Perspectives in ruminant Urea recycling protein efficiency, - - PowerPoint PPT Presentation

Perspectives in ruminant protein efficiency, recycling, and amino acids

Evan Titgemeyer Kansas State University Topics for today

Urea recycling Should I add urea to the diet? Amino acid requirements Should be believe the NRC?

Decreasing dietary CP

Reproduction, diet cost, environment Still meet MP requirement?

• Increase RUP
• Supplement AA

But, are the bacterial happy?

Predicting RDP requirements

Estimate MCP (microbial protein) Estimate efficiency of N capture RAN requirement = MCP ÷ efficiency RAN supply = RDP + recycled urea

(MCP = Microbial Crude Protein) (RAN = Ruminally Available N)

Kennedy, 1980 Rumen ammonia, mg/L Ruminal clearance of urea (L/day) With sucrose Without sucrose

Ruminal Clearance of Urea

Urea Urea VFA (pH 6.2-6.6) NH3

+

• Urease

NH3 Urea movement across epithelium

Serosa Mucosa

Urea Urea NH3 NH3

Serosa Mucosa

MCP Urease NH3

Urea supplementation (% of DM) 0.4 0.8 Diet CP, % 12.6 13.7 14.9 DMI, kg/d 18.1 18.9 19.0 Milk, kg/d 32.7 33.8 34.0 Milk protein, kg/d 0.90 0.94 0.96 Rumen NH3, mM 3.8 6.2 8.2 PUN, mM 3.3 5.5 7.8 Lactating dairy cattle

Rojen et al., 2011

Urea supplementation (% of DM) Nitrogen 0.4 0.8 N Intake, g/d 366 416 457 Urea Production, g/d 113 174 186 Recycled, g/d 75 104 96 Salivary, g/d 11 16 Recycled, % 66 60 52 Lactating dairy cattle

Rojen et al., 2011

Urea = 113 Liver Diet RDP = 240 75

Rojen et al., 2011

Dairy cows fed 12.6% CP diet Urine = 27 NH3 = 105 ??

Saliva = 11

How do we use this information?

Target optimal supply of RAN: ‐ If we know MCP and ruminally recycled urea, then we can calculate the necessary RDP My perspective: ‐ For most lactation diets, deficiencies in RAN are unlikely to exist and certainly not likely to be severe

MP Requirements

‐ NRC (2001) MP requirement = maintenance + milk protein/0.67 ‐ Estimate of efficiency is key! ‐ Efficiency < 0.67 ‐ Efficiency not constant, at least for a herd

Amino acid utilization

Input Output

‐2 ‐1 1 2 3 4 2 4 6 8 10 12

NRC

MP Requirements

NRC, 2001 40 50 60 70 80 90 200 400 600

Milk N Productive N Efficiency = 64% 42% 23% 15%

Casein supplementation, g/d Nitrogen, g/d

Efficiency of MP use in lactating cows

Whitelaw et al., 1986

Efficiency of nutrient use (Individuals vs. herds)

Plasma Lysine

16 20 24 28 32 20 30 40 50 60 70 80 90 100 110

3 6 9 12 15

Nitrogen Retention

Lysine supplementation, g/d

Lesser affinity Greater affinity

AA Requirements

Efficiency of AA use isn’t static ‐ Energy effects ‐ AA role as anabolic stimulus

16 18 20 22 24 26 1 2 3

N retention, g/d Effect of Energy Supply on Methionine Use Supplemental L-Methionine, g/d Schroeder et al., 2006

Efficiency = 11% +Glucose Control +Fat +Propionate +Acetate Efficiency = 21%

75 100 125 150 175 200 225 250 150 300 450 600 750

Low energy intake High energy intake Amino acid supply, g/d Milk protein secretion

MP Requirements

‐ Estimates of maintenance and efficiency are correlated with each other

Input Output

‐2 ‐1 1 2 3 4 2 4 6 8 10 12

NRC Reality

Efficiency of use varies among AA

Average efficiency of AA utilization for growth ‐ Methionine = 26% (11 trials) ‐ Leucine = 38% (4 trials) ‐ Histidine = 64% (2 trials) ‐ Lysine = 47% (3 trials)

AA Requirements

Why hasn’t the 0.67 efficiency ruined the dairy industry? ‐ No one uses it as gospel ‐ Overestimated maintenance requirement balances the underestimated efficiency ‐ MP supply correlated to energy supply ‐ We work over a fairly narrow range

AA Requirements

We have a lot to learn! ‐ Empirical observations of responses to methionine and lysine are useful in predicting times to supplement ‐ At some point, perhaps in 10‐15 years, we’ll have answers on some other amino acids