In vitro degradation dynamics of neutral detergent fiber of signal grass according to supplementation with different sources of nitrogenous compounds and carbohydrates / Dinâmica de degradação in vitro da fibra em detergente neutro de capim-braquiária em função de suplementação com diferentes fontes de compostos nitrogenados e carboidratos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Two experiments were carried out to evaluate the utilization of fibrous carbohydrates from high quality grass by ruminal microorganisms. In the first experiment, it was studied the degradation dynamics of neutral detergent fiber (NDF) from high quality signal grass (Brachiaria decumbens Stapf.) according to supplementation with different sources of carbohydrates (starch or pectin) and (or) different sources of nitrogenous compounds (casein or urea). It was simulated the diet of fatting steers feeding at the raining season, including 30% of concentrate supplementation and 70% of forage. The concentrate was formulated to have 30 % of crude protein (CP) by using starch as energetic source and casein as protein source. Other treatments were constructed by suppressing the energetic or the protein sources in the concentrate and replacing starch by pectin and the crude protein (CP) from casein by CP from the mixture of urea and ammonium sulfate (9:1). Therefore, nine treatments were evaluated: 1. forage; 2. forage + starch; 3. forage + pectin; 4. forage + casein; 5. forage + casein + starch (reference treatment); 6. forage + casein + pectin; 7. forage + urea; 8. forage + urea + starch; and 9. forage + urea + pectin. These treatments were evaluated into ruminal environment simulated by in vitro incubation procedure, being submitted to ten different incubation periods: 0, 3, 6, 9, 12, 24, 36, 48, 72, and 96 hours. The incubation procedure was repeated four times, so there were four evaluations for each incubation period for each treatment. The residual from incubation were analyzed for NDF content, and interpreted by the logistic nonlinear model. It was verified that supplementation including only carbohydrates produced inhibitory effects on degradation rate (kpdNDF). and microorganism growth on potentially degradable NDF (pdNDF) when compared to control treatment (forage). There were reductions of 6.9% and 13.6%; and 2.7% and 4.8% on estimates of these parameters with starch and pectin supplementation, respectively. The isolated addition of casein to the incubation medium reduced kNDFpd 13.6%. Casein addition resulted on a similar pH compared to the observed for the forage treatment. However, it increased the ammonia nitrogen availability. Moreover, the negative effect of casein on kpdNDF can be attributed to amensalistic interactions among microbial species, denominates protein effect. The supplementation including casein and starch or pectin kept the kpdNDF higher than the observed for isolated supplementation with these compounds, even still lower than the kpdNDF from only forage treatment. Urea addition increases kpdNDF 8.2% as a result of the better physical and chemical adequacy of the fermentation environment and the possible absence of amensalistic interactions among microbial species. At the second experiment, it was evaluated the degradation dynamics of NDF from high quality Brachiaria decumbens Stapf in vitro under supplementation with two sources of carbohydrates (starch or pectin ) and different true protein:non-protein nitrogen rates .The experimental materials and procedures were such as in the first experiment. Treatments were constructed from fractional substitution of CP from casein by CP from the urea: ammonium sulfate mixture (9:1) and the substitution of starch by pectin. Therefore, eight treatments were evaluated : A: forage + casein + starch; B: forage + 2/3 CP casein + 1/3 CP U:AS + starch; C: forage + 1/3 CP casein + 2/3 CP U:AS + starch; D: forage + U:AS + starch; E: forage + casein + pectin; F: forage + 2/3 CP casein + 1/3 CP U:AS + pectin; G: forage + 1/3 P casein + 2/3 CB U:AS + pectin; H: forage + U:AS + pectin. Urea supplementation increased 21.7% and 17.0% kpdFDN when compared to casein supplementation for starch and pectin as carbohydrates sources, respectively. Maximum values for kNDFpd were observed for 2/3 U:AS:1/3 casein rate. Therefore, the equilibrium within protein sources into supplements can increase the pdNDF utilization. This behavior would be attributed to lower protein effect, higher availability of degradable peptides into the rumen to supply non-fibrolytic bacterium requirements, and occurrence of positive interactions between microbial species which increase the availability of essential substrates for fibrolytic species.

ASSUNTO(S)

degradabilidade ndf suplementação supplementation nutricao e alimentacao animal fdn degradation

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