Stylized pig surrounded by glowing phosphorus molecules, symbolizing efficient nutrient absorption.

The Pig Phosphorus Puzzle: How Feed Intake Impacts Nutrient Absorption

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Rhea Morgan in Health & Wellness October 2026 • 4 min read.

"Unlocking the secrets of phosphorus digestibility in growing pigs to optimize feed efficiency and reduce environmental impact."


In modern pig farming, maximizing nutrient absorption from feed is crucial for both animal health and environmental sustainability. Phosphorus (P) is a key nutrient, vital for bone development and various metabolic processes. However, the efficiency with which pigs absorb phosphorus can vary, influenced by factors such as the amount of feed they consume.

Recent research has explored how different levels of feed intake (FI) affect the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus in growing pigs. Understanding these dynamics is essential for formulating diets that not only meet the pigs' nutritional needs but also minimize phosphorus excretion, a major contributor to water pollution.

This article breaks down the findings of a detailed study investigating the interplay between feed intake, dietary phosphorus levels, and phosphorus digestibility in growing pigs. We'll explore how these factors interact to influence nutrient absorption and what practical implications these findings have for pig farmers.

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Understanding Phosphorus Use in Growing Pigs

Research on phosphorus nutrition in growing pigs has developed a robust understanding of phosphorus sources, digestion, absorption, bioavailability, excretion, and homeostasis, helping define and meet pigs’ phosphorus requirements. A 2012 meta-analysis examined how dietary phosphorus forms, calcium, and added phytase affect phosphorus digestion and metabolic utilization. Phosphorus from different sources can behave differently during digestion and absorption, resulting in different bioavailability for pigs.

Methods for Assessing Feed Phosphorus

Methods used to determine available phosphorus in swine feeds include relative bioavailability (RBV), apparent total tract digestibility (ATTD), standardized total tract digestibility (STTD), and true total tract digestibility (TTTD). Available phosphorus represents phosphorus digested, absorbed, and available for utilization, while total phosphorus also includes phosphorus that is not available and is mostly bound to phytate. Because pigs’ response to phosphorus intake is complex, optimizing phosphorus utilization requires a multicriteria approach. One approach described in the research uses a mechanistic mathematical model of phosphorus and calcium absorption and deposition in bone and soft tissues.

Decoding Phosphorus Digestibility: The Feed Intake Factor

Stylized pig surrounded by glowing phosphorus molecules, symbolizing efficient nutrient absorption.

A recent study investigated how feed intake influences phosphorus digestibility in pigs, focusing on diets with varying phosphorus concentrations. Researchers used seventy-two barrows, dividing them into groups fed different diets (P-free, low-P, and moderate-P) and varying feed intake levels (3%, 4%, and 5% of body weight per day). The goal was to measure how efficiently the pigs absorbed phosphorus under these different conditions.

The study revealed a few key insights:

  • Feed Intake Matters: The amount of feed pigs consume directly affects how well they absorb phosphorus.
  • Low-P vs. Moderate-P Diets: In pigs fed low-phosphorus diets, changing the amount of feed didn't significantly alter phosphorus absorption. However, in pigs fed moderate-phosphorus diets, increasing feed intake led to decreased phosphorus absorption.
  • Dietary P Level is Key: How pigs respond to different feed intake levels depends on the phosphorus content of their diet.
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Reviewing Phosphorus and Calcium Assessment

A 2021 review examines current methods for assessing phosphorus and calcium bioavailability in pig feed ingredients and estimating pigs’ phosphorus requirements. It also describes promising strategies to decrease phosphorus excretion by growing pigs. The review’s stated aim is to assess nutritional values of feed ingredients and improve the precision of requirement estimates.

Specifically, the study found that with moderate-P diets, as feed intake increased, the ATTD and STTD of phosphorus decreased. This suggests that pigs may have a harder time efficiently absorbing phosphorus when they consume larger amounts of a moderate-phosphorus feed. The impact of feed intake on phosphorus absorption was less pronounced in the low-P diet group.

Practical Takeaways: Optimizing Phosphorus Use in Pig Farming

The research underscores that feed intake level is a critical factor influencing phosphorus digestibility in growing pigs, particularly when they are fed moderate-phosphorus diets. Farmers need to be aware of these interactions to fine-tune their feeding strategies.

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Calcium’s Influence on Phosphorus Absorption

A study using 60 growing male pigs tested whether high dietary calcium reduces phosphorus absorption more in diets supplemented with microbial phytase. The proposed explanation was that high calcium could reduce inositol phosphate degradation and increase phosphorus precipitation. A review of growing-pig phosphorus nutrition describes dietary sources, digestion, absorption, bioavailability, and requirements, while identifying areas of consensus and debate that warrant further investigation.

Phosphorus Supply and Food Security

Phosphorus is essential for life, and its use in agricultural production systems requires attention. Pigs and poultry, both monogastric animals, can contribute significantly to global food security while remaining highly dependent on mineral inorganic phosphorus in their feed. Together, pig and poultry meat represent 70% of global meat, according to the cited source.

These findings support the idea that carefully balancing feed intake and phosphorus levels in pig diets can lead to more efficient nutrient utilization. This not only benefits the animals' health and growth but also reduces phosphorus excretion, contributing to more sustainable farming practices.

Future research should focus on identifying the optimal balance of feed intake and dietary phosphorus levels to maximize nutrient absorption while minimizing environmental impact. By implementing these strategies, the pork industry can move towards more sustainable and efficient production methods.

Endogenous phosphorus losses and hindgut disappearance

  • 128.95 and 153.63 mg/kg DMIWith a phosphorus-free diet using GEL as the protein source, estimated endogenous phosphorus loss was 128.95 mg/kg DMI. The estimate was 153.63 mg/kg DMI when the regression method used diets with increasing SDPP; the reported comparison had p<0.06.[1]Caveat: Standard error = 77.0; p<0.06
  • about 8% lowerThe phosphorus-free-diet estimate was about 8% below the value reported for pigs averaging 53.1 kg fed diets containing 30% GEL.[1]
  • 166.3; standard deviation 35.8 mg/kg DMIAcross cited assessments using phosphorus-free diets with GEL as the protein source, endogenous losses averaged 166.3 mg/kg DMI, with a standard deviation of 35.8 mg/kg DMI.[1]
  • 9.1% to 5.8% percentIn a separate report, apparent hindgut disappearance of phosphorus fell from 9.1% to 5.8% when pigs received a diet supplemented with phytase and monocalcium phosphate.[2]

What the digestibility measures leave visible

The low-phosphorus result is specifically a lack of detected linear or quadratic feed-intake effects on ATTD and STTD, not proof that the measures are identical across intake levels.[3]

ATTD alone does not separate phosphorus originating from the animal from phosphorus originating in feed in the excreta. Accounting for basal endogenous losses in STTD therefore changes what the digestibility measure represents.[4]

How loss estimates and digestibility methods compare

The phosphorus-free-diet loss estimate sits below the cited multi-study average, while the reported standard deviation indicates spread among the values summarized. The separate GEL comparison likewise places the estimate below an earlier reported value, but it is not a direct comparison of identical study conditions.[1]

Across experiments, ATTD estimates for the same feed ingredient can vary. STTD accounts for basal endogenous loss, which is described as a minimal nutrient loss independent of feed composition but influenced by dry matter intake.[4] [5]

What phosphorus digestibility still leaves unresolved

  • How much of the variation in ATTD estimates for a given ingredient reflects differences among experiments, and how much reflects the ingredient itself?[4]
  • How does dry matter intake affect the basal endogenous loss adjustment used to interpret STTD?[5]

Sources

  1. Methodologies for the Determination of Endogenous Phosphorus Losses in Growing Pigs (pmc.ncbi.nlm.nih.gov)
  2. Dependence of the hindgut disappearance of phosphorus in pigs on the quantity of phosphorus entering the hindgut based on a Meta-analysis (pmc.ncbi.nlm.nih.gov)
  3. Effect of feed intake level on the determination of apparent and standardized total tract digestibility of phosphorus for growing pigs (doi.org, 2018)
  4. Methodological aspects of determining phosphorus digestibility in swine: A review (pmc.ncbi.nlm.nih.gov)
  5. Dietary Phosphorus and Calcium Utilization in Growing Pigs: Requirements and Improvements (pmc.ncbi.nlm.nih.gov)

About this Article -

Written with AI assistance from published research, and reviewed by the Mystum team. See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.anifeedsci.2018.10.012, Alternate LINK

Title: Effect Of Feed Intake Level On The Determination Of Apparent And Standardized Total Tract Digestibility Of Phosphorus For Growing Pigs

Subject: Animal Science and Zoology

Journal: Animal Feed Science and Technology

Publisher: Elsevier BV

Authors: J.B. Liu, H.L. Yan, S.C. Cao, J. Liu, H.F. Zhang

Published: 2018-12-01

Everything You Need To Know

1

Why is understanding phosphorus digestibility important in pig farming?

In modern pig farming, phosphorus is crucial for bone development and metabolic processes. The efficiency of phosphorus absorption in pigs is influenced by feed intake. Recent research focuses on how different feed intake levels affect apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus in growing pigs. Understanding these dynamics is essential for formulating diets and minimize phosphorus excretion.

2

How was the impact of feed intake on phosphorus absorption studied in growing pigs?

The study used seventy-two barrows, divided into groups fed diets with varying phosphorus content (P-free, low-P, and moderate-P) and different feed intake levels (3%, 4%, and 5% of body weight per day). Researchers measured how efficiently the pigs absorbed phosphorus under these different conditions.

3

What were the key findings regarding the relationship between feed intake, dietary phosphorus levels, and phosphorus absorption?

The research indicates that the amount of feed pigs consume affects how well they absorb phosphorus. In pigs fed low-phosphorus diets, changes in feed intake didn't significantly alter phosphorus absorption. However, in pigs fed moderate-phosphorus diets, increasing feed intake led to decreased apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus. Thus, the phosphorus content of their diet impacts how pigs respond to different feed intake levels.

4

What practical implications does the research on feed intake and phosphorus digestibility have for pig farmers?

The research highlights that feed intake level influences phosphorus digestibility, especially with moderate-phosphorus diets. As feed intake increased, the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus decreased, indicating pigs may have difficulty absorbing phosphorus when consuming larger amounts of moderate-phosphorus feed. This suggests that optimizing feeding strategies is crucial to maximizing nutrient use and reducing phosphorus excretion.

5

Besides feed intake, what other factors might influence phosphorus absorption in pigs, and how could future research explore these?

While the study focuses on the relationship between feed intake and phosphorus digestibility, other factors influencing phosphorus absorption in pigs include the source of phosphorus in the diet (organic vs. inorganic), the presence of phytase (an enzyme that helps break down phytate, a form of phosphorus indigestible to pigs), and the age and health of the pigs. Further research could explore these interactions to develop even more precise feeding strategies.

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