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Re-alimentation of phosphorus deficient cattle
Large areas of grazing land across northern Australia have phosphorus (P) deficient soils, and hence forages, resulting in low P intake by animals. Feed intake is affected by phosphorus (P) content of the diet, which has consequences for liveweight (LW) gain and skeletal growth. Steers fed a P deficient diet had reduced feed intake, LW gain and hip height (HH) growth over a six month period (MLA Project NBP.537), compared to steers fed a P adequate diet. However, it is unknown how quickly P deficient cattle respond when offered a P supplement and the magnitude of this response. This project examined the response of steers, previously fed diets of different P content and then fed a diet representative of early wet season pasture (~11% crude protein and ~63% digestibility) supplemented with P to provide ~0.25% P/kg DM, over three months. Feed intake, LW gain, HH, bone density, plasma inorganic P (PiP), faecal P (FaecP) and carcass data were collected. The main findings of this project were:
- After adaptation to a high P diet (two weeks), total dry matter (DM) intake was similar between steers within one week of feeding new treatment diets (the exception was two steers that had low P supplement and DM intakes).
- Steers that were previously offered a low P diet had higher LW gain (1.33 kg/d) and HH change (57 mm/100 days) than steers previously offered a high P diet (0.70 kg/d and 34 mm/100 days) during the re-alimentation period. The slower growth rates of steers previously offered a high P diet during the re-alimentation phase was attributed to those animals approaching mature size. The LW gain for the re-alimenting animals was 0.2 kg/d higher, while change in HH was similar, to animals fed a high P diet over the previous 6 months.
- The concentration of P in the faeces and plasma reflected changes in P intake and did not differ between steers that were previously fed diets of different P content.
- Steers that were previously fed a low P diet had lighter and leaner carcasses than steers that were previously fed a high P diet. However, there were no differences in carcass traits when adjusted to a common carcass weight.
The results indicate that feed intake and LW gain of growing cattle that previously had low P intakes, responded immediately to a high P diet. This contrasted to the earlier experiment (P depletion phase) where it took six to eight weeks for a P deficiency to depress feed intake and LW gain. The concentration of P in the plasma and faeces of growing steers responded immediately to P intake and were similar for all animals, regardless of previous P intake (or P status). The results suggest that FaecP:DMD is not indicative of P status (repletion vs. non-repletion) of growing animals but is an indicator of P intake, regardless of previous P intake.
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Realimentation of phosphorus deficient cattle
This page was last updated on 04/09/2018
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