Make no bones about it, lactating females need P

08 December 2016

For the first time, researchers and producers now have an accurate measure of the lifetime impact of phosphorus (P) deficiency on individual animals, with a new bone biopsy technique developed with MLA funding.

Researcher and veterinarian Dr Lisa Kidd of the University of Queensland was using bone histology (microscopic analysis of bones) to measure how varying levels of dietary P affect heifers and cows as part of a larger MLA-funded research project.

Lisa developed the new biopsy technique to measure bone density. It shows, in detail, how much bone tissue animals lose when they mobilise their own P stores to cover dietary shortfalls.

“First calf heifers on low P diets during late pregnancy and lactation had 30% less bone volume than supplemented heifers at the time of weaning,” she said.

“Research has shown these heifers, if not supplemented during late pregnancy and first lactation, produce lighter calves at weaning and do not quickly recover their bone reserves even when an adequate diet is restored.

“In another study we saw that, during late pregnancy, P supplementation helped heifers maintain good bone volume even if the diet was poor as might be seen in the dry season.

“Data is still being analysed but we now know more about how P deficiency affects cattle, particularly during pregnancy and lactation, and how we might tailor supplementation strategies to improve production.”

What can producers do?

Lisa said the production ramifications of being unable to ‘look after’ those young mothers could be considerable.

“We found that on low P diets, mature cows with calves lose even more bone density than heifers because they put more into their calves, particularly during lactation,” she said.

The good news is that mature cows are able to regain their bone density even when on moderate metabolisable energy diets as long as there is adequate P available in the diet.

Lisa said the take-home message was the importance of P supplementation during lactation.

“Lactation is when heifers and cows lose the most bone density and they can do it very quickly on low P diets,” she said.

Further developments

In the future Lisa hopes to help develop crush-side tools such as ultrasound for measuring bone density and also to advance the concept of a producer-usable blood test, validated by her biopsy method and other work.

Information derived from this new bone biopsy technique, similar to that used in human medicine, will also improve the existing P-screen test and validate hormonal tests that measure P-deficiency and other markers developed during the project.

(Animals undergoing biopsies did so under surgical conditions, local anaesthetic and follow-up veterinary care and all animal work had animal ethics approval.)

More information

Dr Lisa Kidd T: 0438 714 876 E: l.kidd@uq.edu.au

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