Comparison of the ruminal metabolism of nitrogen from 15N-labeled alfalfa preserved as hay or as silage.
Alfalfa (Medicago sativa L. cv. AC Blue J) was labeled with 15N during growth in a greenhouse, harvested at early bloom, and preserved as silage (19% dry matter) or as sun-cured hay. The labeled silage and hay were given as single-pulse doses to two lactating Holstein cows fed diets comprising 30% concentrate and 70% alfalfa forage (preserved either as silage or as hay). Labeled forage and ruminal content samples collected for 72 h after dosing were partitioned into N fractions and analyzed for 15N-enrichment. Pool sizes of N compartments and kinetics in the rumen were derived by isotope dilution and by gravimetric measurements. The rate of outflow of total N, determined gravimetrically, was 21% higher with the silage diet than with the hay diet. On both diets, the largest individual flux was associated with the nonprotein, nonammonia, nonmicrobial nitrogen (NPAM-N) pool. As related to the flux of 15N through the acid detergent insoluble N pool, less tracer passed through the solid-phase nonfiber N and the soluble protein-N pools, and more passed through the NPAM-N pool, with silage than with hay. The solid-phase nonfiber N pool, which includes readily available feed N and adherent bacterial- and protozoal-N, constituted the largest N entity in the rumen, followed by the NPAM-N pool. When the forage component of the diet was alfalfa silage, N flux through the NPAM-N pool was remarkably high, and with both methods of preserving alfalfa forage, the exchange of tracer was most intensive through this pool.
Hristov
A N
AN
Research Centre, Agriculture and Agri-Food Canada, Lethbridge, AB. ahristov@uidaho.edu
Huhtanen
P
P
Rode
L M
LM
Acharya
S N
SN
McAllister
T A
TA
D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D005260:Female; D005511:Food Handling / Q000379:methods*; D005519:Food Preservation; D007700:Kinetics; D000455:Medicago sativa; D009584:Nitrogen; D009590:Nitrogen Radioisotopes; D012417:Rumen / Q000378:metabolism*; D012820:Silage / Q000032:analysis
D009590:Nitrogen Radioisotopes; D009584:Nitrogen