Re-alimentation of phosphorus deficient cattle

The Re-alimentation of phosphorus deficient cattle project investigated the responses of phosphorus deficient animals to a high phosphorus supplement.

Summary

Feed intake and liveweight gain are affected by phosphorus (P) content of the diet. For example, in the MLA project, Validation and demonstration of a diagnostic tool for phosphorus status of beef cattle (B.NBP.0537) cattle fed a P deficient diet had reduced feed intake and liveweight gain over a 20 week period.  However, it was unknown how quickly P deficient animals respond when offered a P supplement and the magnitude of the response.

The Re-alimentation of phosphorus deficient cattle project examined the response of animals of various P status to a high P supplement. It used animals generated in B.NBP.0537 and fed them a diet representative of early wet season pasture (~10 to 11% crude protein and 60 to 65% digestibility) supplemented with biofos to provide ~0.25% P/kg DM.  Feed intake, liveweight gain, hip height, bone density, plasma inorganic P, faecal P and carcass data were collected.

This project aimed to:

• determine the response (in terms of feed intake, liveweight gain, faecal and plasma P, hip height and bone density) of P deficient cattle to a high P diet (both the speed at which the response occurs and the magnitude of the response)
• determine if relationships between faecal P:dietary DMD exist in animals that are P deficient and are fed a high P diet
• examine allometric growth in P deficient animals undergoing compensatory gain.

Steers that were previously fed diets with different phosphorus (P) content for six months were fed a diet of approximately 11% crude protein, 63% dry matter digestibility and 0.1% P, with supplementary P supplied to provide a total dietary P content of approximately 0.25% P/kg DM intake for three months. Total dry matter intake of steers that previously had a low P intake was increased to the intake of steers that previously had a high P intake within one week of starting the re-alimentation period (and after a two week adaptation period). Steers that were previously fed a low P (0.09% P) diet increased their liveweight gain (1.33 kg/d) and rate of hip height change (57 mm/100 days) to a higher level than steers that were previously fed a high P diet (0.24% P) (0.70 kg/d and 34 mm/100 days, respectively) during re-alimentation. The concentration of P in the faeces and plasma responded to the high P diet within the first week of feeding, with little difference in concentration between steers, regardless of previous P intake. After three months of re-alimentation on a high P diet, steers that previously had a low P intake had lighter and leaner carcasses with lower dressing percentages than steers that previously had a high P intake, with no differences in ossification score, fat colour or meat pH. This just reflected that, although compensatory growth was occurring, the period of re-alimentation was not long enough for previously P deficient animals to catch up to the control animals. There were no differences in carcass characteristics when data was adjusted to a common carcass weight.

In conclusion, steers that are fed on a low P diet will respond immediately to a high P diet, in terms of feed intake and liveweight gain, and the increased P intake will be reflected in increased concentration of P in the plasma and faeces, regardless of the P content of the diet previously consumed by the steers.

When: 1 September 2011 to 1 July 2012

Contact: Dr Simon Quigley

Collaborator: University of Queensland

More information

For more details, please read the final report summary and download the final report (B.NBP.0565) (PDF, 542.3KB) from Meat & Livestock Australia.