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Ruminal metabolism of ammonia N and rapeseed meal soluble N fraction

Stefanski, T. and Ahvenjarvi, S. and Vanhatalo, A. and Huhtanen, Pekka (2020). Ruminal metabolism of ammonia N and rapeseed meal soluble N fraction. Journal of Dairy Science. 103 , 7081-7093
[Research article]

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The present study was conducted to investigate ruminal N metabolism in dairy cows using N-15 labeled N sources [ammonia N (AN), soluble non-ammonia N (SNAN) from rapeseed meal, and insoluble nonammonia N (NAN) from rapeseed meal]. To describe the observed pattern of N-15 transactions in the rumen, dynamic compartmental models were developed. The experiment consisted of 3 experimental treatments allocated to 4 cows according to a changeover design. The results from 2 treatments (AN and rapeseed meal SNAN) are reported in this paper. Ammonia N and rapeseed SNAN, both labeled with N-15, were administered intraruminally. Rumen evacuations in combination with grab samples from the rumen contents were used to determine ruminal N pool sizes. The N-15-atom% excess was determined in N fractions of rumen digesta samples that were distributed between 0 and 82 h after dosing. For the AN treatment, a 2-compartment model was developed to describe the observed pattern in N-15-atom% excess pool sizes of AN and bacterial NJ and to estimate kinetic parameters of ruminal N-15 transactions. For the SNAN treatment, an additional compartment of SNAN was included in the model. Model simulations were used to estimate N fluxes in the rumen. Both models described the observed pattern of N-15-atom% excess pool sizes accurately, based on small residuals between observed and predicted values. Immediate increases in N-15-atom% excess of bacterial N with AN treatment suggested that microbes absorbed AN from extracellular pools rapidly to maintain sufficient intracellular concentrations. Proportionally 0.69 of the AN dose was recovered as NAN flow from the rumen. A rapid disappearance of labeled SNAN from rumen fluid and appearance in bacterial N pool indicated that, proportionally, 0.56 of SNAN was immediately either adsorbed to bacterial cell surfaces or taken up to intracellular pools. Immediate uptake of labeled SNAN was greater than that of AN (proportionally 0.56 vs. 0.16 of the dose). Degradation rate of SNAN to AN was relatively slow (0.46/h), but only 0.08 of the SNAN dose was estimated to escape ruminal degradation because of rapid uptake by the bacteria. Overall, losses of the N-15 dose as AN absorption and outflow from the rumen were higher (P < 0.01) for the AN than the SNAN treatment (0.31 and 0.11 of the dose, respectively). Consequently, recovery as NAN flow was greater for SNAN than for AN treatment (0.89 vs. 0.69 of the dose). Estimated rate of bacterial N recycling to AN was on average 0.006/h, which suggests that N losses due to intraruminal recycling are small in dairy cows fed at high intake levels. We conclude that SNAN isolated from rapeseed meal had better ruminal N utilization efficiency than AN, as indicated by smaller rurninal N losses as AN (0.11 vs. 0.31 of the dose) and greater bacterial N flow (0.81 vs. 0.69 of the dose). Furthermore, the current findings indicate that rapid adsorption of soluble proteins to bacterial cells plays an important role in ruminal N metabolism.

Authors/Creators:Stefanski, T. and Ahvenjarvi, S. and Vanhatalo, A. and Huhtanen, Pekka
Title:Ruminal metabolism of ammonia N and rapeseed meal soluble N fraction
Series Name/Journal:Journal of Dairy Science
Year of publishing :2020
Page range:7081-7093
Number of Pages:13
Publication Type:Research article
Article category:Scientific peer reviewed
Version:Published version
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 402 Animal and Dairy Science > Animal and Dairy Science.
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Agricultural Science
Keywords:rapeseed, nitrogen, N-15, soluble protein, ammonia
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Additional ID:
Type of IDID
Web of Science (WoS)000565902000001
ID Code:17776
Faculty:VH - Faculty of Veterinary Medicine and Animal Science
Department:(NL, NJ) > Dept. of Agricultural Research for Northern Sweden
(VH) > Dept. of Agricultural Research for Northern Sweden
Deposited By: SLUpub Connector
Deposited On:09 Oct 2020 13:58
Metadata Last Modified:15 Jan 2021 19:46

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