces, using sodium molybdate as a catalyst. Fecal standards containing known chromium contents (0, 2, 4, 6, 8, and 10 g kg-1) were produced from feces of five animals. The chromium content in cattle feces is accurately estimated using digestion techniques based on nitric and perchloric acids, at a 3:1 v v-1 ratio, in one-step digestion, with sodium molybdate as a catalyst.

O objetivo deste trabalho foi avaliar a acurácia de técnicas de digestão com uso dos ácidos nítrico e perclórico, nas razões 2:1, 3:1 e 4:1 v v-1, em um ou dois passos de digestão, na estimação da concentração de cromo em fezes de bovinos, com uso do molibdato de sódio como catalisador. Foram produzidos padrões fecais com conteúdo conhecido de cromo (0, 2, 4, 6, 8 e 10 g kg-1), a partir das fezes de cinco animais. A concentração de cromo em fezes de bovinos é acuradamente estimada com técnicas de digestão baseadas no uso dos ácidos nítrico e perclórico, na razão 3:1 v v-1, em um passo de digestão, com molibdato de sódio como catalisador.

The objective of this work was to evaluate the extent of protein contamination on Klason lignin (KL) in tropical grasses and legumes, and to propose an equation to estimate the protein-free content of Klason lignin (KLp). Five grass (30 samples) and 12 legume species (31 samples) were evaluated. Legumes had higher KL contents. Protein contamination was significant in both grasses and legumes, but greater in legume samples. The model to predict KLp was based on KL and crude protein (CP) contents, as follows: KLp = 0.8807KL - 0.0938KL x D - 0.00338CP (R2=0.935), in which D=0, for grasses, and D=1 for legumes.

O objetivo deste trabalho foi avaliar a extensão da contaminação proteica sobre a lignina Klason (LK) em gramíneas e leguminosas tropicais, e propor uma equação para estimar o conteúdo livre de proteína da lignina Klason (LKp). Foram avaliadas cinco espécies de gramíneas (30 amostras) e 12 de leguminosas (31 amostras). As leguminosas apresentaram maiores teores de LK. A contaminação proteica foi significativa em gramíneas e leguminosas, mas maior em amostras de leguminosas. O modelo para estimar LKp foi baseado nos conteúdos de LK e de proteína bruta (PB), da seguinte forma: LKp = 0,8807LK - 0,0938LK x D - 0,00338PB (R2=0,935), em que D=0, para gramíneas, e D=1 para leguminosas.

Protein and energy requirements of beef cattle, aged between 4 and 18 months old, on tropical pastures, were estimated. Forty-six Nellore calves (138.3 ± 3.4 kg BW and 90-150 days old), kept on pasture, were distributed in a maintenance group (restricted feeding) or in nutritional plans, receiving a supplements with different amounts of protein and carbohydrate or non-supplemented. The net energy requirement for weight gain (NEg) was obtained by linear regression of logarithm of retained energy as a function of logarithm of empty body weight gain. The net energy requirement for maintenance (NEm) was estimated by the exponential relation between heat production and metabolizable energy intake. Net protein requirement for weight gain (RP) was estimated by multiple linear regression of retained protein in the weight gain of empty body (EBWG) and retained energy. The efficiency of metabolizable energy (ME) used for maintenance and for weight gain was 0.55 and 0.26, respectively. The ME requirement for maintenance was 124 kcal EBW-0.75. RP decreased in proportion to body weight increase. NEg and RP may be obtained by equations: RE (Mcal kg-1) = 0.044 x EBW0.75 x EBWG1.1302 and RP (g day-1) = -31.45 + 229.69 x EBWG - 8.75 x RE, respectively.

Objetivou-se estimar as exigências de proteína e energia de bovinos de corte em pastagens tropicais dos 4 até 18 meses de idade. Foram utilizados 46 bezerros Nelore (138,3 ± 3,4 kg e 90-150 dias de idade) em pastagem, distribuídos em um grupo de mantença (alimentação restrita) ou em planos nutricionais, recebendo suplemento com diferentes quantidades de proteína e carboidrato, ou não suplementados. A exigência de energia líquida para ganho de peso (ELg) foi obtida por regressão linear do logaritmo da energia retida em função do logaritmo do ganho de peso corporal vazio. A exigência de energia líquida para mantença (ELm) foi estimada pela relação exponencial entre a produção de calor e consumo de energia metabolizável. A exigência líquida de proteína para ganho de peso (PR) foi estimada pela regressão linear múltipla da proteína retida no ganho de peso de corpo vazio (GPCVZ) e da energia retida. A eficiência de uso da energia metabolizável (EM) para mantença foi de 0,55 e para o ganho de peso foi de 0,26. A exigência de EM para mantença foi de 124 kcal PCVZ-0,75. A PR diminuiu com o aumento do peso corporal. O ELg e PR podem ser obtidos por meio das equações: ELg (Mcal kg-1) = 0,044 x PCVZ0,75 x GPCVZ1,1302, PR (g dia-1) = -31,45 + 229,69 x GPCVZ - 8,75 x ER, respectivamente.

The objective of this work was to evaluate the effects of protein and/or starch supplementation on the nutritional performance of cattle grazing on low-quality tropical forage. Five crossbred steers (Holstein × Gyr) with an average body weight (BW) of 397 kg that were fitted with ruminal and abomasal cannulae were used. The animals were kept in individual signal-grass (Bracharia decumbens) paddocks. Five treatments were evaluated: 1 - control (without supplementation); 2 - supplementation with 1 g of crude protein (CP) per kg of BW; 3 - supplementation with 2.5 g of starch per kg of BW; 4 - supplementation with CP and starch as described for treatments 2 and 3; and 5 - supplementation as described for treatment 4 but replacing the corn starch with a mixture of corn starch and nitrogenous compounds, thereby resulting in an energy supplement of 150 g CP/kg of dry matter. The experiment was performed according to a 5 × 5 Latin square design in a 2 × 2 + 1 factorial arrangement. The forage intake was not affected by any of the factors evaluated in this study. The production of microbial nitrogen in the rumen was not affected by nitrogen or starch supplementation. The apparent nitrogen balance was only increased when both starch and nitrogen were supplied. Supplementation with both starch and nitrogenous compounds for cattle grazing on low-quality tropical forage is characterized by an interactive metabolic effect that increases nitrogen accretion by the animals.

The objective of this study was to estimate and evaluate the contents of apparently digestible fractions of crude protein, ether extract and non-fibrous carbohydrates, the digestible fraction of the neutral detergent fiber and the content of total digestible nutrients (TDN) from the chemical composition of feeds in growing cattle fed different diets. Fourteen F1 Red Angus × Nellore young bulls with average age and weight of 12 months and 287±36 kg were used. Animals were fed elephant grass silage, corn silage or signal grass hay, with or without supplementation of 200 g concentrate per kg of the total diet. The experiment consisted of two 13-days periods, in which the concentrate supplementation was crossed over animals. The values of digestible fractions and the TDN content observed were obtained based on total collection of feces. Several sub-models applied to the different digestible fractions were assessed and discussed. Estimates of the TDN content in the diet were produced from the combination of sub-models applied to the individual digestible fractions. The TDN content was more efficiently predicted from the sub-models proposed by Detmann et al. (2010) when biological procedures for the estimation of the undegradable fraction of the protein and the potentially degradable fraction of the neutral detergent fiber were considered.