Phosphorus for cattle and sheep
Farmnote 36/1990 [Reviewed July 2005]
By Harry Masters, Research Officer, Animal Health Laboratories and Brad McCormick, Regional Veterinary Officer, Derby
Phosphorus is essential for the normal function of all animal tissue.
An animal's phosphorus requirement is already linked to its level of production. Rapidly growing calves and lactating cattle on abundant high quality feed have the greatest requirement for phosphorus; dry stock on survival rations have the least.
Animals compensate for a dietary deficiency of phosphorus by mobilizing it from their bones, so short-term deficiencies can be tolerated without ill effect. If a deficiency continues, appetite is depressed and growth rate, milk yield and fertility are reduced. Severe or prolonged deficiencies cause teeth and bone abnormalities. Animals become lame, showing stiffness, arching of the back, swelling of the joints and a reluctance to move. The coat is rough and dull and bones break easily.
Phosphorus deficient cattle may chew bones which can lead to botulism (toxic paralysis), but bone chewing in sheep is not always a sign of poor phosphorus nutrition.
The phosphorus status of animals can be estimated by chemical analysis of a rib bone.
Phosphorus in improved agricultural areas
Under current management systems phosphorus deficiency is unlikely to occur in sheep or beef cattle that:
- graze in the agricultural areas where phosphate fertilizers have been added to the soil;
- eat rations containing at least 20 per cent lupins or cereal grain.
High producing dairy cattle are the only class of stock in agricultural areas that might sometimes require additional phosphorus. Advisers at District Offices of Agriculture Western Australia can assist in calculating a supplementation strategy tailored to your herd's needs.
Phosphorus supplements should not be given to stock on all grain rations.
An excess of phosphorus in the diet causing a phosphorus/ calcium imbalance is far more common that a phosphorus deficiency in the agricultural regions of Western Australia. See Farmnote No. 56/89 'Hand feeding sheep: add finely ground limestone to grain' (Agdex 430/57).
Phosphorus nutrition in pastoral regions
In Western Australia phosphorus deficiency in livestock is predominantly confined to calves and lactating cattle grazing native herbage in the pastoral regions. All of the Kimberley region, except the paleo-tidal coastal plain, is phosphorus deficient to varying degrees.
The phosphorus content of forage is much lower in the dry season than in the wet, but production responses to phosphorous supplements are far more likely in the wet season. This is because protein and energy are also in short supply during the dry, and correcting a phosphorus deficiency can only restore production to the level allowed by the quality and quantity of feed available.
Phosphorus supplementation strategies for pastoral regions
All classes of stock grazing in phosphorus deficient areas will benefit from phosphorus supplements during the wet season (about 10 g/head/day for breeders and 5 g/day for others).
It is not practical to provide phosphorus during the wet it may be added to any feed supplements offered at the beginning of the dry season.
Supplementing phosphorus to dry stock in energy and protein deficient circumstances will accentuate rather than correct a weight loss situation. Therefore do not feed phosphorus to dry animals when they are losing weight.
However, lactating cows will sometimes benefit from phosphorus during the dry (4 g/head/day), particularly if protein or non-protein nitrogen is given at the same time.
Phosphate supplements
Phosphorus can be provided in dry or roller licks, or added to water. Suitable sources of phosphate include mono ammonium phosphate (MAP), diammonium phosphate (DAP) and dicalcium phosphate (DCP). Both MAP and DAP have the advantage of providing some non-protein nitrogen, while the high calcium content of DCP might be counterproductive in some pastoral situations,
Rock phosphate is not recommended. It contains less available phosphorus than the alternatives, is insoluble in water and is relatively unpalatable. Some sources also contain potentially toxic impurities such as fluorine and cadmium.
Further reading
- Farmnote no. 7/92 'Mineral requirements of the lactating dairy cow' (Agdex 415/65)
- Farmnote no. 8/2004 'Trace element deficiencies in sheep and cattle' (Agdex 400/652)
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