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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 #329262
Title: Relative partitioning of N from alfalfa silage, corn silage, corn grain and soybean meal into milk, urine, and feces, using stable 15N isotope

Author
item BARROS, TIAGO - University Of Wisconsin
item Powell, Joseph
item DANES, MARINA - University Of Wisconsin
item AGUERRE, MATIAS - University Of Wisconsin
item WATTIAUX, MICHEL - University Of Wisconsin

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2017
Publication Date: 5/22/2017
Citation: Barros, T., Powell, J.M., Danes, M.A., Aguerre, M.J., Wattiaux, M.A. 2017. Relative partitioning of N from alfalfa silage, corn silage, corn grain and soybean meal into milk, urine, and feces, using stable 15N isotope. Animal Feed Science and Technology. 229:91-96.

Interpretive Summary: Most cows on confinement dairy farms are fed rations comprised of alfalfa silage, corn silage, corn grain, and a protein supplement, usually soybean meal. To better understand relationships between dairy cow diets and manure nitrogen loss on a typical dairy farm, this experiment investigated how much of the nitrogen contained in alfalfa silage, corn silage, corn grain and soybean meal ends up in milk, urine and feces. Per unit nitrogen in milk, the nitrogen deposited in urine and feces was greatest for the silages followed by corn grain and soybean meal. This information can be used to refine the type and amount of forage, grain and protein supplement fed to dairy cows to maximize nitrogen secretion in milk, and therefore minimize environmental impacts associated with nitrogen excretions in urine and feces.

Technical Abstract: The objective of this study was to determine the relative partitioning of nitrogen (N) in alfalfa silage (AS), corn silage (CS), corn grain (CG) and soybean meal (SBM) in milk, urinary and fecal N in lactating dairy cows. For eleven days, twelve multiparous late-lactation Holstein cows (means ± SD; 264 ± 18 DIM) were fed once a day a pretreatment total mixed ration (TMR) formulated to contain (DM basis) 33.5, 32.5, 19.0, 12.5 and 2.5% of CS, AS, CG, SBM and a mineral-and-vitamin premix, respectively. On the morning of day 12, cows were blocked by milk yield and randomly assigned within block to one of four dietary treatments constructed by replacing one feed ingredient per treatment at natural abundance of 15N from the pretreatment TMR with its homologue 15N-labeled ingredient. Cows were fed dietary treatments for four days (d 12 to 15) and the pretreatment (non-labeled) TMR from day 16 to 19. Feed intake and lactation performance were measured daily whereas total fecal and urinary collections were conducted on each cow every 6 h from day 12 to 19. Feeding 15N-labeled ingredients had no effects on DMI (mean ± SD; 22.0 ± 2.0 kg/d), milk yield (26.4 ± 5.2 kg/d), N intake (631 ± 25 g/d), milk protein concentration (3.47 ± 0.33%) and N use efficiency (milk N/intake N; 23.5 ± 4.6%). The ratio of 15N atom % excess (APE) in urine to 15N APE in milk and the ratio of 15N APE in feces to 15N APE in milk measured on the fourth day of feeding the treatment TMR were used as indicators of relative N partitioning. The 15N APE urine/milk ratio was greater for AS (1.51) than for CS (1.30), which in turn was greater than for the concentrates (1.02 for CG and 0.94 for SBM). In addition, the APE 15N feces/milk ratio was greater in silages than concentrates (2.12 vs. 1.20, respectively). Overall results from this study suggested that for every unit of N secreted in milk, more urinary N and even more fecal N was from silages than from concentrates.