Ammonia-nitrogen release urea samples with different protection to in vitro ruminal degradation

The aim of the study was to compare the protection degree against rumen degradation of 2 slow release urea (SR) prototypes. The study was conducted in a closed batch fermentation system including a negative control (C- no urea) and 3 treatments (T): Urea (U), SR1 (Protigen®- Karizoo, Caldes, Spain) and SR2. Incubations were conducted in triplicate for U, SR1 and SR2 and duplicate for C within period, and in two replicated periods. Isonitrogenous samples (155 mg N) were weighed in glass tubes. Ruminal fluid (RF) was collected from a ruminally fistulated fasted adult cow, filtered through 4 layers of cheesecloth and kept at 39°C. The incubation medium was prepared anaerobically by mixing a N-free buffer solution with RF in a 4:1 ratio. The medium (200 ml) was added to each tube and placed in a 39.0 °C water bath with agitation for 24 h. Each tube was sampled in duplicate at 0, 1, 2, 4, 6, 8 and 24 h of incubation, acidified, and frozen. The day of analysis, samples were centrifuged at 15,000 × g for 15 min and the supernatant analysed for ammonia concentration by spectrophotometry. The NH3-N concentrations at each incubation time (IT) was expressed as the difference between mg of NH3-N/100 ml corrected by their C. Results were analysed as repeated measures using the mixed procedure of SAS, were T, IT and their interaction were used as fixed factors, and period and the GT as random effects. In case of significant interactions, the slice output option was used to determine the IT at which T were different. The concentrations of NH3-N were different among T (P=0.029). The highest mean value was observed with U. SR had slower release of NH3-N compared to U, and SR1 was numerically slower than SR2. IT was significant (P<0.001). Starting from similar N-NH3 among T at time 0, differences became wider over time (26.22, 20.59, 23.43 mg/100 ml at 24 h for U, SR1 and SR2 respectively). The type of coating used to protect U can be a tool to modulate the rate of urea release. Acknowledgements: Trial was supported by “CowficieNcy” project-H2020-MSCA-RISE. We thank Mr. Ramon Vila (Laboratorios Karizoo s.a.) for providing samples.