{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/76829"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/76829","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Ruminal Nitrogen Recycling and Nitrogen Efficiency in Lactating Dairy Cattle","abstract":"Excess nitrogen (N) excretion from animal agriculture results in reduced air and water quality, and poses a risk to human health. Although the dairy industry utilizes milk urea N (MUN) to monitor protein feeding and N excretion, phenotypic diversity among cows may influence MUN and thus bias feed management. An initial study using data from 2 previously published research trials and a field trial, observed that cow had a significant effect on MUN variation. Regression models, utilized to predict MUN, corrected for dietary nutrients and some animal effects, and thus the observed effect of cow on MUN variation may reflect genetic selection decisions of animals with either poor or efficient urea transport. A second trial observed that MUN and PUN concentrations were positively correlated with gut urea clearance, providing evidence for differences in urea transport activity among cows. The presence of urea transport variation suggests that current protein recommendations may not estimate true requirements. A third trial observed that animals fed sub-NRC levels of RDP and RUP had reduced N intake and excretion of fecal N, urinary urea-N, and MUN. Animals maximized N efficiency and had no loss in milk production, suggesting a possible overestimation of RDP and RUP in the current NRC prediction model. The present project provides evidence for phenotypic variation among cows, which may be partially explained by differences in urea transport activity. Future work confirming genetic variation among urea transporters may provide an opportunity to improve feeding management if cow urea efficiency is known.","abstract_html":"Excess nitrogen (N) excretion from animal agriculture results in reduced air and water quality, and poses a risk to human health. Although the dairy industry utilizes milk urea N (MUN) to monitor protein feeding and N excretion, phenotypic diversity among cows may influence MUN and thus bias feed management. An initial study using data from 2 previously published research trials and a field trial, observed that cow had a significant effect on MUN variation. Regression models, utilized to predict MUN, corrected for dietary nutrients and some animal effects, and thus the observed effect of cow on MUN variation may reflect genetic selection decisions of animals with either poor or efficient urea transport. A second trial observed that MUN and PUN concentrations were positively correlated with gut urea clearance, providing evidence for differences in urea transport activity among cows. The presence of urea transport variation suggests that current protein recommendations may not estimate true requirements. A third trial observed that animals fed sub-NRC levels of RDP and RUP had reduced N intake and excretion of fecal N, urinary urea-N, and MUN. Animals maximized N efficiency and had no loss in milk production, suggesting a possible overestimation of RDP and RUP in the current NRC prediction model. The present project provides evidence for phenotypic variation among cows, which may be partially explained by differences in urea transport activity. Future work confirming genetic variation among urea transporters may provide an opportunity to improve feeding management if cow urea efficiency is known.","abstract_has_math":false,"creators":["Aguilar, Michelle"],"institution":"Virginia Tech","degree_name":"Master of Science","degree_level":"masters","degree_discipline":"Dairy Science","degree_department":"Dairy Science","school":null,"contributors":[],"advisors":[],"committee_chairs":["Hanigan, Mark D."],"committee_members":["James, Robert E.","Akers, Robert Michael"],"year":2012,"date_issued":"2012-07-10","date_published":"2012-07-10","updated_at":"2026-07-22T22:20:21Z","subjects":["feeding management","milk urea nitrogen","dietary protein","nitrogen recycling"],"languages":["en_US"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["etd-07242012-133749"],"render_values":[{"text":"etd-07242012-133749","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/10919/76829","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Hanigan, Mark D."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["James, Robert E.","Akers, Robert Michael"]},{"key":"dc:contributor.department","label":"Department","values":["Dairy Science"]},{"key":"dc:creator","label":"Author","values":["Aguilar, Michelle"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2017-04-04T19:49:34Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2017-04-04T19:49:34Z","2016-09-27"]},{"key":"dc:date.issued","label":"Date","values":["2012-07-10"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.dcmitype","label":"Dc Type Dcmitype","values":["Text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Dairy Science"]},{"key":"thesis:degree_level","label":"Degree Level","values":["masters"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["feeding management","milk urea nitrogen","dietary protein","nitrogen recycling"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en_US"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["etd-07242012-133749"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/10919/76829"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Excess nitrogen (N) excretion from animal agriculture results in reduced air and water quality, and poses a risk to human health. Although the dairy industry utilizes milk urea N (MUN) to monitor protein feeding and N excretion, phenotypic diversity among cows may influence MUN and thus bias feed management. An initial study using data from 2 previously published research trials and a field trial, observed that cow had a significant effect on MUN variation. Regression models, utilized to predict MUN, corrected for dietary nutrients and some animal effects, and thus the observed effect of cow on MUN variation may reflect genetic selection decisions of animals with either poor or efficient urea transport. A second trial observed that MUN and PUN concentrations were positively correlated with gut urea clearance, providing evidence for differences in urea transport activity among cows. The presence of urea transport variation suggests that current protein recommendations may not estimate true requirements. A third trial observed that animals fed sub-NRC levels of RDP and RUP had reduced N intake and excretion of fecal N, urinary urea-N, and MUN. Animals maximized N efficiency and had no loss in milk production, suggesting a possible overestimation of RDP and RUP in the current NRC prediction model. The present project provides evidence for phenotypic variation among cows, which may be partially explained by differences in urea transport activity. Future work confirming genetic variation among urea transporters may provide an opportunity to improve feeding management if cow urea efficiency is known."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Master of Science"]},{"key":"dc:title","label":"Title","values":["Ruminal Nitrogen Recycling and Nitrogen Efficiency in Lactating Dairy Cattle"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Hanigan, Mark D."],"dc:contributor.committeemember":["James, Robert E.","Akers, Robert Michael"],"dc:contributor.department":["Dairy Science"],"dc:creator":["Aguilar, Michelle"],"dc:date.accessioned":["2017-04-04T19:49:34Z"],"dc:date.available":["2017-04-04T19:49:34Z","2016-09-27"],"dc:date.issued":["2012-07-10"],"dc:description.abstract":["Excess nitrogen (N) excretion from animal agriculture results in reduced air and water quality, and poses a risk to human health. Although the dairy industry utilizes milk urea N (MUN) to monitor protein feeding and N excretion, phenotypic diversity among cows may influence MUN and thus bias feed management. An initial study using data from 2 previously published research trials and a field trial, observed that cow had a significant effect on MUN variation. Regression models, utilized to predict MUN, corrected for dietary nutrients and some animal effects, and thus the observed effect of cow on MUN variation may reflect genetic selection decisions of animals with either poor or efficient urea transport. A second trial observed that MUN and PUN concentrations were positively correlated with gut urea clearance, providing evidence for differences in urea transport activity among cows. The presence of urea transport variation suggests that current protein recommendations may not estimate true requirements. A third trial observed that animals fed sub-NRC levels of RDP and RUP had reduced N intake and excretion of fecal N, urinary urea-N, and MUN. Animals maximized N efficiency and had no loss in milk production, suggesting a possible overestimation of RDP and RUP in the current NRC prediction model. The present project provides evidence for phenotypic variation among cows, which may be partially explained by differences in urea transport activity. Future work confirming genetic variation among urea transporters may provide an opportunity to improve feeding management if cow urea efficiency is known."],"dc:description.degree":["Master of Science"],"dc:identifier.other":["etd-07242012-133749"],"dc:identifier.uri":["http://hdl.handle.net/10919/76829"],"dc:language.iso":["en_US"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["feeding management","milk urea nitrogen","dietary protein","nitrogen recycling"],"dc:title":["Ruminal Nitrogen Recycling and Nitrogen Efficiency in Lactating Dairy Cattle"],"dc:type":["Thesis"],"dc:type.dcmitype":["Text"],"thesis:degree_discipline":["Dairy Science"],"thesis:degree_level":["masters"],"thesis:degree_name":["Master of Science"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:20:21Z"}