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Dose response to postruminal urea in lactating dairy cattle.

K Nichols1, R Rauch1, L Lippens2

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|August 29, 2023
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Summary

Supplying urea postruminally to dairy cows did not improve dry matter intake (DMI) or nitrogen utilization. Increasing urea levels linearly increased milk urea and urinary excretion, indicating postruminal delivery does not overcome DMI limitations.

Keywords:
dry matter intakemilk nitrogen efficiencynitrogen balanceurea recycling

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Area of Science:

  • Animal Science
  • Ruminant Nutrition
  • Dairy Cattle Metabolism

Background:

  • Dietary urea inclusion in dairy cattle diets is limited by reduced dry matter intake (DMI) and inefficient rumen nitrogen (N) utilization.
  • Postruminal urea supplementation is proposed to overcome these limitations and enhance urea inclusion levels.

Purpose of the Study:

  • To investigate the effects of postruminal urea infusion on DMI, milk production, nutrient utilization, and N balance in dairy cows.
  • To determine if abomasal urea supplementation can mitigate the negative impacts of high urea levels on feed intake and N efficiency.

Main Methods:

  • Four rumen-fistulated Holstein-Friesian dairy cows were used in a 4x4 Latin square design.
  • Urea was continuously infused into the abomasum at four levels (0, 163, 325, 488 g/d), increasing dietary crude protein (CP) by 0-6%.
  • Measurements included DMI, milk yield and composition, nutrient digestibility, rumen fermentation, N balance, and plasma constituents.

Main Results:

  • Dry matter intake and energy-corrected milk yield showed quadratic responses to urea dose, with no overall improvement.
  • Milk urea content, apparent total-tract CP digestibility, and urinary N excretion increased linearly with increasing urea infusion.
  • Postruminal urea supplementation did not mitigate DMI depression at higher inclusion levels.

Conclusions:

  • Postruminal urea delivery does not alleviate the negative effects of increasing urea levels on dry matter intake in dairy cows.
  • While postruminal urea increased N utilization efficiency to some extent, it did not improve overall feed intake or milk production beyond certain levels.