Research brings on-farm P test closer
25 November 2016
New discoveries about phosphorus (P) deficiency in northern beef cattle have put producers a step closer to having a simple on-farm test to accurately assess an animal’s P-status.
Animal endocrinology specialist Dr Stephen Anderson from the University of Queensland is part of an MLA-funded research project that has uncovered new information about how P-deficiency affects both young and mature cows, and revealed new markers that indicate P status in cattle.
“During the past 20 years, very little work has been done on the physiology of P deficiency and most of our current knowledge is based on growing stock,” he said.
“This project aimed to improve our understanding of how cows cope with P deficiency, and has given us new information that producers might use to make better management decisions.”
Stephen said their discovery of new markers that more accurately indicate P status could, potentially, be combined with emerging medical technology to develop a simple crush-side test for use by producers.
“That’s the end game, to make it easier and more cost-effective for producers to manage P deficiency,” he said.
Project background
The research team monitored their test herd of mature Droughtmaster cows for one season and found they were very good at mobilising P and calcium from bone in P-deficient situations, particularly during late pregnancy and the first three months post-calving.
This is in stark contrast to growing cattle, including heifers during their first pregnancy and then lactation.
Stephen warned producers that exposing young lactating cows that are still growing to extreme P deficiency could have serious implications for their longer-term productivity.
“Evidence from MLA’s CashCow project showed that many herds in tough environments cope with this stress by calving only every second year and using the alternate years to replenish their live weight, fat and bone minerals,” he said.
Measuring the markers
The research team discovered that P deficient cows had an increase in the active form of vitamin D3.
“This vitamin D3 promotes gut uptake of both P and calcium from the diet, so if cattle are eating a low P diet, this helps them to extract as much P as possible from their feed,” Stephen said.
“Besides vitamin D3, other markers of P deficiency indicate how much P in the bone is being mobilised, and these can be used to assess a cow’s P status.”
High calcium levels in the blood were also found to indicate low P status.
“When P is mobilised from bone, calcium is trafficked at the same time at the rate of two-calcium-to-one-P-molecule, so in P deficiency high calcium levels appear in a blood test,” Stephen said.
He also said it is possible to use this information to improve the present 'P Screen' test and advance the development of a better crush-side test tool for producers.
Other P deficiency markers uncovered include CTX-1 and an enzyme, Bone Alkaline Phosphatase (BAP).
“CTX-1 is basically a breakdown product that occurs as bone P is mobilised so levels of CTX-1 go up as the animal struggles to supply its own P needs for lactation,” Stephen said.
“The BAP enzyme was also found to increase as animals utilised their P mineral stores.”
What's next?
Stephen said while the project team’s long-term goal was to see the development of a crush-side test for P-status, in the short-term they will continue to investigate nutritional and production responses to improve recommendations on how best to manage the phosphorus nutrition of northern breeder cows.
More information
Dr Stephen Anderson T: 07 3365 4756 E: stephen.anderson@uq.edu.au
