Kidman Springs phosphorus supplementation trial demonstrates >300% ROI

It is well documented that much of northern Australia is phosphorus (P) deficient and that P is required for almost every vital bodily function in cattle. However, supplement sales figures and industry feedback indicates that the majority of northern properties in P deficient areas are not supplementing their cattle with P over the wet season. Current thinking is that producers must not believe that they will get a good enough return feeding a P supplement to justify the expense and hassle of feeding supplement over the wet season. Past studies have shown that P supplementation increases growth, however, there have been few studies that have found a significant improvement in reproductive performance from P supplementation in northern Australia and quantified the benefit. This may be a reason why adoption has been so low.

A trial commenced in 2014 at the Victoria River Research Station, Kidman Springs, to quantify the benefits of P supplementation. This trial will provide producers in P deficient areas with definitive data on the effects of supplementing females with P so that they are able to make better informed supplementation decisions.

Brahman heifers born in 2014 were randomly allocated to either a +P (where phosphorus was supplied in the supplement) or –P (where phosphorus was not included in the supplement) treatment and grazed in neighbouring paddocks that were tested as acutely P deficient. Treatments swap paddocks in May each year to minimise paddock effects. Treatments are managed exactly the same year round, with the exception that their loose lick supplements either contain P (+P) or do not (-P). Composition of lick fed to each treatment can be seen in Table 1.

Note: Soil test Colwell P levels: Acutely deficient: ≤4mg P/kg | Deficient: 5mg P/kg | Marginal: 6-8mg P/kg

Table 1. Composition of trial supplements

Wet seasonDry season
Loose lick ingredients+P-P+P-P
Ridley Biofos MCP42.5%25%
Ammonium sulphate (Gran Am)7.5%7.5%10%10%


Key results

While the trial is ongoing, there are already very compelling preliminary results coming through.

2016-17 data (1st calf)

The +P group were, on average, 66 kg heavier at the end of their first mating (April 2016) and pregnancy rates were 10% higher in +P maiden heifers. Calf loss was similar in both treatments but re-conception rates were 25% higher in the +P first lactation heifers.

When the calves were weaned in May 2017 the +P lactating heifers were, on average, 120 kg heavier than –P treatment heifers. In addition to this, the average weaning weight of calves was 34 kg heavier from the +P treatment. The +P treatment weaned 3,072 kg more calves than the –P treatment. Based on a 2017 price for weaners of $3.50, the additional 3,072 kg weaned from the +P treatment equates to an additional $10,751 (the study started with 91 heifers in +P and 89 in –P).

Also the mortality rate from the start of the study to when the first calves were weaned was 7% higher in –P treatment heifers (ie. 8% in –P vs 1% in +P).

2017-18 data (2nd calf)

At the weaning muster in May 2018, the average weight of the cows in the +P treatment was 69 kg heavier than the –P treatment (in both wet and dry cows) and the wet cow pregnancy rate was 37% higher for the +P treatment. On average the weaning weight of calves from the +P treatment were 13 kg heavier than the –P calves. The total weight of calves weaned from the +P treatment was 2,806 kg more than from the –P treatment.

A more thorough economic analysis will be undertaken as the project progresses, but the very basic comparison shown in Table 2 shows that the return on investment in P supplementation in this study has been high.

By May 2018, the total value of calves weaned from the treatment was $19,169 more from +P, while the total cost of the supplement consumed by each treatment was $5,529 more by +P (comparing the cost of the supplement consumed by +P year round to the cost of supplement consumed by –P in the dry season only). This gives a cumulative return on investment of nearly 350%. Table 3 shows the results to date from the trial.

Table 2. Cost:Benefit information on P supplementation in the Kidman Springs trial

Total weight of extra calves from +P (kg)Price ($/kg)Extra value of calves weaned from +PExtra cost of supplement from +PCumulative return on investment (extra value/extra cost)
*total value of extra supplement consumed by +P up to May 2017
**total value of extra supplement consumed by +P up to May 2018

It should be noted that while the trial is showing positive benefits of P supplementation that the response on other properties will vary depending on the level of P deficiency in the soil. Where P deficiency is not as severe the benefits of P supplementation may not be as great. While soil testing can provide an indication of P deficiency, it is not considered definitive. Currently the most reliable method of assessing P status of the herd is by taking blood samples of growing animals (that have not been eating P supplement or drinking milk) at the end of the wet season and testing for plasma inorganic phosphorus. These could be one year old animals running with breeders to get a P status from breeder paddocks.

Table 3. Results from the Kidman Springs P supplement trial

2014-17 Data (until first calves weaned)
Heifer post weaning weight (at location)(kg)1751750
Maiden heifer pre-mating weight (kg)23827032
Maiden heifer post mating weight (kg)32739265
Pre-calving weight  (kg)32439369
Weight when calves weaned  (kg)262382120
Maiden pregnancy percentage (%)607010
Calf loss rate (%)2221-1
1st lactation heifer pregnancy rate (%)5 (n=39)30 (n=50)25
Mortality rate to 3.5 y.o (%)81-7
Weaning weight of calves  (kg)13917334
2017-18 Data (year after first calves weaned)-P+PDifference
Dry cow pregnancy percentage (%)92 (n=50)96 (n=48)4
Dry cow average weight (kg)42449369
Wet cow pregnancy percentage (%)20 (n=30)57 (n=42)37
Wet cow average weight (kg)35742669
Calf loss rate (%)2116-5
Weaning weight of calves (kg)17218513
First lactation heifers without phosphorus supplementation in February 2017 at Kidman Springs in backward store condition

Image 1. -P first lactation heifers Feb 2017



First lactation heifers that had been supplied phosphorus supplementation in February 2017 at Kidman Springs in store condition

Image 2. +P first lactation heifers Feb 2017



First lactation heifers without phosphorus supplementation in May 2017 at Kidman Springs in poor condition at time of weaning

Image 3. -P first lactation heifers at weaning in May 2017



First lactation heifers provided with phosphorus supplementation in May 2017 at Kidman Springs in store condition at weaning.

Image 4. +P first lactation heifers at weaning in May 2017



Cows without phosphorus supplementation in February 2018 at Kidman Springs in store condition

Image 5. -P cows in March 2018



Cows provided phosphorus supplementation in March 2018 at Kidman Springs in forward store condition

Image 6. +P cows in March 2018

Additional information about this project can be found on the Effects of phosphorus supplementation on Brahman females at Kidman Springs (VRRS) project page.

For more information contact: Tim Schatz, Principal Livestock Research Officer, NT Department of Industry, Tourism and Trade, Tel:  08 89992332 e:

This project has been funded by the Northern Territory Department of Industry, Tourism and Trade.