Technical note: correction of net portal absorption of nitrogen compounds for differences in methods: first step of a meta-analysis.
The objective of this study was to evaluate the usefulness of correcting net portal absorption (NPA) of urea-N, ammonia, and AA-N for differences in methods before their inclusion into a meta-analysis. It was hypothesized that the difference, or portal-drained viscera (PDV) balance, between N inputs (apparently digested N plus urea-N) and outputs (ammonia plus AA-N) was 0 in the absence of measurement errors and based on the assumption that other sources of N inputs and outputs were relatively small and balanced each other. A database was built from 44 publications that reported data from 129 treatments (sheep, n = 71; beef cattle, n = 32; and dairy cows, n = 26). When necessary, NPA of urea-N (n = 38) and ammonia (n = 35) results were recalculated on a whole-blood basis, whereas NPA of AA-N (n = 87) was recalculated for all the N from AA transferred across the PDV rather than only the N from the alpha-amino group. Before corrections, PDV balance averaged 22.9% of N ingested (SD 29.0) for all treatments; after corrections, PDV balance significantly decreased to 10.2% of N ingested (SD 34.7). No difference in PDV balance was observed among species before or after corrections. Correcting NPA of urea-N, ammonia, and AA-N increased the accuracy without improving precision. Therefore, from a biological perspective, recalculating reported data seems appropriate to reduce bias due to differences in methods because this approach reduces the excess in N inputs relative to N outputs.
Martineau
R
R
Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, Quebec, Canada.
Ortigues-Marty
I
I
Vernet
J
J
Lapierre
H
H
D000596:Amino Acids / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D005260:Female; D007408:Intestinal Absorption / Q000502:physiology*; D015201:Meta-Analysis as Topic; D009584:Nitrogen / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*; D014508:Urea / Q000378:metabolism
D000596:Amino Acids; D000641:Ammonia; D014508:Urea; D009584:Nitrogen