GRASS HAYS EVALUATION BY IN VITRO GAS PRODUCTION

GRASS HAYS EVALUATION BY IN VITRO GAS PRODUCTION TECHNIQUE 1 VELHO, J. P. 2, GENRO, T. C. M. 3, HAYGERT-VELHO, I. M. P. 4, SILVEIRA, V. C. P. 5 1 – Research supported by Federal University of Santa Maria, EMBRAPA South Livestock Centre and FAPERGS. 2 – M. Sc. Student, Federal University of Rio Grande do Sul. Scholarship by CNPq. velhojp@ig. com. br 3 – Dr. Sc. , Researcher at FEPAGRO, São Gabriel, RS, Brasil. cristina@cppsul. embrapa. br 4 – Dr. Sc. , Student, Federal University of Rio Grande do Sul. imphaygert@yahoo. com. br 5 – Ph. D. , Researcher at EMBRAPA South Livestock Centre. vicentesilveira@smail. ufsm. br INTRODUCTION RESULTS AND DISCUSSION The development of domestic ruminants is influenced by inherent factors of the animal, by food and by the interaction between animal and the food. Yet, the nutritional value of the food depends on the kind of the soil, climatic conditions, vegetal species, hay stage and so on. Due to this big variation on the hay quality, it becomes necessary to know the nutritional value of each species, what is fundamental to the formulation of diets more appropriated to nutritional demand of animals. On Table 1, the average values of the partial composition of food and gas production bromate considering France et al. (1993) model are shown. On the figure 1, we can notice the cumulative production of gas in each evaluated food. Despite of the differences of the species and hay stage among the foragings none of the studied variable showed significant statistical different (P>. 05), considering that the physicochemical composition of the foragings were similar related to the import of dry material, fiber in neutral detergent and nitrogen. There was no difference among the species and neither among hay stages. However, there is a difference from a percentual point among the species in the respective hay stages for the degradation rate values. Valadares Filho et al. (2002) present higher values for degradation rates (3, 16 %/h-1) of coast cross grass between 46 and 60 days of growing than Cynodon 1 of this experiment, considering that the grass had a better quality, had 10. 25% of crude protein and 78. 8% of fiber in neutral detergent. We emphasize that the other mentioned authors used the nylon mobile bag “in situ”. The hay stage “per si” is not good indicator for the nutritive value of plants for ruminants, when evaluated by in vitro gas production technique. We intended to evaluate the degradation rate of hays Cynodon and Setaria in two hay stages produced in Rio Grande do Sul, using semi-automated in vitro gas production technique, with agreement to Maurício et al. (1999). MATERIALS AND METHODS The present study was accomplished at Laboratory of Animal Nutrition in the EMBRAPA South Livestock center and it evaluated the kinetic parameters of hay fermentation: Cynodon (Cynodon dactylon L. Pers. versus Coast cross 1) in vegetative stadium with 45 days of deferiment (Cynodon 1) and Cynodon (Cynodon dactylon L. Pers. versus Coast cross 1) in florescence stage (Cynodon 2) and Setaria (Setaria sphcelata) in vegetative stadium (Setaria 1) and florescence stage (Setaria 2). One gram sample was incubated in each flask (in triple) with capacity for 160 ml from which 90 ml were occupied through cultivation according to Theodorou et al (1994) and 10 ml of ruminal inoculator, remaining 60 ml for gas expansion from fermentation. The shot of 50 ml by culture was done five hours before inoculation of the flasks, which were hold in incubator at 39ºC. Ruminal inoculator was withdrawn of an adult cow, Holstein race, with 650 kg liveweight, non-lactate, that had the natural range of Rio Grande do Sul as range, with no fast before the collect. Besides ruminal liquid collect, it was taken a part of solid material from rumen and shaked with the liquid in liquefier on the proportion of 1: 1 during five seconds. After that, they were filtrated in nylon bag with porosity of 48 micron. Table 1. Partial bromate composition and gas production parameters estimated by the France et al. (1993) model. Grass hays DM (%) NDF (%DM) CP (%DM) A 1 (m. L) Lag 1 (Hora) 1 (%. h-1) Cynodon 1 93. 91 87. 89 5. 61 179 1. 89 2. 6 Cynodon 2 93. 84 81. 16 5. 90 158 1. 68 2. 7 Setaria 1 94. 00 80. 01 6. 77 158 2. 53 1. 6 Setaria 2 93. 62 87. 20 4. 78 143 2. 29 1. 7 A = Maximum potential of gas production; Lag = Lag time; = Rate of gas production 1 – Averages followed by different letters in the same column differ statistically at the level at 5% by pdiff test. The pressure of the gas accumulation resulted from fermentation was measured using a pressure transducer and the conversion of pressure into volume was done using the equation: y = -0, 9831 + 4, 8533 P + 0, 0583 P 2, described by Velho et al. (2003). Preestablished times for reading pressure and volume were 2, 4, 6, 8, 10, 12, 16, 20, 24, 30, 36, 48, 72 and 96 after the beginning of incubation. The obtained results were subjected to the France et al. (1993) model Y = A – BQt Z√t, where Q = e-b, Z = e-c, B = eb. T + c√T and: Y = Gas production (m. L); t = incubation time (hour); A = the value of assíntota for “pool” size of gas (m. L); T = “lag time”; b = h-1 and c = h-0, 5. The obtained parameters were statistically analyzed by SAS (1989) software. FIGURE 1. Cumulative gas production.