Impact of buffer turnover rate on outflow of n compounds in a semi-continuous culture fermenter (RUSITEC)

CLAUDIO ANTONIO POZO; MATEUS LENHART MORAES; CECILIA CAJARVILLE; GILBERTO V. KOZLOSKI

Ubatuba

Workshop; Proceedings of the 9th Workshop on Modelling Nutrient Digestion and Utilization in Farm Animals (MODNUT); 2019

Introduction The degradation rate (kd) is a key parameter for estimating the rumen degradable protein (RDP) fraction of feedstuffs, as by using the equation: A + B(kd/kd+kp), where A and B are the soluble and insoluble protein fractions, respectively, and kp is the passage rate from rumen (NRC, 2001). The values of Kd reported in most nutritional systems were conventionally estimated through the in situ technique (Orskov and McDonald, 1979). This method, however, is based on the determination of disappearance of N compounds from bags, which may occur by the leakage from sample through the bag pores, not necessarily implying degradation by ruminal bacteria. This leakage of sample can involve in an overestimation of the RDP fraction of the crude protein (Bach et al., 2008), which could be exacerbated by an increased passage rate (kp). Thus, we aimed to evaluate the effect of the liquid fraction kp on N compounds profile outflow in semi-continuous culture fermenters.Materials and methods Five semi-continuous culture fermenters were used in an incomplete 3 x 3 Latin square design. The three runs trials were carried out on 9 days each, with 4 days of adaptation and 5 days of sample collection. Each fermenter received daily 10g of the diet in nylon bags with porosity of 50μm. The incubated diet was composed by corn silage (0.60), corn grain (0.21) and soybean meal (0.19). The liquid effluent was removed daily and sampled for N, α-amino-N, peptide-N and ammonia-N analysis. Statistical analysis was carried out using the MIXED procedure of SAS, and linear effects of treatments were analyzed by regression. Results Increasing the passage rate of the liquid fraction did not affect the N degradation or ammonia-N flow, however, increased linearly the peptide-N flow, the total N flow and the total N flow to disappeared N ratio, and decreased linearly the α-amino-N flow. Conclusion The outflow of soluble peptides, as proportion of the N which disappeared from sample, increased linearly at increased buffer infusion rate in the semi-continuous fermenter. This result indicate that the in situ technique overestimate the degradable and underestimate the undegradable protein fraction of feedstuffs.