Beef producers in northern Australia are one step closer to having a simple on-farm test to accurately assess an animal’s P status. 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.
Research funded by Meat & Livestock Australia (MLA) is helping scientists discover better markers of P-status in cattle, which could soon result in the development of a crush-side test.
Animal endocrinology specialist Dr Stephen Anderson from the University of Queensland is part of a 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,” Dr Anderson 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.”
Dr Anderson said the 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.
Dr Anderson said 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.
He said this was is in stark contrast to growing cattle, including heifers during their first pregnancy and then lactation.
Dr Anderson 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.
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,” Dr Anderson 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-calciumto-one-P-molecule, so in P deficiency high calcium levels appear in a blood test,” Dr Anderson said.
He said it is also 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,” Dr Anderson said.
“The BAP enzyme was also found to increase as animals utilised their P mineral stores.”
Dr Anderson said while the project team’s long-term goal was to see the development of a crushside test for P-status, in the short-term they would continue to investigate nutritional and production responses to improve recommendations on how best to manage the P nutrition of northern breeder cows.
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