Research Shows Finishing Pigs Can Thrive on Lower Phosphorus Diets

By Elizabeth McCann, Agri-Food and Biosciences Institute, Hillsborough - Phosphorus (P) is an essential nutrient for pigs and is vital for bone formation and growth. Deficiency of P can lead to welfare and health problems including rickets, poor fertility and reduced production performance.
calendar icon 27 December 2006
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However, P is also a major contributor to the eutrophication of waterways in Northern Ireland and given these environmental concerns, the P levels in pig diets have been lowered to reduce P excretion. Research at the Agri-Food and Biosciences Institute, Hillsborough (in collaboration with John Thompson and Sons Ltd., Devenish Nutrition Ltd. and Department of Agriculture and Rural Development for Northern Ireland) has shown that the total P in diets for growing pigs could be reduced by 0.1% (0.6 to 0.5% total P on a fresh basis).

This research has impacted positively on the environment with substantially less P excretion from pig production. The Research Group has also identified the need to examine the level of P in finishing diets and a trial was conducted to investigate the effect of different levels of P in diets for finishing pigs.


The most commonly used and widely available feed ingredients were used to formulate finishing pig diets to provide three different levels of total P (0.6, 0.5 and 0.45% (fresh basis)). It was not possible to formulate a finisher diet to contain less than 0.45% total P due to the need to supply other dietary nutrients at required levels and also because of the difficulty in sourcing raw feed ingredients containing low levels of total P. The trial was conducted in two parts.

Part A was a performance trial which used 560 Landrace x Large White pigs housed in pens of eight from approximately 40kg to slaughter at approximately 95kg. Liveweight gain (LWG), feed intake and feed conversion ratio (FCR) were recorded during this period. Part B was a digestibility trial which involved 20 LRxLW boars housed individually to enable collection of faeces and urine.

There was no significant effect of dietary P level on performance (Table 1) with all three levels giving similar results. This indicates that the lowest level of total P (0.45%, fresh basis) is adequate to drive growth. However, previous work by this Research Group has shown that growth is not always a precise indicator of P status and that P balance data gives a fuller picture.

The P digestibility and balance figures determined in this study are given in Table 2 and clearly show that dietary P level (0.6, 0.5 or 0.45% total P, fresh basis) had no effect on P digestibility. This supports the growth data and is further evidence that the lowest level of P (0.45% total P) is adequate for finishing pigs (at the reported level of feed intake). Taking digestibility of P at 48%, offering the 0.45% total P diet supplies 0.22% available P which has previously been reported to be adequate for finishing pigs. Offering finishing diets containing 0.6% total P increased urinary excretion of P by 46% which would be harmful to the environment and indicates that P is oversupplied.


  • 0.45% total P (fresh basis) is sufficient to supply adequate P for growth and metabolism in finishing pigs.
  • It is not possible to formulate finishing pig diets to levels lower than 0.45% total P (fresh basis).
  • 0.6% total P (fresh basis) results in an oversupply of P to finishing pigs and increases urinary P loss.
  • If all finishing pigs in Northern Ireland were offered diets based on 0.45% P rather than 0.6% P, loss of P to the environment would be reduced by 86t/year.
Table 1 The effect of dietary P level on pig performance (40 to 95kg)
0.6% total P
0.5% total P
0.45% total P
Liveweight gain (g/d)
Feed intake (kg/d)
Feed conversion ratio

Table 2 The effect of dietary P level on P digestibility and balance
0.6% total P
0.5% total P
0.45% total P
P digestibility (%)
Faecal excretion (g/d)
Urinary excretion (g/d)

December 2006
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