How Low Can We Go: Nitrogen in Dairy Rations- Mike Van Amburgh

Protein Formulation for High Producing Lactating Dairy Cattle: What are our practical limits?
Mike Van Amburgh
Department of Animal Science

Outline
What are the efficiencies of nitrogen utilization
for lactating dairy cattle and what that might
mean for ration formulation
Discuss some of what we have learned about
nitrogen metabolism
Some research studies and farm examples
Summary

Improving Efficiency of Use of Intake Nitrogen
Opportunities exist – need refining
On farm N efficiencies (milk N:feed N)
20 to 32%
Theoretical efficiency limit 40 to 45% in lactating dairy cattle (Van Vuuren and Meijs, 1987; Hvelplund and Madsen, 1995)
Practical limit is ~ 38 to 40% (groups are achieving this)
Requires refinement of current ration formulation models – better balancing for rumen N and post-ruminal amino acids
Requires refinement of feeding management – reduce variation associated with feed, management

Improving Efficiency of Nitrogen Use
Milk protein output is a function of energy supply and amino acid balance
Urine N is variable and is a function of excess nitrogen intake and recycling
Urine N is most volatile form – so reducing it will reduce the environmental impact and improve efficiency
High levels of urinary indicate:
Overfeeding total protein
High rumen N balance relative to microbial demand
Can use monitoring tools like milk urea nitrogen to diagnose independent of production responses

Value of the “Safety Factor”
500 cows
With forage availability, ration can be balanced at 15% CP for level of production (85 lbs/d, 52.5 lb DMI)
Nutritionist level decision – “safety factor” – doesn’t want cows to lose milk, doesn’t want to lose customer
Management considerations - variation
Cost of 15% vs 15.5% in SBM equiv. ~1 lb = $0.20/cow/d or $36,500/year

Impacts of source and amounts of CP on intestinal supply of N and performance of cows
Ipharraguerre and Clark, 2005

Urinary N is variable form of excreted N Fecal N is fairly constant

Nitrogen excretion in milk, feces and urine based on N intake in lactating dairy cattle – under controlled conditions of energy as first limiting: 88 lb milk/d @53 lb DMI range in CP intake 14 to 18.7%

CNCPS v6.1 Nutrient Excretion – Manure
and Manure Nitrogen

RDP Required in Diet DM
Determined by the amount and type of fermentable carbohydrates in the diet
Dairy NRC (2001): 9 – 11% of diet DM
For diets common to the Northeast: 10.4 – 10.8%
Rely on feed intake and MUN to make final decision
MUN levels of 8 to 10 mg/dl are ideal – need to manage well
CNCPSv6.1 RDP levels as low as 7.6% with good performance – again need to manage well

Blood Urea
Ammonia
N intake
Urinary
Urea

Effect of forage preservation method on urea N production and recycling (Ouellet et al., 2004)
6 cows, 3x3 Latin square
Diets:
60% forage, 40% concentrate (14.5% CP) fed 12x/d
3 different forages:
Sun-cured hay, 10.1% CP
Formic acid-treated silage (12.0% CP)
Microbial inoculated silage (12.2% CP)

Ouellet et al., 2004
Form of forage preservation had little effect on urea N
production and recycling

Lysine and Methionine ratios
Current recommendations
Rulquin
MET: 2.50% of metabolizable protein supply
LYS: 7.30% of metabolizable protein supply
These are similar to 2001 Dairy NRC (2.40 and 7.20%)
Current Recommendations
MET: >2.20% of MP supply
LYS: >6.80% of MP supply
While maintaining a 3:1 ratio of LYS:MET
With new implementation of CNCPS v6.1, factorial calculations appear more in line with ratios.

Limiting amino acids in lactating dairy cows
Met, Lys, and His identified most often as first limiting (but His is questionable in US diets)
Met: when most RUP is provided by oilseed meals, animal-derived proteins, or a combination of the two
Lys: when corn or feeds of corn origin provide most or all dietary RUP
His: when grass silage, barley and oat diets are fed with or without feather meal as sole source of supplemental RUP
Chuck Schwab

Herd Level Examples of Improved Nitrogen Efficiency

Example Herd A – 54 lb DMI, 92 lb Milk

Example Herd Ingredients – 54 lb DMI, 92 lb Milk

Example herd B - 53 lb DMI, 89 lb milk

Herd C
Current stats
DMI 50 lb
CP 15.8%
NDF 30.2%
Actual milk 84 lb
ME allowable 83.5 lb
MP allowable 91 lb
True protein 3.1%
Fat 3.7%
Met 2.3% MP
Lys 6.77% MP

Herd C
Concentrate mix contains Smartamine and Alimet

Herd C

What was the impact on N excretion?
Our calculations indicate ~60 g N/cow/d
less urinary excretion
1100 cows = ~26.5 tons N less in the
environment over 365 d lactation
In 2009, that was $0.40/cow/d reduced
feed costs

Herd Example - D
1050 cows – High group characterized
1,542 lb BW
~100 DIM
59.5 lb DMI
15.8% CP
60% Forage
120 lb milk/d
Milk:Feed (Feed efficiency): 1.99

Herd Example - D
NDF, %DM: 30.9
Starch, % DM: 28.7
Sugar, % DM: 5.4
Ether extract, % DM: 5.1
%Forage: 60.1
Forage NDF, %BW: 0.94

Herd Example - D
Productive N : N Intake – 38%!
Remember – most farms are
25 to 30%
Productive N: Urinary N – 1.33:1
Most farms are 0.6 to 0.8:1

Summary:We have the opportunity to lower protein intakes to reduce the environmental impact of dairy farms and improved income over feed costsWe are getting better at balancing at the limits of protein requirements for lactating cowsAs we approach the absolute requirement, it provides us with the opportunity to estimate the opportunity cost of feed and nutrient managementAny effort to do this will require greater intensity of management and adherence to SOP’s

How Low Can We Go: Nitrogen in Dairy Rations- Mike Van Amburgh

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