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.

Two experiments were carried out to evaluate the effect of supplementation with different nitrogenous compounds on the activities of carboxymethil cellulase (CMCase) and glutamate dehydrogenase (GDH). In the first experiment, four treatments were evaluated in vitro: cellulose, cellulose with casein, cellulose with urea, and cellulose with casamino acids. After 6, 12 and 24 hours of incubation, CMCase and GDH activity, pH, and concentrations of ammonia nitrogen (AN) and microbial protein were measured. In the three incubation periods, the concentration of AN was higher when urea was used as a supplemental source of nitrogen. The activity of CMCase was higher with the addition of urea and casamino acids when compared with the control and the casein treatment. Supplementation with casamino acids provided higher GDH activity when compared with the control at 6 hours of incubation. At 12 hours of incubation, the GHD activity was also stimulated by casein. At 24 hours, there was no difference in GHD activity among treatments. In the second experiment, three rumen-fistulated bulls were used for in situ evaluation. Animals were fed Tifton hay (Cynodon sp.) ad libitum. The treatments consisted of control (no supplementation), supplementation with non-protein nitrogenous compounds (urea and ammonium sulphate, 9:1) and supplementation with protein (albumin). In treatments with nitrogenous compound supplementation, 1 g of crude protein/kg of body weight was supplied. The experiment was conducted in a 3 × 3 Latin square design. The measurements were performed at 6, 12 and 24 hours after supplementation. No difference in GDH activity was observed among treatments. The control treatment showed higher CMCase activity when compared with the treatments containing supplemental sources of nitrogen. However, urea supplementation provided higher CMCase activity compared to albumin.

Objetivou-se avaliar os efeitos de diferentes formas químicas de compostos nitrogenados (proteicos e não-proteicos) e de carboidratos (amiláceos e fibra solúvel) sobre o consumo, a digestibilidade e a síntese ruminal de proteína microbiana em bovinos sob suplementação durante o período das águas. Foram utilizados cinco novilhos mestiços Holandês × Zebu, com peso vivo (PV) médio inicial de 211 ± 35 kg, fistulados no rúmen e abomaso. Os tratamentos foram: controle (somente pasto); e suplementos formulados à base de milho + farelo de soja; milho + ureia; polpa cítrica + farelo de soja; e polpa cítrica + ureia. Os suplementos foram balanceados para apresentar 30% de proteína bruta (PB), com base na matéria seca (MS), e fornecidos na quantidade de 3 g/kg PV. O experimento foi conduzido segundo delineamento em quadrado latino 5 × 5, em esquema fatorial 2 × 2 + 1, composto de duas fontes de compostos nitrogenados, duas fontes de carboidratos e tratamento controle. O consumo de pasto reduziu com o fornecimento de suplementos, com coeficiente médio de substituição de 2,11 g de MS de pasto/g de MS de suplemento. A suplementação não alterou os coeficientes de digestibilidade total e ruminação da MS nem o teor dietético de nutrientes digestíveis totais (NDT). Os animais sob suplementação apresentaram maiores coeficientes de digestibilidade total e ruminal da proteína bruta. A eficiência de síntese de proteína microbiana (EFSM), média de 123,1 g PB microbiana/kg de NDT, não foi alterada pela suplementação. Contudo, os animais sob suplementação com milho apresentaram maior EFSM em comparação aos animais sob suplementação com polpa cítrica (137,6 e 106,1 g PB microbiana/kg de NDT, respectivamente). A suplementação proteico-energética para bovinos mantidos em pastos tropicais durante o período das águas não causa benefícios nutricionais, o que reflete o alto coeficiente de substituição da forragem pelo suplemento.

The objective of this work was to evaluate the effects of different chemical forms of nitrogenous compounds (protein and non-protein) and carbohydrates (starch and soluble fiber) on intake, digestibility, and ruminal synthesis of microbial protein in cattle supplemented during rainy season. It was used five crossbred Holstein × Zebu steers, with average initial body weight of 211 ± 35 kg and fistulated in the rumen and abomasum. The treatments were: control (only pasture), and supplements based on corn + soybean meal; corn + urea, citrus pulp + soybean meal, and citrus pulp + urea. The supplements were balanced to present 30% of crude protein (CP), on dry matter (DM) basis, and provided at 3 g/kg BW. The experiment was carried out according to a 5 × 5 Latin square design in a 2 × 2 + 1 factorial arrangement, composed of two sources of nitrogenous compounds, two sources of carbohydrates and a control treatment. Pasture intake was reduced when supplements were fed to animals, with average substitution coefficient of 2.11 g of DM of pasture/g of DM of supplement. Supplementation did not alter the total and ruminal digestibility coefficients of DM and the dietary content of total digestible nutrients (TDN) neither. Supplemented animals presented higher ruminal and total digestibility coefficients of CP than non-supplemented animals. The efficiency of microbial protein synthesis (EMPS), average of 123.1g of microbial CP/kg, was not changed by supplementation. However, animals supplemented with corn presented higher EMPS in comparison to animals supplemented with citrus pulp (137.6 and 106.1 g microbial CP/kg of TDN, respectively). Protein-energy supplementation for cattle grazing in tropical pastures during rainy season does not cause nutritional benefits, which reflects the high coefficient of substitution of forage by the supplement.

Objetivou-se avaliar o perfil de excreção fecal e o vício de tempo curto dos indicadores externos óxido crômico e dióxido de titânio e dos indicadores internos matéria seca indigestível (MSi), fibra em detergente neutro indigestível (FDNi) e fibra em detergente ácido indigestível (FDAi) em ensaio de digestão com bovinos alimentados com diferentes dietas. Foram utilizados 14 novilhos F1 Red Angus × Nelore, não-castrados, com idade e peso médios de 12 meses e 287 kg, mantidos em baias individuais. Os animais foram alimentados com silagem de capim-elefante, silagem de milho ou feno de capim-braquiária, suplementados ou não com 20% de mistura concentrada. O experimento foi constituído de dois períodos de 13 dias, segundo delineamento em quadrado latino 2 × 2, com agrupamento de sete quadrados. Os animais receberam diariamente 10 g de óxido crômico e 10 g de dióxido de titânio por meio de sonda esofágica. Foram realizadas coletas fecais pontuais (grab samples), diretamente do reto dos animais, nos horários de 1h30, 3h00, 4h30, 6h00, 7h30, 9h00, 10h30, 12h00, 13h30, 15h00, 16h30, 18h00, 19h30, 21h00, 22h30 e 24h00. Não foram observados efeitos das forragens ou dos níveis de concentrado sobre a dimensão do ciclo excretório. O período fundamental do ciclo excretório foi de 15,06 e 18,66 horas para o óxido crômico e dióxido de titânio, e de 9,93; 9,29 e 10,55 horas para MSi, FDNi e FDAi respectivamente. Verificou-se maior amplitude de oscilação para os indicadores externos. Considerando-se conjuntamente as características dos indicadores avaliados, recomendam-se delineamentos de amostragem fecal com o mínimo de quatro coletas, distribuídas ao longo do dia ou somente no período diurno, para obtenção de estimativas de excreção fecal isentas de vício de tempo curto.

The objective of this work was to evaluate the fecal excretion profile and the short term bias of the external markers chromic oxide and titanium dioxide and the internal markers indigestible dry matter (iDM), indigestible neutral detergent fiber (iNDF) and indigestible acid detergent fiber (iADF) in a digestion trial with cattle fed different diets. Fourteen F1 Red Angus × Nellore bulls averaging 12 months old and 287 kg were kept in individual stalls. The animals were fed elephant grass silage, corn silage or signal grass hay, supplemented or not with 20% of concentrate mixture. The experiment consisted of two 13-day experimental periods according to a 2 × 2 Latin square design with seven squares grouping. The animals received 10 g of chromic oxide and 10 g of titanium dioxide through esophageal sounder daily. Fecal grab samples were obtained directly from the rectum of the animals at 1:30 a.m., 3:00 a.m., 4:30 a.m., 6:00 a.m., 7:30 a.m., 9:00 a.m., 10:30 a.m., 12:00 p.m., 1:30 p.m., 3:00 p.m., 4:30 p.m., 6:00 p.m., 7:30 p.m., 9:00 p.m., 10:30 p.m. and 12:00 a.m. There was no effect of forages or concentrate levels on the dimension of excretory cycle. The fundamental period of excretory cycle was 15.06 and 18.66 hours for chromic oxide and titanium dioxide, respectively and 9.93, 9.29 and 10.55 hours for iDM, iNDF and iADF, respectively. The oscillation range was higher for external markers. Considering the characteristics of all evaluated markers together, it is recommended fecal sampling designs with at least four collections, distributed during the day or only in the diurnal period for obtaining fecal excretion estimates free of short term bias.

Objetivou-se avaliar o efeito da suplementação proteica e/ou com carboidratos sobre a degradação ruminal da fibra em detergente neutro (FDN) de forragem tropical de alta qualidade. No experimento, foi simulada a suplementação de bovinos em terminação sob pastejo durante o período chuvoso (70% de forragem e 30% de concentrado, com base na matéria seca). Como forragem basal utilizou-se amostra de capim-elefante (Pennisetum purpureum Schum.) cortado aos 21 dias de rebrotação. O concentrado utilizado no tratamento-base foi formulado de forma a apresentar 30% de proteína bruta, com amido como componente energético e caseína como componente proteico. Os tratamentos foram construídos mediante o não-fornecimento das fontes proteica e/ou energética do suplemento e substituição total do amido por pectina. Desta forma, avaliaram-se seis tratamentos (1. forragem; 2. forragem + amido; 3. forragem + pectina; 4. forragem + caseína; 5. forragem + caseína + amido; e 6. forragem + caseína + pectina) em ambiente ruminal simulado por incubação in vitro em diversos tempos de incubação: 0, 3, 6, 9, 12, 24, 36, 48, 72 e 96 horas. O procedimento de incubação foi repetido cinco vezes, perfazendo o total de cinco avaliações por tempo de incubação para cada tratamento. Os resíduos de incubação foram avaliados quanto ao teor de FDN e interpretados por intermédio de modelo não-linear logístico. A suplementação isolada com amido ou pectina reduziu em 9,9 e 8,4% a taxa de degradação da FDN potencialmente degradável (FDNpd). Efeitos similares foram verificados com a suplementação exclusivamente proteica, com redução de 19,1% sobre a taxa de degradação da FDNpd. A suplementação conjunta com proteína e carboidratos promove redução dos efeitos deletérios da suplementação isolada com esses compostos.

The objective was to evaluate the effect of protein and (or) carbohydrate supplementation on the rumen degradation of neutral detergent fiber (NDF) from high-quality tropical forage. The experiment simulated the supplementation of finishing cattle under grazing during the rainy season (70:30 forage to concentrate ratio, as dry matter basis). Samples of elephant grass (Pennisetum purpureum Schum.) cut after 21 days regrowth were used as basal forage. The concentrate used was formulated to contain 30% crude protein, using starch as the energetic source and casein as the protein source. The treatments were established by omission of the protein and/or energy source and replacement of starch by pectin. Thus, six treatments were evaluated: 1. Forage, 2. Forage plus Starch, 3. Forage plus Pectin, 4.Forage plus Casein, 5. Forage plus Casein plus Starch and 6. Forage plus Casein plus Pectin. The treatments were evaluated under rumen environment, simulated by in vitro incubation, where the experimental diets were submitted to different incubation periods: 0, 3, 6, 9, 12, 24, 36, 48, 72, and 96 hours. The incubation procedure was repeated five times so that five evaluations within each incubation time were made for each treatment. The incubation residues were evaluated according to their NDF contents and interpreted using a non-linear logistic model. It was observed that the exclusive supplementation with starch or pectin depressed 9.9 and 8.4% the degradation rate of potentially degradable NDF. A similar effect was observed with exclusive supplementation with protein, where a decrease of 19.1% on the degradation rate of potentially degradable NDF was observed. As carbohydrates and protein were supplemented together, a decrease in negative effect on NDF degradation was observed.

Objetivou-se avaliar o efeito da suplementação protéica e/ou com carboidratos sobre a degradação ruminal da fibra em detergente neutro (FDN) de forragem de baixa qualidade. Simulou-se a suplementação de bovinos em terminação, sob pastejo em Brachiaria decumbens de baixa qualidade, durante o período seco (70% de forragem e 30% de concentrado, com base na matéria seca). O concentrado referente ao tratamento base foi formulado de forma a apresentar 30% de proteína bruta, utilizando-se amido, como componente energético, e caseína, como componente protéico. Os tratamentos foram construídos a partir da omissão do fornecimento das fontes protéica e/ou energética do suplemento, associando-se, ainda, a substituição total do amido por pectina. Desta forma, seis foram os tratamentos avaliados: 1. forragem; 2. forragem + amido; 3. forragem + pectina; 4. forragem + caseína; 5. forragem + caseína + amido; e 6. forragem + caseína + pectina. Os tratamentos foram avaliados em ambiente ruminal simulado por incubação in vitro e submetidos a diferentes tempos de incubação: 0, 3, 6, 9, 12, 24, 36, 48, 72 e 96 horas. O procedimento de incubação foi repetido quatro vezes, perfazendo-se o total de quatro avaliações por tempo de incubação para cada tratamento. Os resíduos de incubação foram avaliados quanto ao teor de FDN e interpretados por intermédio de modelo não-linear logístico. Observou-se que a taxa de degradação da FDN potencialmente degradável (FDNpd) foi ampliada em cerca de 46% com a suplementação com caseína, resultando em incrementos de 14,6% sobre a fração efetivamente degradada. Observou-se efeito de menor amplitude com a inclusão ou alteração da fonte de carboidrato suplementar. A suplementação com amido causou redução na taxa de degradação da FDNpd, ao passo que a suplementação com pectina não afetou este parâmetro em comparação à ausência de carboidratos. Na presença de caseína, a suplementação com amido elevou o tempo de latência discreta para a degradação da FDN.

The effect of the protein and (or) carbohydrates supplementation on the rumen degradation of neutral detergent fiber (NDF) from low quality forage was evaluated. The experiment simulated the supplementation of finishing cattle grazing low quality Brachiaria decumbens pasture during dry season (70:30 forage to concentrate ration, %DM). The concentrate referring to the basal treatment was formulated to contain 30% CP, using starch as the energetic source and casein as the protein source. The treatments were established by omission of protein and (or) carbohydrates sources, associated with substitution of starch by pectin. In that way, six treatments were evaluated: 1. Forage, 2. Forage plus Starch, 3. Forage plus Pectin, 4.Forage plus Casein, 5. Forage plus casein plus starch and 6. Forage plus casein plus pectin. The treatments were evaluated under rumen environment, simulated by in vitro incubation, where the experimental diets were submitted to different incubation periods: 0, 3, 6, 9, 12, 24, 36, 48, 72, and 96 hours. The incubation procedure was repeated four times in a way that four evaluations within each incubation time were done for each treatment. The incubation residues were evaluated according to its contents of NDF and interpreted using a non-linear logistic model. It was observed that the degradation rate of potentially degradable NDF (pdNDF) was increased almost 46% with casein supplementation, resulting in an increment of 14.6% on the effective degraded fraction. A minor effect was observed with the inclusion or substitution of the supplemental carbohydrate source. The starch supplementation resulted in reduction on pdNDF degradation rate, whereas the supplementation with pectin did not affected this parameter, when compared to no carbohydrate supplementation. In the presence of casein, the starch supplementation raised the discrete lag time for NDF degradation.