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

Loose lick ingredients Wet season +P Wet season -P Dry season +P Dry season -P
Ridley Biofos MCP 42.5% 25%
Salt 50% 73.5% 40% 65%
Ammonium sulphate (Gran Am) 7.5% 7.5% 10% 10%
Urea 25% 25%
Limestone 17.5%

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 +P Extra cost of supplement from +P Cumulative return on investment (extra value/extra cost)
2017 3072 $3.50 $10751 $3839* 280%
2018 2806 $3.00 $8417 $5529**
TOTAL 5878 $19619 $5529** 347%

*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 supplementation trial

2014-2017 Data (until first calves weaned) -P +P Difference
No. 14 heifer weaning weight (kg) 175 175 0
Maiden heifer pre-mating weight (kg) 238 270 32
Maiden heifer post mating weight (kg) 327 392 65
Pre-calving weight (kg) 324 393 69
Weight when calves weaned (kg) 262 382 120
Maiden pregnancy percentage (%) 60 70 10
Calf loss rate (%) 22 21 -1
1st lactation heifer pregnancy rate (%) 5 (n=39) 30 (n=50) 25
Mortality rate to 3.5 years old (%) 8 1 -7
Weaning weight of calves (kg) 139 173 34
2017-2018 Data (year after first calves weaned) -P +P Difference
Dry cow pregnancy percentage (%) 92 (n=50) 96 (n=48) 4
Dry cow average weight (kg) 424 493 69
Wet cow pregnancy percentage (%) 20 (n=30) 57 (n=42) 37
Wet cow average weight (kg) 357 426 69
Calf loss rate (%) 21 16 -5
Weaning weight of calves (kg) 172 185 13
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

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

This project has been funded by the Northern Territory Department of Primary Industry and Resources.