Meta-analysis-based estimates of the efficiency of phosphorus utilisation by dairy cows

Area of Science:

• Animal Nutrition
• Environmental Science
• Agricultural Science

Background:

• Phosphorus (P) is essential for animal functions, but its excretion poses environmental risks.
• Accurate P supply is vital for dairy cows to meet nutritional needs and minimize environmental impact.
• Current P requirement calculations incorporate milk secretion and tissue deposition, using a P utilization efficiency factor.

Purpose of the Study:

• To estimate the efficiency of phosphorus utilization in dairy cows, considering varying P supplies.
• To analyze the relationship between P intake, P excretion (fecal and urinary), and P utilization efficiency.
• To provide data-driven insights for optimizing P supply in dairy cattle diets.

Main Methods:

• A meta-analysis was conducted using 399 observations from 77 studies on dairy cows.
• Standardized P digestibility was calculated, corrected for endogenous fecal P losses.
• Linear and non-linear regressions analyzed P excretion and digestibility in relation to P intake and supply relative to requirements.

Main Results:

• Phosphorus intake above requirements was primarily excreted in feces.
• Urinary P excretion was minor at feed P concentrations below 5.2 g/kg dry matter.
• The estimated standardized P digestibility, representing P utilization efficiency at marginal P supply, was 83%.

Conclusions:

• The study estimates phosphorus utilization efficiency in dairy cows at 83%.
• Excess phosphorus intake is mainly excreted via feces.
• Differentiating P utilization efficiency by P source or lactation stage is not supported by the data for adequate P supply.