Degradabilidade ruminal e digestibilidade in vitro da matéria seca de gramíneas de Cynodon spp em quatro idades de rebrota

Abstract

There were two trials where the first evaluated the in situ degradability of dry matter (DM) and neutral detergent fiber (NDF) of five cultivars of the genus Cynodon in four ages of regrowth, and the second in vitro digestibility of dry matter of the same cultivar and age of regrowth of the first test. In both experiments were considered plant parts (stem + leaf sheath and blade) and the whole plant. Both experiments were carried out within the sector of Animal Science, Faculty of Agricultural Sciences (FCA) at the Federal University of Grande Dourados (UFGD), located in Dourados - MS. We evaluated five varieties of Cynodon, where: Tifton 85, Jiggs, Russell, Tifton 68 and Vaquero, distributed in randomized blocks with split plots. Before starting the work was carried out to standardize the cut in all plots. The cuts were made to 28, 48, 63 and 79 days after the cut for uniformity. To assess the ruminal degradability were used three crossbred, castrated male, aged approximately 38 months and average weight of 400 kg live weight fitted with ruminal cannula using the technique in situ. The materials were incubated in the rumen in the 0, 6, 12, 36, 48 and 96 hours. The design was randomized blocks in factorial, 4 x 5 (ages four and five varieties of cut) and three repetitions. To test the in vitro digestibility of DM (IVDMD) was used in vitro methodology. The rumen fluid necessary for the assessment was collected from cannulated animals fed hay Cynodon. The experimental design was randomized blocks with treatments arranged in a split plot, with the five genotypes under study plots and cut the ages of four subplots, with four replications. The highest values for the kinetic parameters of the DM degradability of whole plant were obtained for the Tifton 68, 24.04, 47.96, 72.00 and 45.60% respectively for the soluble fraction, potentially degradable fraction, potential degradability and degradability effective (5% / h). Same behavior can be observed for the leaf, Tifton 68 with values of 26.65% to fraction "a", 42.85% to fraction "b" 69.50 and 46.69% for "DP" and "DE" respectively. As for the stalk Tifton 85 and Jiggs presented similar to Tifton 68. NDF degradability for the best overall values were expressed as Tifton 68, except for the potentially degradable fraction of the whole plant and leaf and stem and the potential degradability of the leaf, where the horsepower was similar to Tifton 85. The best values for the parameters of ruminal degradation of dry matter and neutral detergent fiber were expressed as Tifton 68 and Tifton 85, as the smallest decreases with advancing maturity, which allows greater flexibility of management for these cultivars. To Jiggs, Russell and Vaquero intervals between cuts or grazing should be shorter to minimize the effect of maturity on the degradability of these cultivars. In the evaluation of in vitro digestibility of dry matter of entireplant, leaf and stem the slide showed statistical differences among the cultivars, and Tifton 68 expressed the highest values, 78,15; 81,72 and 75,45% respectively for the whole plant , leaf and stem. With increasing age of regrowth of forage caused a reduction in the levels of digestibility for all cultivars. Since Jiggs, Russell and Vaquero should have a higher frequency of cut, because of the low IVDMD showed after the 48 days of regrowth.