Dinâmica de degradação in vitro da fibra em detergente neutro de forragens tropicais em função de suplementação protéica e/ou energética / In vitro degradation dynamics of tropical forages neutral detergent fiber according to protein and/or energy supplementation

AUTOR(ES)

Viviane Aparecida Carli Costa

DATA DE PUBLICAÇÃO

2006

RESUMO

The current thesis was based on two in vitro trials aiming at assessing the effect of protein and/or energy supplementation on ruminal degradation of fibrous carbohydrates of tropical forages. At Experiment 1, it was evaluated the effect of protein and/or energy supplementation on the utilization of fibrous carbohydrates from low quality forage by ruminal microorganisms. The experiment simulated the supplementation of finishing cattle grazing low quality Brachiaria decumbens pasture during the dry season (70:30 forage to concentrate ratio, as dry matter basis). The concentrate used was formulated to contain 30% of crude protein, using starch as the energetic source and casein as the proteic source. The treatments were established by omission of the proteic and/or energetic source of the supplement, associated with the total 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 ruminal 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 content of neutral detergent fiber (NDF) and interpreted using a non-linear logistic model. It was observed that the degradation rate of the potentially degradable NDF (pdNDF) increased almost 46% with casein supplementation (0.0261 and 0.0381 h-1), resulting in an increment of 14.6% in 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 the degradation rate of pdNDF, whereas pectin supplementation did not affect this parameter, when compared to the treatment without carbohydrate supplementation. In the presence of casein, the starch supplementation raised the discrete lag time of NDF degradation. At Experiment 2, it was evaluated the effect of protein and/or energy supplementation on ruminal degradation of fibrous carbohydrates from high quality forage. The evaluation procedures and the forage to concentrate ratio were similar to those used at Experiment 1. Instead of Brachiaria decumbens, samples of elephant-grass (pennisetum purpureum, 21 days of regrowth) were used as basal forage. The treatments were established by omission of the proteic and/or energetic source of the supplement, associated with total substitution of starch by pectin and of crude protein from casein by crude protein from the mixture urea:ammonium sulfate (9:1). The nine treatments were: 1. Forage; 2. Forage plus Starch; 3. Forage plus Pectin; 4.Forage plus Casein; 5. Forage plus Casein plus Starch; 6. Forage plus Casein plus Pectin; 7. Forage plus Urea; 8. Forage plus Urea plus Starch and 9. Forage plus Urea plus Pectin. When submitted to exclusive supplementation of protein or energy, it was detected a reduction in the pdNDF degradation rate. On the other hand, the negative effects of the individual supplementation with protein or energy were or not eliminated according to the final composition of the supplement. The negative effects of the individual supplementation on the pdNDF degradation rate were maintained when casein and pectin or starch and urea were used concomitantly. Conversely, similar degradation rates to that of the basal forage were obtained with the combinations pectin and urea, and starch and casein.

ASSUNTO(S)

amido casein nutrição nutricao e alimentacao animal beef cattle bovino de corte nutrition diet supplements caseína fibras suplementos dietéticos starch degradabilidade fibers degradation

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