In vitro method for determining the ruminal degradation rate of rapeseed meal protein using 15N isotope labelled ammonia nitrogen
Ahvenjarvi, S.; Stefanski, T.; Huhtanen, P.
An in vitro method based on observations of N-14 and N-15 isotope fluxes between ammonia N and non-ammonia (NAN) pools was established to study the ruminal degradation rate of rapeseed meal protein. Feed protein equal to 125 mg of N/I was incubated in the presence of rumen fluid, mineral buffer, and a carbohydrate mixture formulated to provide a constant supply of fermentable energy over the entire incubation period. The ammonia N was labelled with the 15N isotope, and the incubations were carried out for 0, 0.5, 1, 1.5, 2, 3, 4. 5, 6, 8, and 10 h. A model with six pools was used to estimate the rate of protein degradation to ammonia N and the rate of microbial N synthesis from ammonia N. The parameter values were adjusted based on the sizes of the ammonia N-14. ammonia N-15, (14)NAN, and (15)NAN pools observed at different time points over the incubation period. The rate of rapeseed meal N degradation was 0.06/h (0.028 standard deviation between runs), and the predicted effective protein degradability was 0.38 (0.122 standard deviation between runs). The current approach seemed appropriate for determining microbial N synthesis from ammonia N, but measurement of the direct incorporation of amino acids into microbial N may be required to adequately characterize the metabolic events involved in ruminal protein degradation. (C) 2009 Elsevier B.V. All rights reserved.
Modelling; Protein degradation; Rumen
Animal Feed Science and Technology
2009, Volym: 153, nummer: 1-2, sidor: 88-100
Utgivare: Elsevier Masson
Animal and Dairy Science
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