Phosphorus supplementation of cattle in northern Australia

How to diagnose phosphorus deficiency | Develop a phosphorus management plan | Breeder management | Effect of phosphorus on productivity | When to supplement with phosphorus | Managing intake | Economics of phosphorus supplementation | More information

Phosphorus deficiency is a major problem for grazing cattle in much of northern Australia because of the low soil phosphorus levels in many soils. Whilst phosphorus is important in all bodily processes, the major impact of phosphorus deficiency in cattle is a significant reduction in appetite. This results in lower pasture intake and consequently lower energy and protein intake.

The reduction in nutrient intake affects the breeder’s ability to maintain body condition, resulting in lower weaning rates and increased mortality. Milk production is also reduced leading to lower weaning weights. In growing cattle, the lower nutrient intake produces lower growth rates. All of these impacts have serious consequences for production and profitability.

Other symptoms of phosphorus deficiency include bone chewing (increases the risk of botulism), chewing of other objects (rocks, sticks, wire, etc.), stiff gait, peg leg and bone breakages.

Watch this six minute video summarising the issues phosphorus deficiency causes in a herd, signs of phosphorus deficiency and the production gains that can be made as a result of supplementation:

The webinars below provide more information on phosphorus requirements and supplementation of breeders and growing cattle:

How to diagnose phosphorus deficiency

It is important to know if a specific mob or paddock is phosphorus deficient and if cattle will respond to phosphorus supplementation. There are a variety of ways to assess whether phosphorus deficiency is a problem.

  1. Observation – symptoms of phosphorus deficiency in cattle are described above.
  2. Soil and pasture tests – soil and land type mapping and information can give an indication of the potential for a phosphorus deficiency. See the Land types of Queensland page for more information. Soil and pasture tests can determine the phosphorus concentration in the soil and plants, however they are of limited value because most grazing paddocks contain a mixture of soils and land types. The selective grazing of cattle means that simply testing the available plants is not representative of the diet consumed.
  3. Blood – the ‘P-screen’ test is currently the most reliable method of assessing the phosphorus status of a mob of cattle. This test cannot be used on breeders, therefore samples from growing cattle (not lactating or pregnant) running in the breeder paddock are used to assess the breeder mob. Testing is undertaken at the end of the wet season while growing cattle are still gaining weight and not on phosphorus supplements.

To prepare for using the P-screen test in the 2019-20 wet season, read this quick fact sheet (Testing cattle for P status 2020, PDF, 200 KB) or contact your local beef extension officer for assistance.

Watch this webinar for more detailed information on diagnosing phosphorus deficiency: “How do we identify and evaluate phosphorus deficiency in grazing cattle”.

Phosphorus supplementation

Develop a phosphorus management plan

Developing a phosphorus management plan for a property starts with understanding the relative productivity and phosphorus status of land types within paddocks (here is an example). Land type mapping is an invaluable resource for property planning and herd management. Land type maps can be obtained using FORAGE or Qld Globe and land type information is located

Phosphorus management has an overall effect on the management of a herd and the timeliness of operations like moving cattle, weaning, joining period, supplement delivery. You can use something like this  example herd management calendar to plan your year.

Breeder management

Lactation significantly increases the phosphorus requirements of breeders, therefore weaning management is an important component of managing phosphorus deficiency. Timely weaning of breeders and if appropriate, early weaning, enables breeders to better cope with low phosphorus pastures. The reduced requirements for energy, protein and phosphorus as a result of weaning can markedly improve body condition.

Calving at the most suitable time for the region and avoiding cows lactating for long periods in the dry season will also mitigate the effects of low phosphorus diets. Where controlled mating is not feasible, breeder segregation systems can enable out of season calving cows to be better managed.

For more information about the nutritional management of breeders, including managing the breeder body condition score to maximise reproductive potential,

Effect of phosphorus on the productivity of the breeder herd

A research project at the Victoria River Research Station (Kidman Springs), NT, has found a substantial effect on the productivity of breeders when they do not have adequate phosphorus in the diet. Cows supplemented with phosphorus showed increased reconception rates and produced heavier weaners. Read more about the “Effect of phosphorus supplementation on Brahman females at Kidman Springs” project, including the latest project update.

Cattle consume loose phosphorus supplementation

When to supplement with phosphorus

In the wet season when energy and protein levels in grass are at their peak, phosphorus is the first limiting nutrient on phosphorus deficient country. Correcting this deficiency in the diet allows cattle to increase their intake of energy and protein from the grass, meaning there are huge productivity gains to be made in supplementing with phosphorus in the wet season. The challenge for most producers is getting cattle to eat a supplement when there is green grass everywhere.

Because of the high phosphorus requirements for late pregnancy and lactation, phosphorus should be included in dry season supplements for breeders in deficient country.

Choosing phosphorus supplements

Phosphorus  can be fed to cattle in the form of loose licks, liquid supplements, blocks, or via water medication. Supplements need to be assessed on the cost of supplying the nutrients required, infrastructure requirements and the practicalities of feeding. A critical component of supplement selection and management is ensuring that the required nutrient intakes are achieved in the most cost effective manner. Consequently, the palatability of supplements is an important consideration and may require changes to achieve the target intake.

The principal sources of phosphorus in supplements are:

  • Di-calcium phosphate (DCP)
  • Mono di-calcium phosphate (MDCP)

Each method of supplying nutrients to cattle has both positive and negative aspects that may also impact the supplement strategy chosen. Here are some of the pros and cons for popular phosphorus supplementation methods:

Loose licks

  • Low cost/kg phosphorus
  • Recipe can be customised to achieve target intakes
  • Need shelters in wet.

Liquid supplements

  • Adding P supplements (i.e. MDCP/DCP) to molasses can be a useful strategy where target intakes are hard to achieve
  • Technical grade mono ammonium phosphate (MAP) can be added to roller drum and dunder mixes. Technical grade product has to be used because fertiliser grade products can contain unacceptable levels of fluorine and/or heavy metals.

Wet season blocks

  • High cost/kg phosphorus
  • Weather resistant
  • Easy to distribute before wet
  • Composition cannot be changed once purchased
  • Target P intakes are often not achieved.

Water medication

  • Uniform intake across mob
  • Alternative watering locations in the wet season (e.g. creeks) can make achieving target intakes difficult
  • Water quality can present problems with medicator operation.

Managing phosphorus intake

It is important to know the phosphorus supplement requirements of the classes of cattle at different times of the year on the property’s land types. More information on cattle phosphorus supplement requirements can be found in the “Phosphorus management of beef cattle in northern Australia, PDF 2.2 MB)” handbook.

Feeding phosphorus in the wet season can be challenging. To achieve target intakes, time has to be invested in identifying the most suitable phosphorus source and supplement composition and training animals to eat supplements.

Guides for intake targets are listed in the table below, taking into consideration class of animal and level of phosphorus deficiency.


Table 1. Recommended supplementary phosphorus intakes for different classes of cattle and levels of phosphorus deficiency (Phosphorus management of beef cattle in northern Australia, MLA 2012).

Class of animalWeight (kg)Target weight
gain`` (kg/day)
Recommended supplementary P intake (g/hd/day) for three levels of phosphorus deficiency
Acutely deficientDeficientMarginally deficient
Steers & heifers200021Nil
Steers & heifers2000.3431
Steers & heifers2000.6641
Steers & heifers2000.9852
Steers & heifers2001.21072
Steers & heifers400-0.32NilNil
Steers & heifers4000321
Steers & heifers4000.3541
Steers & heifers4000.6752
Steers & heifers4000.9962
Steers & heifers4001.21183
Pregnant breeders *400-0.3321
Pregnant breeders *4000531
Pregnant breeders *4000.3741
Pregnant breeders *4000.6962
Lactating breeders +400-0.3752
Lactating breeders +4000962
Lactating breeders +4000.31172
Lactating breeders +4000.61283
`` Target weight gains are the potential daily weight gain based on the diet quality when P is not limiting.
* Late pregnant breeders, last three months of pregnancy.
+ Lactating cows, producing 5 kg milk/day.


Good supplement intake records are critical to ensure target phosphorus intakes are achieved and for managing the cost of supplementation. Download our lick intake calculator here:

Economics of phosphorus supplementation

Economic analyses and producer case studies demonstrate that phosphorus supplementation in deficient country is a very cost effective strategy for beef businesses. More information on the latest phosphorus economics and the benefits modelled for beef businesses in the Fitzroy region of Queensland and the Katherine area in the Northern Territory can be found in an article written by Dr Maree Bowen (Department of Agriculture and FisheriesPrincipal Research Scientist) and Fred Chudleigh (Department of Agriculture and Fisheries Principal Economist), “Improving beef business performance with phosphorus supplementation“.

Help with managing phosphorus

Our FutureBeef staff are here to help! Contact your local extension officer to talk about your phosphorus management plan (Word, 200 KB), or watch this short clip demonstrating how Department of Agriculture and Fisheries staff and resources have helped other northern beef producers develop a cost effective strategic phosphorus supplementation program using P blood testing and property land type mapping.

Cattle under covered lick shed eating loose phosphorus supplementation


Images supplied by Bernie English and Joe Rolfe.

Information compiled by Kylie Hopkins and Mick Sullivan, Extension Officers, Queensland Department of Agriculture and Fisheries.