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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Dairy Forage Research » Research » Publications at this Location » Publication #330452
Title: Predicting nitrogen excretion in commercial grazing system dairy farms

Author
item AARONS, SHARON - Department Of Primary Industries
item GOURLEY, CAMERON J. - Department Of Primary Industries
item Powell, Joseph

Submitted to: International Nitrogen Conference
Publication Type: Proceedings
Publication Acceptance Date: 9/9/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Improving nitrogen (N) management on dairy farms is best facilitated through management of dairy cow feed N intakes (NI), due to strong associations between NI, feed N use efficiencies (NUE, proportion of NI secreted as milk N) and manure N excretion (Nex). Milk urea N (MUN) has also been used as an indicator of excess feed N in dairy systems. While a number of predictive relationships between these parameters have been developed for confinement-based dairy systems, less information is available for grazing dairy systems. Feed NI, Nex and MUN data were determined from surveys and samples collected during five quarterly visits over a year on 43 commercial grazing-based dairy farms representing a wide range of production systems. Relationships were assessed between feed NI, Nex, feed NUE and MUN using this information. The range of regression parameters was generally similar to those reported in the literature for confinement-based dairy systems. The coefficient of determination for the relationship between Nex and NI (Nex = 0.84NIn - 23.6; R2=0.97) was greater than the literature, however, probably due to the metabolic models and other methods used to estimate NI and Nex. Feed NUE declined with feed crude protein (CP) concentration (NUE = -0.79CP + 35.9; R2=0.50) and NI (NUE = -0.009NIn + 25.9; R2=0.08). Mean MUN (12.7 mg/dL) for these grazing system dairy cows was similar to levels reported for confinement dairy herds. Significant but weak relationships were observed between MUN and feed CP (R2=0.19), MUN and NUE (R2=0.10) and MUN and ExN (R2=0.17). These weak relationships were most likely due to the wide range of breeds, feeding systems and milk production levels on these grazing-based farms, compared to stronger MUN relationships determined for more uniform and controlled feeding that occurs for experimental herds and confinement dairy systems reported elsewhere. The relationships suggest that feed models, samples and data collected on farms could be used to predict NI and Nex for grazing system lactating dairy cows.