Kidman Springs study finds substantial benefits from phosphorus supplementation

Many readers will be aware of the Phosphorus supplementation study that has been running at the NT Department of Industry, Tourism and Trade’s Victoria River Research Station (Kidman Springs) since 2014. Major benefits from P supplementation have been demonstrated over the last few years, but this year’s results have been even more dramatic and indicate that P supplementation is one of the most important things that cattle producers in P deficient areas can do to improve profitability.

“The effect of P deficiency on cows that raised their second calf over the 2018/19 wet season was quite confronting,” said Principal Livestock Research Officer, Tim Schatz. “The body condition of lactating cows in the P- treatment (received no P supplement) had deteriorated to the point where the decision was made to stop the study due to animal welfare concerns. While the study was scheduled to run for another year, we felt that the huge differences between the treatments should be enough to convince people of the benefits of P supplementation and that running the study for another year would not be necessary.”

The poor body condition of lactating cows in the P- treatment resulted in much lower pregnancy rates than in lactating P supplemented (P+) cows (P- = 8%, P+ = 70%). The reason for the dramatic deterioration in P- treatment cows during their second lactation is likely to be because so much P had been drained from their systems during their first and second lactations.

“If cows don’t get enough P from their diet when they are lactating, they mobilise P from their bones and tissues to put into milk. This was confirmed by blood testing which found that blood P levels were adequate in calves from P- cows but were very low in the P- cows. This drain of P over two lactations without P stocks being replenished by supplementation seems to have resulted in the P- treatment crashing,” explained Mr Schatz.

The return

“Each year, more calves and heavier calves were weaned from the P+ treatment, so the total weight of calves weaned from the P+ group was substantially more than from the P- group,” recounted Mr Schatz. “In 2017, 2018 and 2019, an extra 3072 kg, 2804 kg and 5932 kg of weaners was weaned from the P+ treatment group. Over the first three calf crops, an extra 11.8 tonnes of calves were weaned from the P+ treatment and this was worth about $379 per heifer originally allocated to the treatments.

We conducted a very basic economic comparison of the profitability of the P+ treatment by dividing the extra value of the weaners produced from the P+ treatment in each year by the cumulative extra cost of the P+ supplement to that point. What we found was that the cumulative return on investment for the P+ treatment was 280% in 2017, 347% in 2018 and had risen to 513% by 2019; but this only tells part of the story.”

The cumulative mortality rate in P- treatment cows was 13% higher than the P+ cows and the average weight of the P+ cows was 96 kg heavier.

“It is likely that the mortality rate in P- would have been even higher if the study had not been stopped in May 2019 and extensive efforts made to improve the cows’ body condition. Cows in need of intervention were segregated in a small holding paddock and provided with hay, molasses, pellets and P supplement until their body condition improved. We suspect that the mortality rate is likely to have been higher if the study had been done with larger mobs in bigger paddocks, as occurs on commercial properties, where uneven grazing around water points means that cows have to walk further between water and pasture each day (and hence burn up more energy).

This sort of a return on investment is quite staggering and although it is not a proper economic evaluation, it indicates how great an effect that P supplementation can have on the profitability of properties in P deficient areas. We will be undertaking a full economic evaluation in the near future,” concluded Mr Schatz.


Cows that have received phosphorus supplementation as part of the supplementation trial are in body condition score 2 and above on a 1-5 scale.
Image 1. Cows from the P+ treatment at the conclusion of the trial, May 2019.

Cows that did not received phosphorus supplementation as part of the supplementation trial are in a very poor body condition score.
Image 2. Cows from the P- treatment, at the conclusion of the trial, May 2019.


The study began in mid 2014 when 179 Brahman weaner heifers were randomly allocated to treatments that either received P in their supplement (P+) or did not (P-).  The treatment groups grazed two similar, acutely P deficient neighbouring paddocks. The paddocks were set stocked and the treatments swapped paddocks at the first round muster (in May) each year to minimise any paddock effect. The loose lick supplement was distributed twice-weekly and fed year-round.

The heifers were first mated at two years of age for four months, from late December 2015, with the first calf crop weaned in May 2017. Two more calf crops were weaned before the study concluded at the weaning muster in May 2019.

This study has documented the large effects on productivity and profitability that providing P supplements to heifers and cows can have when they are grazing P deficient country. It has shown very large returns on investment from P supplementation and is already resulting in increased adoption of P supplementation.  However, it should be noted that the response will vary depending on the level of P deficiency and benefits of this scale may not be seen where P deficiency is not as severe.

To read more about the project, including a summary of the results and further details about the design of the trial, click here.