New phosphorus findings

MLA-funded phosphorus (P) research projects for northern Australia have unearthed new information to help improve breeder management in phosphorus-deficient areas.

Senior researcher Dr Rob Dixon of the Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, said some of the good news is that mature breeders are more resilient to short-term P deficiency than previously thought.

“Unlike growing cattle, mature breeders are able to mobilise their own body reserves to reduce the negative effects of short-term P deficiencies,” he said.

This is in contrast to most previous P nutrition research findings which have been based on growing cattle.

“It was always expected that the responses of growing cattle would represent those of other stock classes, however, this project has shown that’s not the case,” Rob said.

“We found that breeders can, to some extent, use body reserves of P to meet a short-term P deficiency in the diet, just as they can use body reserves of fat to get through a metabolisable energy shortage during the dry season.”

The research team found that mature Droughtmaster cows fed a high P diet during pregnancy that were in good body condition and P status at calving could mostly maintain milk production and calf growth for at least three months while on P-deficient diets.

Don't break the bank

However, Rob explained that producers need to be mindful that using up an animal's P reserves comes at a cost.

“Our results showed that producers could expect calves at three months old to be slightly lighter (10-20kg) than those calves on mothers with adequate P diets,” he said.

“However the P-deficient cows were 50kg, or an entire body condition score (scale 1 to 5), lighter.”

Rob said a good way for producers to think about this research finding is to consider that P, similar to fat, for a mature cow is like having savings in the bank.

“The animals can draw on their P ‘savings’ during times of low availability but these P ‘savings’ have to be replaced,” he said.

Rob said cows that are ‘overdrawn’ for long periods need time to recover their body reserves.

“At this stage we do not have a good understanding of the diet and time required to achieve this for breeders in northern production systems,” he said.

“Sustained low P diets are evident in lower cow body condition scores, delayed pregnancies, poor lactation performance and reduced calf/ weaner weights.”

Rob said the management impact of these findings is that producers can be confident they have more flexibility in their management program to supplement mature breeder cows with P.

“The basic recommendation for management has been that P supplements should be fed during the wet season because this is when there are the largest responses to P supplements – this recommendation still stands,” he said.

“However, when it is not possible to feed during the early-wet season then P supplements should be started as soon as possible from the mid-wet season.

“Using body P reserves of the mature cow during lactation can be helpful but they have to be replenished later in the annual cycle.”

Rob said outcomes from the research would assist with next year’s planned update of MLA’s producer phosphorus manual for the northern cattle industry.

Contact:

Dr Rob Dixon T: 07 4843 2639 E: rob.dixon@daf.qld.gov.au